We shall see that there is no such thing as the flow of time. Yet the idea of it is pure common sense. We take it so much for granted that it is assumed in the very structure of our language. In A Comprehensive Grammar of the English Language, Randolph Quirk and his co-authors explain the common-sense concept of time with the aid of the diagram shown in Figure 11.1. Each point on the line represents a particular, fixed moment. The triangle ‘
’ indicates where the ‘continuously moving point, the present moment’, is located on the line. It is supposed to be moving from left to right. Some people, like Shakespeare in the sonnet quoted above, think of particular events as being ‘fixed’, and the line itself as moving past them (from right to left in Figure 11.1), so that moments from the future sweep past the present moment to become past moments.
What do we mean by ‘time can be thought of as a line?’ We mean that just as a line can be thought of as a sequence of points at different positions, so any moving or changing object can be thought of as a sequence of motionless ‘snapshot’ versions of itself, one at each moment. To say that each point on the line represents a particular moment is to say that we can imagine all the snapshots stacked together along the line, as in Figure 11.2. Some of them show the rotating arrow as it was in the past, some show it as it will be in the future, and one of them — the one to which the moving is currently pointing — shows the arrow as it is now, though a moment later that particular version of the arrow will be in the past because the will have moved on. The instantaneous versions of an object collectively are the moving object in much the way that a sequence of still pictures projected onto a screen collectively are a moving picture. None of them, individually, ever changes. Change consists of their being designated (‘illuminated’) in sequence by the moving (the ‘movie projector’) so that, one by one, they take it in turn to be in the present.
Grammarians nowadays try not to make value-judgements about how language is used; they try only to record, analyse and understand it. Therefore Quirk et al. are in no way to blame for the quality of the theory of time that they describe. They do not claim that it is a good theory. They claim only, and I think quite correctly, that it is our theory. Unfortunately it is not a good theory. To put it bluntly, the reason why the common-sense theory of time is inherently mysterious is that it is inherently nonsensical. It is not just that it is factually inaccurate. We shall see that, even in its own terms, it does not make sense.
…‘time can be thought of as a line (theoretically, of infinite length) on which is located, as a continuously moving point, the present moment. Anything ahead of the present moment is in the future, and anything behind it is in the past.’
FIGURE 11.1 The common-sense concept of time that is assumed in the English language (based on Quirk et al., A Comprehensive Grammar of the English Language, p. 175).
This is perhaps surprising. We have become used to modifying our common sense to conform to scientific discoveries. Common sense frequently turns out to be false, even badly false. But it is unusual for common sense to be nonsense in a matter of everyday experience. Yet that is what has happened here.
Consider Figure 11.2 again. It illustrates the motion of two entities. One of them is a rotating arrow, shown as a sequence of snapshots. The other is the moving ‘present moment’, sweeping through the picture from left to right. But the motion of the present moment is not shown in the picture as a sequence of snapshots. Instead, one particular moment is singled out by the , highlighted in darker lines and uniquely labelled ‘(now)’. Thus, even though ‘now’ is said by the caption to be moving across the picture, only one snapshot of it, at one particular moment, is shown.
FIGURE 11.2 A moving object as a sequence of ‘snapshots’, which become the present moment one by one.
Why? After all, the whole point of this picture is to show what happens over an extended period, not just at one moment. If we had wanted the picture to show only one moment, we need not have bothered to show more than one snapshot of the rotating arrow either. The picture is supposed to illustrate the common-sense theory that any moving or changing object is a sequence of snapshots, one for each moment. So if the is moving, why do we not show a sequence of snapshots of it too? The single snapshot shown must be only one of many that would exist if this were a true description of how time works. In fact, the picture is positively misleading as it stands: it shows the not moving, but rather coming into existence at a particular moment and then immediately ceasing to exist. If that were so, it would make ‘now’ a fixed moment. It makes no difference that I have added a label ‘Motion of the present moment’, and a dashed arrow to indicate that the is moving to the right. What the picture itself shows, and what Quirk et al.’s diagram (Figure 11.1) also shows, is the never reaching any moment other than the highlighted one.
At best, one could say that Figure 11.2 is a hybrid picture which perversely illustrates motion in two different ways. In regard to the moving arrow it illustrates the common-sense theory of time. But it merely states that the present moment is moving, while illustrating it as not moving. How should we alter the picture so that it will illustrate the common-sense theory of time in regard to the motion of the present moment as well as the motion of the arrow? By including more snapshots of the ‘’, one for each moment, each indicating where ‘now’ is at that moment. And where is that? Obviously, at each moment, ‘now’ is that moment. For example, at midnight the ‘’ must point to the snapshot of the arrow taken at midnight; at 1.00 a.m. it must point to the 1.00 a.m. snapshot, and so on. Therefore the picture should look like Figure 11.3.
This amended picture illustrates motion satisfactorily, but we are now left with a severely pared-down concept of time. The common-sense idea that a moving object is a sequence of instantaneous versions of itself remains, but the other common-sense idea — of the flow of time — has gone. In this picture there is no ‘continuously moving point, the present moment’, sweeping through the fixed moments one by one. There is no process by which any fixed moment starts out in the future, becomes the present and is then relegated to the past. The multiple instances of the symbols and ‘(now)’ no longer distinguish one moment from others, and are therefore superfluous. The picture would illustrate the motion of the rotating arrow just as well if they were removed. So there is no single ‘present moment’, except subjectively. From the point of view of an observer at a particular moment, that moment is indeed singled out, and may uniquely be called ‘now’ by that observer, just as any position in space is singled out as ‘here’ from the point of view of an observer at that position. But objectively, no moment is privileged as being more ‘now’ than the others, just as no position is privileged as being more ‘here’ than other positions. The subjective ‘here’ may move through space, as the observer moves. Does the subjective ‘now’ likewise move through time? Are Figures 11.1 and 11.2 correct after all, in that they illustrate time from the point of view of an observer at a particular moment? Certainly not. Even subjectively, ‘now’ does not move through time. It is often said that the present seems to be moving forwards in time because the present is defined only relative to our consciousness, and our consciousness is sweeping forwards through the moments. But our consciousness does not, and could not, do that. When we say that our consciousness ‘seems’ to pass from one moment to the next we are merely paraphrasing the common-sense theory of the flow of time. But it makes no more sense to think of a single ‘moment of which we are conscious’ moving from one moment to another than it does to think of a single present moment, or anything else, doing so. Nothing can move from one moment to another. To exist at all at a particular moment means to exist there for ever. Our consciousness exists at all our (waking) moments.