The flow of time

Introduction – 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 a study in the psycho-biology of time – and specifically the flow of time. For more general background see the Wikipedia article on time.

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

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First published on the internet – 1 March 2019