Theories on the perception of the passage of time
By Steve Humphrey
Illustrations by Andrea Hutchinson
Intuitively, we speak of the passage of time, such as Labor Day is coming up, but we have passed the Fourth of July. Alternatively, we talk as if we are moving through time, such as, I’m approaching my 70th birthday. This language seems to imply that something is moving, but what is it and what is it moving through? How can time pass? If we insist that it does, it makes sense to ask how fast it is passing. The glib response would be, “One second per second, silly.” But does this make any sense? Motion is the change of position over time, but how can one change one’s position in time over time? If we had a second sort of time, say God’s time — some religions hold that God operates outside of our time — then our time could pass at a certain rate relative to God’s time. But then we might ask, how fast does God’s time pass? This leads to an infinite regress.
Those who believe that time passes have a dynamic view of time, in which the present moment, the “now,” separates the past from the future and its motion turns the future into the present and then into the past. There are several versions of this. In one version, the future doesn’t exist, but the present and past do. In this theory, the past and present are fixed, while the future is open and undetermined. In another version, called “Presentism,” only the present exists, meaning, only events occurring now actually exist. Additionally, future events will exist and past events did exist, but only present events are real. However, this raises additional questions. How long does the present last? It can’t be instantaneous since we seem to experience the present as having some duration, if only briefly. This is referred to as the “specious present.” Neurological science tells us that our perception and consciousness of experiences lag actual events by approximately two-tenths of a second. That means, by the time we are aware of something, it has already happened. Further, it is assumed that the now is universal, meaning it makes sense to talk of what is happening now throughout the universe. If there is an appetite for it, I will discuss the Special Theory of Relativity in my next column, and that theory implies the Relativity of Simultaneity, according to which what counts as “now” will be different for people in different states of motion.
An alternative to the dynamic theory is the static block theory. According to this theory, every event, whether past, present or future, is equally real and determinate. Future events, though unknown, are fixed and real, and we can no more change the future than we can the past. We can affect the future through our actions in the present, but we cannot change the future. There is only one future, one set of events that will occur, that seems to deny free will. This theory was discussed centuries ago by theologians worried about God’s divine foreknowledge. If God knows what you are going to do, can your choices truly be said to be free? In the block theory, “now” operates as an indexical, like “here” or “I.” When I say “I am here” and you say “I am here,” they have different meanings because “I” and “here” signify different things in the two utterances. So, according to the block theory, every event is now for someone experiencing that event and there is no unique moment which is now.
In the physical sciences, no importance is ascribed to any individual moment that might be now. The same physical laws apply to all phenomena in the block theory, and these laws have been tested over and over and found to be very successful. So the question arises, if our best theory of the physical world conflicts with our naïve intuitions, what are we to believe? We will see that this conflict goes much further than just the notion of the now. I will talk more about this conundrum in a future column, so stay tuned for next month’s further discussion on time.
Steve Humphrey has a Ph.D in the history and philosophy of science, with a specialty in philosophy of physics. He teaches courses in these subjects at the University of California, Santa Barbara, and has taught them at the University of Louisville.