Suppose you had to explain to someone, who did not already know, what it means to say that time passes. What might you say? Perhaps you would explain that different times are arranged in an ordered series with a direction: Monday precedes Tuesday, Tuesday precedes Wednesday, and so on. But if time passes and space does not, then this cannot be the whole story. After all, locations in space are also ordered: London is to the north of Paris, Paris is to the north of Marseille, and so on. And even if space had an intrinsic direction, this would not make it the case that space passed. A direction only requires that there be an asymmetry; but a mere asymmetry would not explain the notion of passing.
Instead, you might appeal to experience. We experience time passing throughout our lives, or so it is claimed. Different people will give different accounts of the details. Some will emphasise the fact that experienced change, such as motion, has a dynamic quality that is absent from any spatial analogue, such as a difference in the weather between London and Paris. Others will emphasise the feeling that we are located at a single moment, the present time, but we constantly “move” through time, away from the past and toward the future. Perhaps others will appeal to the role of memory. But whatever the details, it may seem clear that there is some aspect of the way we experience time that allows us to grasp what is meant by “the passage of time”, and that tells us that time is indeed passing. Nothing, you may say, could be more familiar.
Unfortunately, however, things are not as they seem. The first sign of trouble lies in the fact that, as many physicists have noted, the passage of time does not feature explicitly in descriptions of the world couched in the vocabulary of physics. This is not to assume, question-beggingly, that time, as it features in physics, does not pass. It is just to say that physics requires only that there be a time series, and says nothing about one time being present, or time passing. Questions about the passage of time belong to metaphysics, not physics. But although we can adjudicate between competing theories of physics through observation, we cannot normally do the same for metaphysics. Putative metaphysical features are of the wrong kind to be possible objects of experience.
There are many ways to see the problem. Here is one: in order for experience to tell us something about the world, our experiences must have an appropriate sensitivity to the way things are. Your visual experience tells you about the words that you are reading because your visual experiences are sensitive to what is written. Had the words been different, the configuration of your brain, and thus your experience, would have been different in a corresponding way. If, instead, your experiences would have been the same, regardless of what was written, then you would not really be seeing.
There is no way for experience to be sensitive to whether or not time passes. This would require that the state of one’s brain be sensitive to whether or not time passes; and this cannot be so. For if we compare two theories that agree on which sentences of physics are true, but disagree on whether time passes, then because the two theories agree about which physical events occur, they cannot differ in what they say about the configuration of anyone’s brain. So, whether or not time passed, your experiences would be exactly as they actually are.
Here is another way to see the problem: As you read this page, there is an element of your visual experience, E, that concerns the words that you are reading, and other elements that concern the edge of the page, the side of the computer monitor, and so on. There is no deep mystery about how the elements and their objects match up. There is, for example, a single causal chain that leads from the words to E, and no similar chain from the words to any other element of experience. But the supposed passage of time would affect the whole physical world in the same way. Consequently it is hard to see what could make it the case that any one aspect of your experience, rather than any other, concerned the passage of time.
If, as suggested above, we have no way to grasp what it means for time to pass except through experience, and if, as I have argued, no experience could really be an experience of time passing, then we cannot claim to properly understand what it would be for there to be a mind-independent passage of time. The claim that time really passes is therefore empty, and should be abandoned. Instead, although there is a time series, there is no single ‘now’, and no passage. This raises the question of why we experience time in the way that we do. Answering this question is an important, fascinating and neglected project for metaphysics and the philosophy of mind.
Featured image: Clock by geralt. Public domain via Pixabay.