Does time pass?
By Adrian Bardon
In the early 5th century BCE a group of philosophers from the Greek colony of Elea formed a school of thought devoted to the notion that sense perception — as opposed to reason — is a poor guide to reality. The leader of this school was known as Parmenides. He left behind scraps of a long prose poem about the true nature of time and change. This work, On Nature, is one of the earliest surviving examples of philosophical argumentation.
Our perception of the world is of a world of change, of motion and transience. Parmenides was convinced that the reality is quite different. He argued as follows. The ordinary notion of change indicates some thing or state of a thing going from being future to being present to being past. Yet we also ordinarily contrast the what is — i.e., the present state of things — with the what is not — i.e., the merely possible or long gone. The future doesn’t actually exist; if it did, then it would exist now! But then nothing can go from actually being future to being present: if the future is not real, then the present state of things cannot come to be from a future state of things. Hence, change is impossible and illusory. Parmenides concluded that the world is really a timeless, static unity. The terms ‘past,’ ‘present,’ ‘future’ do not designate intrinsic properties of things or events.
It would be difficult to come up with a proposition that meets with any less agreement in our everyday experience. How can we even imagine a world without the passage of time? The lived experience of the flow of a river, the enjoyment of a melody, and the decisions we make from moment to moment that depend on what we think is happening now — and what might be coming up — all speak irresistibly in favor of change. Parmenides must have gone wrong somewhere!
And yet the vision of a static universe, with no intrinsic past, present, or future, finds powerful validation in Einstein’s Special Theory of Relativity. According to that well-confirmed theory, two events that are simultaneous to an observer in one inertial reference frame will not be to a different observer moving relative to the first one. Since there is no absolute motion, there is no privileged vantage point that fixes which events are really simultaneous and which are not. This means that the set of events ‘present’ to one observer is different from another’s set; neither is justified in identifying a particular moment that everyone should agree is the present moment. The same goes for pastness and futurity: an event one observer considers past may be present, or even future, for another, depending on its relative distance and their relative velocity. If there is no privileged vantage point from which to determine the ‘truth’ of the matter — and the whole point of relativity is that there is not — then temporal properties like past, present, and future cannot possibly be aspects of reality. They must be subjective and perspectival in nature.
Of all things, whether a loved one’s death occurs in the past or in the future carries immense significance to us. Yet Einstein insists otherwise in a famous letter eulogizing his friend Michele Besso:
Now Besso has departed from this strange world a little ahead of me. That means nothing. People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.
We know that the designation ‘here’ is purely perspectival: my ‘here’ may be your ‘there,’ and vice-versa. From the universe’s perspective, the designation ‘now’ is no more an objective designation than ‘here.’ (Think what odd consequences follow from treating designations like ‘past’ as real properties of objects and events. This would entail, for example, that something even now is happening to the Battle of Waterloo: it is becoming more past.)
No doubt our biology requires us to think differently. We have evolved as conscious beings who act on the basis of beliefs. Agency requires us to think in terms of what has been accomplished and what is to be done next. Beings like us must think in terms of “now is the time to feed / fight / escape / go to the department meeting.” Even though no moment is privileged, at any given moment we are convinced by our experience, and by that moment’s memories and anticipations, that the time is now. Consciousness of change and the passage of time is irreducible, inescapable. There is no guarantee, however, that even biologically necessary representations of the world speak the truth of the world as it is in itself.
Adrian Bardon is Associate Professor of Philosophy at Wake Forest University. He is the author of A Brief History of the Philosophy of Time.