Aristotle and time

It turns out to be interesting to compare Aristotle’s ideas about time with my insights about time and quantum physics. There are striking similarities.

A quote from Physics, book 4.11:

But neither does time exist without change; for when the state of our own minds does not change at all, or we have not noticed its changing, we do not realize that time has elapsed, any more than those who are fabled to sleep among the heroes in Sardinia do when they are awakened; for they connect the earlier ‘now’ with the later and make them one, cutting out the interval because of their failure to notice it.

So, just as, if the ‘now’ were not different but one and the same, there would not have been time, so too when its difference escapes our notice the interval does not seem to be time. If, then, the non-realization of the existence of time happens to us when we do not distinguish any change, but the soul seems to stay in one indivisible state, and when we perceive and distinguish we say time has elapsed, evidently time is not independent of movement and change. It is evident, then, that time is neither movement nor independent of movement.

Aristotle says here that time does not exist without change being perceived by our [consciousness]. If no change is experienced, then we also won’t experience time. So time is not the same as change or movement, but it is not independent of it.

Now we perceive movement and time together: for even when it is dark and we are not being affected through the body, if any movement takes place in the mind we at once suppose that some time also has elapsed; and not only that but also, when some time is thought to have passed, some movement also along with it seems to have taken place. Hence time is either movement or something that belongs to movement. Since then it is not movement, it must be the other.

If we observe a ‘before’ and an ‘after’, which is observing a change, then there is time. But time is not equal to change. Time results from the comparison between two now moments. We define the sequence of nows ourselves by assigning it an ‘before and’ after ‘.

When, therefore, we perceive the ‘now’ one, and neither as before and after in a motion nor as an identity but in relation to a ‘before’ and an ‘after’, no time is thought to have elapsed, because there has been no motion either. On the other hand, when we do perceive a ‘before’ and an ‘after’, then we say that there is time. For time is just this-number of motion in respect of ‘before’ and ‘after’.

The ‘now’ itself does not change, but the moments recorded in every ‘now’ do.

The delayed quantum eraser

This vision of Aristotle on time reminds strongly of the conclusions about time that can be drawn from studying the results of delayed choice quantum eraser experiments. In a simple double-slit experiment, observable interference will always occur behind the double-slit. A pattern of dark and light bands. It invariably shows up whether photons, electrons, atoms or even larger molecules are sent through a double slit.

In the delayed choice experiments, in principle, photons are sent through a double slit, and simultaneously information is collected about which slit the photon has passed. The measured information about the passed slit is randomly either recorded or irrevocably destroyed in order to determine the effect of available information about the passed slit on the interference pattern. The experimental results are in line with the predictions of quantum mechanics but nevertheless very intriguing.

• If information is available about through which slit the photon has passed, the result of the experiment is affected in such a way (no interference) that the conclusion has to be that the photon state wave must already have collapsed in the slit manifesting a physical photon there.
• The experiment is set up in such a way that the moment in time when that information is measured and recorded follows in time sequence after the photon appeared (manifested) in the slit.

At first glance, this looks like an effect back into the past, retrocausality. However, this doesn’t mean that we can change the past. Once measured, the past is irrevocably fixed. But as soon as we involve the active observer, retrocausality is no longer needed as an explanation. The observer will by his conscious observation only fix the order of events at that moment . It is then not the instrumental detection of the slit passage that exerts an effect on the interference behavior of the photon. History – the sequence of now moments – is fixed by the observer’s attention. That’s time.

In short, quantum physics seems to confirm Aristotle’s ideas about time. Now we can see an important difference between experienced time and clock time. The latter was introduced by Newton in the 16th century as the only model of time of importance in physics. With that the observer was sidelined and was no longer an important player in the physical universe. But quantum physics seems to restore experienced time as something that also plays a role in physics. The conscious observer acting as an information processor becomes thus an active participant in the universe again.