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Time

Introduction

This article on time is a major diversion from the site’s major themes. I have included it because it addresses those elements of the world that frame our entire existence, and which still challenge our best philosophy and science.

Space and time are the stage on which all our experience is acted out. Immanuel Kant insisted that space and time are forms of mental representation that we must presuppose in order to have any experience at all: they were the form of all perception. So, for Kant, space and time are not properties of objects in the external world but the preconditions for perception itself. They are therefore a priori and necessary. He leaves us with the question of the degree to which space and time are mental constructs rather that properties of the world. That science has fused our intuitive understanding of space and time into a single category space-time suggests that he was on to something!

Mostly I have included this discussion because even a cursory examination of the topic warns us to expect linguistic, philosophical, physical and biological complications, so it is an exercise for any philosopher, amateur or professional, scientist or not. It has been included in its unfinished state for the few who might find the topic interesting and because it occupied my spare moments for a couple of years.

Of particular interest is the way that science is now taking on a topic that was once regarded as deeply philosophical.

Before looking into the philosophy, let’s examine the science and begin by making the observation that ‘time’ is one of the many subjects whose contents are, at least in part, being taken over by neuroscience.[6]

Biology

The physics of relativity tells us that us that time exists objectively in the universe itself. Identical clocks carried in two aeroplanes, one of which does a circuit of the earth, will end up telling different times (even though the difference is extremely small). Relativity also drives us to the conclusion that past, present, and future are a matter of perspective, not something universal. And yet we experience time in our minds since we have no (known) dedicated sensory organ. It is this perception of time in our brains that can be subjected to scientific investigation.

Our minds begin with the ordering of events and their causality (much of philosophical interest here). In other words we have experience episodic memories and sequences. Research suggests that our experience of ‘What: where: when’ – of space and time – occurs in the lateral and medial entorhinal cortex that send signals into the hippocampus; that representations of space and time are generated by the same regions of the brain. Obviously there are subjective elements to our perception of time – the less we are doing, the less we are engaged with something, the slower time seems to pass and this can be detected by MRI studies in the neural insular cortex.

Th relation between experienced time and time in the world is the puzzle. Clearly experienced time is our user-friendly biological app helping us to cope with the world. Though under relativity there is no objective ‘now’ it is difficult to know why we would have evolved a sense of the present if it wasn’t special in some way. This unification of explanation is a task that unites our best physics, biology, and philosophy.

With ‘What is time?”’ as a central question we can begin the investigation with language and our intuitions.

Language

Language is the starting point because it frames the way we communicate our ideas, it cannot be assumed that we share a common foundation of ideas and that we can develop our discussion from there. Time is clearly a semantically rich concept: to proceed productively we must isolate the individual strands in the rope of semantics.

The call to ‘define your terms’ is sensible because it means we can set off from a common starting point: it is also a good way to scan the overall temporal landscape.

Semantics
The meaning of a word is its use‘ is a valuable maxim because it reminds me that although I might think that I personally have distilled the essence of a particular word meaning, this needs to be squared with the everyday understanding of the people around me. The meaning of a word is not what I think it should be, it is what others determine it to be. In trying to answer the question ‘What is time?’, the dictionary is a good place to start.

Some words have simple meanings, they can be defined briefly in terms of the necessary and sufficient conditions needed satisfy all circumstances; their meaning stand alone and distinct. Such words are in the minority. Words like this, with discrete meanings are unusual. Most word meanings are linked to the meanings of other words like the fibres of a rope. Our wished-for discrete necessary and sufficient conditions are rarely met in everyday speech. Some words are semantically rich with many meanings, senses, or associations, one word consisting in effect of a collection of meanings all with a family resemblance; others are less semantically diverse.

‘Time’ is clearly a word of extraordinary semantic richness. If we want to know what we mean by ‘time’ then we must unravel the many threads of meaning that are woven together to create a family resemblance.

The problem of polysemy
Constantly defining terms is tedious for everyone and so we simply dont bother: we jump right in assuming that either we have a common understanding of what we are talking about, or that meanings will become evident as we proceed. Time words like ‘now’, ‘presentism’, and ‘change’ all have multiple meanings and, more than most philosophical topics, it seems that the philosophy of time carries an overload of polysemy. In a superficially innocent sentence like ‘Time is now’ if we accept that ‘time’ has at least four distinct meanings and ‘now’ at least three then we are already there is a multitude of possible cases to consider in any comprehensive discussion let alone the many intergrading shades of possible meaning.

Dictionary definition
It is an interesting exercise comparing dictionary definitions of time to establish a set of time-related words (see diagram). If we have definitions as follows: ‘Duration – a measured or continuous period of time‘. ‘Time – a stretch or space of continued existence or the interval between two events, actions, conditions or states‘ … then despite some subtle nuances of meaning we have little hesitation in saying that time and duration are essentially the same thing.

One way of doing this is to simply look in a dictionary and see how time is defined and follow the path taken by its various senses (see below).

Concise Oxford Dictionary - 1964

Concise Oxford Dictionary – 1964
Paths between major senses of th word ‘time’
Arrows pointing both ways indicate circularity

Macquarie Dictionary - 1984

Macquarie Dictionary – 1984
Paths between major senses of th word ‘time’
Arrows pointing both ways indicate circularity

Unpacking the semantics of ‘time’
The word ‘time’ itself is the most frequently used noun in the English language with other temporal words like ‘day’ and ’year’ ranking in the top ten. To avoid discussions proceeding at cross-purposes we must, at the outset, isolate the major different meanings of ‘time’.

Here are just a few nuances of meaning (senses) or roles for time in everyday language:

• time as now, or as a stated time (What time is it? 3 o’clock.)
• time as duration (How much time was needed? It took an hour.)
• time as orientation (The space ship traveled backwards in time.)
• time as an affect (We all had a good time.)
• time as movement (The older you get, the faster time flies.)
• time as agency when used as a verb (I will time the race.)
• time expressing multiplication (Three times four.)
• time as a prison sentence (He is doing time.)
• time as tense – past, present (now) and future – expressed through the tenses will be, is and was (At some future time .. etc.)
• time as tenseless sequence or date – the ordering sequence before, simultaneous with and after

The Australian Pocket Oxford Dictionary 4th edn lists 20 usages.

For our purposes it is enough to note that the semantically rich word ‘time’ denotes a wide range of concepts all sharing a family resemblance. We need to isolate those meanings that are of philosophical or scientific interest to see how they are interrelated.

A full justification for the following taxonomy and the relationship between its contents will emerge in later discussion. For the time the major senses of ‘time’ relevant to scientific and philosophical discussion are ;listed below:

A semantic taxonomy of ‘time’

DF = definition

There are three core meanings that we can attribute to the word ‘time’ as used in philosophical and scientific discourse: duration – DF a temporal interval; succession – DF the sequence of things (times and events (facts, people or objects)) which may be either earlier than, simultaneous with or later than the present (now), or one-another; time as an object or relation.

The definitions given here are not intended as strict or formal, they are not stipulative definitions but approximations to everyday usage or place-markers: they will serve their purpose, even in this loose form.
To simplify later discussion whenever one of these loose definitions is given it is accompanied by the letters DF and each of the various meanings is given an abbreviation, so ‘duration’ is indicated by T(d).

Duration series, T(d)
The word “duration” is used in two important senses:

Time (restricted duration), T(rd)
This is duration in a restricted sense as DF a temporal interval: a period of lapsed or lapsing time.

For example:

“He spoke for a short time” (lapsed time)
“The recession lasted for three years” (lapsed time)
“My birthday is getting closer” (lapsing time)

Time (unrestricted duration) T(ud)
This is duration in an unrestricted sense as DF continued existence.

For example:

“Everything exists in time”
“Time like an ever flowing stream bears all its sons away”

Succession series
Time is generally perceived and characterised as change that follows a definite order of succession expressed in the sequential relations earlier than, simultaneous with, and later than. Many philosophers believe this relation to be our most basic understanding of temporality. This order of temporal relations, which tells us when things happen, is treated in two very different and important ways. Either relations are targeted on the present (now), which we can call time (change) or T(c) or on one-another, which we can call time (permanence) or T(p). The language of these succession series does not always use the word ‘time’ itself, but time is implicit in its use.

Time (change), T(c)
This category encompasses what Cambridge philosopher John McTaggart referred to as the A-series, a temporal ordering which, he believed, encompassed real change. This is the language of temporal becoming with its associations of movement, flow and passage, its dynamism coming from statements made in relation to an ever-changing present (now). Thus times and events appear to move in some sense by passing from future, to present, to past (temporal passage).

What things may have these relations?

Well, we may distinguish what can be called the A-scale of times (which includes moments or particular durations (intervals)), and the A-series of events (taken to include facts, people and things). The significance of the distinction between times and events will become apparent later. In everyday language present events and A-times can be of any duration.

Being past, present or future are properties of tensed facts. The language we employ for this form of time uses not only the words past, present or future but also the grammatical tenses was = past, is = present and will be = future. But note that statements are also philosophically tensed if they can be placed in past, present or future in relation to the present (now) by words (temporal indicators) like yesterday, soon, now, or next week. In other words something may be philosophically tensed without using tensed verbs.

A philosophical tense is therefore a position in the time T(c) series (of past, present (now), future) defined by its location (and often duration) from the present (now).

For example:

“It is raining” rain simultaneous with the present (now)
“The party was yesterday” party one day earlier than the present (now)
“The next party is in three days” party three days later than the present (now)
“It is time for a cup of tea” cup of tea simultaneous with the present (now)
“The time is now 3 o’clock” clock time simultaneous with the present (now)
“I’ll see you soon” seeing you slightly later than the present (now)
“It is 4 pm” 4 pm simultaneous with the present (now)

Statements made using T(c) have truth values that also change. For example, “My birthday is in three days time” will change in truth-value as time lapses. The truth-value of statements made using such temporal indicators will therefore depend on the time (context) of their utterance and are thus said to be indexical, or token-reflexive.

T(c) is sometimes referred to as having temporal properties because it deals with things having the properties past, present and future. This contrasts with the temporal relations of T(p). However, T(c) is also relational but the temporal relations target the relations of the tenses to the present (now) rather than one-another.

T(c) indicates when in relation to the present (now) cf. T(p). Because T(c) involves change it is often referred to as a world of Becoming.

Time (permanence), T(p)
This category encompasses what McTaggart referred to as the B-series, a static temporal ordering in which DF statements of the relations earlier than, simultaneous with, and later than are made in relation to each other not in relation to ‘now’. McTaggart claimed that this series does not encompass real change. As before, there is a B-scale of times and a B-series of events.

Statements about time T(p) have truth-values that remain the same. Because the present (now) is irrelevant to this series, there is no need for language that uses tense; statements using the B-scale and B-series are tenseless statements. This is the impersonal, timeless and tenseless language expressing the changeless truths of maths, logic and some philosophy.

A date is a position in the T(p) series defined by its location (and often duration) from other events.
McTaggart’s B-series is said to be static because the dates of events and times do not change. The B-scale times and B-series events of time T(p) do not appear to move, only the present (now) of time T(c) seems to move.

The date of an event is related by its duration to another event and this date never changes because the duration between the two events never changes. For example “My 50th birthday occurred before my 25th wedding anniversary” if true, will always be true. The year 2001 is a date because it (unchangingly, that is truly) relates to the year 1.

Other examples:

“It rains on January 26 2001.” rain simultaneous with January 26 2001
“The party was on the same day as her birthday.” party simultaneous with birthday (also tensed)
“The Christmas party is on the last day of term.” next party later than this party
“The eclipse is in 2010” eclipse simultaneous with 2010
“Before tea” something earlier than tea
“Tea is served at 4 pm” tea simultaneous with clock reading 4 pm

B-times are not defined by how much earlier or later they are than the present but how much earlier or later than each other. The year 2001 includes all those events occurring between 2001 and 2002 years after Christ’s birth.

T(p) is treated as static or permanent because, T(c) there is no temporal movement or passage, and the relations between the times and events are unchanging as are the truth-values of statements about the series.

T(p) indicates when in relation to other events cf. T(c). Because T(p) does not entail change it is often referred to as the world of Being.

Similarities of T(c) and T(p) time-scales:

• Defined by the same temporal relations (earlier/simultaneous/later)
• Put events in the same order
• Measure time in the same way as durations or moments
• They are isomorphic (if a B moment is present, the times on one scale has counterparts on the other – if it is now (A-time) 2020 (B-time) then next year which is 1 year away (A-time) is 2021 (B-time))

Differences between the T(c) and T(p) time-scales:

• A B-time is a position in time defined by its relations to another time or event; an A-time is a position in time defined by its relations to the present (now)
• Durations of the B-scale remain the same; those of the A-scale are constantly changing, increasing into the past and decreasing into the future
• Statements about time (p) have truth-values that remain the same; those of the A-scale change.

1.2.3 Object and relation series
Most sentences use the word “time” either in the sense of an object – that is, something having an existence independent of other objects and events – or as a relation between objects or events. This usage is critical to our basic understanding of time, as there is the implication that time is either absolute or relational. In discussing time it is extremely difficult not to write or speak about it as though it is distinct from other things, even if this is not the intention.

Time as an object, T(a)
This is the prevailing use of the word “time” as a moment, instant, or substrate to existence that is separate from other things. It infers absolute time by treating time DF as an object existing independently of other things. The strength of this temporal separation from other things as expressed in various sentences seems to be a matter of degree.

For example:

“I will be with you in a moment” (cf. I will be with you in 5 minutes)
“The events were separated by time intervals of one minute” (cf. the events were one minute apart)
“The events occurred at the same moment in time” (cf. the events were simultaneous)
“Everything exists in time” (cf. everything there is, exists)

Time as a relation, T(r)
This is identical with the time (p) category??? which treats time as DF a relation between times or events that does not imply time as something separate from the things themselves.

“My 50th birthday is before my 25th wedding anniversary”
“The year 2001”

Time as a name, T(n)
We often refer to time in a generic way as a kind of name DF using the word “time” as a name.

For example:

“I am studying the philosophy of time”
“Is it possible to give a definition of time?”

Physical time, T(*)
Occasionally the word ‘time’ is used to indicate scientific or physical time (space-time). This is a sense not quite covered by those already given.

For example:

“According to Relativity, time is an aspect of the universe”

Time as now, T(now)
This is objective time, the physical boundary between determinacy and indeterminacy, which we experience as the specious present: sometimes also called the present moment or, more imprecisely, the present.

metaphor – ‘as if’ talk
Language needs to be highly practical if it is to facilitate our interaction with the world so it is not surprising to discover that language is much like a physics toolbox. Nouns provide us with objects or substances to work on, verbs provide us with causation as agents act on objects, pronouns locate all this in space, and verb tenses place it in time.

Our mental and linguistic physics toolbox is fine-tuned to permit a life lived without constant doubt and confusion. But there are some things that language does not address well and among these are abstract ideas. It is so difficult describing concepts like space and time that we resort to metaphor and analogy using ‘as if’ talk to colour our language and make things more concrete. Using metaphor brings concepts into the world of the familiar. So, for example, we ‘keep time‘, ‘tell time‘, and ‘pass through time‘, ‘save time‘, ‘spend time‘, and ‘waste time‘. If we break the law we might ‘do time‘. Time ‘flows‘ and ‘unfolds‘, sometimes we are ‘carried along with time‘ or perhaps ‘time passes us by‘ and maybe, just occasionally, ‘time stands still‘. Most significantly we have a better intuitive understanding of space than we do of time and so one way of describing time is through the metaphor of space. ‘My birthday is getting closer‘, ‘It has been a long time coming‘ … even equating time directly to space ‘It all happened in a short space of time‘.

The important point about metaphor is that it allows us to make inferences by giving us a framework for our reasoning, a framework grounded in the familiar and everyday. If time is really like space then we know that something can really be temporally close or distant.

What are we to make of all this metaphor? Put simply, metaphor can help or hinder – but we cannot always tell which one of these is coming out on top. We just need to be aware that metaphors allow us to use reason from one domain of knowledge to that of another, and that we are more gullible to accepting metaphor as reality than we care to admit.

We have already alluded to this in space-time-speak.

So, much of the mystery and puzzlement associated with time can be attributed to the assumptions carried mischievously hidden in the language we use to describe it. Firstly there is the problem of polysemy, the word ‘time’ having many many meanings. This accounts for some of time’s paradoxes, puzzles, and conundrums since we can be talking at cross purposes about different things. Secondly, because time is an obscure and abstract phenomenon we resort to the use of metaphor as a lever in the construction of inferences (see Science communication). This is fine provided it is legitimate to make such inferences but we need to be careful whenever we see a metaphor, to use the best ones, be aware that they can be contradictory, and remembering that much time talk is ‘as-if’ talk.

Here are some of the many ways time and metaphor merge.

The force of the following will only become apparent after reading and absorbing all PARTS.

Time-as-object talk (time is an object)
The most frequent error in the language of time is to unwittingly treat time as an object. If we think time really is an object that is fine but we need to be aware of what we are doing when we say ‘Time is flying by’ or ‘Set aside a block of time’.

So, talk about time often proceeds with an assumption of T(a). Time treated as an object in this way gratuitously gives it an independent existence, like a substance or container in which events happen (see also hypostasis speak). This possibly a product of our metaphorical mode of thought.

If you are a Relationalist referring to time T(r) then expressions such as ‘the events occurred at the same moment in time’ and ‘the events were separated in time by one minute’ and ‘an interval of time’ imply time (a) and are distinctly misleading. Replacing these expressions with phrases such as ‘the events occurred together’ and ‘the events were one minute apart’, ‘a time interval’ is much more conducive to time (r).

It may, of course, be argued that time (a) is not necessarily implied by the use of objectifying language. Be that as it may, replacement of such talk goes a long way to clearing the field of play for the Relationalist.

Examples like this are blatant: but at other times the role that language is playing is more subtle. Would ‘everything exists in time’ be acceptable to both views, and if not, how could it be rephrased? ‘In time’, ‘through time’ and ‘time itself’ are all problematic.

All uses of the word ‘time’ need to be scrutinized to see whether they imply that time is an object or a relation.
(Similarly for events?)

Space-time-talk & the qualitative differences of space and time
In everyday language we imply that time has little to do with space, and space has little to do with time. They are, in reality, closely analogous, so we often use similar or identical terminology for them when they are, in fact, qualitatively different. For example, duration and extension/expansion are qualitatively different. Thus a length of time is not the same as a length of space, even though we refer to lengths in both cases. There are many cross-referencing words like this including ‘gap’, ‘interval’ and ‘position’ but the analogy of space and time is pressed when we speak of a ‘long time’ or, at its extreme,a space of time. So we must beware of temporalizing space, and spatializing time. Movement (passage) of time is not the same as movement in/of space.

Stanford psychologist Lera Boroditsky has researched the human mental representation of time in terms of spatial metaphor and representation. Her work has shown that although spatial metaphor is universal there is considerable variation between cultures and social groups in the way this metaphor is expressed. Time is regarded as stationary or moving with people and events stationary or moving in relation to it, it is infinite or bounded, expressed as distance or quantity (English speakers mostly use distance – ‘A long time’, while Greek speakers use quantity – ‘Much time’), orientated horizontally or vertically, left to right, right to left, front to back, back to front, or along geographic coordinates (east-west). The way time is conceptualised is strongly related to the way particular languages treat time, the particular metaphors used, and the orientation of the written language (Arabic and Hebrew languages orientate time from right to left). English speakers tend to use horizontal metaphors, mandarin speakers vertical ones. The Australian Pormpuraaw languages orientate time by absolute direction (compass points).[1]

Once again the obvious cases are straightforward but there are many subtle problems to contend with as time becomes space-like and space becomes time-like. Can time have a ‘direction’, this seems a spatial term that would operate better with a temporal word. We often speak of time as ‘linear’ but although this word might feel right it does not make temporal sense. When language is teased out is may well be that a concept of space-time underlies the categories we refer to in isolation as ‘space’ and ‘time’.

Time & motion talk (time is motion)
Science, mathematics, logic and many philosophers claim that ‘becoming’ (with its past, present, future and transitive ‘now’ as expressed through the tenses is, was and will be) confuses the true representation of reality which is tenseless. That is, the dependence on tenses is a human construct with no foundation in reality.

Although this view is contentious it is the preferred approach of the above disciplines, which either ignore tense or use the present tense as a kind of a temporal language.

The context of motion and time generally involves four items: an observer, motion, objects, and locations (?times?). Motion suggests two options: either time is moving and the observer and objects are still, which involves language of the kind ‘Christmas is getting near’, ‘Time is passing’, or the observer is moving and time is still, which involves language of the kind ‘We’re getting closer to Christmas’. In both cases the metaphorical aspect of the language is challenged when we ask about the speed of this motion, although we do say ‘Time seems to go faster every day’. The situation is further complicated by blatantly treating time as an object in motion like a bird as in ‘Time flies by’ (three metaphors together time as a bird, time as object, time as motion).

Hypertime-talk (time is motion at a particular speed)
We cannot, without qualification, speak of time moving as it begs the question ‘How fast does time move?’ a question requiring the postulation of another time to measure the original time: that is, a hypertime, which would in turn move at a certain rate – leading us into an infinite regress.

This might seem like an obvious slip, but ‘moving’ time (a form of space-time talk) can creep insidiously into all kinds of discussion and is entrenched in everyday language. As we have seen, it may be claimed that motion of time is simply a metaphorical way of referring to something analogous (but qualitatively different from) spatial movement. However, it is as well to be aware of what is being said. One frequent error is to imply that time moves up a space-time diagram that already has time as a dimension.

Hypostasis-talk (events are motion in time)
We have already seen hypostasis in operation through the substantiation of time. In a similar way it is a simple matter to confuse events (or properties) with substances. We can infer, for example, that events move or change which is clearly not the case. Though this might appear an obvious error it is one that is easily made and often difficult to detect. It is not unusual to find assertions that events (which are changes) are changing themselves, which is plainly absurd.

Matter, time and space talk
Although we might not be sure of our philosophical position we should always be aware of the implications of what we are saying and always be alert to the alignment between what we assume is reality and what our words are saying. Space, time and matter give us ample opportunity to confuse concepts. Through our language we almost invariably treat them as separate. But if we are to believe relativity, then matter, space and time are inextricably linked rather than being separate things.

This is just one of many examples of science becoming more concerned with relations and less concerned with objects. We may not be able to account for this effectively in the way we use language but we should be aware of its implications.

Discrete-talk (time is discrete units)
We speak of time using the language of discrete units – as moments, hours, days – when physically it is generally portrayed as being continuous. If we treat time like number, or as being additive, then we incur all the problems of cardinality (counting). That is, problems of infinities, numerical systems, relations of addition and subtraction, discreteness vs continuity (density) and more. Discrete-speak is necessary for communication but it carries a heavy load of potential theoretical difficulty.

Time semantic talk
From the analysis of the semantic field of time it isclearly necessary to be aware of the various senses in which we speak of time, most notably time (as duration), time (as past, present, future) and time (as now).

Possible-world talk (past and future as places)
If we believe, with the presentist, that everything happens in the present, then there is a form of everyday language that is confusing. It is the way we speak of the past and future as though they are existing worlds. For example, we say “I will make the sandwiches tomorrow”, “I will do better in the future”. This kind of everyday language is harmless except that it creates the impression that there is a kind of world in the past or future that we “move into” or “move out of” as we go along. Whereas, in fact, we are always in the present, the future and tomorrow never come. To be pedantically logical we should say something like “I will make the sandwiches tomorrow, in the present”, “I will do better in the present of the future”.

Spatialization talk (time is space)
Probably the most obvious way we use metaphor in everyday language is in the use of spatial terms: we describe time in the terms of space. So we say ‘It was a long time’. ‘In the distant future’, ‘For a short period’, ‘A length of time’ and, best of all, ‘A large space of time’.

Direction talk (succession as direction)
We constantly speak of the ‘direction’ of time: we look ‘forward’ to holidays and we look ‘back’ at a mistake. On reflection this is clearly spatial metaphor. Time does not go forward and back any more than it goes up or down, left or right, sideways, north or south. It is worth making the effort to use more appropriate words for what we are trying to say.

Commentary

Because time is abstract and difficult to describe we treat it as something else in our lives that is more concrete and this allows us to make inferences (see Metaphor in Scientific communication). We mostly do this by using metaphor (‘as if’ language). So we try treating time as though it were a physical object, perhaps a physical object in motion, maybe an object moving at different speeds, or perhaps time is an object and we are in motion in some way. Perhaps time is abstract in the same way that space is abstract and we can learn about it by treating it as space? There are more metphorical ways of speaking and thinking about time but all this is manifest in the way we speak about time. We keep time, tell time, and pass through time. Time flows, unfolds, and passes by. We generally describe time in terms of space so ‘It was a long time’. ‘In the distant future’, ‘For a short period’, ‘A length of time’ and, best of all, ‘A large space of time’. Perhaps all this metaphor makes for colourful general communication but it does not help us to think scientifically.

Already it is clear that part of the mystery of time lies in polysemy (its many meanings) – that when we talk of ‘time’ we are referring to many different things, so it is not surprising that, taken at face value, time is a concept that is likely to confuse.

We are now in a position to draw a distinction between at least nine major strands of meaning in the semantic cloud of ‘time’, each with its own set of semantic relations. These temporal categories can be listed with their codes as follows:

Time (restricted duration) = T(rd) sub-divided into fixed intervals T(rd,fi), flexible intervals T(rd,fl)
Time (unrestricted duration) = T(ud)
Time (change) = T(c) which may be represented as a time T(ct) or as an event T(ce)
Time (permanence) = T(p)
Time (absolute) = T(a)
Time (relational) = T(r)
Time (general name) = T(n)
Time (physical time, space-time)= T(*)
Time (now) = T(now)

+ = semantic independence <> = semantic overlap

Semantic analysis alone has given us great insight into the many ways we think about time but it has not helped us answer the questions it poses. Is time an object? Does it move? Is time just a relation between things?

Confusion arising from the question “What is time?” derives not only from the difficulty of understanding the nature of time itself. There is also the complex semantic web we use to describe its many-sided character. For the philosopher, coming to grips with time is in large part a process of clarifying the language and concepts we use to explain, describe and interact with it. After all, it is clear from the four simple definitions of time given above that one reason why time is frequently characterised as deeply mysterious is because it means different things to different people.

Relativity theory tells us that there is no such thing as time by itself, but rather space-time. What consequences would there be if we tried to tidy up our everyday language by using the word “space-time” instead of the word “time”? Would it make sense to do this?

How are the various time words conceptually related? We often use the words “time” and “duration” interchangeably – but do they mean the same thing? Are there occasions when it is clearly preferable to use one of these words rather than the other? It can hardly be doubted that differences in meaning between these and other interrelated time words can cause confusion.

Is it possible to cut through these semantic difficulties and expose the metaphysical reality of time remembering that w can only communicate about time through language?

When we think of physical time it seems primitive; that is, an ultimate feature of the universe that cannot be reduced to something more simple or fundamental. We might consider space and time are ultimate irrationals of the universe whose presence is irrefutable but whose understanding is forever beyond our (direct) grasp.

Does time really exist in any sense at all other than in our minds? The following articles will look more closely at this question.

All the difficulties and puzzles we associate with time are interwoven in such a complex way that it is difficult to follow one particular thread of thinking from beginning to end. To help achieve this I have tried to cover many aspects by asking specific questions as follows:

How does language influence our understanding of time?
Is time a physical object?
In what sense does time flow?

Two observations can immediately be made about time. Firstly, as a word that is semantically extremely rich with many nuances of meaning we can anticipate ambiguity. Secondly time, being an abstract phenomenon, we can also anticipate the liberal use of metaphor to provide concrete examples of the way we can make inferences about time and its properties (see Scientific communication).

If we are to make sense of time then we must surely begin by analyzing the words and language that we use to describe and understand it: there is no alternative but to tease out the various ideas, doing our best to understand how they are connected and it what way. To do this will require a conceptual and semantic analysis and this will be the topic of this first article.

Intuitions must be the second topic to tackle because when doubt sets in it is to our intuitions that we look for support: we need to know as sooon as possible how strong this fall-back position is. What aspects of time are subjective, a consequence of our uniquely human perspective, or a matter of psychological projection? This topic is developed in Time 3 – Flow.

Aristotle defined time as ‘the number of movement in respect of ‘before’ and ‘after’”. Later, Plotinus pointed out that time is not a number, time is what is being numbered. Similarly, ‘before’ and ‘after’ in the sense in which Aristotle meant them were clearly not spatially before and after one-another, they were temporally before and after one-another i.e. ‘before’ and ‘after’ in time. So, Plotinus argued, on both counts Aristotle was providing a circular definition by defining time in terms of itself. This line of argument can be applied to other definitions. We might say, time is not succession itself, but succession in time.

Time is often defined in terms of change, but as soon as we examine the notion of change we are driven to talk about time, so perhaps time and change are, in fact, same thing?

When we think of time in this way we may be thinking of it as ‘duration’ – which dictionaries describe in either an unrestricted sense as ‘continued existence’ or in a restricted sense as a ‘measured or measurable interval’. However, in day-to-day language time is a rich and complex concept with so many nuances of meaning that any short definition would be totally inadequate!

The flow of time

Clearly time does not literally flow in the universe any more than words literally flow from our mouths. Flow-talk is metaphor that makes time space-like, giving expression to the vague sense of continual change or passage that we experience as events seem to transition from future, to present, to past.

Flow-talk allows us to reason about time spatially, as though it were a solid object, like water moving in space. Sometimes it is time itself that is moving (‘time passing by’), sometimes we are moving (‘we are getting closer to Christmas’) and sometimes we and time are moving together (on a ‘river of time’). Given that time does not flow like water, does that mean that it does not flow in any sense at all?

This article is, in many ways, a study of the psycho-biology of time.

Water

Water flow is a material object moving in space
But time is not a material object. What exactly is the feeling of time passing, and what words or images can we use to adequately express it?
Courtesy Wikimedia Commons
Krankenstand, acc. 4 Sept. 2015

Being & Becoming
The conundrum of flow has divided philosophers of time, from the ancients to the present day, into two broadly-defined schools of thought, each with their own set of associated viewpoints. For this reason the flow of time is a good place to launch into the philosophy of time, with the ancient pre-Socratic Greek philosophers and their distinction between, on the one hand, an eternal and unchanging world of Being as proposed by Parmenides and Zeno and, on the other hand, a world of constant change or Becoming as claimed by Heraclitus (see Socrates, Plato, Aristotle).

Over much of the 20th century philosophical discussion of this issue has followed the work of Cambridge philosopher John McTaggart and his paper ‘The Unreality of Time‘ which was published in 1908 at about the same time as Einstein’s scientific papers on the relativity of motion, space and time. McTaggart was an idealist and his paper seemed to distil several key problems about the nature of time. On the one hand we relate events and times to ‘now’ such that we have a past, present and future: this he called the A-series. On the other hand we relate events and times to each other as before, simultaneous with, and after: this he called the B-series. The A-series describes temporal becoming with statements involving tensed language using the verbs ‘is’, ‘was’ and ‘will be’. Language is tensed not only by the use of tensed verbs but also by any language that defines a location (and distance) in relation to now. “I take an exam next week” and “tomorrow I stay at home” are both philosophically tensed. Note that both the tenses and truth values of statements in the A Series will change depending on the position of ‘now’ when the statements are made. In the A-series events undergo a transition from future, to present, to past.

Nowadays these two opposing positions are referred to as the static and dynamic theories of time, sometimes expressed in terms of two ways of ordering events in time, either earlier than, later than, or simultaneous with (the static B-series), or as past, present, and future (the dynamic A-series). Both static and dynamic theories acknowledge tensed beliefs, say that I went to Rome a year ago and an aeroplane is now passing overhead. However the dynamic theory holds that these beliefs are made objectively true by facts about past, present and future, the static theory claims that what makes these statements objectively true are tenseless facts: that a plane is now passing overhead is simultaneous with my belief about the plane and that I went to Rome in 2014. For the dynamic theory truth values about events can change based on now. It is true that ‘I am alive today’ but 200 years from now, in the future, ‘I will be dead’, when the former statement becomes false.

As the static and dynamic theories are so fundamental to the philosophy of time I will set them out briefly below along with some objections:

The dynamic theory of time
This is the everyday belief of our common sense in which time and change are real but the past and future are not. Now is how we refer to the moment of constant change that is occurring in the universe and our minds.

If you accept that we live in a world of constant change (a world of Becoming) then you are likely to also think that the passage of time is a real, objective aspect of the universe. In the philosophy of time this view is usually linked to other ideas about time: McTaggart’s A-theory, presentism, the 3D endurance of objects, and the use of tensed language (language referring to past, present and future). The other ideas mentioned will be examined later but for our purposes here it is sufficient to explain, in a general way, how the world works for a presentist.

Presentism
For the presentist there is a moment in time, now, during which change is occurring. The future is what has not yet happened, the past is what has already happened, and the present is what is happening now. The only real and objective experience we have of events occurs when the events take place in the present and part of our experience in the present involves the mental process of relating to the past and future by means of anticipation and remembrance.

Objections

  • There is no objective ‘now’. Now is a part of our subjective experience, it is not an objective part of the world
  • Any reference to motion or change must refer to times other than the present, to motion over a period of time. How can this be if we claim that only the present is real.
  • There may be change as an ordering of events (A occurs before B) but not change involving the passage of time from future to present to past. The world is ‘timelessly’ one way at one moment then another way at a subsequent moment
  • How can we claim the reality of past facts if only the present is real?
  • If temporal passage is an objective aspect of the universe, that time really does move, then we should be able to detect an objective ‘now’, objective ‘flow’, and objective succession
  • We mark change and the reality of time through the transition from future to present to past but any event demonstrates all three properties, which is not coherent. It we claim that these properties are successive, that each event only has these properties at certain times, then we are again committed to the reality of past, prsent and future
  • The dynamic aspect of time seeks to find something about time itself that is distinct from its space-like representation as movement. This is usually presented in relation to the moving now and time’s direction but if this kind of movement is objective, then it makes sense to attach a rate but we cannot measure the speed of time using time
  • There nothing objectively special about a spatial location and similarly there is nothing special about a temporal location (like ‘now’)
  • Past, present and future have no role in the representation of the distribution of events in space-time
  • What is ‘here’ depends on the location of a person making a statement (it is subjective); so also for ‘now’
  • If there is no privileged vantage point in space-time that determines which events are simultaneous the past, present, and future cannot be objective properties. Without a real ppf there can be no passage of time and no temporal flow

The static theory of time
This is the theory of time revealed by logic and science in which past, present and future exist equally. Events occur like entries in a diary: before, after, or simultaneous with others … but there is no ‘moving now’ and events do not have the properties of being past, present and future.

The static theory of time, the world of Being, is is associated with McTaggart’s B-theory, eternalism, 4D perdurance, and tenseless language.

Eternalism
The static theory regards flow as an illusion because the present, or ‘now’, is not an intrinsic objective feature of the world, rather it is an extrinsic subjective evaluation made by an observer. For the eternalist Now is not an object that changes, it is the world that changes, so real change is a succession, a relation of before and after, not a relation between an observer and the world. On this view events simply ‘exist’ they do not ‘happen’. Metaphor spatialises time by mistakenly reasoning it as a physical object that is first in one place (the future) moving to another (the present) and then another (the past). But clearly we cannot apply this spatial reasoning to time because space and time are not the same: events (configurations of the universe) do not move (although the objects making up events may. Past, present and future are therefore subjective perspectival terms. ‘Since Einstein, events dont ‘happen’ they simply exist in a four-dimensional space-time continuum‘.

If we accept this critique of the dynamic theory of time then we need to find a more convincing way of representing change over time; we need a way to reconfigure passage and our illusory perspective on past, present and future in an objective way that does not imply flow. If we accept that there is no past, present and future then either everything happens at once (which is contrary to all our experience of succession) or past, present, and future are either false or highly ambiguous categories – perhaps time is, a it were, laid out before us without such distinctions (since it is we, and not the universe, that create these categories). If ‘now’ is a mental construct that does not actually exist in the world itself then an event may be future, present, or past, and this is the claim of the eternalist. The static theory of time avoids the apparent contradiction of temporal properties changing over time while preserving our sense of events being ordered in time: change just means that the universe is in one state at one moment and in a different state in another.

Eternalism & the block universe
Static theorists view the the whole of space and time as a four-dimensional grid (the space-time manifold or block universe) with each event located in its own unique part of the space-time grid. This allows us to envision the whole of time in the same way that we can envision the whole of space. The block universe spatialises time but has the advantage of revealing space-time for scientific inspection and precise mathematical representation, the world configured one way at moment X and another way at moment Y. We might use a mental representation as time slices in a loaf of space or as the sequence of individual frames of a celluloid movie. There is no place in this representation for past, present, and future. If we represent ourselves in the block universe we are protracted in space-time so that only one space-time slice of us exists timelessly at any particular point in space-time; the dynamic theory implies we exist in our entirety, even as time ‘passes’.

The block universe representation of space-time is, however, a god-like or Newtonian absolutist view of the universe of space and time from outside the system; it is a view from no-where and no-when. As human beings we exist within space and time so we do not have this privileged god-like view. Observers in different reference frames will have different representations of the block. Our view of space and time is complicated in two ways. Firstly, through the relativistic problems created by distance and explained in Einstein’s theory of relativity. Secondly, through our specifically human way of sensing only a limited portion of the space-time grid – that which has been historically important in the adaptation of our species to its own particular space-time environment (see Time-Now).

So, for the B(lock Being)-theorist all events are equal, related not by past, present and future which are specifically human attributions, but by being before, simultaneous with, and after each other. Einstein regarded the distinction between past, present, and future as a ‘stubbornly persistent illusion‘.[2]

Objections

  • Einstein or not, the presentist finds it difficult not to see the block universe itself as simply a highly effective scientific and mathematical tool. Nothing actually happens in the past or future. Dinosaurs are not fighting now in a world we call the past. And space-stations are not orbiting the moon now in a world we call the future. We cannot actually visit the past or the future. How can we possibly make sense of the vast span of human evolution and the universe if past, present, and future are an illusion? Is this some kind of word game?
  • The rephrasing of tensed language, say be using fixed dates, removes all sense of transience that we think must exist. How can we possibly rephrase tensed language into a meaningful tenseless language that we can use in everyday speech?
  • If time really does not ‘lapse’ (flow) then how do we account for the perception we have that it does
  • Dynamic change produces a reaction to certain events which we call causation. In the static theory ‘effects’ exist timelessly later than their ’causes’. This means we need to re-think our usual way of expressing causation, natual laws, and scientific explanation

Language
As we focus on the logic and physics of time we forget the power of language and mental representation. In attempting to express abstract notions like space and time we, consciously or unconsciously, use words that we think can assist our understanding. In so doing we find ourselves describing space in terms of time, and time in terms of space. Because we are more familiar with spatial than temporal objects it is not surprising that we constantly spatialise time, as in the extreme expression ‘A long space of time’. ‘Movement’ like ‘direction’ is a spatial word; it does not help us to use this language in relation to time. We can think that the trap of metaphor is too obvious and trivial for serious concern and in the face of more important philosophical problems. But nowhere is the power of language more evident than in the language of flow and direction. Movement itself is spatial language. All this can interfere with our thinking about time. Perhaps the best example relates to the ‘direction’ of time. One moment’s reflection tells us that time, whatever it is, does not go up or down; it does not move north or south … and yet we are comfortable in saying ‘time does not go backwards’. If you accept ‘time does not go backwards’ but do not accept ‘time goes up’ then you are a victim of metaphor influencing mental representation. We would do ourselves a favour by using more appropriate language when this is possible.

We continue with the problems of metaphor. Time, like now, is not an object moving in space like a wave-front of change, or a container, or a frame in which things happen. Past and future are not places so nothing can be in them. An event simply is. Even so, though ‘flow’ and ‘passage’ may be erroneous and subjective words, what we are trying to express when we use these words may nevertheless exist objectively in the world. We use metaphor, we spatialise time, because it is extremely difficult to express what time actually does. But by recognising the error of spatialising time by speaking about ‘flow’ we assume we have made an error in thinking about time’s objective reality. Time does not ‘flow’ but it does do ‘something’. We need a language of time that expresses what time does in non-spatial terms, that exorcises spatial words like ‘flow’, ‘passage’,’movement’ and ‘direction’. Fortunately we do have the appropriate words: we should use them more. We say that time ‘lapses’ or that it ‘elapses’. From this perspective our problem about time is not so much its objectivity but its abstraction or ineffability, the inadequacy of language to express what it is.

Put simply, we should not be ashamed of spatilalising time because it is extremely difficult to use words to express precisely and unambiguously what time does. Time seems flow-like or space-like while not being identical to these things. ‘Flow’ is a spatial word – but time is not spatial so it cannot flow … but it does do something, it does something temporal. From this point of view the problem we are confronting is linguistic and there is a solution to the problem. Our solution is to find a non-spatial word to describe what time does, and fortunately we do have one – and that word is ‘lapse’. Because I think the word ‘lapse’ is less confusing than the word ‘flow’, I shall use it from now on.

I believe we now have a better understanding of the subjective reality of the lapse of time, but what about its objectivity? After all time lapse, like time flow, could still be a product of the subjective mind, not the objective universe.

Australian philosopher Huw Price, currently Bertrand Russell Professor of Philosophy at Cambridge University, suggests three possible ways of establishing time’s objective lapse: (a) by identifying an objective present moment or now; (b) by establishing an objective sequence of earlier and later or; (c) by identifying something about time that is genuinely and objectively dynamic. He is not hopeful that any of these can be achieved, stating that ‘… it is difficult to see what coherent sense can be made of these notions, let alone how they could be supported by evidence or argument’.[1]

Let’s take each of these in turn.

(a) The objective now, privileged present
For the eternalist tensed statements like ‘I will be 21 tomorrow‘, ‘Everyone is now singing ‘Happy Birthday”, and ‘I was 21 last year‘ are statements about our human perspective on the world as seen through memory and anticipation. They may be useful as aspects of our experience that are absolutely necessary for daily existence, but they are not part of the objective world. The eternalist does not deny the past and future as the presentist does. The presentist maintaining that tensed propositions must be taken seriously because they can change their truth values over time; for the eternalist this is of no consequence.

The physics of relativity tells us that different observers represent the universe of space-time in different ways: since there is no absolute motion each observer has a different viewpoint and there can be no consensus on the simultaneity of events. This would certainly indicate that past, present, and future are simply a matter of perspective – and since they are not objective properties of the world there can be no passage of time and no dynamic change.

But the eternalist who supports McTaggart’s B-theory (past, present, and future are problematic but events nevertheless occur in a fixed temporal order) are also challenged.

There is no present moment.

(b) Objective temporal succession – before and after
The view that there is a constantly changing present moment when things are actually happening (that what is about to happen does not exist yet and what has happened has gone and therefore no longer exists) has been called ‘presentism’. Yet again we must be aware that now is not an object itself but a particular state of affairs. If we imagine the history of the universe set out before us from beginning to end then now is like a wave or spotlight illuminating one part, one particular configuration of space and time, as it moves from the Big Bang to the Heat Death.

Price objects to this characterisation on the grounds that now cannot be both exclusive (one moment is objectively distinguished) and inclusive (all moments get their turn). If the present moment is all that truly exists (exclusivity) then how can we possibly make any claims about other moments, as when we do history or consider what happened yesterday (inclusivity)? But doesn’t presentism allow that change has happened and that it will happen – that change can be represented without a distinguished moment (inclusivity)? If we have a distinguished present moment then either we lose change (because there is no change in past and future) or we accept change in an inclusive way, in which case there can be no distinguished present moment.

This parallels McTaggart’s conclusion about the unreality of time when he argues that there is no time without change that occurs in relation to future, present and past and since any individual event must exhibit all three then this characterisation of time is contradictory and therefore incoherent – hence time’s unreality. Price expresses a similar point by saying that the presentist treats past, present and future equally (inclusive) while at the same time claiming a unique present moment (exclusive) which is inconsistent.

Truth values appear to change over time and maybe that gives the sense of flow, but again this is all in relation to a possibly fictitious now or present. We can re-write the changing A-theory truth ‘It is sunny now’ to the explicit ‘It is sunny in Melbourne Australia at 10-00 am on thurday 6 June 2016’ which wil always be true and do not therefore flow.

Objective direction
Like ‘flow’, ‘direction’ is clearly a spatial metaphor since time does not go up or down, north or south in the same way as a solid object.

So where does this sense of direction come from?

‘Direction’ seems to lie in the succession of past and future, earlier and later, an apparent temporal asymmetry (anisotropy) that has no spatial counterpart. But what makes the earlier-later distinction an objective fact of the universe? Physicists (Boltzmann, Reichenbach, see Price) argue that the direction of time is a local matter reflecting the nature of entropy increase in a particular region of spacetime.

(c) Objective dynamism
Can we identifying something objective about time that is genuinely dynamic?

Certainly we have some sense of time passing, even though that passing might not be quite the same as the way we sense the movement of physical objects in relation to one-another and ourselves. The coming and going of day and night and the seasons, not to mention our physical aging are all ways in which we experience and communicate with one-another about the passage of time. So where does this feeling of ‘movement’ come from: is it an aspect of the universe that we sense in the same way that we sense heat or light, or is it purely a product of our inner psychology, something added to the world by our minds? Certainly the feeling of flow is an objective aspect of our minds. But the feeling may not be grounded in objective reality; perhaps we can express what is going on quite simply by saying that we experience a mental anticipation of events that then actually occur and subsequently become part of our memory: in our minds the future is our mental anticipation and the past is our memory of what has occurred. The inexorable continuity of minutes, days, and seasons is rather like the relentless flow of a river and we are captured by this metaphor.

Mental time-line & movement
My birthday in the future on 6 October 2005 will be 1767 days from “now”, 4 December 2000. Assuming I survive that long, my birthday will get closer and closer until the actual day of celebration in the present, after which it will recede further and further into the past.

Our entire sense of the “movement” of time is derived from the lapse of time in the present. The only objective aspect of any such scenario is the physical lapse of time and our sense of this lapse. The clock measures the lapse of time in the present. The “approaching” date of my birthday which we often “visualise” as a diminishing spatial interval is, in fact, a projected calculation of a duration of time in the present that will diminish until the birthday will happen in the present.

The passage of time, our sense of temporal movement, is generally attributed to a motion of events from future to present to past. It has been asserted that a better explanation is that it is the lapse of time in the present. However, there is a complex of related ideas that, in combination, gives us a strong sense of movement. These include:

• The “movement” of now, as lapse of time, to produce changing facts and truth-values about now
• Spatialization of the language of time by constant reference to spatial extension and contraction implying physical movement i.e. varying temporal intervals, distances, and lengths of time, or the temporal accretion/accumulation of facts and/or events and/or time
• The arrow of time with its language of directional movement “forwards” into the future and “backwards” into the past (whether this is real or not is irrelevant to the impression given by the language)
• Our perception of change, succession, and continuity
• Colourful metaphorical language i.e. watches “running fast”, time “flowing”
• Physical objects and events seem to pass into, through, and out of existence, and for anything to change it must become older
• The constant processing of information in the brain

Commentary

The challenge to the philosophy of time is to reconcile the seemingly ineliminable dynamic passage of time from future to present to past – with the static theory of time that follows as a consequence from logic, biology, and physics.[3]

Having familiarised ourselves with the arena of temporal discourse it is now clear that one-time metaphysical questions be addressed, at least in large part, by cognitive science and linguistics. What do we mean when we talk about ‘now’? Where does the feeling of motion come from as time ‘passes? Do we have a unique and limited perception of space and time simply because we are the animal Homo sapiens?

We lack the words to describe time and so we treat it as an object in space, reasoning about it in the same way that we reason about spatial objects. Soon seeing the error of spatializing time we spot the inappropriateness of metaphor and conclude that time cannot move. Common sense reinforces this conclusion when we try to imagine time moving like a physical object moves. We internalise the idea of time spatially as a time-line visualizing temporal intervals extending into the future and past in a spatial way, confused by language, perception, and the ineffability of time itself.

One way out of this dilemma is to use time words for temporal objects and space words for spatial objects. So, for example, rather than saying that ‘time flows’ we could say that ‘time lapses’ and add that time lapse is similar to spatial flow. This is just one way of indicating that time has space-like properties without actually making it space-like. Spatial objects move (flow), temporal objects lapse: moving and lapsing feel very similar. This could solve much of our problem. Past, present and future, do not flow, they are not moving objects at all, they are simply time lapsing. But we always want to say much more than this.

The metaphor of time’s flow-talk seems to mangle all meaning. We have: change as motion; time as a physical object; time as a moving physical object; time as static with moving events, properties and people; time orientated positionally in space (in front, behind, moving left to right, above, below etc.); now as a (moving) physical object (like a beam of light, a wave).

Time itself does not move (spatially) so in this sense the “passage” of time is a myth.The lapse of time always occurs in the present so nothing moves from future to past. However, the lapse of time (temporal ‘movement’) is real and objective; it produces the sensation of spatial movement and the aging of everything in the universe. When we refer to the ‘passage’ of time we are referring metaphorically to an objective temporal effect. There is a lapse of time in the present, not a movement of events from future to present to past.

The single most intractable difficulty is the way we “visualize” the durations between one event and another. We imagine time (spatially) as extending or stretching between events, not as a lapse of time in the present. We can, of course, represent time graphically as a line on a chart or graph. This is particularly significant in the case of time because we are representing a lapse of time using a spatial representation (a line or axis on a chart) when space is precisely what time is not. We are representing something in a form it cannot assume. Of course temperature is not a line on a graph either, but in this case its graphical representation does not present the same kind of problem. In spite of all this, the linear representation of time does not lead to errors of calculation, only serious errors of imagery. We can cope mentally with space because of our awareness of extended objects: but time has no tangible counterparts. That is one major reason why its reality is so often in question.

Spatialization of time is very difficult to exorcise. We generally think of “amounts” of time in terms of lateral spatial extension. The lapse of time cannot have a direction. Direction relates things in space. But in everyday language we erroneously force time to go up and down, or from side to side. So, for example, the future lies “ahead” and the past “behind”, with events and times being greater or lesser “distances” away from us along the future-past axis. With the realization that temporal “distance” is nothing more than time lapsing in the present and therefore not extending outwards on either side, we are then tempted to think of time lapsing, not along a horizontal axis but in a cumulative sense on a vertical axis. “Amounts” of time then “build up” or “accrete”, as do facts and events, in a kind of “additive” or way in the present so that the past then becomes a quantity of time “accumulating” “below” us, and the future is time “above” us waiting to join the heap below.

All this spatial imagery is harmless in everyday discourse, but it is counterproductive in coming to grips with the concept of time lapse and the reality of time. It can also lead to . Even relatively space-neutral words like “interval” can be interpreted spatially.

The only solution for the philosopher and scientist keen not to be misled by temporal spatialization and hypostatisation is to use words like “lapse” and “elapse” in preference to “passage” or “flow”, and “duration” in preference to the words “distance”, “accretion”, “interval”, “approaching”, “receding” and so on. An expression like “temporal extension” is an oxymoron. Since we define space as extension, then we are here referring to time directly as space as when we speak of a “long time”. The metaphors are endless as we are led inexorably towards … finally … a “space of time”.

One way of removing flow is to regard events as passing from being indeterminate to determinate. This is a change in property that does not carry the burden of movement in the same way as ppf. Presentists deal with flow as being the coming into existence of facts and new states of affairs without the commitment to events themselves moving in any way.

This is all part of the struggle to distinguish time from space, and dynamic and static theories of time and their likely objectivity. Price notes how the temporal character of conscious experience (its phenomenology), even if misguided, requires explanation suggesting that we mistakenly regard ourselves as fixed points and that time therefore flows past us.[5]

It seems that science and logic can tell us something about the nature of the world that is almost impossible for us, as adapted biological organisms, to accept.

Timeline
1905 – Einsteins theory of General Relativity makes space-time physical, not just metaphorical

Change

The previous article article on the flow of time discussed the dynamic and static theories of time that have occupied philosophers throughout history pointing out the way we seem to mark time in two distinct ways, either with the changing properties of past, present, and future, or with the fixed relationship of before and after. Past, present and future are established in relation to an ever-changing point in time that we call ‘now’ or the present. The relationship ‘before’ and ‘after’ does not refer to or need the idea of ‘now’, it is simply a ‘timeless’ relationship between events … it does not demand that things ‘flow’, ‘move’, or ‘lapse’. This second static view of time is the one preferred by science which finds no need for temporal flow. And yet change in the universe seems undeniable, a primitive, brute fact.

How can we possibly claim that change is a subjective phenomenon, just something we feel, rather than something that is actually going on outside our minds? Various philosophers have claimed that not only is change in the universe real, time does not exist as an object in the universe separate from other things, time is simply change itself. Notable among these philosophers was Plato’s student Aristotle who regarded time as a unit system used to count, order, or measure things. The tradition has continued to the present day with, for example, the Australian philosopher Jack Smart describing time as the ‘dimension of change‘. If we are struggling to define time in terms of change then the denial of change itself is very useful – because it means that the reality of time can be quickly denied too.

So what have we learned about change in the course of history?

Permanence & change
The philosophical conundrum of permanence and change in the universe dates back to at least the Eleatic pre-Socratic philosophers and was expressed by Plato through his ideas of Being and Becoming (see Socrates, Plato, Aristotle). It is easy to dismiss this dichotomy of thought as fanciful and unproductive philosophical speculation but it is still with us today in modern science with science taking the more ‘other-worldly’ view. The pre-Socratic philosophers Parmenides and Zeno argued that change was a kind of idea in the mind – they were what we earlier called idealists. To make the point about the subjectivity of change Zeno (c.490-430 BCE) devised a number of space-time paradoxes and a couple of these are well worth thinking about here.

First, there was the Paradox of Achilles and the Tortoise. We imagine Achilles racing a tortoise. He gives the tortoise a head start. To catch the tortoise he must first reach the point where the tortoise started – but by that time he reaches that point the tortoise will, of course, have moved forward. He must therefore now reach the point that the tortoise has got to. But again, when he does so the tortoise will have moved forward again. At this point it becomes clear that Achilles can never catch up, so the tortoise wins the race. How can that possibly be?

The second is the Paradox of the Arrow. A flying arrow is an excellent example of change because it demonstrates the motion of an object in space. Zeno pointed out, however, that if something is in motion then it must be in motion now, not in the past (when it was somewhere else) or the future (when it will be somewhere else). But at the brief instant of time which has no past or future the arrow can only occupy a space equal to its own size: it is therefore at rest. The same reasoning can be applied to all motion: movement and change are illusory. These idealists believed that the true nature of the world, its timeless perfection, is only evident to us when we ignore the evidence of our senses and apply strict reason. Aristotle and others have given compelling answers to these paradoxes but they express the flavour of problems that arise in philosophical discussion.

Parmenides (c. 485 BCE) is less easily dismissed. He also had a tricky question that he framed in the form of a prose poem. Here he argued that change involves something becoming something else in a transition we can only interpret as the reality of transition from future to present to past. For example, we treat the past as real when we say ‘it is a fact that I was driving my chariot to work this morning‘. But we also treat reality as applying to now. But if past events were real then they would be now, they would be present! More specifically we talk about non-present things as if they were real when we know that they are actually nothing; we treat events as ‘something’ coming out of the future, which is ‘nothing’, and ‘something’ in the present passes into ‘nothing’ in the past – but how can something become nothing? Where does it go? Variations of Parmenides’s concerns are still with us today.

We are tempted to say that of course things dont pass into nothing: a rock, for example, endures. But wouldn’t time still be passing while the rock endures? Parmenides pointed out that anything that endures must have temporal parts, those existing now, those that did exist, and those that will exist. But an existing rock surely cannot have non-existing parts? For Parmenides this is another way of demonstrating the illusion of change and time.

If you are puzzled by these paradoxes then you can look them up on the web and see the standard replies. Aristotle’s answers were not based on the evidence of the senses but on reason (Zeno and Parmenides considered the evidence of the senses as illusory, so Aristotle could not use sensory evidence to defend an alternative point of view). There are modern-day compelling answers to Zeno’s paradoxes but Parmenides has continued to mesmerise the philosophical mind because when we describe change we appear to commit ourselves to the reality of past and future while at the same time being tempted to deny their existence.

There is no doubt that in the attempt to reduce time to its simplest form philosophers have fallen back on the brute fact of change. We simply cannot imagine a change that does not require a temporal interval T(rd) and, most significantly, we measure time using movement and change so it is difficult, if not impossible, to dissociate ourselves from this aspect of time. The idea of an instant of zero duration is incoherent. Indeed, the argument that time is change itself is very persuasive and since Aristotle considered time to be way of thinking about the way events are objectively related he did not think that time was a kind of idea in the mind, it had reality in the universe, he was a relationist.

The conclusions we reach about time and its relationship to change will depend largely on a simple underlying assumption: whether time exists in its own right as a physical part of the universe with an identity of its own or whether it only exists as a relation between things. The physics of this question will be discussed in Time 6- Physical time.

Billiards

Time-lapse photograph of an eight-ball break
‘Time is change’
Courtesy Wikimedia Commons

Semantics of change
First some tidying up around the linguistic edges. Change, like time itself, is a complex concept. As metaphor we frequently associate change with spatial rather than temporal change so we need to be on our guard for difficuties associated with making time space-like and space time-like. Then there is polysemy. We can, for example, differentiate between intrinsic and extrinsic change. When we say a poker ‘changes’ from hot to cold this is an actual change in physical properties of the poker but when we say a road changes from bitumen to gravel this is not an intrinsic change in the road surface but a change in perspective relating to someone travelling on the road.

Time as change, T(c), is undoubtedly semantically and conceptually the most complex aspect of time T(n). The relationship between change T(c), physical time T(*), absolute time T(a) and relational time T(r) is critical to our general philosophical conclusions. There are three major difficulties:

• T(c) entails the temporal categories ‘now’, ‘past’, ‘present’, ‘future’ and the temporal relations of ‘earlier/before’, ‘simultaneous with’ and ‘later than/after’ both as they relate successively to one-another and to events
• There is then the interrelationship between T(c), T(a), T(r), and T(*)
• Finally there is the determination of the subjective and objective elements of these various categories

Central to the philosophical discussion is whether or not we regard ‘now’ as a product simply of human perception or whether it has some objective basis in the world. ‘Now’ has a similar meaning to ‘present’ being difficult to define without circularity. However, ‘now’ does have a more urgent sense than we usually attribute to ‘present’ and this needs recognition in any semantic taxonomy. For the purposes of this account this distinction will be drawn more finely by defining ‘now’ as DF the indeterminacy of the future (unknown) giving way to the determinacy of the past (known): the coming into being of determinate reality (objective). Note that this definition is given in the present tense and also that it is not ‘the moment when’ now occurs. Now is our perception of time itself. ‘Now’ is the only semantic element of the semantic taxonomy (excluding T(a) and T(r)) that does not exist in T(ud). ‘Present’ is defined more innocuously as DF the current state of affairs or now as perceived and acted upon by humans.

Succession
Semantically ‘change’ is very closely related to the notion of ‘succession’. However, if we link duration T(ud, rd)] strongly to the notion of time, as most people would, then this diminishes the semantic impact of succession although there is clearly semantic overlap.

TIME, SPACE & CHANGE
Time has been described by at least one philosopher as the dimension of change (see Smart, Encyclopaedia Britannica). A change is something having incompatible properties at different times: that is, a variation over time in the properties of something.

Separating space & time
Philosopher McTaggart maintained that permanent truths, say, that on any weekday I am in bed at 6 am and at work at 8 am, do not demonstrate change. We are inclined to say that if I am in bed at 6 am and at work at 8 am on the same day then something must have changed. McTaggart stressed that on close inspection the two facts as presented were unchanging facts that could not constitute change itself. He claimed that change must involve changing facts about how things are now: it is only the present time (now) that keeps changing and this is the only true change: it is temporal change and we refer to it as the passage of time.

McTaggart noted that time and space are closely related and this shows up in our language. We even speak of a large space of time. What makes the dimension of time genuinely different from the dimension of space is that time seems to flow in some sense while the dimension of space does not.

Space and temporal intervals seem totally different. Maybe we can compare the two by making time space-like, and space time-like, then we will be comparing similar things. So perhaps it possible to tease out the difference between space and time by asking a precise question involving space, time, and change? For example: ‘What is the difference between poker 1 that is hot at one end and cold at the other, and poker 2 that is hot at first and cold later?’

We cantake a time-like view of the poker question by temporalizing space (describing it in terms of time, the spatial differences of the poker that is hot at one end and cold at the other) by answering:

(1) The difference is that poker 2 is hot before it is cold, but poker 1 is hot and cold at the same time.

This is true, but presents us with a contradiction. How can a poker be hot and cold at the same time? To resolve the contradiction it is necessary to point out the omitted spatial information, that the poker is hot in one place and cold in another. It is important to note that when we temporalize space like this it is immediately obvious because of the apparent contradiction.

Now we can spatialize time (describing the temporal difference as though it were a spatial one) by answering:

(2) The difference is that poker 1 is hot in one place and cold in another, and poker 2 is hot and cold in the same place.

This is also true but again there is a contradiction. How can the poker be hot and cold in the same place? The contradiction is resolved by pointing out the omitted temporal information, that poker 2 is hot before it is cold in the same place. Thus, when we spatialize time we omit the essential before and after relationship.

Endurantism vs perdurantism
In trying to get to the true nature of space and time we can accept that the poker has separate spatial parts; but can it, in a similar way, have separate temporal parts? Do objects have temporal extension in the same way that they have spatial extension?

The controversy endurantism vs perdurantism combines several separate debates including the following (at least): eternalism vs presentism; A-theory and A-properties vs B-theory and B-properties; differences between space, time and space-time; the true nature of physical objects and events; the true nature of change; and as usual, and most importantly, the question of whether we should treat time as a relation or an object. Endurantists maintain that all temporal parts must entail the entire poker (3D, temporal, A-series, presentist, Becoming) perdurantists (4D, atemporal, B-series, eternalist, Being) maintain that they do not.

Perhaps the most telling difference between 3-D and 4-D is that there is generally an entailment of presentism with 3-D, and eternalism with 4-D with their corresponding temporal and ontological commitments. We are once again talking about the A series (absolute) view of the world and the B series (relational) view of the world. 3-D is temporal: it uses language relating to past, present and future, the A series. 4-D is atemporal: it is timeless and removes all talk of tenses, the B series. For example, 3-D temporal part-hood is irreducibly relative to times. A 3-D’ist can either say “I am 2.2 m tall”, in which case it is assumed that what is said assumes 2.2 m tall now (tensed). Or she can say “I was 0.1 cm tall in 1945” (tenseless?). This is our everyday way of speaking. The perdurantist places no ontological emphasis on tensed language. Therefore since my space-time worm includes my height as being say 0.0001 m to 2.2 m the temporary properties of being 2 cm or 2 m tall are had simpliciter depending on which part of my space-time worm we are talking about. Both heights exist unconditionally and equally in my space-time worm. Being human I want to add the subjective now to locate the height in my time. Thus in the perdurantists tenseless world Socrates exists tenselessly as a part of the total space-time-scape while the endurantist says Socrates exist(ed) (wholly) because clearly he does not exist now. Just as here is not spatially privileged, so now is not temporally privileged.

For the perdurantist objects have temporal extension in the same way that they have spatial extension. We should think not of 3-D objects in time but of spatio-temporal objects in regions of space-time. Spatially, an object can have one property in one place and a different one at another and the whole object exist. But temporally we are tempted to say that the temporal whole exists all at once, unless we adopt the ontology of eternalism. The 4-D’ist must be temporally neutral and tenseless in the location of events and objects in space-time.

The difference between 4-D and 3-D can be seen in what they imply about change. In a world where substance is permanent, what changes is the properties or relations, or aspects of them? Endurance theory holds that change involves properties or relations coming into or going out of existence because if the past and future do not exist there is no place for them to come from or to go to. For perdurance the properties and relations never come into or go out of existence because if the future exists then the properties and relations already exist before the change takes place.

What is it that physicists are measuring when they measure time in the 4-D manifold? Which part of the space-time-scape are they measuring and why that particular piece – to locate that piece of time we must assume A-properties.
[The Block Universe is temporally closed, quantum mechanics is temporally open. To be explored later].

Semantics of ‘change’
Let’s try to isolate the idea of spatial change from that of temporal change. Over a distance (space) of 1 km a road surface might change from bitumen to gravel. This is a spatial change in the road, not a temporal change. Certainly the way the word ‘change’ is being used here follows common usage since we say ‘The road changes from bitumen to gravel’. Would we say that this is genuine change?

There are three important points to be made about this example that seem to distinguish spatial change from temporal change.

If we think of spatial change as the movement of a whole object from one place to another then this movement will take time; so itis not just a spatial change. So if we assume that spatial change of objects involves change(s) to spatial parts, not to the whole object then we might say that one spatial part of a road is bitumen, the other spatial part is gravel, one does not literally change into the other. But we should note that this is not the way we gnenerally understand change. Viewing the road from above in a helicopter one part of the road is gravel, the other is bitumen. We generally refer to spatial change when we have an externally defined direction from which to view the change – as when we travel along a road that changes from bitumen to gravel. The road was bitumen before it was gravel which is a temporal change.

In contrast, temporal change, such as that of a poker being hot before it is cold, involves the whole of the poker. (this difference is examined in more detail in ).

So we have two difficulties. Firstly, there is the word ‘change’ used as metaphor. Spatial change of the type bitumen to gravel on a road is not a change in physical properties (intrinsic change), it is better described with the word ‘difference’. The bitumen and gravel have remained the same. Indeed, because they have remained the same, we are surely entitled to say that they have not undergone true change at all.

When viewing change in this way we feel justified in claiming that the only true change is temporal change and that spatial change is far better referred to as difference (since nothing actually changes). Also the temporal before and after of temporal change implies ‘direction’ that is intrinsic (a part of the sequence of change). The before and after of spatial change has only extrinsic ‘direction’ (a direction that is imposed from without). This is a critical distinction: temporal direction, unlike spatial direction, is not a matter of human perspective. We can be assertive about this.

We can recognise the vagaries of language by asserting that spatial change as an object having different properties at different places (spatial change) is metaphor for real change which occurs when an object has different properties at different times (temporal change).

We can summarise the differences between temporal and spatial change as follows:

• Temporal change involves things changing their intrinsic properties. Spatial change is not intrinsic change
• Time has an intrinsic ‘before’ and ‘after’ (generally referred to as ‘direction’) while the ‘before’ and ‘after’ of space is extrinsic
• The ‘before’ and ‘after’ of temporal change is real change while the language of spatial change is ‘as if’ metaphor
• Spatial change is more appropriately referred to as ‘difference’
• When we spatialize time or temporalize space then essential information is lost

Our examination of the poker indicates that the isolation of space and time does not seem possible: it can only be treated as a kind of thought experiment. Although we can imagine spatial difference and temporal change as sepearate entities, especially in our everyday language, we can see under analysis that underlying everyday language there is not space and time but space-time. Everything that exists, exists ‘in time’.

Before and after
If the analysis above is correct then reference to ‘before’ and ‘after’ are intrinsic to time but extrinsic to space.

The nature of temporal change
Accepting temporal change as true change this can now be thought of in three ways:

1. Relations at times
The poker is hot before it is cold

This asserts that objects stand in different relations at different times in the same way that parts of the poker have particular spatial relations. This seems to deny change because at t1 the poker is hot (and that will always be true) and at t2 the poker is cold (and that will also always be true), so, when expressed in this way, there is no true change. Of course, we might impose true change by adding that t1 is before t2 (see discussion ).

2. Perdurance as temporal parts
The poker is hot at t1 and cold at t2
Change involves one temporally extended object (t1) having one part with one property (p1) (hot poker) and another temporal part (p2) with another property (p2) (cold poker). Change is treated the same way as spatial difference. Also the properties now attach to temporal parts: there is no whole thing (the poker) that changes its properties. Assumes eternalism: things exist equally over time. (see discussion)

3. Endurance as a whole
The poker is now hot and will be cold
The only properties the poker has are those that it has now, so it can never have incompatible properties. An object is wholly present at every moment of its existence. Assumes presentism; things only truly exist in the present. (see discussion )

ABSOLUTE AND RELATIONAL TIME AND CHANGE
If time is an object, it may well exist independently of change. If time is a relation then it only exists with change.

For the Relationalist time is change so time can only exist if there are objects with properties in spatial and temporal relations. McTaggart’s B series is relational because if, as B theorists maintain, the relations earlier than and later than involve primitive temporal relations, then the temporal relations are between things – time is not something in addition to those relations.

For the Absolutist, if time is independent of other things then it is equally obvious that it cannot be reduced to any of them, no matter how appealing that might be. If time (a) is independent of change then it cannot be change. Change then occurs in time and not vice-versa. Defenders of Absolute time maintain that although we may need change to measure time, that does not mean that it is impossible to have time without change. There may be a time that began earlier than our universe; time without events; time without objects; time with no beginning or no end – we simply do not know. If now is time itself (or change as McTaggart claimed) and we relate past, present and future to now, as we do in McTaggart’s A series, then we are treating it as an object: that is, as absolute.

McTaggart’s A series treats time as now, as an object, and therefore as absolute. McTaggart’s B series treats time as absent (a relation) since, according to McTaggart, it lacks true change as nothing relates to the truth-changing now. B-theorists who maintain that the B series entails primitive temporal relations must also assert time as a relation between things (not to now) and therefore relational.
When we ask a question such as “Can we imagine a world with time but no change?” it is important to remember that.

A material object can no more exist with zero duration than with zero length or breadth.

Strong arguments have been forwarded for the theoretical possibility of time and changeless worlds (see Shoemaker, ).

PAST, PRESENT, FUTURE
Most questions in the metaphysics of time lead to the questionable basis in reality of past, present and future (ppf). This does not, at first, appear to raise a problem. After all, we understand, think and act on the ideas of ppf without any practical difficulties or philosophical puzzlement. The key question, however, is what is it that makes a statement that something is ppf true or false?

Mellor (1998, pg.2) poses the problem by asking what makes a statement like ‘e is past’ true when it is true, namely when it is said at any time (t) later than e? He then offers our alternative replies that either e has the property of being past (A-theory), or e is earlier than t (B-theory).

But this is to pose the question in an unfair way because it both assumes the B-theory as a solution (the statement is true because t is later than e), and illustrates its detached perspective on the world (e and t are being observed by a third “timeless” party). The reason the statement ‘e is past’ is true at the time when it is actually said, is not because the statement was made later than e. The objective feature in reality that makes the statement true is that the time when the statement was made was later than e. We call that particular time the present, or now. (The time when it was made is a B-fact) BUT presentism.

In the context of this argument, presenting the problem in terms of statements is to superimpose the linguistic on the metaphysical: it is both unnecessary and confusing.

ONTOLOGY OF TIME
There are eight possible combinations in which past, present and future may be allocated existence or reality. What combinations may be called real or objective?
Only the following have been taken seriously:

• The past, present and future exist equally (eternalism)
• The past and present exist but not the future (past-presentism)
• Only the present exists (presentism)
• Only the present exists but the past is more real than the future

Eternalism will be dealt with in the chapter on Permanence. For the time being past, present and future are considered from the point of view of presentism.

THE PAST
Common sense tells us that the past is in some sense real. Fossils display to us the times when dinosaurs roamed the earth and the empty cup of tea in front of me indicates what has been going on in the more recent past. But our feeling is that only the present truly exists – or at least that it exists in a very special way. Is the immediacy of the present real or in some way a function of our conscious awareness?

If only the present is real then what are we to make of past and future events? For, if there are no past events, there can be no temporal series.The past is what has already happened. It is the totality of objects, their properties and spatiotemporal relationships that occurred in a present that no longer pertains. Nothing ever happens in the past. Things only happen in the present. What is objective – that which is real in the world outside our minds – is the objects, their properties and spatiotemporal relationships as they pertain now. Because many of the objects and relationships that occurred in the past, persist in the present there is a strong sense in which the past remains with us, so that we feel that it is real now. But it is not the past that is real now, only the persisting objects, properties and relationships.
We also feel that the past is with us because we can clearly recall past events. However, all memories of things from the past necessarily occur in the present and are subjective. A memory is, of course, a real and objective mental process in the present. But it is only a representation of something that has already happened, and it is not accessible to other people: it is the past event itself that is objective and real, not its representation in our minds. In other words, we cannot visit the past physically (objectively). We can only have subjective memories, recollections and imaginings of things that occurred, or might have occurred, in the past.

The past, we feel, no longer exists. However, there are facts that we believe about the past: that dinosaurs existed, as did Greek philosophers, ammonites, Elvis Presley and so on. Though not existing now, these facts have greater reality than assertions about the future. Can we argue that it is a fact that something in the future will be the case? Only the present exists but the past is more real than the future.

We need a clear and objective view of the past. It has already been noted that the process of aging is the lapse of time in the present. So is Socrates now over 1000 years old? Socrates does not exist so he cannot be aging, although we can calculate how long it is since he existed. There are some dinosaur bones that exist now and they are tens of millions of years old and still aging.

We feel that we have conclusive evidence of events that occurred in the past. Using tensed language we say that dinosaurs existed in the past. To capture a sense of the reality of past events we could say that dinosaurs exist, but they do not exist now. The future is what has not yet happened .We cannot say that anything exists in the future.

PRESENT AND PRESENT EXPERIENCE
Intuitively all our experience takes place in the present: this is the common sense view of the world. We catch trains, set watches, watch sporting events world-wide and view the ebb and flow of stock markets and currency values as a world community. These are all public events that occur in a public now that is accepted universally without question. We believe that biological species and the universe itself has reached a particular historical phase of evolution that we refer to as now. If we are deceived about the reality of now, then we are all deceived together. There must then be a collective “subjectivity”.

Direct awareness of things and events seems to justify their being present, and that earlier events that we remember are past. But when we look down a telescope we see past events, things that happened light years ago, as present. So can we be deceived – is presence a matter of awareness, or our human perspective or some other subjective influence?

The B theory cannot account for the following aspects of the presentness of events:

• We sense that we are at a particular stage in the evolution both of the universe and biological organisms that we call now. There is no evidence of any future – we are not visited from people of the future or have any kind of experience of things in a time beyond now.
• There is a completely unquestioned world-wide communality of now as instanced by an agreed synchronisation of, for example, watches, sporting events world-wide, and the ebb and flow of stock markets and currencies. If these are illusory or subjective then they are to humanity as a whole.
• For the B theorist the present is simply an indexical (token reflexive) relationship to statements. When we refer to the present or now we simply mean “simultaneous with this utterance”. But there are many occasions that we regard as present when nothing is uttered.
• B theory relates awareness of A-times to dates but we may be aware of the present regardless of any dates

It should be noted, however, that for the B theorist presentness is a feature of our awareness rather than a feature of events: we must distinguish between our experiences and our present-tensed beliefs about them.
Although “E is present” cannot be translated into tenseless language, what makes it true is that it occurs at the same time as the awareness of it!?

HERE AND NOW
‘Here’ is the spatial analogue of ‘now’. Just as A-times relate to now, so A-places relate to here: and just as B-times do not relate to now but to each other, so B-places do not relate to here but to each other. It is notable that although many people believe in temporal A-facts (e.g. that an event itself has the property of being now), no-one believes in A-places (e.g. that Melbourne itself has the property of being here). Things and events in space are literally neither here nor there.

We have isolated three meanings of present – do these have spatial analogues?

The presence of experience – our awareness that all our experiences and actions are present (same as below?)

Specious present (now) – my now, the perceived immediate moment appropriate to human action = my here.
Contextual present (now) – contextual now i.e. present second or present century = contextual here i.e. the town or planet that is here.
Present (now) – the physical temporal boundary between determinacy and indeterminacy (mind-independent), the true A-time of an event (what is the true A-time of a soccer match?) – no spatial analogue

We need to determine similarities and differences between here and now, as this may be a significant difference between space and time – now being associated with temporal change and there being no objective here? What is the relationship between here and now? Are they completely congruent? If they are then whenever we make an assertion about now then there should be an equivalent assertion about here.

A-THEORIST B-THEORIST
Theory of space assumes hereness and thereness are mind-independent properties of objects over and above their locations and the fact that the objects are near the places we occupy Hereness and thereness are mind-dependent properties. All that exists are objects, their spatial locations and relations to other objects. Our experience of space is just our experience of these locations and relations
Presentness is something we experience in addition to an event’s occurring: it is not simply the occurrence of an event, or the simultaneity of the event and our experience of it. We do not know what it is but we know what it is not, and we can sense it. It is something we experience in addition to the event itself which tells us that the event is now. B-theorists say that this is precisely what A-theorists deny. When we experience an object as here, do we experience it as more than the object and its nearness to us? If this were all we experienced then we would not know the object was here. Rejected. Hereness is not something extra.
We cannot choose the times we can be at We can choose the places we can be at
We feel that the present exists in an objectively privileged way. Past and future do not seem so important. We do not feel that here is spatially privileged.
Past and future events are not equally real. Temporally distant events do not occur at the same time as temporally near ones. Objects elsewhere are equally real. Distant objects exist at the same time as near objects.
Present is characterised by a changing set of events – the feel of movement Here has no sense of change or movement. If we move from place to place we would not adopt the A theory anyway
The space analogy suggests no experience beyond simultaneity is needed to experience presentness

Presentism
The ontology outlined so far is called presentism. Presentism is the view that only present objects exist, all other objects are unreal. An inventory of all the things that exist would not include any non-present objects. The only things that exist are those that presently exist. Associated with this view is the assumption that time is not like space.
We want to say that it is not that the objects of the past do not exist but that they do not exist right now. This is not possible because the presentist wants to say that the set of all that exists changes over time.
The presentist position is that of common sense, the position that most people would take when first asked their view on what exists. However, such a position has many problems because much of our language is devoted to things in the future and things in the past, namely non-present objects that the presentist claims do not exist. It has already been observed that most of our mental activity involves an interplay of anticipation and recollection. When our mind is focused on the present we are hardly aware of its activity as when we are playing a competitive game of table-tennis, driving on a dangerous road or watching a thrilling movie.
Problems for the presentist include:

• There can be no singular (specific) propositions about non-present objects. For example the statement “Socrates was a philosopher”. Presentism must maintain that when Socrates was no longer present, singular propositions about him must also go
• If there are no non-present objects then no-one and nothing can stand in any relation to any non-present object. I cannot be my great grandfather’s grandson. For the same reason nothing today can stand in a causal relation to something in the past – my feeling seedy because I drank too much last night for example
• There can be no propositions about non-present times
• Presentism is possibly in conflict wit the theory of relativity. The STR demonstrates that simultaneity with here and now does not pick out a unique set of events across the whole of space. So if only the present exists then it may be thought that you must shrink what exists to what is going on here and now – that nothing exists outside your present spatial location as well as your temporal location

The presentist and eternalist agree that Socrates does not presently exist and that he existed. However, the eternalist would claim ‘There is such a thing as Socrates, which does not exist at the current time’. According to presentist there simply is no such object as Socrates. In other words for eternalists and presentists what exists and what is present do not amount to the same thing. They agree over what is present, but not about what exists. Non-presentists can argue that while Socrates is not present right now, nevertheless he exists now.

If the past and future do not exist, then the presentist must explain the sense in which statements about the past and future are true.

Presentism and modality
The debate about presentism vs eternalism is similar to the modal debate about actualism (everything that exists is actual) vs possibilism (non-actual things exist). Actualism is the philosophical position that everything there is, everything that can be said to exist in any sense, is actual. But that there is nothing beyond actuality. This stands in contrast to possibilism which includes things that are non actual but which could have been. Possibilism is sometimes accepted as referring to theoretical abstract objects which actually exist. They may be termed mere posssibilia or contingently non-actual individuals.
Actualists would generally be presentists and assert that the actual world is congruent with present time.

It may be argued that time is fundamentally like modality and unlike the dimensions of space. In logic the modal operators “it is necessary that” and “it is possible that” work in the same way as the tense operators “is”, “was” and “will”. Also abstract worlds and abstract times are similar and finally, according to the presentist, the past and future are as unreal as the merely possible. There is no reason to think that being real at a remote temporal location is like being real at a remote spatial location.

Modal realists have non-actual objects in their ontology (Lewis), while the ontology of modal actualists is restricted to the objects in the actual world (Plantinga, Adams). For these two positions to be opposed, both must agree that what exists and what is actual are not the same.

Presentism and change
Properties past, present, futureMcTaggart’s A series gains much of its feeling of true change by the passage of events from future through present to past. He says “every event must be past, present or future”. But how can an event be future except in an anticipating mind? And, if the future does not exist how can any event have the property “future”. Nothing real can have the property of being future because the future, no matter how apparently inevitable, does not yet exist; it has not yet happened. In short, nothing can pass from the future to the present. The future is a human (sentient being) projection – put simply, an anticipation. There can be no properties of past, present and future are simply a nonsense.

PRESENTISM VS ETERNALISM
In contrast, eternalism maintains that time is like space. For space there is no special status given to things that are here. Things in other places, say London and New York, are just as real as those here in Melbourne. By the same token, for the eternalist there is no special status given to things that are present (now). So, things exist in space that are not here, and things exist in time that are not now: these things are said by the eternalist to be merely past and merely future entities. They exist now, even though they are not currently present and they would be on the inventory of things that exist. So to say that things are merely past or merely future is to assert the eternalist position. Past, present and future, the eternalist argues, are an anthropocentrism that leads us to false assumptions about the existence of objects. This is because we emphasize the non-existence of the past (and future). Eternalists point out that just as here is a relative place, so now is a relative time. When we say there are no trees here (the emphasis is on place) we don’t mean that there are no trees – after all there are quite likely to be trees somewhere. Similarly when we say “Dinosaurs do not exist” what we mean is “Dinosaurs do not exist now” (the emphasis is on time) – then it is possible that there are dinosaurs somewhen. The grammatical omission of the now distorts our interpretation of what the sentence means and therefore alters our understanding of what exists and what does not exist.

FUTURE
The future is what has not yet happened. We can imagine things that could not happen in the real world there also appear to be many things that are possible; things that are very likely and others that seem inevitable. Our anticipation of the future, coupled with the predictability and apparent inevitability of many events give us the impression that there is much in the future that is fixed or determined. No matter how inevitable events might seem, the unexpected is possible. The future has not yet happened. No matter how inevitable things seem in the future they only happen in the present. Nothing happens in the future and nothing is inevitable. All of the experiences we have of the future must be subjective and, of course, they must take place in the present. The only objective experience is our experience of an event itself, as it happens.
According to the B theory past, present and future exist equally and future tense statements have a truth value – the principle of bivalence (that every statement is either true or false) remains intact: future facts are truth-makers for future tense statements.

For the A-theory there are no future facts – so what are the truthmakersfor future tense statements: present facts? In which case determinism seems to follow? But it is possible to deny that future contingents have a truth-value because it means that every statement can be either proved or disproved, which is false. This is sometimes called intuitionism. Does this escape the argument?

If we hold that the future does not exist then clearly durations set into the future are human projections based on previous experiences. For example, if I have a birthday X days ahead based on a calculation made today, then I can say that the temporal interval will be 1 day less at the same time tomorrow. After 1 day has passed the interval will be 1 day less and the day of the birthday will be getting nearer based on my knowledge and experience of calendars and dates. Two important points follow:

This is lapse of time in the present (nothing is getting shorter or closer, or further away)
• Neither the birthday nor the durationsl are moving in any sense, this is metaphorical language, but more importantly neither the birthday nor the temporal interval (as extended time) real in any sense, they are anticipations, mental constructs. They are real in minds only.

But the birthday really is X days ahead! There is something in my mind AND surely something in reality? All we have in reality is X days worth of time lapse in the present.
There is no event later than a present event.

For the eternalist, past, present and future exist equally. However, in the world of the presentist and common sense, the future does not exist. Certainly there are possibilities and probabilities (possibilism) even apparent inevitabilities (fatalism), but events cannot exist in the future or have the property of being future in any meaningful way.

We do not perceive future events because we can only perceive earlier events as memory in the now – this is a causal relation. But maybe this causal relation is mind-dependent, our particular human perspective from within time. Could or does the future affect the past?

To say that the future does not exist means we must abandon all talk of the past and future. There is neither a McTaggart A or B series, A because there are no such things as future events to have the property of being future – we cannot talk of what we will do next year? At most the future is a set of objective possibilities, some of which may happen.
Denying that future events exist does not make judgements about the future meaningless. Judgements may be true or false then depending on whether or not they are instantiated.
All statements about the future must be general because they are about the merely possible. It is ony actuality, th forse of existence, which produces a discrete unity. Future must be general, past may be singular.

Both deliberation and action are causative in relation to the future. Not all existence is the outcome of necessity (determined?)
Do future contingents have a truth value – or not yet have a truth value – or no truth value at all. Do truth values change over time?
The agents concept of time is modal
Possibility -> actuality -> necessity

What can we say about future contingents (events that have not yet happened and are causally undetermined)? For example, if we say “tomorrow there will be an earthquake in the South-east pacific”. How are we to judge the truth value of such a statement?

• If there was an earthquake the following day then it was true
• It cannot be true or false because there are no facts to which the statements can correspond
Now, if we say “tomorrow there either there will be an earthquake or there will not be an earthquake”
What is the truth value of this statement?

• One of the cases must be true so the statement is true
• If neither of the possibilities can be said to be true or false then how can the two in combination be said to be true?
• If either is true then are we committed to fatalism? Logical determinism assumes that every proposition about the future is either true or false according to the law of excluded middle which says that all statements must be either true or false in contrast to the posoition asserting that nothing can be said of the future. It seems that the law of excluded middle robs us of our freedom of choice

This problem has spawned several logics including 3-valued logics and chronological or tensed logic.
If the past and future do not exist then we must explain the sense in which statements about the past and future are true.

• We remember the past but not the future
• We think we can change the future but not the past
• We assume in the present we are performing actions that add to the past but not the future
• The future contains possibilities in a way that the past does not

Statements about the future must be general. Statements about the past may be singular.

“What will happen will happen” is a harmless tautology
“What will happen will happen of necessity” amounts to fatalism

Possibilism
There are three forms of possibilism.

1. Those things that exist are actual – they have an intrinsic ontological property, existence or actuality. A possibilist is someone who believes that there are things that are not actual, indeed the actual is only a small proportion of what there is. This is a distinction between what there is and what is actual. The sort of things that are not actual are unborn children, non-actual brothers and sisters and so on.

2. It may be claimed that there is no difference between what is and what exists and therefore to say “there are things that don’t exist” is nonsense. The possibilist then agrees that everything there is exists, but that not everything that exists is actual. This seems to be a word game in which is has been renamed existence and existence has been renamed actuality. The possibilist has simply replaced two modes of being with two modes of existence – actual existence and possible existence. The possibilist will believe this is acceptable, others will not.

3. An alternative to 2. is that being and existence are the same but there is no special ontological property or mode of being that separates merely possible objects from actual ones. Here, again, actuality is different from existence. Actuality is not a property but a relation where things are spatially or temporally related. Then, non-actual things are simply things that occupy worlds other than ours – things that exist but are spatially and temporally unrelated to us. The semantic corollary is that “actual” is indexical, its reference being given by the context of its utterance. “Howard actually exists” then means that Howard occupies the same world as the speaker.
Thus 3., like 2., acknowledges the comprehensive character of existence but without primitive properties or existential modes of actuality.

Fatalism
A fatalist thinks the future is fixed or determined in the same way as the past – that there is nothing we can change. That, for example, given the conditions now in their entirety, there is only one way in which things can happen next – this in turn producing a situation from which it is not possible for anything else to happen.

Augustine’s conundrum
]][Before then it is only an anticipated date or event. After the event it moves into the past but exists only as a memory, even though I can always state with great accuracy how far back that birthday occurred and I can remember objects and events that truly existed at least at that time. Assuming the event of my birthday only truly exists when it is happening but does not truly exist before or after the day on which it occurs, how can I speak of it approaching or receding? (Do events exist or are there only things that change?) See past, present, future. So, does only the present truly exist? Is there any sense in which the past can exist?]]] Events, time or whatever comes out of what does not yet exist, passes through what has no duration and moves into what no longer exists. Augustine’s solution was to conclude that the future is anticipation and the past, memory. In other words past, present and future have no objective reality. He asked “If the future and past exist I would like to know where they are”. He was spatializing time. We must beware of diagrams and spatial metaphors.

Tenses
Is the division of time into past, present, future and the tenses was, is and will be (A-series) with events approaching and receding (flowing) truly part of the objective world, or is it a construct of the human mind?

Perhaps we can represent the world simply in terms of before and after and at the same time (B-series statements) without any need for tenses. This is the timeless (eternal) language of mathematics and logic. We can argue that when we say that the Olympics was one year ago, this can be stated with no loss of meaning in terms of B-series language, not in terms of pastness, presentness and futurity.

Defenders of A-series statements and flowing time as objective are called process philosophers (Whitehead, Bergson) or, perhaps, in a modern form presentists (Sider), while defenders of the B-series as the only objective expression of reality are defenders of the Block Universe or eternalists (Williams, Armstrong, Smart, Grunbaum, Quine) and more recently (Mellor, Price). The latter point out that the present has no special objective status and there is no objective flow of time. Tensers claim that the B-series does not capture the essence of time as it does not adequately express change: it does not have a direction and therefore is no different from a spatial series. Only the A series generates true temporal relations. B series has primitive temporal relations while A series does not (Oaklander).

It undeniably seems as though time flows. If past, present and future all exist equally then present events must have some characteristics (such as a relation or property) which make them special and distinguishable. But then if we were to imagine transposing the events-at-times of the 3D universe (said to be dynamic or flowing) into events-at-temporal-locations of a 4D block universe (said to be static) there would be no difference. Each moment would produce a space-time slice and that would include slices of our mental states (which would be just the same as those in the 3D universe) – so there would be no difference.

NOW OBJECTS EVENTS
ACTUAL MENTAL PRESENT END/PERD PRESENT END/PERD
PRESENTISM X X X
ETERNALISM X X X
SPENCERISM X X X

Something does not become present in the same way that it becomes hot
We cannot defime memory without reference to a past event and we cannot define the future wothout reference to a future event – circular.

EVENTS AND THEIR ONTOLOGY
To define the universe in a sentence is not a simple task. However, let us define the physical universe as the totality of objects, their properties and their spatio-temporal relationships. These relationships are constantly changing in time (ud). An event is DF a particular set of objects and their spatio-temporal relations and properties over a designated duration. We could designate a childbirth, a collision of subatomic particles and a football match as three different events. So, for example, a football match is the changing properties and spatio-temporal relations of objects associated with the football match for the duration of the game. This is the objective football match. There are also many subjective aspects to the match such as: the many people looking forward to it; imagining the match approaching from the future; the thrill for individual members of the crowd when their team scores a goal and so on. An event may have a subjective component (e.g. my enjoying the goals and the win at the end) and an objective component (the spatiotemporal relationships and properties of the players and other objects related to the game over the duration of the game).

Is change a change in events, or a change in spatio-temporal relationships of things. Can events change in any meaningful way? Do events exist in any meaningful way?

Events, objects and properties

Duration

A complete theory of time T(n) must explain why everything does not happen at once, that is, why there are durations (temporal intervals) at all.

Durations are the temporal stuff of science and everyday life, the way we relate time to watches, clocks, daily, weekly, annual, and seasonal routines.

Floral clock

Floral Clock
‘Time is duration’
Duration one of several sub-categories of the more general category ‘time’.
Duration is measured by temporal intervals (time lapses): ticks, seconds, years, breaths, heart-beats and so on
Courtesy Wikimedia Commons

Semantic taxonomy
We have already noted the semantic complexity of ‘time’ T(n), and semantic simplicity of ‘duration’ T (ud, rd). Is duration what we ‘really’ mean by time? Intuitively duration is not time itself but a DF temporal interval, or lapse of time. We speak of duration in general terms as in ‘The match was of long duration’ (as T(ud)) or a particular duration (as T(rd)) as in ‘The match lasted for two hours’. We might ask why time should be anything in addition to duration itself. This may be true but, if so, then we need to deal with a linguistic problem. We do not, ask: “What duration is it?”, “Did he travel backwards in duration?”, “Duration went quickly today?”, “Did dinosaurs live at some duration in the past?”. This is not just a matter of a difference in the conventional usage of words but a real difference in meaning between the words ‘duration’ and ‘time’, the former being much more restrictive. However, we can bear in mind that language could be treating time metaphorically and erroneously as an object so that an interval cannot serve the same role in a sentence.

The fact that duration carries less semantic baggage makes it a more straightforward concept to manage.

Why does time have duration?

But the notion of duration intergrades with the ideas of permanence and change. Nevertheless, in this context the succession series do not appear to be of primary importance, so the analysis of duration cannot be totally reduced to a consideration of McTaggart’s A Series and B Series.

At issue here is the reality of now, past, present and future, whether some or all of these are subjective or objective, together with the nature of temporal flow and accretion.

In PART 1 duration was defined in two senses in accordance with its primary lexical definitions as either DF a temporal interval of restricted durationT(rd) or simply DF continued existence as unrestricted duration T(ud). T(ud) is unbounded and T(rd) is a bounded period of time. Both semantic categories are semantically simple: indeed, it is extremely difficult to define the notion of duration without circularity.
Of these two temporal categories T(rd) is employed both philosophically and in everyday language much more frequently than T(ud).

T(rd) is of two kinds: firstly, those intervals that last for a fixed period e.g. one hour, or one breath (the unit does not matter) – these we can call fixed intervals T(rd, fi) and secondly, those intervals that increase or decrease, as when the interval from now to the arrival of a plane decreases or the interval from now to the Big Bang increases – these we can call flexible intervals T(rd, fl)

3.2.1.1 Fixed intervals (rd, fi)
For a fixed interval there is nothing undergoing change: ‘now’ is irrelevant and therefore T(c) is not involved. A fixed interval or ‘block’ of time, say 20 minutes, entails an earlier than and later than relation, a beginning and an end that are in permanent relations. Thus the duration lasts 20 minutes, the start being at t1 (which is before t2) and ending at t2 (which is after t1). However, in the current context it is the duration that is paramount not its boundaries (t1 and t2), or their temporal relations (t1 earlier than t2, t2 later than t1).

3.2.1.2 Flexible intervals T (rd, fl)
In the case of the flexible interval, ‘now’ defines either the beginning or end of the interval and so we are dealing with T(c), the time of change, and therefore a changing interval. This is true even though we might be referring to a ‘now’ in the past, as when we ran to catch a train with the time to its departure getting ‘closer’.

Fixed interval = T(rd) <> T(p)= T(rd, fi, p)
Flexible interval = T(rd) <> T(c) = T(rd, fl, c)

3.2.2 The distinction between duration and succession
It is now clear that the notion of duration although linked to the idea of temporal succession and the semantic categories of permanence T(p)] and change T(c) also has its own semantic emphasis. The concept of duration T(rd,ud) is semantically closely linked to the idea of succession as T(p,c) through the temporal relations earlier than, simultaneous with and later than, the temporal relations focused on the present T(c), and one-another in T(p).

It is tempting to assume that fixed and flexible intervals immediately reduce to durations within the A and B-time-scales and series of T(p) and T(c) respectively. However, in succession series (McTaggart’s A and B series) the emphasis or focus of meaning is on the temporal relations of events or times either to each other or to the present (now). Duration series T(rd, ud) focus on the amount of time: it is, so-to-speak, about quantities, not relations.
So the idea of duration, especially T(ud), maintains some semantic independence from the semantics of succession. T(c) is intimately bound up with change, passage, and flow while duration is more closely allied semantically with the more stable idea of the interval (duration). This tension is demonstrated when we place duration in the semantic arena of T(c) by asking ‘Does duration flow?’. ‘My breakfast is 3 hours before my lunch’. ‘The Battle of Waterloo was many years after the Battle of Hastings’. These B-time intervals (the latter also tensed) are not so clearly different (examine).

3.1 Measured time
Using a stop-watch we can measure time as it lapses in the present. We could measure, say, 11 seconds as an athlete runs 100 metres. As the athlete was running, the measurement was being made in the present. That present later became past, but the reading on the stop-watch indicated the time that had lapsed during the race. In that way at any time in the future (at that present) it would be possible to know once again how long it took to run the race. There is nothing complicated or mysterious about this. The time was measured in the present (the only way it could be measured) objectively. The event then ‘receded’ into the past but a record of it could be recalled for the present ‘now’ and at any future ‘now’. There is no need to postulate that time is in the mind. We can now describe measuring time in terms of past, present and future.

When we are recording the duration of an event we are measuring a duration in the present T(rd,fl,c) so that in the future (when the event is past) we shall know (at that ‘now’) how long the event lasted (in the past) T(rd,fi,p)]. While we are actually recording the race we are measuring a flexible, changing, open-ended duration T(rd, fl, c). When the measurement has been made we are left with a fixed, permanent, closed duration T(rd,fi,p).

3.2 Consciousness, past, present, future and duration
A fixed duration T(rd,fi), say 20 minutes, cannot exist instantaneously, because then it would not be 20 minutes. But we can think of 20 minutes all at once in our mind’s clock: in fact we can easily think of 20 minutes in less than a second. We estimate, for example, that it takes 20 minutes to walk to the train, 20 minutes to eat breakfast, and so on. Clearly the thought of 20 minutes is subjective (it is interesting to reflect on the way we think of durations: they are like thought-feelings, a kind of test-run of an actual interval based on previous experience). The thought of 20 minutes is subjective because it occurs only in the mind, I am imagining what that 20 minutes would be like when it actually occurred.

So is there such a thing as objective time, and if so, can we explain it?

I shall leave the justification of objective time until later. But for the time being state dogmatically that objective time is the ever-lapsing ‘now’, the boundary between determinacy and indeterminacy: this is time itself T(*).

It is tempting to assume that the actual completed physical acts of walking to the station and eating breakfast entail objective fixed intervals of 20 minutes. After all, we have measured them using machines (clocks) in a publicly conventional and accepted manner. However, there is an important difference between the actual lapse of time and its representation as an interval.
The actual 20 minutes walking to the station is objective because it involves the real transition of measured time.*****

The actual 20 minutes is objective because it involved a real duration of 20 minutes (see also objectivity of duration), just as the actual running of the race took 11 seconds. It is the time taken when we are actually walking, eating and timing races that is objective. Times in the future and past are not actual. We cannot be in the past or future. All time that is not presently lapsing is a form of memory or anticipation or a form of representation: for simplicity we shall refer to all temporal references that do not involve the lapse of time in the present as representations.

Since we only experience a brief present moment, anything lasting longer than a snatch of time must have past. We are therefore driven to the perhaps startling conclusion that durations (temporal intervals) are subjective representations without reality in the external world.

(But how long is the present? Is there a now that is part of the universe or is this experiential, our consciousness at work, how do we age if there is no duration, why do we have a notion of duration, do we need it?)
This difference seems quite obvious when described in this way. However, we are constantly confusing subjective and objective intervals.
We cannot measure flexible temporal intervals present [time (rd,fl, c)] like spatial intervals because the beginning and end of these durations cannot co-exist: that is, they do not occur at the same time. We cannot experience the start and finish together. Hence duration. In contrast we can experience the beginning and end of a spatial interval at the same time, and we can experience the beginning and end of a fixed interval at the same time because it is a representation – it is not time itself. The time on a clock is, perhaps, analagous to the reading on a thermometer: it is a representation of time not time itself. In the sense that it is a publicly and scientifically accepted (conventional) representation then it is an objective measurement, but it is not time itself.
[If events in the future and past do not exist then what reference point do we have for the measurement of “movement”?

3.1 OBJECTIVITY OF DURATION
Modern physics uses measured temporal intervals as a cornerstone of its explanation of space-time and therefore the universe. Time (n) is said to be woven into the objective fabric of the universe as space-time. Our work lives are subjugated to what can be achieved in a particular time interval and our public lives are synchronized around publicly accepted, i.e. conventional, temporal intervals

Aging
Objective duration, time (ud), is manifest through the aging of all the material things of the universe including, of course, biological organisms. Measured time of clocks is objective time whether we regard it as time taken (duration) and absolute or simply the movement of the hands of a clock. The difficulty in asserting that time is just a relation is that duration is marked, not just by the relations of hands to clocks and other temporal measuring methods, but to the physical aging process of animate and inanimate matter. With the lapse of 10 minutes we are all 10 minutes physically older as are the rocks and every other material thing around us. Thus, even in physics text books that indicate a relationalist view of time (*), definitions of time are spoken of not relationally but as time taken i.e. a time that is independent of the measuring device.
Duration on these terms is an objective reality – it is part of the universe itself, not something mental, unique to sentient beings.
If duration is part of the physical universe then it should be amenable to scientific explanation. There is the debate as to whether time is, indeed, anything other than a relationship between things (see Chapter 2). There is, at present, no satisfactory physical explanation of duration. Indeed, this may be seen as good grounds for doubting its true existence. In space, duration is the interval taken by light to pass from a source to an observer. But how do we explain what that interval is? And how do we explain the intervals between events on Earth? What form would a satisfying explanation of duration take?
[Radiocarbon dating of substances in the earth enables us to track the amount of time that has elapsed (more or less) between the formation of those substances and the present day. The increasing time interval (fl) between my receding birthday and now is marked physically by my aging.]

3.1.2 Absolute or relational duration
When we say the time is 9-05 am is there a moment in time that exists independently of the events that occur then?
We may say that the duration of one day is a relation, in the first instance, between the Sun and one rotation of the Earth. Or perhaps we could describe it as 2 rotations of the hour hand on a clock. Either way it surely cannot be argued that 24 hours is just one rotation of the Earth in relation to he Sun, or the rotation of hands on the clock dial. In general we use the language of absolute time to say that 24 hours is “a period of time” which we cannot describe except that we certainly feel it. It is, we could say, the temporal interval between one sunrise and another, or “time taken” for 2 rotations of the minute hand. Using this language we are suggesting that the temporal interval is something over and above a relationship. The hands have measured out something real, even though we cannot see it, taste it or touch it. We do feel it. We know roughly what one minute and one day feels like. But then these feelings might be deceiving us as may the language about time be falsely suggesting absolute time. Neither may correspond to anything real in the objective world. At present there is no decision procedure for this dilemma. Physics cannot resolve this dilemma except to suggest that absolute time is an unnecessary hypothesis.
Either you believe this or you do not. If you believe it then the time of duration is absolute, something independent of the relationship. If not then time (restricted duration) is relational.
If we are quiet with our eyes closed and all we can hear is the ticking of a clock we feel that time is lapsing. If the clock suddenly stops then we still feel time is lapsing. Of course, this might be simply our consciousness and nothing to do with time itself. But then why should we doubt our senses? It is a strong sense. If we feel the temperature rising, do we suddenly doubt ourselves and ask could this be something subjective, something that happens in our imaginations?
[What is the difference between the time in the morning when hands in the same place as the hands of the clock in the evening? They are effectively the same time – but one is earlier than the other (after a day) – indicates absolute time]

3.3 CONSCIOUSNESS AND TIME
Is it possible to differentiate the objective and subjective aspects of time through an analysis of temporal intervals? To do this would relieve considerable philosophical frustration confronting scientists and philosophers alike.

3.3.1Consciousness and fixed intervals
A fixed interval, say 20 minutes, cannot exist all at once, because then it would not be 20 minutes. But we can think of 20 minutes in our mind’s clock: in fact we can easily think of 20 minutes in less than a second. We estimate, for example, that it takes 20 minutes to walk to the train, 20 minutes to eat breakfast, and so on. Clearly the thought of 20 minutes is subjective (it is interesting to reflect on the way we think of time in its various forms, generally it is like a thought-feeling, a kind of test-run of an actual interval). Of course the actual completed physical acts of walking to the station and eating breakfast entail an objective fixed interval of 20 minutes. The thought of 20 minutes is subjective because it occurs only in the mind, I am imagining what that 20 minutes would be like when experienced in the external world. The actual 20 minutes is objective because it involved a real duration of 20 minutes (see also objectivity of duration).
This difference seems quite obvious when pointed out like this. However, we are constantly confusing subjective and objective intervals.
At this stage it is important to simply acknowledge that there really are such things as subjective and objective temporal intervals.
When I say “My birthday is 5 days away”; this is true in the sense that 5 days worth of time must elapse in the present before my birthday occurs. It cant be in the future because the future does not indeed exist, and indeed nothing in the future exists. All the future means is – “has not happened yet”.
We say, let us suppose, that light takes 6 minutes to reach us from the Sun. And we say that this is an objective and proven fact of physics.

3.3.2 Consciousness and flexible intervals
We experience everything in the present (an extended treatment of presentism is given in Chapter ). Memories and anticipations do not take us literally into the future or back into the past. Everything ages in the present. Things that are old have aged in the present for a ??large interval.
We know what the “passing” of one day feels like and so, just as we can imagine 20 minutes all at once, so we can imagine (in the present) a birthday five days away approaching, getting closer each day. That is, we know what it is like for 5 days to elapse in the present. The anticipation (imagination) of this interval of time is subjective in the way that our imagination of 20 minutes was subjective. There is clearly no birthday literally approaching from the future. We are anticipating or mentally projecting into the future using our imagination based on previous experience.
In just the same way that we feel (in the present) the birthday “approaching from the future”, we also feel it (in the present) “receding into the past – slipping further away each day”. Again, the birthday is not literally moving away from the present. This too is subjective exactly as before. There is therefore a subjective symmetry of feeling about “approaching” events and “receding” events.
We are now therefore tempted to say that the impressions we have of the past and future are purely subjective which, if we believe what has just been said, must be true. But this is not the whole truth.
As we have also seen, durations are also objective. Things age in the present as time elapses in the present. Duration has a physical effect on us. But duration does not extend into the past. The subjective “receding” of time into the past occurs at the same time as the real elapse of objective time in the present. The duration between now and some event in the past is both mental and physical: it exists both in my mind and in reality.
There are several important assertions here:

• the past can be subjective, or objective, or both ,and we need to distinguish which it is that we are concerned with in any discussion. For example, when we are talking of receding birthdays, although the language is colourful, what we are discussing may be objective (as an objective duration) or subjective (to do with a mental projection), or both, depending on the context
• subjective approaching and receding intervals give a feeling of symmetry to the past and future
• the past also has objective intervals of various amounts of lapsed time while the future has no such intervals; therefore there is an objective asymmetry between past and future. The subjective symmetry and objective asymmetry lead to much confusion over past, present and future and their tenses
• time elapses steadily in the present (now), not in the past or future
• ***physical objects, including ourselves, persist. However, the now simply defines the moment of determinacy/indeterinacy. So my mind has, as it were, adapted to the lapse of time.
So, how are we to interpret the sentence
“My birthday is 5 days away and getting closer every day”
After all, my birthday is getting closer all the time. I can even draw a line and show how that gets “shorter and shorter” as time “goes by”. We feel that if we were to use different words to describe this situation it could not alter the fact that things get closer in time and further away in time.
Firstly, we must distinguish between the lapse of time and the particular event that is “approaching” or “receding”.
All that is happening objectively is that time is elapsing in the present. Events happen in the present – they cannot “move”. Our minds add all the complication to this situation.
The problem is simply the spatialisation of time. Nothing is “approaching” or “receding”, all we have is the lapse of time in the present. We can (in the present) mentally imagine, or even mathematically calculate the temporal interval (time (rd)) that must occur before something can occur in the present. Similarly for the interval that has elapsed since something happened in the present. Note that this is a temporal interval – it is not a spatial one.
We cannot resist saying that that interval gets “shorter” or “longer”, it is a “distance” that becomes “nearer” and “closer” or “further away” and “more distant” and so on. All of these spatial words are so entrenched in usage that we think of time lapse spatially and therefore things (events) must “move”, and temporal “movement” feels like spatial movement. But time lapse does not have spatial extension.
Since events do not literally “move” then the feeling of temporal “movement” must come from time lapse itself.
As a clock ticks we say time is “passing”, and after a while we say time has “gone by”. This is similar to saying the temperature has gone “up” – obviously temperature does not literally go “up” – it is the mercury in the thermometer that goes up. Similarly time is not literally “passing” or “going by”, these words simply convey the impression of something that is definitely going on, some kind of activity, but something extremely difficult to describe. Or, at least, something that we almost always describe using inappropriate space words.
[We are concerned here specifically with time (now) which is the physical lapse of time uncomplicated with the notions of past, present and future ???it is temporal “movement” uncontaminated by the notions of change or succession – it is time itself which we experience as now.] “When a duration of 5 days has occurred my birthday will happen”
“After a period of 5 days it will be my birthday” [this is absolute interpretation – there MUST be a period of time, not a succession of events. EXPLORE]

We need a remedy for this misrepresentation. One obvious solution is to use non-spatial words. Words like duration, period and lapse will help; words like interval are fairly neutral but still have slight spatial connotations.
Metaphor is an aspect of our language that gives it colour, excitement and interest. The important question here is whether there are any serious consequences in taking the metaphors of time literally.
The lapse of time in the present affects equally the “decreasing” duration needed for something to happen in the present and the “increasing” duration of something that happened (in the past!!!!). Language???

It would now be a simple matter to say that there is no passage of time, that time does not literally move and all such talk is an illusion. It should be remembered, however, that the “passage of time” refers not to something that is an invention of the human mind.
Whatever time (now) does is real and objective. There is temporal “movement” it is simply that “movement” is not a good choice of word.
If the question is “does time literally move”, then the answer is “No, temporal passage is a myth”. If the question is “is there something objective we call time, for which we have an inadequate vocabulary to describe what it does, but which gives us the sensation of movement?” then the answer is “Yes” there is temporal passage.
If forced to take a position I would say that I believe in temporal passage.
[How DO we think of time when we do not think of it spatially?
When we use spatial words we are nevertheless thinking of them and treating them as temporal]

3.3.2.1Temporal accretion, extension, length, distance and movement
We think of time’s “passing” as similar to putting beads on a necklace or adding numbers to a series. It is compared to a pencil drawing a line, where the emergence of the line at the pencil point is akin to the now and the drawn line similar to a fixed past. Thus the pencil line of the universe and our lives is continuously extending. We are tempted to say that now is accumulating or accreting more time (as moments or events) at the front of the line as it “flows” in the direction of the future.
Alternatively an Absolutist might consider a temporal item, say a moment, starting at the beginning of a day and moving through it much as a train travels through the countryside (except there are no stations). Whilst a Relationalist could imagine a number of events forming an increasing temporal series. As the day progresses the temporal series gets larger, pushing us along with it so-to-speak as there are more and more events.
The lapse of time is real and objective. But time is not space.
Because we cannot express clearly what the now does, that is, whate the alapse of time is like, and because space is, in many ways, similar to time, we therefore use the words of space and mathematics (length, number, movement) thereby spatializing time. We use the language of metaphor and analogy to describe time, and then take this language literally. We not only speak of it in spatial terms but we also think of it that way. It seems that our brains cannot grasp time as time, only time as space.
Objective time does not extend, accrete or lengthen; it does not accumulate events or things of any kind, or in any way. All of these metaphors are creations of our imagination in the attempt to explain now and elapsed time. We speak and think of a “length” of time because that is our habit and often the way we visualize temporal intervals. But time does not have “length” or number (which invites all the criticism that can be levelled at the attribution of time with cardinality), it simply elapses in the now. Objective time does not push us further away from the Big Bang and there is no accretion at the “edge” or “front” that we call now. The feeling that now moves, and that the movement is akin to that of a river or stream is obviously genuine. But movement is essentially a word applied to objects in space, not in time. Temporal “movement” is different from movement in space (see Chapter ).
Of course we can represent time spatially, as a line, for example, but the time itself is not a line; it does not extend in space.

***3.1.7.1 Consequences of spatializing time
Even if this case is accepted it might be asserted that spatialization of time is a trivial misdemeanour. We say the temperature goes “up”, presumably because mercury, which measures temperature, expands upwards in a thermometer. Temperature does not literally go upwards. Mercury is not temperature, but a measure of temperature. Similarly clocks are not time but a measure of time. Treating time as space in a literal way can lead to scientific error. Direction is a spatial term (is it?). To say that time has direction is to make a category mistake. To imagine when we represent time graphically that we a representing time as it is – is an error.
We seem biologically incapable – that is our minds are not structured – to deal with time in a rational way. We do not understand time so clearly as we understand space.

?3.1.4 Consciousness/ past, present future/ events
The past is evident to us through material objects that are aging in the present [time(ud)]. We can, for example, hold the bones of a dinosaur that lived are over 60 million years ago. Those bones will, of course, still be aging in the present. However, we cannot know how that dinosaur died except from what we can deduce from the physical remains. The actual event of the dinosaur’s death, the relations of all the objects at the time of its death and how they changed, occurred in the dinosaur’s present and this cannot be literally revealed to us (unless someone shot a film).
Events have physical reality only as they happen. As my birthday recedes (subjectively) into the past I can remember (in the present) the giving of presents and the people singing “Happy Birthday to you”. But these events have no physical correspondents, they are memories and therefore subjective. However, the people at my birthday might exist now as also might the bottle of wine I was given as a present – but the event does not. An event is simply particular relations of objects. An object is a very dull event?
The significance of this is that, as we have noted, the past for us is both objective and subjective. Because there is physical evidence of the past that is real now we are, by association, inclined to think that the events of the past are also real now; but they exist only in our imaginations.

Duration and objects
Events, then do not age, it is physical objects that age. Temporal relations directly relate events, thewy do not relate things? Continuants endure.

3.2 CONTINUED EXISTENCE
We sense time (unrestricted duration) every moment of our lives. Our cycle from birth to death bears simple and blunt testament to its existence, as does the evolving universe and the fact that we can decipher its history. Everything that is actual is aging – it exists in time (ud) or persists.
Time (ud) is attributed great significance in poetry, and literature in general, as a great leveler of humanity. In time (unrestricted duration) we are born, flourish, decay and die. Everything that exists, exists and ages in time (ud) which is continual directional change. The sense of movement and direction we get from time has been referred to philosophically as pure becoming. The incessant “flow” of time is an important part of becoming but it is not all of it. It is called pure because any other kind of change presupposes this kind of change – everything ages because everything is in time (ud). Time (ud) is clearly objective for the reasons stated already and the fact that we can decipher its history. The aging of organisms and rocks is a simple objective fact.
We can treat continued existence which does not necessarily presuppose events (Absolute Time). A measured duration is the relation between objects or events (Relational Time). Time (ud) can therefore be used to denote either Absolute or Relational time.
We often, in frustration, append “in time” onto sentences to give the sense of time (ud) although everything in the universe is “in time” so it is interesting to try and see what purpose this device serves.

****We may not know what it is or why it is, but we do know that it is. Duration is real. Temporal intervals are different from spatial intervals but because it is similar in many ways we use similar language to explain it. For this reason we speak metaphorically of the passage or movement of time when we refer to the process of accretion that occurs in the now. That is, movement in time is qualitatively different from movement in space.

SUMMARY
It now becomes clear that there are two major issues to address in the philosophy of time. Firstly, what is the true nature of objective, physical time [time (*)]? Secondly, how do all the semantic categories of the semantic taxonomy relate to time * and each other.
It has become clear in the preceding discussion that true physical time is the now of existence. Now has been aptly described as the knife-edge between the determinacy of the past and the indeterminacy of the future. Physical time elapses (“passes”) in the present only but it does not move (see Flow of time later). In talking about time, which is different from space, we use the same words and thinking that we use for space. Our perceptions of the past and future are in some ways subjective and some ways objective. However, as objective physical time elapses (the time we measure with watches), we age, as does every material thing in the universe. This is the objective result of time (ud).
We now need to distinguish more temporal categories: the subjective temporal intervals of the past and the objective temporal intervals of the past. How does the now relate to duration?
We are closest to the movement of time when we actually measure it (duration). That is movement (causal attainment?). Philosophically the important point is that we are measuring the objective temporal motion of the now. This is public time that is in the objective world. As the man took 10 seconds to run the race he also aged by 10 seconds.
Our temporal concepts are constructed from (defined as) temporal relations i.e. earlier than, simultaneous with, and later than.
One major task of philosophy is to determine which tasks are truly in the domain of philosophy and which tasks lie in the domain of science. Objective phenomena should be amenable to the treatment of observation ad experiment and are not the business of philosophy although philosophy can, of course, assist in the clarification of the concepts. So far we may tentatively draw the following conclusions:

SEMANTIC CATEGORY CODE EMPIRICAL STATUS R A
Time (restricted duration) = (rd,c) subjective and objective 
Time (restricted duration) = (rd, p) subjective and objective 
Time (unrestricted duration) = (ud) objective 
Time (change) = (c) subjective and objective 
Time (permanence) = (p) subjective and objective? 

Time (absolute) = (a) unknown
Time (relational) = (r) unknown

Time (a) and time (r) are subsets of the above.
Can be relational and/or absolute???
Chapters 4-7 will look more closely at resolving these issues.
[difference ppf, now & duration] [there is an amount/interval of lapsed time – not a length]

Duration, persistence, endurance, perdurance
Persistence is analogous to temporal extension.
In a 4-D world we can understand the passage of time as the accretion of fresh slices of reality. This gives us a distinctive before and after sense.

Duration and McTaggart
McTaggart’s A and B series are treated by philosophers as central to the problems of time. Do they encompass duration.
Firstly both are relational but only in the sense that they locate time either to now (A series) or to one-another B-series. Do they deal with intervals? Do statements like:”I will do that tomorrow (next year, in a minute)” and “I will do my homework before I watch television” encompass flexible and fixed intervals? The McTaggart succession series locate events in time in an essentially relational (not vs absolute sense) way. Earlier than and later than do not account for duration. More examples of statements.

Now

In the article on the flow of time it was suggested that time does not flow or move in the way that spatial objects move. When we talk about the ‘flow’ of time we are using the movement of spatial objects as a metaphor (we are spatializing time by using the metaphor of moving objects as being similar to the way that we sense time). To remove some of the ambiguity that arises when we spatialize time we can use time words instead of space words. The word ‘lapse’ was suggested as a time word to express the feeling of ‘passage’ that we associate with time.

Usain Bolt

Mens’ 100 m London Olympics 2012
Usain Bolt clocks 9.63 seconds
How does physics give us a universal measure of time and how does our biology influence our perception of time?
Courtesy Wikimedia Commons
Darren Wilkinson Accessed 8 Sept. 2015

This article considers three key aspects of time lapse:

Firstly, we think that time lapse occurs right now in the present, but what exactly do we mean when we refer to ‘now’ or the ‘present’: can we be more precise by giving ‘now’ an actual temporal duration? Perhaps physics and biology can help here.

Secondly, is it possible to say whether the lapse of time in the present or ‘now’ is a purely subjective or human perspective, something going on in our minds that does not relate to objective factors in the universe?

Thirdly, how can we account for the dynamic sensation we experience with time, the sense of passage, flow, and passing that we associate with time?

What do we mean by ‘now’?
Now, presentism, & historyt
A scientific world view explains that at the moment of the Big Bang the universe consisted of undifferentiated plasma and that subsequently, over a long time interval,it has differentiated into the matter of the galaxies we see today. Part of this process of cosmic evolution has been the evolution of life and human beings. Whatever we mean by ‘now’ or ‘the present’ the whole of time and space and its history is not laid out in front of us all at once. We assume that this process has taken place over a time interval and, in spite of relativity, the Big Bang clearly does not exist now even though we may see evidence of its past occurrence within the universe.

We can create precise theoretical and mathematical models that explain what it would have been like when it happened but to suggest, like the eternalist, that the belief in a current state of the universe is illusory, that all historical moments of the universe exist equally, is totally counter-intuitive. Physicists are even able to tell us approximately what the universe would have been like in the now three seconds after the Big Bang. We sense that the present is real in a way that the past and future are not. The future is what is later than now, the past is what was earlier than now and the present is what is simultaneous with now.

Clearly the inanimate world does not have the conscious memory and anticipation that surrounds the human perception of now, but the presence in geological strata of fossils of extinct animals are like a physical ‘memory’ or record of things past – they mark a once-existent ‘now’ of long ago. The eternalist needs very convincing evidence to demonstrate that when we infer a past ‘now’ from fossils and rock strata observed in the present, we are in fact deluding ourselves with subjective notions of past, present and future.

The duration of Now
The word ‘now’ like the word ‘time’ is riddled with polysemy so we cannot hope for precision here. However, for our purposes we can consider three major senses:

• The cosmic now – a near-durationless instant, the smallest possible lapse of time – sometimes called the punctiform present or punctal point – a notion derived from mathematics: the extremely brief objective moment defining the boundary between determinacy and indeterminacy (physics)
• The specious present – ‘now’ as we percieve it in daily life (biology)
• A contextual now – an interval of time relating to the linguistic context (linguistics)

1. The cosmic now – the now of physics
The cosmic now is the temporal equivalent of a spatial point in mathematics: it is a theoretically durationless point in time, like the theoretical mathematical point in space that has no length, height or breadth. There are sound mathematical reasons for such theoretical entities but time without duration is an incoherent objective concept.

The punctiform present is the shortest possible time interval over which change can occur, the knife-edge of temporal change in the universe. We do not know if time, like matter, is composed of meaningful physical units. Perhaps it is , or theoretically infinitely divisible. For the presentist, and our purposes, the cosmic now is an imperceptibly brief duration of time during which there is an objective change in the configuration of the universe. The cosmic now is the moment where the indeterminacy of the future gives way to the determinacy of the past, the emergence of determinate reality.

The punctiform present is not an advancing ‘now’ moving through time, it is more a measure of change: however, we sense it as dynamic and this aspect is discussed in (3).

Now and Relativity
We do not have a god’s-eye view of the universe outside of space and time from which we could see the universe in a particular configuration at a particular time. Instead we exist ‘within’ space and time and, like other objects, are subject to the effects of relativity. In speaking of relativity, and in giving examples of time dilation it is conventional to refer to ‘observers’ and the ‘observer’s frame of reference’. This has given the spurious impression that relativity is a function of the perceiving mind. After all, it is the ‘observer’ who sees the surprising consequences of relativity. In fact, the critical factors are the conditions that pertain at particular places and times: whether there are observers there or not is irrelevant. Frames of reference have nothing to do with the people that may or may not be in them as ‘observers’.

Light takes time to reach us. As you read these words you are doing so with light emitted a billionth of a second ago, the other side of the room about 10 billionth of a second, the moon 1.5 seconds, the sun 8 minutes. The presentist may be assumed to believe that what is happening now on Sirius is simultaneous with what is happening now on Earth. But if Sirius is 10 light years away – according to the frame of reference there may be 20 years difference in calculated simultaneity. Spatial locations moving relative to one-another will have a different perspective on what is happening now. By implication there is now absolute now. Owing to the restrictions imposed by the speed of light there are relativistic adjustments to be made on cross-cosmos comparisons of ‘now’ but each place in the universe has its now. By this view now or the present is part of the objective world and therefore not the product of our particular perspective.

2. The subjective or specious present – the experience & perception of time – the now of biology
The experience and perception of time is discussed by Le Poidevin (2015).

We see colours, hear sounds, feel the effects of gravity, and are aware of temperature – all through our senses, but how is time perceived? Though we may think of time-perception in relation to change, the non-simultaneity or order of events, or the ideas of past, present and future – it is probably duration that is most obvious.

So how and where, then, do we sense duration?

If we imagine counting the ticks of a clock as a way of marking duration then our awareness of time lapse as something that is mind-independent (the ticking of a clock) is registered in our brain in the form of some kind of memory trace. It is as though the longer ago an event occurred the weaker is the trace, thus giving us a measure of duration. Successful estimation of time intervals is present across the animal kingdom.

In an interval of any duration there will be earlier and later parts, a past and a present. This suggests that the present, now, must be durationless. Considering the finite speed of both light and sound it appears that we can only ever perceive what has past but we are adapted to experience only the very recent past, except when we are star-gazing.

As soon as we become aware of the present it has become past. When we listen to a piece of music we seem to retain notes or phrases in our heads as a brief memory, so that within our subjective present we can enjoy the sensation of a combination of successive notes, not just each note as an individual and separate experience. If we are familiar with the music then within that present moment we may also eagerly anticipate a few notes to come. The same applies when we listen to a spoken sentence. In this way our subjective present may incorporate parts of both the past and future. There is no precise answer to questions about the length of our perceived present and that is presumably why it has become known as the ‘specious present’. In a loose and general sense we can regard the specious present as that brief period of time in which we react to objective external stimuli, say our response-time when driving or playing table tennis. Presumably the duration of the specious present relates to our short-term memory and assorted mental processing including brief memories and anticipations that take place before we become aware that some particular perceptions are being replaced by others.

Human and animal perception of time is a matter for empirical science. In the case of human beings it is studied as mental chronometry in experimental psychology. Mental chronometry records brain response times to various percepts under many conditions. If we take our response time when driving as an example of the specious present then it is about 1.5 seconds, and for a responding click on a smartphone it is about 0.3 seconds.

There are obvious psychological constraints to what we can encompass in our present. We do not see the rapid refreshing of a TV screen or the individual pictures that make up a celluloid movie although we know that they exist. This suggests a possible connection between our sense of duration and our vision.

Now as an evolved adaptation
Each animal species has a set of senses as evolved adaptations that are a consequence of that animal’s historic environments. Collectively these senses determine the perceived reality of that animal’s world. We can determine to some extent the range of the senses of animals, their sensitivity to smell and so on. Though we cannot experience what they experience we have some idea of the nature of their sensory world. Clearly the experienced reality of a herring is
different from that of a bird or human being. We also know that the perceived reality of humans, unaided by technology, is not privileged over other species: birds see better than us, dogs have a more highly developed sense of smell and hearing, whales hear better underwater and so on. One feature of our senses is that they sample only part of what it is possible to sense. Humans hear and see within a limited range of what it is possible to hear and see, since we use only those waves of sound and light that aided our survival in the past. In a similar way we are biologically attuned to the range of time durations that were of adaptive value to us in the past. A cloud of bats flying inside a cave, in order to avoid collision, must be much more finely tuned to short time intervals than us. It seems reasonable to suppose that time-sense will be roughly related to factors like body size and energy expenditure.Many organisms respond far more rapidly than us to changes in their environment. There is little doubt that the length of our human specious present is a biological adaptation that allowed us to respond effectively to stimuli and threats in our historic environment. The specious present (largely unconscious) will also be different for different animals since many animals respond to time lapses are imperceptible to us.

Our interest is in the implications of the specious present for the philosophy of time. We can conclude from the above that the period of time we generally refer to as ‘now’ is not the perception of a universal now but a biological temporal adaptation unique to the human species and loosely indicated by our reaction times; it is our human perceptual time-reality. Our human specious present will be of different duration to that of other animals and it is not privileged over theirs, it is simply a consequence of our own particular evolutionary history – just as the colours we see and sounds we hear are different from those of other animals. We accept the limitations of out spatial perception, acknowledging that many animals perceive space in different ways from us, discriminating shorter or longer distances, but we find this difficult to accept for time which we feel must be the same for all creatures.

The brain as a temporal sense-organ
Time is not generally included as one of our senses, perhaps this is a shortcoming. There seems no reason why our human sense of time should be considered any different from our other five senses of touch, taste, sight, hearing, and smell. Unlike other senses time-sense does nothave a dedicated sense organ: maybe it is an integration of the other senses as a brain process. Another difficulty is that our five of touch, hearing, sight, sound and smell all responding to physical stimuli: smell molecules, light waves, sound waves and so on. What physical object are we sensing when we sense time? How do we perceive time?

The dynamic quality of time
Perhaps we do not sense time itself but other things? Now seems to be constantly changing as new experiences are perceived and processed in our brains. If our brain is acting like a sense organ then we sense not only a fixed term present or now that lasts about 0.3-1.5 seconds but also a now that is constantly changing and hence our sense of ‘lapse’. How can this be explained? If the lapse (flow) of time is a subjective matter then it requires psychological explanation? There is no shortage of possibilities:

• The lapse of time from future, to present, to past with its associated changing facts and truth-values has the feeling of movement
• Spatialized language of time (watches ‘running fast’, time ‘passing by’ etc.) implying the movement, spatial extension and contraction, varying temporal intervals expressed like distances or lengths, even the temporal accretion of facts and events – all suggest movement
• The arrow of time with its language of directional movement ‘forwards’ and the impossibility of time going ‘backwards’ suggests spatial movement in a direction
• Our perception of change, succession, and continuity are all reminiscent of spatial movement
• Physical objects and events seem to pass into, through, and out of existence, and for anything to change it must become older
• The incessant processing of information in the brain also suggests continuity

The specious present: past, present, future
We might say that the future is anticipation and the past is remembrance. Philosopher of time Adrian Bardon from Wake Forest University describes it as psychological projection that is indispensable for us to maintain a coherent reprsentation of the world. He notes Kant‘s observation that mental recollection of its nature must entail past and present, that we have an innate sense of temporal succession, and that space and time are necessary mental constructs constraining our spatial and temporal perception to ‘here’ and ‘now’, adaptive ideas without which we could not survive: we must impose order on the world whether it objectively exists or not.

Perhaps we can understand the temporal perspectival subjectivity of past, present, and future by using the spatial perspectival analogy of my computer being ‘here’ and your computer being ‘there’ while for you this situation is reversed.

3. Contextual present
A further sense of the present or now relates more to linguistic usage than a cosmic or perceived now. In everyday language we employ a highly variable, in fact unlimited, period corresponding to now or the present. With this usage the interval referred to as present depends on the context. For example, if we wish to draw attention to any particular duration that includes now, then we refer to that as the present. So, if we are timing a race we might speak of the present second, if we are on a long plane flight we might refer to the present hour, when giving a history lesson encompassing many thousands of years we might even talk about ‘this year’ as a present or current year, even the ‘present millenium’, and so on.

So, we can divide the present into smaller and smaller temporal intervals or units of duration. Yes, we do seem to have a ‘reaction time’ that correlates well with what we tend to call ‘now’. But no matter what interval of time we call ‘present’ (say an almost immeasurable instant, a reaction time of 0.3-2 seconds, a minute, or hour) we find ourselves relating to things that occurred before and after others. Augustine of Hippo pointed out that we cannot measure time if: it has no duration, or if it is not yet in existence, or if it has passed. And yet we do measure time. Augustine believed that time only exists as memory, sensation and anticipation and it is these that we measure when we measure time. He too was an idealist.

Both the specious present and contextual present indicate perspectival aspects of the present. However, it is argued here that, as with human perception in general, though we have a distinctly human perspective on time this does not necessarily mean that time or the world do not exist or that our perception is illusory, we are simply sampling a limited part of the whole in our own particular human way.

SUMMARY
Any coherent philosophy of time must be clear about what is meant by ‘now’.

Two major usages of the word ‘now’ have been isolated, one used in the world of mathematics and physics, the other in the world of common linguistic usage and biology. For the purposes of physics ‘now’ is the smallest duration of time in which change can occur and be represented mathematically. This ‘now’ of physics can be represented as a punctiform point in the space-time grid of the block universe in which all points are treated as existing equally.

The ‘now’ of everyday experience and common usage, although sometimes used contextually to refer to almost any duration, mostly refers to an ill-defined duration (the specious present) roughly corresponding to the human reaction-time, a period of around half to one second. We know that durations in the universe can extend from the smallest possible duration to the duration of the universe. Our biological awareness of time is restricted to the range of duration that has been most important for our survival as biological organisms. Most important here has been our reaction time (different from that of many other organisms). Just as our hearing is only aware of a limited range of sound waves (those that have been historically adaptive) so we are only aware of those durations of time that have been historically adaptive, that have allowed us in the past to respond in a timely way. We do not have an inner sense of a millennium (although we can imagine some extremely long-living organism that might have such a sense) because millennia are not part of our experienced world. And we must assume that the minute durations that some animals are aware of (like bats in a cave) and which are imperceptible to us, have been of inconsequential adaptive value to us.

So we need to distinguish between the ‘now’ (or ‘present’) of physics which is the smallest knife-edge duration in the universe and the everyday ‘now’ of biology which is a uniquely human perspective on time.

Philosophically it is important to note that because humans have a perspective on time this does not mean that ‘now’, the present, is itself illusory. Our senses interpret a vibrating column of air as sound and a light wave as a particular colour. Sound and colour are our biological way of perceiving sound and light waves and this is undoubtedly perceived differently in different animals. Though our perception of light and sound is our perspective, our perceived reality, that does not mean that the waves themselves are illusory, they do exist objectively in the universe, it is just that we cannot know them directly. Similarly we perceive objective change, even though we interpret it in our specifically human way.

I argue that our experiential or specious ‘now’ is a biological adaptation to a particular range of duration, a reaction time of roughly 0.3-2 seconds that has been of historical evolutionary significance. The cosmic now is the smallest unit of time that can register change. Even so, in our pursuit of time it is the cosmic now, T(*), that we must follow. Biological now, T(now) is our biological evolutionary response to T(*), it is the way we feel about time.

It is true that T(now) is subject-dependent and that we are projecting times onto the world (projectivism), and also true that we are perceiving time from an anthropocentric human perspective (perspectivalism). But it is a mistake to assume that projectivism and perspectivalism have no objective counterpart – the counterpart is change in the world outside our minds, in the external world, as T(*), the universal boundary between determinacy and indeterminacy.

References
Le Poidevin, R. The Experience and Perception of Time. The Stanford Encyclopedia of Philosophy (Summer 2015 Edition), E.N. Zalta (ed.), http://plato.stanford.edu/archives/sum2015/entries/time-experience/

Physical time

What is physical time?

Perhaps the most challenging and most rewarding aspect of time is the question of its actual physical nature.

Einstein & Physicists

Solvay Conference Brussels (1927)
The world’s top physicists. Einstein in the center.
Photograph by Benjamin Couprie, Institut International de Physique Solvay, Brussels, Belgium. From back to front and from left to right : Auguste Piccard, Émile Henriot, Paul Ehrenfest, Édouard Herzen, Théophile de Donder, Erwin Schrödinger, Jules-Émile Verschaffelt, Wolfgang Pauli, Werner Heisenberg, Ralph Howard Fowler, Léon Brillouin, Peter Debye, Martin Knudsen, William Lawrence Bragg, Hendrik Anthony Kramers, Paul Dirac, Arthur Compton, Louis de Broglie, Max Born, Niels Bohr, Irving Langmuir, Max Planck, Marie Skłodowska Curie, Hendrik Lorentz, Albert Einstein, Paul Langevin, Charles-Eugène Guye, Charles Thomson Rees Wilson, Owen Willans Richardson This picture is also available with names at the bottom.
Courtesy Wikipedia Commons
Benjamin Couprie Acc. 14 Sept 2015

We have seen how the idealist philosophers focused their attention on what we now recognise as subjective aspects of time: the sense of its dynamic flow and changing of speed with our individual mood; our perception of the properties of past, present and future; our understanding of ‘now’; and our specifically human perspective on space and time in general. Not surprisingly they concluded that time, on these terms, was a product of the mind.

One of the most discussed idealist philosophers of the early twentieth century was Cambridge University’s McTaggart who wrote the philosophically highly influential paper ‘The Unreality of Time‘ in 1908. This was at the same time that Einstein was working on his theories of relativity. Einstein’s work would produce a seachange in attitude towards time as he demonstrated conclusively that although there may be subjective aspects to time, it was also part of the very physical fabric of the universe – it undoubtedly did exist ‘out there’.

The articles Time – Flow and Time – Now dealt with the psycho-biology of time, articles Time – Change and Time – Duration were concerned mainly with the philosophical logic of time. This article examines our evolving understanding of time in the discipline of physics.

Physical time
Has science located a physical object (albeit one that cannot be seen, touched, heard, tasted, or smelled) called time or is time best regarded as a property of the universe (like light or heat) or a relation between events?

When we say that one minute has passed, we know roughly what the interval of time we call a minute feels like. We regard this as an estimate because, as we have seen, psychological time is not precise. For a precise answer we use a watch which measures one minute exactly. In contrast to various subjective aspects of time, measured physical or public time, the time on clocks and watches, is accepted by everyone without question. We might ponder the ultimate nature of time but our behaviour in response to durations measured by clocks leaves no doubt that togther we acknowledge it as real. Time is part of the objective world investigated by science and is the most precisely measured physical parameter. Measurements of time in physics are critical to many of our basic physical concepts – rate, space-time, current, velocity, power, force and acceleration are all defined using with time as a critical parameter.

But what exactly is it that our watches are measuring? There is of course the movement of the hands on the clock, but isn’t there also the interval or duration between the hands being first at position 1 and then at position 2, whatever that duration is … ? Would time exist if there were no material objects in the universe? Does physical time exist independently of objects like clocks and revolving celestial bodies like the orbiting planets, or is it defined by them and their relations?

An examination of three influential views about time, referred to as Absolute, Relational and Relative time, will introduce historical arguments betwen physicists about the nature of time before we look more closely at the elements of physical time today.

THREE THEORIES OF PHYSICAL TIME
Absolute (realist) time
Most people feel intuitively that time is not a part of the physical universe but transcends it in some way – that it is independent of objects and events and exists in its own right (that it is absolute). It is as though time (and space) ‘contain’ events. So, if all activity in the universe were to cease completely, then we imagine that events would be frozen but time itself would march on regardless. If objects and events were removed from the universe then something would remain, and we could call what remained space and time.

The most comprehensive view of time in physics after the ancient Greeks was that of Isaac Newton (1642-1726) who maintained that time was absolute in the way just described.

A characteristic of absolute time is that it is eternal. It would not seem to make sense to ask when absolute time began or when it will end because we cannot imagine such a time. If we are told that time had a beginning then we inevitably ask ‘What was happening before that beginning?‘ Time, we feel, must always have been present everywhere.

The classical Newtonian view, therefore, was that absolute time was eternal, with an existence of its own independent of people, space, the universe and its events. It was treated as a kind of substance, container or substrate for events, so events happen in time. Sound waves require something, say, the atmosphere or water to push against: they cannot be propagated in a vacuum. Newton believed that space had a similar kind of atmosphere, which was called the ether, which was the substrate that light could push against.

For Newton, the passage of absolute time was the same for all people and objects in the universe (even though perception of it might vary). As a consequence, all observers with identical measuring devices would be in agreement about the sequence and timing of particular events.

Newton’s exact words were:

‘Absolute, true, and mathematical time, in and of itself, and from its own nature flows uniformly [equably] without reference to anything external. By another name it is called duration. Relative, apparent and common time is any sensible external measure of duration by means of motion. Such measures (for example, an hour, a day, a month, a year) are commonly used instead of true time.’

Our language reinforces the view of time as independent ‘stuff’. We speak of the ‘flow’ of time and an ‘instant’ or ‘moment’ of time and of events occurring in time, as though time is an object separate from events.

We can summarize Newtonian Absolute Time as follows:

• The duration of an event is independent of observers (frames of reference)
• Simultaneity of events is independent of frames of reference
• Duration is the same regardless of motion and gravity
• The metric of time is intrinsic to the temporal interval. That is, the units of time are the same everywhere (it flows “equably”)
• Time is a substrate or medium in which physical events occur (it is independent from other items in the universe)
• Time is infinite as it is totally independent of an existent or non-existent physical universe

It should be noted that in his statement Newton distinguished two kinds of time – Absolute (true and mathematical), and Relative (apparent and common) or, as we should now say, relational time. Absolute time was, presumably, metaphysical because relational time, he said, was founded on sense perceptions.

It is often implied that his absolute time was an empirical aberration with more to do with his theism that his science – but this is not necessarily so (see later).

Relational (reductionist) time
Liebnitz (1646-1716) was a mathematician, philosopher and contemporary of Newton’s who did not share Newton’s views on Absolute Time. The two crossed paths on several issues. It is still uncertain, for example, whether we should thank Newton or Liebniz for the calculus.

For Liebnitz time did not have an existence of its own but was defined by events within the universe. This contrasted strongly with Newton’s idea of time as ultimately something unchanging (in the sense that it is transcendent, even though for Newtin it ‘flowed’). In other words Liebnitz believed that at its most basic, time could be reduced to change.

Liebnitz’s view was similar to that of many ancient philosophers who equated time with change. Plato (427-327 B.C.) maintained that time did not exist in its own right but was a characteristic or property of the universe. Aristotle (384-322 B.C.) considered time and events mutually dependent. We measure ‘movement by time and time by movement‘ he had stated, ‘so they define one-another, time being like a sequential numbering process with a ‘before’ or past and ‘after’ or future‘.

For Liebnitz time was simply the fact that we experience ideas and events one after another – in succession. In Liebnitz’ words, time was ‘the order of succession of phenomena’ or ‘the successive order of things’ – the overall ordering of non-simultaneous events. This has undergone revision and restatement until nowadays relationalism is taken to mean that, essentially, there is nothing to space and time over and above spatial and temporal relationships. All talk about temporal items such as moments and instants can be reduced to talk about events and their relationships. Change and motion exist but time does not: the concept of time exists in order to make sense of change. The physical or metaphysical referents for time concepts are either incoherent, unverifiable or superfluous. We should not talk and think of time and space but of times and places.

We define and understand time through events. We measure time because it is related to something that is happening. To obtain useful regular intervals we use regular motions (isochronous intervals) – the hands on a clock have moved, a pendulum has swung, or the Earth has rotated on its axis: it is relational. Similarly spatial relationalism argues that the intervals between objects fully describe their position without reference to any underlying non-material absolute space. Relations, like properties, are not something in addition to what has them, but an aspect of the thing that has them.

Time is no longer like a separate substance or container, an image that can be regarded as the source of much confusion. Events do not occur in time but time is, as it were, “created” by a sequence of events. Thus simultaneous events do not occur at the same moment in time (Absolute Time view) but simply occur together (Relational Time view). And events are sequential, not because they occur in different instants of time, but because they occur in a definite order. For Relational Time it is simpler and more realistic to say that events happen one minute apart, than to say that they are separated in time by one minute.

On the Relationist view Absolute Time becomes, at best, an unnecessary hypothesis. The question of infinite time would depend on whether ‘events’ had a beginning and whether they will have an end. Without a physical universe there could be no Relational Time. The prevailing current view would be that time began with the Big Bang but will continue indefinitely as we do not envisage a complete end to the universe.

In spite of their differences, Liebnitz would have agreed with Newton that identical measuring devices would give the same readings of the sequence and timing of particular events in the universe.

Relational Time has great appeal because it removes the transcendental, mysterious component of Absolute time and equates time with tangible events in the physical universe. If time is no more than a sequence of events then Absolute time becomes a simple misunderstanding – it has no independent existence of its own and its mystery dissolves. It also allows us to clear away some muddy language.

Relational time is thus a simple and practical solution to questions about time. It has appeal to science because it removes an unnecessary metaphysical object; it is Occam’s razor in action.

It may be claimed that succession (or change) creates the idea of time in our minds. Liebnitz, however, maintained that the succession of events in the world was time.

Objections
• Relativism does not appear to deal effectively with the durational aspect of time – the important interval between events is not explained satisfactorily. Time has ‘betweenness’; everything does not happen at once. It is not possible to conceive of succession without duration. And it seems impossible to think of duration without succession (at least in our minds).

In summary, Relational Time is a function of the universe, being a sequence of events or relations between things, rather than having an independent existence of its own. Time is not like a vast invisible container in which things happen (Absolute Time) but a relationship between events. No events: no time. (Relational time).

For Newton the universe had a clock, the movement of the planets. For Liebnitz the universe was a clock. Leibniz, like Newton, presumed that the “rate of passage” of time was the same throughout the universe so that the sequence, timing and simultaneity of events would be the same for any observer. Newton and Liebnitz agreed on many aspects of time, differing only on the critical nature of its existence. This was a very important difference though. With a relational view of space and time questions such as “Where in space did the universe emerge?” or “Was time ticking away before the Big Bang?” are no longer necessary.

We can summarize Liebniz’s Relational theory of time as follows:

• The duration of an event is independent of observers (frames of reference)
• Simultaneity of events is independent of observers
• Duration is the same regardless of motion and gravity
• The metric of time is intrinsic to the temporal interval. That is, the units of time are the same everywhere (it flows “equably”)
• Time is not a substrate or medium in which physical events occur but it coexists with (is relational to) things in the universe
• Whether time is infinite or not depends on the existence or non-existence of events (a physical universe)

Relative time
Although the competing Relational and Absolute views of time presented conflicting outlooks on the true nature of time, they agreed on the sequence in which events occurred and the association of particular times with particular events.

Einstein (1879-1987) radically changed our understanding of time measurement. The Theory of Relativity was a total re-examination and replacement of the Newtonian physical laws of motion. Basic to this theory of motion was the realization that there is no object in the universe that can serve as a stationary reference point acting as a standard for measurement. All measurements of motion are made relative to other objects – hence the theory of relativity.

According to Relativity, time is an aspect of the universe (in agreement with the relational view of time) but it is possible for measurements of time to differ between observers. We now have the introduction of an observer into our understanding of time – because it is the observer that gives us our frame of reference for measurement. This marked a major change in thinking.

Space-time (time at a distance)
Newton regarded space and time as independent entities and assumed that time would be the same for every person and object in the universe. For Einstein all events in the universe were defined in four dimensions (three of space and one of time). This is not counter to common sense because we generally define an event by when and where it took place. Since space and time are measured together (distances in space being defined in terms of time and the speed of light as light-years) scientists now speak of space-time, or the space-time continuum (which describes the geometry of the universe – sometimes called the 4-D manifold, which is mathematician Riemann’s term for space). A point in space is also a point in time, called a world-point. Matter then traces out world-lines. If world lines intersect then objects have collided. A point in space is an event in space-time. It is important to note that under this theory time and space are interwoven physically, not just metaphorically: space shrinks as time expands.

No matter how strongly our common sense tells us time and space are separate, the objective world of physics recognizes only a 4-dimensional continuum that is neither time nor space. Different observers may not agree on particular measurements of space and time but they can agree on suitable combinations of the two.

It is not possible to take equal-moment slices through space-time in an absolute and universal way. Each individual will have a different slicing (see Block Universe). We might note in passing that space, time and space-time do not have an intrinsic metric. That is, the units we use for space and time are purely of convenience and convention. We should therefore beware of equating geometry and chronology.
Light is at the very core of the theory of Relativity because it is the signal used to measure space and time across the universe.

Two important properties of light are critical for Relativity. Firstly, its speed is finite and calculable. Secondly, it is absolute (the same regardless of the relative velocity of any observer).

Historically, it would seem that as light emerged as a physical absolute, time became relative and Einstein convincingly wove time into the very fabric of the universe.

Philosophically it in important to note that what is independently real is what does not vary from one reference frame to another and that can only be achieved through space-time. Space-time interval measurements between events provide the scientifically invariant fact independent of one’s own state of motion.

The speed of light
The speed of light was first determined in 1675 by the Danish astronomer A. Roemer from observations he made of the eclipses of the moons of Jupiter. The discovery that the speed of light was finite (not instantaneous or infinite as Newton believed) was of profound importance because we use light to take many measurements, notably those of outer space.

In 1887 Americans Albert Michelson and Edward Morley carried out experiments comparing the speed of light while varying the speeds of the points of observation. To their surprise it was found that the speed of light was always the same, being constant at 300,000 km/s. Contrary to intuition, the speed of light is not relative to the speeds of observer and source but is the same for all observers whatever their relative motion. As a result of these experiments the speed of light is now recognized as a universal constant – a physical absolute.

This discovery also had other far-reaching and counter-intuitive implications that emerged when Einstein showed in his Theory of Relativity that, relative to an observer, objects nearing the speed of light approach infinite mass, their length shrinks towards zero, and time expands towards infinity. It should be noted, however, that the effects (time dilation, size diminution, and mass increase) only become noticeable at speeds approaching the speed of light; for everyday situations the mathematics of Newton’s laws of motion are perfectly adequate.

Since we observe events through the medium of light and light has a finite speed it is immediately evident that we do not observe events instantaneously. Someone close to an event will see that event before someone who is further away. The light from the Moon takes a half second to reach Earth, and from the Sun it takes 8.3 minutes. The time scale of a particular observer is generally referred to as proper time, defined as the time that would be given by a clock at rest with respect to a particular observer. This is often compared with coordinate time which is the time which an observer assigns to a distant event, knowing its distance away, the speed of the signal (usually light), and the proper time at which it was observed.

Wave structure of light
Paradoxically light displays the characters of both particles and waves.

Although the speed of light is constant regardless of the motion of the observer, its wave structure varies according to the relative velocities of the observer and object.

Wave frequencies increase with increase in the speed at which objects approach each other, and decrease with decreasing relative speeds. A longer wavelength produces a reddening or red shift, and a shortening wavelength produces a bluing or blue shift of light. This is the Doppler Effect – where the number of wave crests per second arriving from a receding source is fewer than those actually emitted from the source (this also occurs with sound waves, which lower in pitch as an object moves away). Only particles with zero mass at rest can travel at the speed of light and the photon can only travel at the speed of light. As the energy of a photon decreases, its wavelength increases. For example, light loses energy in a gravitational field producing a red shift.

A colour shift is a natural clock, being the interval between successive crests of a light wave. In 1929 the American astronomer Hubble observed a red shift in the universe that indicated clearly that it was undergoing rapid expansion in all directions. The background galaxies of the universe are receding from one-another at a rate that is proportional to their distances from one-another as measured by the red shift and the most distant galaxies appear to be moving away from us at close to the speed of light.

This was compelling evidence for the origin of the universe in a Big Bang.

The Special Theory of Relativity
Einstein’s Special Theory of Relativity (STR) of 1905 dealt with unaccelerated frames – those under uniform motion – referred to as an inertial frame of reference.

As we have seen, the time interval measured in a reference frame in which a clock is at rest is called the proper time. Einstein showed mathematically that if two observers are moving at constant velocity relative to each other, it appears to each that the time on the other’s clock would be slowed down, a phenomenon known as time dilation. This is so because there is no preferred frame of reference. The first direct test of time dilation occurred in 1941, 36 years after Einstein’s theory, and it confirmed his theory. Though Relativity runs counter to common sense its conclusions are now backed up by abundant experimental evidence.
[M – But what produces this effect? Is it actual or apparent due to the fact that light takes time to travel distances? Because of the peculiar behaviour of light waves and also because light has a finite speed and therefore takes time to travel large distances.]

One obvious outcome of the STR is that there is a multiplicity of time frames in the universe associated with different observers.

It is important to remember that the STR deals with uniform motion.

Imagine that an astronaut, A, left Earth travelling close to the speed of light, returning in several years to meet his twin, B, who remained on Earth. Under STR it would appear to both that the time of the other person would be slowed down. Each would think that they would be the younger when they eventually meet – which is not possible in reality. This situation is referred to as the “twins paradox”. In fact, astronaut A would be the younger. While the Earthling B may be considered in an inertial frame, the astronaut A has undergone acceleration and deceleration and is therefore to be treated under General Relativity (see below). The two frames of reference are not equivalent.

The General Theory of Relativity
The General Theory of Relativity (GTR) of 1916 dealt with accelerated observers – those experiencing gravitation (which produces the same effects as acceleration and deceleration). The faster an object moves, the slower time passes for someone observing that object. At the speed of light it would appear to an observer that the object had frozen still.

Einstein found that gravity also has an effect on time which passes more slowly on larger masses. One second on Earth is equal to 1.0000025 s on the Sun, equivalent to a difference of 1 second in 6 days.

The GTR demonstrated the way light rays are deflected by gravitational masses. Einstein came to realize that it was incorrect to think of gravitation as causing a distortion or warping of time – it was a warping of time or, more accurately space-time. The geometry of space-time is often represented as a trampoline-like grid with the gravity of solid objects puckering its surface, the bends in the lines being the bending of light towards sources of gravity. Space-time does not therefore operate in straight lines (Euclidian geometry) but exhibits curvature where mass exerts a gravitational pull on light (Riemannian geometry). Gravity is not a field of force but a curvature in the geometry of space-time, an effect known as gravitational lensing. Physicists now prefer to say that bodies do not “feel” gravitational forces but respond to the curvature of space-time in their vicinity. It should be pointed out that STR has had wider recognition and experimental verification than GTR.

STR established space and time as the inextricably linked space-time. GTR demonstrated space-time acting on and being acted on by matter.

Earth is responsible for 2 time warps, which tend to cancel one-another – one due to the Earth’s rotation, the other to its gravity. The higher up you go, the faster time runs relative to clocks lower down.

It is sobering to know that from a pulsar, which has a “gravitational field” a billion times stronger than the Earth, time is slowed by 20% relative to the Earth – so the Earth would appear only 3.5 (not 5) billion years old.

Both Newton and Einstein regarded the universe as being in more or less the same state throughout its history.

In contrast to both Absolute Time and Relational Time we can list the features of Relative time as follows:

• The duration of an event is dependent on the observer (frame of reference)
• Simultaneity of events is dependent on the observer (frame of reference)
• Duration will vary with relative motion and gravity
• The metric of time is intrinsic to the temporal interval. That is, the units of time are the same everywhere (it flows “equably”) Time passes at different relative rates
• Whether time is infinite or not depends on the existence or non-existence of events (a physical universe)

SUBSTANTIVALISM (SUBSTANTIALISM) VS RELATIONALISM
During the 18th and 19th centuries the Absolute view of time held sway, to be taken over in the 20th century by Relationalism. With the advent of Relativity in the 20th century the old Absolute vs Relational controversy changed to accommodate modern physics. Since time over vast distances could only be measured using space, the distinct concepts of time and space became superceded by the notion of space-time.

Spacetime as substance
Continuous physical fields are now recognized as physical entities; they are distributed throughout space so there are no unoccupied locations – there is no empty space. Space-time is a field that not only acts upon material objects but is also acted upon by them. The new interpretation of space-time was that it is substance-like, or substantival, acting like a container in which events occur. It is a system of space-time points in which events are located and, like a container, it exists distinctly from its contents. This is Minkowskian space-time in the case of STR which acts like a container. Riemannian space-time of GTR posits that the curvature of space-time as determined by the matter present, and it, in turn, determines how bodies will move. Here the substantivalist can no longer claim that the “container” is independent of what it contains. It is significant that although space-time interacts with the matter in the universe, it is nevertheless distinct from it: in this sense it may be said to be Absolute and the old Absolute-Relational distinction dissolves away.

It should be noted that the word “relativity” refers to the covariance of spatial and temporal intervals; it does not imply that it is the relations of material objects that are physically significant.

If it is argued that only material objects truly exist then the debate remains relevant and unresolved.

The problem of inertia
Newton’s Law of Inertia states that a body remains at rest or continues in uniform motion in a straight line (or “right” line as he called it) unless acted upon by an external force. Such a statement begs the question of motion in relation to what? This cannot be answered by referring to local bodies such as the Earth’s spinning surface (objects themselves generally in non-uniform motion) – his answer was absolute space and time. This is distinct from an absolute state of rest which Newton acknowledged was a matter of convention. [The inertial centre of gravity is the centre of the universe…]

• The problem is acceleration in general and rotation in particular. It is expressed most dramatically through a series of real situations and thought experiments:
• Is the bulge at the centre of the Earth due to its rotation relative to anything? Would it be there if the universe rotated around the Earth and the Earth was still (if that makes sense)? Would the bulge steadily decrease if matter were gradually removed from the universe?
• Imagine two balls in space attached to one another by a piece of string, then rotate them about their axis. The string will be taught but they will not be rotating relative to one-another. If the balls are like ballooons filled with water and one is rotated about its axis will the centre bulge? If so is this due to its rotation relative to the rest of the universe. If the matter in the universe were gradualy removed would the bulge decrease?
• Are the centrifugal, centripetal and coriolus forces intrinsic or extrinsic (or neither or both)?

Thus Newton postulated immovable space (as he called it) as the centre of the system of the universe. This did not change for Einstein who stated himself that space-time is endowed with physical qualities that enable it to establish the local inertial frames, but “the idea of motion may not be applied to it”.

For the purposes of dynamical analysis, motion must be referred to an absolute background metric of rectilinear inertial coordinates rather than to relations between (local) material bodies, or even classical fields. We cannot infer everything important about an object’s state of motion simply from its distances from nearby objects. In this sense both Newtonian and relativistic physics find it necessary to invoke absolute space. It seems that position and velocity are relative, but accelerations have absolute significance independent of the relations between material bodies (at least locally).

In developing his GTR Einstein hoped that the field equations represented true relationalism but he was to find out, to his dismay, from Schwartzchild that there is a preferred coordinate system. GTR correlates the relations between objects (including fields) and the absolute background metric. This metric is affected by, but not determined by, the distribution of objects. So space-time is itself an absolute entity exerting influence on fields and material bodies.

The prevailing ethos of the time was relationalist and proponents like Mach anticipated that space-time, like Absolute space, could be eliminated by denying that it has any physical significance. Mach believed that the average state of motion of matter in the universe counted as the basic inertial field – what he called the distant stars. However, it is now acknowledged that this basic inertial field cannot be attributed to the distribution of matter and energy in space (the distant stars), we simply have to assume a plausible absolute inertial background field.

[Local inertia is determined by geodesic motion in the local region which is a function of the local space-time. Local geometry is affected by the space-time geometry of the universe. Local inertia is the result of an imposed deflection from geodesic motion through local space-time whose character is determined by the distribution of matter throughout the universe. The dynamic state of everything in its totality, determines the framework in which any particular thing moves, and the inertial effects that arise from that motion.]

A dense mass will cause a depression of space-time, (rotational) motion drags space-time in the direction of rotation. This is called frame-dragging (Lense-Thirring effect, gravitomagnetism).

Absolute and Relative time each have major arguments to confront:

If time is the relation between things how do we account for the reality of the “moving” now with its imprint on, not only the limited lives of biological organisms, but also the evolution and ageing of the entire physical universe. The argument that now is a peculiarity of human perception or in some way illusory is difficult to sustain. In other words now is not a special relation between human beings and the world – now is a real and objective aspect of the universe: it would exist in the universe whether humans were present or not. [is this what R claims???] There is also the problem of duration – events have duration that seems real.

For Absolute time there is the problem that we can have no Absolute measure of time itself. If the Earth were to suddenly rotate at twice the speed (this being our natural clock), apart from a whole range of physical effects there would be obvious discrepancies in relation to our biological and other clocks. If atomic clocks sped up or slowed down, for whatever reason, we would be aware of the problem in relation to other measuring devices. All our measurement of time is in relation to something else. But if Absolute time exists independently of these clocks (which are only measuring time in relation to one-another), then we are entitled to ask what it would be like for the universe and/or our clocks, and/or ourselves, if Absolute Time itself were to speed up or slow down. Could we measure its speed in any way? If we answer that there would be no noticeable difference then the question of the relevance and, indeed, the existence of Absolute Time arises again. Can we know if time of the past, relative to time of today passed more quickly or more slowly? Since we know that time passes more slowly in a dense place such as the Sun relative to us, then it seems safe to assume that time passed at differing rates as the universe evolved.

Could physical time be unreal? Many philosophers through the ages have thought so.

There are other philosophers who claim just the opposite. Physical, measured time, lies firmly in the objective world (see also objectivity of time). Newton’s time was precisely measurable. Einstein’s time was precisely measurable but had to take into account relative motion and gravity. Einstein placed time strongly within the physical world and, it seems, completely removed any transcendental associations. Time was not “just there”, or necessarily linked to “events” but part of the very physical fabric of the universe. Time is now the most accurately measured physical parameter.

It should be emphasized that in speaking of the relativity of time, it really is the time that is relative, not our experience of it, nor the operations of the measuring devices we use.
Space-time is a measurable physical parameter, present in the universe even, we assume, in the absence of humans. In this sense it exists as an objective reality.
The paradoxes of time (see, for example, McTaggart’s paradox) and intangible nature of time has persuaded many philosophers that it is not real. This is certainly contrary to common sense and our scientific theories, many of which have time at their core.

[And yet physicists use time as a key concept that they regard as being at the very bedrock of the objective universe and its laws (Davies, 1995). Einstein established that time was very much a part of the objective physical world. In hardly needs to be added that it is, in many ways, the most basic aspect of our subjective inner world too.

For physical time we can simply accept time as the latest accepted definition of t given by physicists.] However, this leaves ample room for debate about the nature of its existence. We can hardly doubt that it exists, how it exists is another matter.

Relative time
The Relative view of time presented by Einstein introduced a new factor, the frame of reference which was used for measurement. Thus a particular event might be associated with different times depending on the frame of reference and this was a development not anticipated by either Relational or Absolute time.

The ‘equable’ time of Newton, although a measurable aspect of the physical world, had a now that was the same time throughout the universe. With Relativity there was, on a universal scale, no longer the time but my time and your time depending on relative motion and the effects of gravity. The time dilation of STR involved speed, and that of GTR accelerations or gravity (regarded by Einstein as equivalent).

Time, we now know, “passes” at different rates in one part of the universe relative to another, and in a mathematically predictable way.

SUMMARY
Absolute time (A) as articulated by Newton, views time as existing independently of space, things and events. It is treated as a substance or container in which other things exist and events happen. “Moments” of time are thus separate from objects and events. This position finds modern proponents in a modification called substantivalism.

Relational time (R) as originally articulated by Liebnitz maintains that time does not have a separate, independent existence but coexists with objects and events. Relativity emphasizes the significance of the relationship between observers and events. Relational time expresses the prevailing view of modern science.Isaac Newton’s view of time corresponded to our everyday intuition that there is a sort-of universal cosmic clock proceeding at a universal rate. Space and time are discrete. ‘Now’ is exactly the same across the universe. Space was like a container or environment within which the events of the universe happen.

Einstein showed that physical time, the time that we see marked by the movement of hands on clocks, can proceed at different rates under the influence of relative motion and gravitation. And ‘now’ (whatever temporal interval is selected) will depend on the spatiotemporal circumstances at one part of the universe compared to those at another. There is an intimate and roughly reciprocal connection between motion ‘through’ space and the passage of time: the more speed, the less time. From your location in time and space the watch, and all movement, on someone moving towards you is moving slower than if they were standing still. This is because part of their motion in time is being diverted into motion in space. Two locations that are not in relative motion would show identical time.

Clarke-Maxwell had shown that the speed of light was constant; it was fixed regardless of the motion of its observers. Einstein realized that if speed is a measure of space (distance) and time (duration) then, depending on the circumstances (motion and gravity) space and time must vary if the speed of light is to remain fixed. Space can shrink and time can expand (dilate) depending on how you are moving. Theoretically watching someone moving close to the speedof light means that they would appear to live much longer than the usual life span. Motion through space affects passage through time.

In a sense Einstein had realised that the two discrete scientific categories space and time were so closely interconnected that they were better regarded as a single physical entity, spacetime, in much the same way that a biologist might decide that two organisms once given different names were in fact the same species and therefore better understood under one name. ‘Spacetime’ was a linguistic marker of a physical reality.

Taking Einstein’s theory seriously challenges our sense of past, present, and future. We can think of time’s lapsing as either continuous (becoming) or as myriad discrete moments like the refreshing images on a TV or the individual frames of a celluloid movie that we do not notice. Indeed, we can envisage the entire history of the universe laid out as a spacetimescape, as a ‘block’ of spacetime with spacetime coordinates marking out everything.

During one cosmic time-slice of this block which we might call ‘now’ (lasting, say, 1.5 seconds for humans) we can imagine events happening across the universe in this now-slice. We might also think that wherever you were in the now-slice there would be agreement about what was going on elsewhere across the universe during that now-slice. But Einstein showed that if we take motion into account the now-slices will be different and depend on the location where the ‘now’ slice is cut. Someone in the Andromeda galaxy not moving relative to you on earth will agree with you on the contents of their now-slice. But if there is relative motion then watches would disagree and the now-slices would be different. Moving away from you would give a now-slice terminating in your past and moving towards you would give a now-slice terminating in your future. And over vast distances these discrepancies in time can be 100s of years, even millennia. So there would be disagreement about what was past, present and future. Relative motion leads to watches moving out of synchronisation.

Einstein’s physics demonstrated that since no perspective is privileged then we must take past, present and future as equally real. Each individual has a distinct past, present and future but this may not agree with that of other people (locations) in the universe. There is a sense in which time just is, it is static, eternal and timeless. On this view we must think of time spatially, so that, just as all space is out there in the universe, so too is all of time too – it is not confined to a now-slice. The equations of physics do not pick out one now as special from another. Moments are: they just exist: the Platonic world of Being.

One way in which Absolute and R time can be contrasted is in developing a model of the history of our universe. In a universe of Absolute time and Absolute space matter would be visualized as expanding outward into empty space through the void (ether). In a relational universe our whole universe is expanding so there is a combined motion outwards of space, time and matter.

Be careful of Absolute and R. – Newton was possibly correct: duration is Absolute (we sense it); R is the measure of Absolute by motion. If the question what is time is the same as the question what is duration then this could well be a matter for physics.

Although we speak of time as separate from space in everyday language, technically we are, for the most part, speaking of space as well. In this way the concept of space-time has relevance in day-to-day life as well as science. It would seem that the scientific description of space-time as having time-like and space-like dimensions has echoes in our day-to-day understanding of space and time through the following questions:

• Whether time is Absolute (moments) or R (a relation between things and/or events) it is manifest as events (change)
• An event proceeds by a succession or temporal ordering (temporal relations) of two kinds: before and after (B series), or past, present and future (A series). The A series is sometimes treated as a human construct
• Events have an asymmetry (irreversible direction – they are anisotropic – see Arrow of time)
• Events have (and are sometimes separated by) duration (a temporal interval) which is measured in units of convenience and convention
• The measured duration of events (the intervals between events), may differ according to the relations between their frames of reference. That is, events succeed each other at a particular rate that is determined by relative motion and gravity (curvature of space-time)
• Temporal length and temporal motion are qualitatively different from spatial length and spatial motion
• Everything exists in time and therefore ages as “now” extends the time frame of the universe as a process of temporal becoming (flow of time), often construed as a human construct that has no meaning in the objective world

A pi-meson exists for 10-16 seconds.
It is noteworthy that, in spite of the incredible precision of modern timekeeping, no time scale can be proved to be uniform by measurement, as measurement is always a relative activity – although this is of no consequence to everyday affairs. We therefore have no way of knowing whether time at one historical epoch passed at a different rate relative to the time of another historical epoch.

Time, space, matter (mass-energy) and motion are inextricably interlinked? What is separate and what inextricable – how and why?

Does time have properties? Is an hour an event (things endure, durations do not) – therefore time does not exist any more than events!? Existence of changes and events.

Although we measure time, we are also physically aware of it.

Continuity mathematically is termed denseness which is infinite divisibilty. The modern notion of continuity is different.

In what sense does time (space-time) exist?
[Substantival space-time] When we ponder the question “in what way does (space)time exist?” we seem to come, at different times, to different conclusions! Sometimes time seems to be undeniably real, almost substantial, and apart from other things. At other times this independence seems like a deception such that time becomes like an aspect of other things, as if it were a property or product of the universe, or a relationship between things.

Is time a thing (individual), a property or a relation? Or something else?

Absolute Time (A) and Relational Time (R) represent the two major views about the nature of existence of time, and we have already examined these in some detail.

We can now state these two major positions simply and clearly.

For R, if there are no events (or things) standing in temporal relations to each other, then time would not exist. In fact, time is the temporal relations between events or things. For R, time co-exists with the universe rather than being separate from it. For A, time could exist even if there were no events (no change). Absolute space-time could exist, even if there was no matter in the universe. In contrast R maintains that space-time is nothing but material objects, their events, and the spatio-temporal relationships between them.

Science emphasizes time as R in character because we measure it in relation to objects and events such as the movement of hands or numbers on a clock. This is all that is needed for the practical purposes of science, so Absolute can be denied or treated as an unnecessary hypothesis.
Although it is perfectly clear that time cannot be measured without change or events, the important point at issue here is whether time can exist without change.

Our everyday language and assumptions treat time as something separate that is content-independent. Most people feel intuitively that empty space and eventless time are a possibility.

Absolute treats time as a substance, solid or thing-in-itself, a kind of container within which the events of the universe happen. Philosophically time in this form is referred to as an individual. Giving something the character of a substance is called hypostasis.

According to Absolute there are temporal individuals such as moments: for R there are only temporal relations.

Historically Liebnitz and the early Einstein maintained that R was the only view consistent with science. It is possible to postulate an absolute space-time that could exist, even if there was no matter in the universe. Likewise a relational theory would maintain that space-time is nothing but material objects, their events, and the spatio-temporal relationships between them.

But in recent times absolute theories have gained ground so that there is now no convergence of opinion on this central issue. Nowadays absolute theories are called “substantival” or “substantial” if space-time is treated as a kind of substance, an “antecedent arena for events”, “substrata for properties” or somesuch. Einstein maintained a loose Absolute in his later days although it must be pointed out that the container metaphor might work for STR but GTR requires curvature of space-time be affected by the distribution of matter, so it does not seem plausible here.

In the early 21st century the A-R distinction has blurred. Time appears to be real and absolute in the sense that space-time is like a substance (albeit extremely “thin”) or container that occupies the whole of the universe – there is no empty space. It is relational in the sense that we assume that space-time originated with the Big Bang and is not an independent ‘stuff’ but interacting with (co-existing with) the matter of the universe.
Time is a physical product of the universe that co-exists with it. It is not independent of the universe but can be treated as a real substance (it is substantival). It is best understood through the notion of duration. We measure duration in relation to the regular behaviour of objects within the universe.
[Distinguish between times mode of existence, origin and nature. How is time separate from events and objects – explore the new approach]

Commentary on time

I have built up a picture of what I believe is close to a contemporary picture of what we mean by time. It began with the simple observation that as used in everyday language time is not just one thing but many. It was claimed that we are now in a position to draw a distinction between subjective aspects of time (that is, aspects of our perception of time and limitations imposed by our species-specific biology) and the objective time investigated by physics.

Already we can begin to make our own asessment of some of the historical definitions that have been given in answer to the question ‘What is time?’

Plato – ‘The moving image of eternity’
Aristotle – ‘The number of movement in respect of ‘before’ and ‘after’
Immanuel Kant – ‘Transcendental … a pure form of sensible intuition … the form of inner sense … not an object . i.e. the dimension in which our own experiences are ordered’
John Locke – ‘Duration set out by measures’
Whitrow – ‘An aspect of the relationship between an observer and the universe: it co-exists with the universe’ Author of the book ‘What is Time’, 1972
John Smart -‘The dimension of change’ (Australian philos’er, quoted Encyclopaedia Brittanica)
Albert Einstein – ‘Past, present, and future exist simultaneously’ and in discussing Minkowski’s Space World interpretation of Relativity: ‘Since there exists in this four dimensional structure [space-time] no longer any sections which represent “now” objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence’(Relativity, 1952)
David Mellor -‘The dimension of causation’ (Cambridge University Philosopher of Time)

STATEMENT OF A PHILOSOPHY OF TIME
[Numbers in square brackets indicate chapter sections where statements are elaborated]

In the Epilogue to ‘A Brief History of the Philosophy of Time’ (2013) Adrian Bardon draws together the threads of contemporary thinking on time.

From the temporal idealists we have learned important lessons about both time and science itself. The only way we can understand the world outside our minds is through the mediation of our minds: we can never know if our representations of the world are accurate except through their explanatory power, simplicity, and application, not through a direct knowledge of nature itself. This does not cast us into a world of subjective uncertainty as we have every reason to believe that the mapping of our scientific explanations onto the world, our representations of the world, are becoming increasingly accurate. However, we can confidently expect that our particular way of understanding and experiencing the world will be a consequence of its biologically adaptive value to us as Homo sapiens. As conscious living organisms we are both deeply aware of and totally dependent on here and now. No doubt there is more to be gleaned about this from phenomenology and evolutionary psychology even if scientifically and philosophically we are persuaded by the early twentieth century philosophical and scientific work of McTaggart and Einstein that there is no special privileged moving now that we occupy.

A word in support of philosophy. We can quickly dismiss philosophy as being concerned with the unproductive niggling at unanswerable or meaningless questions. I hope that this series of articles has shown how philosophy, in fact, helps us to both identify the meaningless questions and locate the tough and abstract but answerable ones and to therefore make progress.

The ultimate constituents of the universe may be continuous, or discrete, or both – we do not know. It is conventional to segregate the universe into space, time and matter (mass-energy) but even a simple distinction like this is contentious. How can we unambiguously define each of these entities without reference to the others? We know from Relativity that space, time and matter interact in a way that makes their physical and theoretical isolation questionable. It has, for example, been postulated that matter is highly condensed space-time. In particular we learn from General Relativity that space and time are inextricably co-variantly woven together in the fabric of the universe, any measurement of one affecting that of the other. Nevertheless, since time is a separate dimension of space-time and because there are many occasions (especially in daily life) when the space-like component of space-time is irrelevant to discussion, it becomes meaningful to speak of time alone, although the underlying co-variant relationship with space should always be kept in mind.

Within the physical universe of space-time we cannot say with certainty whether space-time is substantival (absolute), that is, existing independently from other things as a substrate, or simply relational. This is a long-standing debate that is still not fully resolved. However, it is the view presented here that time is an objective part of the fabric of the universe and should be treated philosophically as an object, not as a relation. In other words time, contrary to much philosophical thinking – most notably that of McTaggart – is real. Perhaps the most persuasive demonstrations of its reality came after McTaggart’s paper of 1908 (which claimed the unreality of time) through Einstein’s predictions of time dilation. For example, after a period of time clocks on aircraft circling the Earth give different readings relative to clocks on Earth, and it is possible to calculate the precise difference according to Relativity theory. Such experiments are remarkable because they are counterintuitive and demonstrate the physical reality of time and its physical effects in situations that are independent of human percepts.

If we accept the physical reality of time, how does this bear on the complex semantic web of temporal ideas that are presented to us in everyday discourse? The future plays a vital role in all of our lives and yet few would claim that it is real. In claiming that it is unreal we are not denying that it is of vital, possibly critical, importance to our mental functioning, but that it has no reality beyond our minds in the external world. What are the subjective and objective components of time?

In everyday discourse (and some scientific discourse) it is extremely significant that the word time is used with several meanings. This bears strongly on philosophical discussion yet is not apparent in the literature.

The future is what has not yet happened, the past is what has happened, and the present is what is happening now. Nothing happens in the future or the past but we can subjectively anticipate, imagine or project into the future, and have memories and imaginative scenarios of the past. But all anticipation and memory is subjective and, most importantly, it occurs in the present. Since there is no objective past or future now, nothing can flow from future through present to past except in our minds: events just happen, they cannot literally move towards us from the future, except as calculated subjective projections. However, time does lapse in the present and this gives us the sensation of movement that we call the passage of time. Time lapse is real and objective but it is not spatial, and time is not a substance, therefore its description using spatial and substance words such as length, flow, distance and passage is metaphor. Temporal “passage” as literal spatial and substantial movement is illusory, but as lapse of time which feels like spatial movement it is objective and real, it is just that the spatial language so often used is inappropriate. Time lapses in the present and is temporal not spatial. All spatial talk of accretion and extension is similarly inappropriate, as is talk of things coming into, and going out of, existence. All this implies movement of events or things into and out of the past and future. There are simply changes in the present.

In summary, the present is real and consists of our subjective response, the specious present, to the objective now, which is time itself. The past and future are not objective constituents of the universe but subjective memory and anticipation. Therefore monadic temporal properties like pastness, presentness and futurity, and being one week past, 1 day future etc (A-properties) have no objective counterparts.

Objective, physical time is the now: what has been described as the knife-edge between what we call past and future, between indeterminacy and determinacy; the actuality between potentiality and unalterable necessity: it is different from the psychological now. The place of now in the universe will depend on its relativistic frame of reference but it is, nevertheless, an objective part of the physical world. There was a now at the Big Bang and a now as the universe and biological organisms evolved, and that cosmic now did not depend for its existence on the presence of human observers. The history of the universe, of the rock strata and the fossils they contain, and of the organisms that have evolved, bear witness to an objective now of the past.

We sense time always, but measure it using clocks of various kinds – instruments with isochronous intervals. The human psychological now (specious present) is not of a precise length but of a period suitable for our biological adaptation to the threats and needs of our environment. It is sufficiently short to make us concentrate when driving cars or playing table-tennis – occasions when our judgement of now can be critical. The psychological now is an adaptation to the objective now of the universe. When people in different countries tune in to a football match on television, the simultaneous now is not a common illusion or a mutual convention, it is a public and objective reality. The now of the universe is divisible to the finest precision of our most accurate clocks and finer still.

Time is not simply the temporal relations between events. The relations of earlier than, simultaneous with and later than do not account for duration, which we can both sense and measure.

Time is not space: it is not the movement of the hands, or the flashing of numbers on a clock (it is the temporal intervals they represent); it is not change (although we can hardly imagine time without change); it is not spatial length as represented by a line (although we can represent time with a line, time is not the line itself). Temporal length as represented by the aging of everything that is actual. Time moves in the sense that temporal distances can increase and decrease, but these are not spatial distances, and therefore the movement of time is not the same as the movement of a river. It therefore does not make sense to ask how fast time flows.

Since all the major aspects of time we have considered – becoming, duration are objective, they are therefore part of the empirical world and therefore essentially a matter for science (physics) rather than metaphysics, although philosophy can assist in clarifying concepts.

The solution to the problems of time cannot be semantic – it must be empirical.
[The description of time is largely an empirical matter.
What time actually is, and the role it plays in language] Time is an unspace-like dimension.

BIBLIOGRAPHY
History & general background
Callender,C. (ed.) 2011. The Oxford Handbook of the Philosophy of Time. Oxford University Press: Oxford

Causation
Trisel, B.A. (1999). The causal attainment theory of temporal passage. Sorites 10: 60-73.
*Tooley, M. (1997). Time, tense and causation. Clarendon Press, Oxford.

Four-dimensionalism (3D/4D)
*Prior, A. (1968). Changes in events and changes in things. In: Papers on time and tense. OUP, London. An account of tensed discourse in terms of modal logic.
Butterfield, J. (1984). Spatial and temporal parts. The Philosophical Quarterly 35: 32-44.
Heller, M. (1993). Varieties of four dimensionalism. Australasian Journal of Philosophy 71: 47-59.
Markosian, N. (1994). The 3D/4D controversy and non-present objects. Philosophical Papers 23: 243-249.
Mellor, D.H. The time of our lives. Royal Institute of Philosophy lecture, available on the web www.dar.cam.ac.uk/dhm11/TimeLives.html
Parsons, J. (2001). Must a four-dimensionalist believe in temporal parts? Post-final version, internet.
Sider, T.R. (1997). Four-dimensionalism. The Philosophical Review 106: 197-231.
Smart, J.J.C. (1963). Philosophy and scientific realism. Routledge and Kegan Paul, London.
Smart, J.J.C. Time In: Edwards, P. (ed). The encyclopaedia of philosophy. Collier-MacMillan, London.

Arrow of time
Price, H. (1996). Times arrow & Archimedes point: new directions in the physics of time. OUP, Oxford.
Coveny, P. & Highfield, R. (1990). The arrow of time. Fawcett Columbine, New York.

Relativity
*Hickenfuss, I. (1975). The existence of space and time. Clarendon Press, Oxford.
Smart, J.J.C. Spatializing time. In Gale (1967)
Edwards, P. (ed.) (1973). Problems of space and time. Collier-McMillan, London.

Absolute & relational time & substantivism
Rynasiewicz, R. (1996). Absolute versus relational space-time an outmoded debate? J. Philosophy 93: 279-306.
Shoemaker, S. (1969). Time without change. Journal of Philosophy 6: 363-381.
*Hoefer, C. (1998). Absolute vs relational space-time: for better or worse the debate goes on. British Journal of the Philosophy of Science 49:

Space and time
Taylor, R. (1955). Spatial and temporal analogies and the concept of identity. Journal of Philosophy 52:
*Stein, H. (1968). On Einstein-Minkowski space-time. The Journal of Philosophy 65: 5-23.

General
*Audi 103A911C (1999). Cambridge encyclopaedia of philosophy.
Bardon, A. 2013. A Brief History of the Philosophy of Time. Oxford University Press: Oxford
*Butterfield, J. (ed.) (2000). The arguments of time. OUP
*Craig, E. (ed) (1998). Routledge encyclopaedia of philosophy. Routledge
Gale, R.M. (1967). The philosophy of time. Macmillan Reissued 1978
*Gale, R.M. (1968). The language of time. Routledge & Kegan Paul,
Aveni, I. (1989). Empires of time. Basic Books, New York.
Davies, P. (1995). About time. Penguin, London.
Flood, R. & Lockwood, M. (eds)(1988). The nature of time. Basil Blackwell, Oxford.
Fraser, J.T. (ed.) (1968). The voices of time. Allen Lane The Penguin Press, London.
Hawking, S. (1997). A brief history of time. Bantam, Sydney.
LePoidevin, R. & McBeath, M. (eds) (1993). The philosophy of time. Oxford University Press.
Newton-Smith, W.H. (1980). The structure of time. Routledge & Kegan Paul, London.
Pendleton, R.L. (2000). Time and supervenience. Members.aol.com/pendletonz/time_supervenience.html.
Penrose, R. (1994). Shadows of the mind. OUP, Melbourne.
Poidevin & Macbeath (1993). The philosophy of time. OUP
Royal Observatory Greenwich information leaflets. www.rog.nmm.ac.uk
Smart, J.J.C. ( ).Encyclopaedia Britannica. Time.
Whitrow, G.J. (1961). The natural philosophy of time. Thomas Nelson, London.
Whitrow, G.J. (1972). What is time? Thames & Hudson, London.
Whitrow, G.J. (1989). Time in history. O.U.P., Oxford.
Wilson, C. (ed.) (1980). The book of time. Jacaranda Press, Milton.

Presentism
*Bigelow, J. (1996). Presentism and properties. In J. E. Tomberlin (ed.) Philosophical Perspectives 10, Metaphysics: 35-52. Blackwell, Cambridge Ma.
*Prior, A. (1967). Past, present and future. OUP
Chown, M. (2000). Backwards to the future. New Scientist 165(2224): 26-31.
Gale, R. (1969). Here and now. The Monist 53: 396-409.
Garson, J.W. (1969). Here and now. The Monist 53: 469-477.
Markosian, N. (2001->). A defense of presentism. Markosian web site.
*Oaklander, N. (1994). Bigelow, possible worlds … Analysis 54(4): 244
*Prior, A.N. (1959). Thank goodness that’s over. Philosophy 34: 12-17.
Seager, W. (?). The reality of now.
*Smith, Q. (1988). The phenomenology of A-time. Dialogos 52: 143-153.
Taylor, R. (1962). Fatalism. Philosophical Review 71: 56-66.
Williams, C. (1992). The phenomenology of B-time. Southern Journal of Philosophy 30: 123-137.

Becoming
* Prior, A.N. (1968) Changes in events and changes in things. In LePoidevin & McBeath.
Brooke Alan Trisel (1999). The causal attainment theory of temporal passage. Sorites 10: 60-73. Abby2tris@cs.com
Broad, C.D. (1938). Ostensible temporality. In Gale (1967).
Markosian, N. (1993). How fast does time pass? Philosophy and phenomenological Research 53: 829-844.
Markosian, N. (1992). On language and the passage of time. Phiosophical Studis 66: 1-26.
Markosian, N. (2001?). Review of: Semantics, tense and time. By Ludlow, P. Cambridge, MA.
*Mundle, C.W.K. (1966). Augustine’s pervasive error concerning time. Philosophy 41: 165-168.
Russell, B. (1915). On the experience of time. The Monist 25: 212-233.
Smart, J.J.C. (1949). The rivers of time. Mind 58: 483-494.
Williams, D.C. (1951). The myth of passage. Journal of Philosophy 48: 457-472.
Markosian, N. (1993). How fast does time pass? Philosophy and Phenomenological Research 53: 829-844.
*Smith, Q. (1987). Problems with the new tenseless theory of time. Philosophical Studies 52: 371-392.

McTaggart
Mellor, D. (1998). Real Time II. Routledge, New York.
Craig, W.L. (2001) McTaggart’ paradox and temporal solipsism. Aust. J Phil. (March)
McTaggart, J.M.E (1908). The unreality of time. Mind 18: 457-484.
Oaklander, L. N. (1993->). Time and change. Updated paper available on the web
*Oaklander, N. (2000). A & B time …..Journal of Philosophical Research ….
Parsons, J. (2001). A-theory for B-theorists. Josh Parsons Web Page.
*Dyke, H. (2001). Tensed meaning: a tenseless account. J. Philosophical Research
*Dyke, H. (2001). Tokens, dates and tenseless truth conditions. Synthese
*Dyke, H. (2002). Thank goodness that’s over – the evolutionary story. Ratio
*Callender, C. (ed.) (2002). Time, reality and experience. CUP
The last three minutes.

Possibilism – time and modality
Bigelow, J. (1991). Worlds enough for time. Noûs 25: 1-19.
Menzel, C. (2000). Three types of possibilism. Stanford Encyclopaedia. Internet.
Lewis, D.
*Dowe, P. (2000?) Fiction and time travel. Internet.
*Dowe, P. (2000). The case for time travel. Philosophy 75: 441-451.
*Keller, S. & Nelson, M. (2001). Why presentists should believe in time travel. Australasian Journal of Philosophy
Lewis, D. K. (1986). On the plurality of worlds. Blackwell, Oxford.
*Lucas, J.R. (1989). The future. Blackwell, Oxford.

Glossary
Duration – A temporal interval
Endurantism – the view that material objects persist as three-dimensional objects wholly present at every moment of their existence
Eternalism – the past, present and future exist equally
Now – the indeterminacy of the future (unknown, subjective) giving way to the determinacy of the past (known, objective): the coming into being of determinate reality (objective). Note that this definition is given in the present tense and also that it is not ‘the moment when’ now occurs. Now is time itself. Now is the only semantic element of the semantic taxonomy (excluding T(a) and T(r)) that does not exist in time T(ud)
Perdurantists think that objects have both spatial and temporal parts, while endurantists think that they only have spatial parts. From an endurantist point of view, however, it is difficult even to say what temporal parts are supposed to be. Your temporal parts are parts of you which lie in the past or in the future>
Present – the current state of affairs or now as perceived and acted upon by humans
Past-presentism – The past and present exist but not the future
Presentism – only the present exists
Succession – The sequence of things (times and events;(facts, people or objects) which may be either earlier than, simultaneous with or later than the present (now), or one-another

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