Ever since I was little, I've wondered what time is. St. Augustine wrote in Confessions, Book XI:
What, then, is time? There can be no quick and easy answer, for it is no simple matter even to understand what it is, let alone find words to explain it. Yet, in our conversation, no word is more familiarly used or more easily recognized than 'time'. We certainly understand what is meant by the word both when we use it ourselves and when we hear it used by others.I've never had a good definition for time. If I were pushed, I would probably say something along the lines of this: time is an arbitrary, agreed-upon set of intervals used to measure the passage of natural processes, or . . . er, time. Any definition appears bound to end up being a bit tautological.
What, then, is time? I know well enough what it is, provided that nobody asks me; but if I am asked what it is and try to explain, I am baffled.
There are widely divergent views about its meaning, hence it is difficult to provide an uncontroversial and clear definition of time. The Oxford English Dictionary defines it as "the indefinite continued progress of existence and events in the past, present, and future, regarded as a whole". Another standard dictionary definition is "a non-spatial linear continuum wherein events occur in an apparently irreversible order."Wikipedia.
After perusing the old physics textbook I have here, I am more certain than ever that I have no idea what time is. I happened upon the famous twin-in-a-rocketship illustration of special relativity's feature of time-dilation:
One of two twins boards a fast spaceship for a journey to a distant star. The other stays behind on earth. Imagine that there are two clocks at earth and star . . . . There is a clock on the spaceship . . . . When the ship arrives at the distant star, less time will hae elapsed on the ship clock than on the earth and star clocks. Now the ship turns around and comes home. . . . [L]ess time elapses on the ship clock, and the travelling twin arrives home younger than the earthbound twin. Depending on how far and how fast the travelling twin goeds, the difference in ages could be arbitrarily large. The travelling twin could even return to earth millions of years in the future, even though only hours had elapsed on the ship. . . .Richard Wolfson & Jay M. Pasachoff, Physics:Extended with Modern Physics (1990); see also Time Dilation at Wikipedia; Pierre Boulle, The Planet of the Apes
Could [time dilation] really happen? I could, and it has. Atomic clocks are now so accurate that experiments have been done to detect the miniscule time difference between a clock flown around the earth on an airplane and one left behind.
Often, I think the one aspect of time that seems most concrete and understandable to me is the second law of thermodynamics (entropy). As Stephen Hawking explains,
the laws of science do not distinguish between the past and future, [or the forward and backward directions of time] . . . . Yet there is a big difference between the forward and backward directions of real time in ordinary life. Imagine a cup of water falling off a table and breaking into pieces on the floor. If you take a film of this, you can easily tell whether it is being run forward or backward. If you run it backward you will see the pieces suddenly gather themselves together off the floor and jump back to form a whole cup on the table. You can tell that the film is being run backward because this kind of behavior is never observed in ordinary life. . . .Stephen Hawking, A Brief History of Time p. 144.
The explanation that is usually given as to why we don't see broken cups gathering themselves together off the floor and jumping back onto the table is that it is forbidden by the second law of thermodynamics. This says that in any closed system, disorder, or entropy, always increases with time.
Entropy is a fundamental rule I can understand. So maybe that is one process that goes on inexorably, we watch it, and we call it time. Okay, I know that's dumb, but when I was a kid, I thought I was a genius because I had debunked -- in my own mind -- the whole ridiculous concept of time. At age ten or eleven, I was feeling pretty good about myself because I had "figured out" that time doesn't exist: we exist in a perpetual present -- there is no past or future -- we simply watch natural processes happening in this never-ending present (food decaying, cells breaking down as people and organisms age, rocks eroding, etc.), and we call that the passage of time. I concluded that time was just an abstraction we pasted onto entirely mechanical, physical processes; that is, there was no time out there that was coming or going, there were only physical and chemical processes happening (watch gears moving, skin shedding, earth spinning). If these material processes were altered, that would alter the flow of "time". Actually, it wouldn't because there was no "time" to be altered. Dumb, yes -- but not bad for ten, huh?
Anyway, my idea was not as breathtakingly original as I imagined. It appears Leibniz and Kant were onto this a few centuries earlier
Leibniz and others thought of time as a fundamental part of an abstract conceptual framework, together with space and number, within which we sequence events, quantify their duration, and compare the motions of objects. In this view, time does not refer to any kind of entity that "flows", that objects "move through", or that is a "container" for events. . . .Wikipedia. Interestingly, Nagarjuna, the founder of the Madhyamika school of Mahayana Buddhism, had a similar analysis of time
Immanuel Kant, in the Critique of Pure Reason, described time as an a priori notion that allows us (together with other a priori notions such as space) to comprehend sense experience. With Kant, neither space nor time are conceived as substances, but rather both are elements of a systematic framework necessarily structuring the experiences of any rational agent. Spatial measurements are used to quantify how far apart objects are, and temporal measurements are used to quantify how far apart events occur.
Nagarjuna examines time and finds that it cannot be conceived of as an entity existing independently of temporal phenomena. Nagarjuna begins with the conventional division of time into past, present, and future. He then argues than not one of these can be said to inherently exist.From The Nature of Time.
The present and the future either depend on the past or they do not. If they do, then they must in some sense already be present implicitly in the past, in which case their distinction with the past does not make sense. If they do not, then there can be no relation or connection to the past, and it makes no sense to talk of them as linked phases of time. Instead, time must itself be regarded as a set of relations among temporal phenomena, and nothing in itself.
I still sort of believe time does not exist, although it seems it's apparently not a simple matter of separating matter from time. In any event, one thing is clear: the passage of time, as experienced subjectively, certainly does speed up dramatically as you get older. The last ten years have been a blur. It seems there are some explanations for this. It is a bit frightening: I wish I could have those endless summer afternoons back. 1982 felt like forever -- in a wonderful way.
I'll end with a question I share with St. Augustine:
If the future and past do exist, I want to know where they are.