We tend to think of scientists as hard-nosed realists trading in reliable evidence and the most compelling explanations available to us. But they are are also metaphysicians struggling to come to terms with the nature of reality. This seemingly more speculatve and counter-intuitive side of science is evident to anyone who has pondered space-time and relativity, quantum mechanics, quantum entanglement, string theory, M-theory, and the multiverse.
For pre-Socratic ancient Greek philosopher Democritus (c. 460–370 BCE) all existence was made up of indivisible atoms. By the Middle Ages the work of Aristotle had been rediscovered and was preferred – a universe of earth, air, fire and water. This was before the advent of modern science which today, we might say, represents the universe through the concepts of matter, energy, space, and time. The relationship between these ideas remains in many ways a matter of metaphysics with science delving ever deeper into the fabric of the cosmos through the limitations of human perception, cognition and language but aided by scientific instruments which have been one of the most useful products of scientific endeavour.
Space and time are so fundamental to existence that I think every scientist should understand something of their place in the history and philosophy of science and the scientific struggle to come to terms with their physical nature. Is it still possible to agree with one of the greatest philosophers of all time, the Enlightenment’s Immanuel Kant (1724-1804) who believed that space and time were constructs of the human mind – absolutely necessary for our existence, but with no foundation in objective fact … that we are, as it were, born equipped with psychological space-time spectacles that help us to survive and give structure to what is a blurred reality.
In the investigation of time I believe we encounter some of the most challenging and exciting questions that science can ask. This is a journey for anyone who is genuinely curious about the nature of existence and the history and philosophy of science. For me it has been an exciting journey taking me out of my intellectual and botanical comfort zone into the world of physics, words, philosophy and ideas – opening up many fascinating scientific paths and revealing many intellectual tools that I would like to share with you.
This series of seven articles is mostly concerned with, as it were, the stage on which the universe struts its stuff – the substrate, scenery, or backdrop to all existence – the cosmically entangled space and time. The philosophy of time, like much metaphysics, is rapidly ceding ground to science – to linguistics (the complexity of temporal semantics); to experimental psychology and cognitive science (the way we perceive time); and to physics, the way time is addressed by relativity and quantum mechanics. Here I shall try to unpack some of the mystery of time.
The paradox of time
On the one hand time seems strange and indescribably abstract. How can we possibly communicate that weird feeling of time’s ‘flow’ and the way it passes quickly when we are enjoying ourselves and slowly when we are bored. Looked at in this way time is highly subjective, a product of our imagination and psychology, perhaps a mental confusion or, when we talk of its ‘flow’, maybe an aberration of language.
On the other hand, suppose we place two identical precision clocks, one in each of two aircraft standing side-by-side on a runway. If we then compare the times on the two clocks after one aircraft has circled the world they will be different. Though the difference between the times is extremely small, it is real, and it can be accurately calculated even before the plane takes off. This is because physics has shown that time is not a product of our minds but is woven into the very fabric of the universe and its consequences can be calculated mathematically with great precision.
How do we account for these two very different perceptions of time?
Trying to unravel exactly what we mean by ‘time’ is an excellent way of exploring the difficult relationship between metaphysics, science, and language.
This is not everyone’s cup of tea because it is hard work: it can only be an introduction to the topic (what more could a botanist do?) and will not add to what is already known about time (although it will take a rather different approach from traditional work on the philosophy of time) but I think it can usefully demonstrate the systematic approach that has been taken by humanity in thinking about one of life’s greatest mysteries. The experts can chuckle up their sleeves at my efforts but, if you persevere, I hope that you too can enjoy the sensation of pushing at the exciting boundaries of language, metaphysics, and science in a topic that still has a long way to run.
My objective here was not to challenge the physics of time (although I discuss some of the background physics) but more to examine the idea of time as it is embedded in language – which is much more than the concept of time as handed to us by physicists. For ease of exposition I have considered a broad range of views while taking a particular point of view because this gives the reader something to hook on to and challenge. You will find many loose ends in the flow of ideas. But, if you are interested, see if you can fill in some of the gaps and let me know what you think.
We understand and interact with time (Greek – kronos, Old English – tima, physical symbol t.) in our everyday lives without confusion: lived time is uncomplicated.
It is the idea of time that is difficult to grasp because, although we can sense time and measure it, we cannot see, taste or touch it. We are therefore uncertain about its true nature and suspect that it may be in some sense illusory. As we have seen above, our suspicions are reinforced when we examine our everyday understanding of time more closely only to be confronted with apparent contradictions, puzzles, and paradoxes.
Science provides little comfort because, at face value, it presents us with counter-intuitive ideas like relativity and quantum mechanics that are so contrary to common sense.
What is time?
Philosophically we are trying to determine the nature of time – its ontological status. Put more plainly we are asking ‘Is time real. Does it exist independently of other things or is it a product of other things, or a relationship between things. Is it best described as a property of matter or the universe? Perhaps it is none of these things but simply a creation of the human mind? Are there some aspects of time that lie within the objective universe of physics, and others that are added by our minds?’
If you have never thought much about the nature of time then perhaps, with these questions in mind, you might pause for a wjile and form an opinion of your own before we move on.
Realists, relationists, & idealists
To help put some order into our thinking about time we can loosely divide those who have thought deeply about time into three groups: temporal idealists those who believe that time is a subjective matter rather than an objective part of the world (Zeno, Parmenides, Augustine, Kant, Locke, McTaggart); temporal realists who maintain that time is an objective part of the physical universe (Newton, Einstein, Hawking); and temporal relationists who understand time as a measure of change, a way of relating objective events (Plato, Aristotle, Liebnitz).
These three viewpoints were all argued and defended in Ancient Greece, and all three views still have strong advocates today. We can let these ancient Greeks introduce us to some of the major arguments for and against the three major positions on the philosophy of time.
Ancient Greek philosophers of time
When we measure weight, temperature, sound, and light using special instruments what we are actually measuring is quite difficult to describe and define. Today we might have sophisticated physical explanations for light, sound, and heat, although the idea of gravity as simply an attractive force between solid objects borders on the spooky. We nevertheless tend to accept all these phenomena as objective parts of the world: we do not think they are illusory inventions of our minds. So what exactly does that special instrument, the clock, measure … and does time differ in some special way from these other subjects of physics?
Plato had mixed views. When he declared that time would stop if the planets ceased their motion he was expressing the opinion of a relationist but he also claimed that time cannot be changed itself, because change can be quick or slow but time passes equally everywhere. Here he appears to be taking the side of the realist with time being independent of other things, his view being later expressed in a slightly different form by Isaac Newton, that ‘Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external …’
Though Plato’s views on time were not very well developed his brief description of time as ‘The moving image of eternity’ is an extraordinarily profound and poetic sentiment.
Plato’s student Aristotle did not believe that time was a ‘thing’ in the universe like water in which everything happened; it was simply a measure of change going on in the world, like the regular motions of the planets.
Up against Aristotle were the views of the Eleatic pre-Socratic philosophers of southern Italy most notable of these being Parmenides and his pupil Zeno. These two men agreed with Aristotle that there could be no time without change but denied the reality of time by denying the reality of change. How could they possibly make such a superficially outlandish claim?
One way of challenging change was to render the idea of motion incoherent and to do this Zeno posed a famous set of motion paradoxes: we can consider just two.
First, imagine the sprinter Achilles racing a tortoise. Giving the tortoise a start he must first reach the point A where the tortoise started by which time the tortoise has reached point B … so now Achilles must get to point B … by which time the tortoise is and point C … and so on. So Achilles, it appears, can never pass the tortoise.
Second, what could be a better example of motion than an arrow in flight? But motion is a fact about the arrow right now, not in its past or future. But since in the instant of now the arrow only occupies a space equivalent to its own length it must be at rest.
With these and other tricky examples Zeno claimed that reason and logic demonstrate that motion and change are illusory and since change is illusory then so too is time. The world is in fact unchanging and eternal.
Zeno was attempting to show, using reason, the way the world of appearance, our sense experience, can be deceived. In order to counter Zeno’s examples effectively Aristotle needed to use reason rather than the evidence of the senses. For Aristotle time was not identical to change, it was more like something being measured and the measuring device – not a process, more like a number used to describe processes in nature, the way numbers are used for counting. In other words time was just a unit system used to measure, order, or count things. For Aristotle motion must occur over some number interval like km/hour thus making Zeno’s idea of an instant of zero duration incoherent. He also claimed that the abstract and infinitesimal values of mathematics cannot be compared to actual changes in the world. These arguments can be followed in more detail on the web. Though Aristotle disposed of Zeno’s ingenious arguments he did not fare so well against Zeno’s teacher Parmenides whose arguments in favour of idealism were rather different.
In a clever fifth century BC prose poem Parmenides notes that we speak of past and future as though they were real while at the same time giving special existential value to the current moment or now. This leads to contradictions because when we speak of change we are driven to conclude that past and future are both real and unreal. A rock endures unchanged, but time still seems to pass while it is enduring. Parmenides argues that even an enduring thing must have temporal parts, one temporal part existing now and another(s) in the past. But the past is not real, so how can it exist in the past when there is only now? If the present is all that really exists then how can things pass out of present existence – where do they go? Parmenides argues, like Zeno, that since nothing can come into and pass out of existence then we must actually live in an eternal, timeless, and changeless world with change being a trick of our senses.
Aristotle’s answer, which we will not discuss here, is not convincing since he side-steps the issue that change commits us to the reality of a future from which a new situation arises and the reality of the past into which it goes. If we then say ‘but the future and past are not real, only the present is real’ then there can be no passing and there is therefore no change. Aristotle didn’t really find an answer to this dilemma.
The problem of definition
Ask four people to give a simple definition of time and they might answer that time is: ‘change’, ‘now’, ‘duration’, ‘space-time’ – concepts that seem hardly related to one-another – and yet we can understand why each reply was chosen. This draws attention to the point that if we want to answer the question ‘What is time?‘ then a logical place to start is with a communally-agreed definition rather than with the esoteric views of individuals – that is, the various senses discussed in a reputable dictionary. It is already abundantly clear that the word ‘time’ is complex in meaning.
The dictionary and language is an excellent place to begin our exploration and this will be the topic of the second article.
 see Boroditsky, chapter 20
 Bardon, p. 18
Bardon, A. 2013. A Brief hstory of the Philosophy of Time. Oxford University Press: Oxford
Boroditsky,L. 2011. Chapter 20 How Languages Construct Time. In Dehaene, S. & Brannon, E. eds Space, Time and Numbers in the Brain. Elsevier: London
Today we live in a comfortable age of knowing – much of the scientific work has indeed been done and the natural world though, as always, uppermost in our survival, nevertheless does not carry the threat of the unknown that so plagued our ancestors. The scientific novice learns the accumulated scientific wisdom of the past and, if they then do research, will probably contribute a small piece of knowledge within a small segment of a particular discipline. This is the way most science makes steady progress but it does not always feed the deep curiosity we feel about the mystery of existence. Investigating time can give us some sense of the grand scale of the universe, a feeling that must have been experienced by many of the early scientists and philosophers: it confronts our ignorance and challenges us to continue the search for answers.
Redn. As scientists we must remember that the phenomena of the world are not true or false, better or worse, only our scientific representations of the world (our theories, descriptions etc. as expressed mostly in language and mathematics). We must therefore begin by looking at the language we use to describe time.
But on almost every front we confront difficulties: can we give a satisfying definition of time? Is there an ultimate unit or division of time or is it continuous and infinitely divisible? How is time related to change and how can we account for permanence in change? Could time exist without events? How are time and space related and can they be analyzed separately? Can our everyday understanding of time be reconciled with the space-time of physics? What philosophical problems are raised by relativity and its conclusions about time? Can the scientific portrayal of a block universe of ‘timeless’ space-time (described in philosophically tenseless language) be reconciled with our strong sense of past, present and future (expressed in philosophically tensed language)? Does time flow in any sense at all? Do past, present (now) and future all exist? Is the future less real than the present or past? Is temporal becoming, the now of existence, an objective feature of the universe or a function of our consciousness or perception? Does the form of everyday language misrepresent the reality of time and influence the way we perceive it? Is there a direction or arrow to time and, if so, how do we account for it? How is time related to causality and does it make sense to suggest that the future could influence the present? Could time travel ever be possible? Can we tidy up the language of time to remove at least some sources of potential confusion?