David Foster Wallace started his 2005 commence speech to the graduating class at Kenyon with this short story:
There are these two young fish swimming along and they happen to meet an older fish swimming the other way, who nods at them and says, “Morning, boys. How’s the water?” And the two young fish swim on for a bit, and then eventually one of them looks over at the other and goes, “What the hell is water?”
We are just like those two young fish when it comes to time. We live in time. We use time to measure out our lives. But when it comes right down to it, what the hell is time?
Throughout history there have been innumerable attempts to describe and explain and define time but no one as yet has been able to do so in any really satisfying manner. When asked “what is time anyway” Janna Levin, professor of physics and astronomy at Barnard College was refreshingly honest in her response: “Hmm. I’m not sure anyone can give you a fair answer to that question.”
Before Einstein most people believed there was an absolute time throughout the universe that everyone could agree on. Many people still think this. However Einstein discovered what has since been experimentally proven: there is no universal now. There is no absolute time throughout the universe. Whether two events are simultaneous is relative to the observer. The concepts of past, present and future vary depending on where you are and how fast you are going.
Researchers have shown that gravity can slow clocks. Time passes a little bit slower at sea level compared to the top of a mountain, because you’re a bit closer to Earth’s gravity. If you’re traveling at a very high speed or near a massive object like a planet, time will seem to pass more slowly for you compared to someone who’s farther away from the gravitational pull or moving more slowly. In most cases such effects are so small they don’t really matter in our everyday lives which is why most of us still believe in something like absolute time. However, the difference in the speed of clocks at different heights above the earth is crucial in calculating GPS positions and even more critical for space exploration.
Does time have a beginning? Will it ever end? We don’t know the answer. Einstein proposed the idea that we live in four dimensions, something we call spacetime. Specifying our position in spacetime requires the usual three spacial dimensions (north/south, east/west, up/down) and one time dimension. It seems absolutely clear that space and time are this kind of unified thing but time is oddly different from the other three dimensions. We can go back and forth in the three spacial dimensions: north or south, east or west, up or down. But we can’t move backward in time, only forward. This has been called the Arrow of Time. (See Sean Carroll From Eternity To Here)
Why can’t we move backward in time? Eggs break but they do not reassemble. Water spills but it does not jump back into the glass. Why not? I suppose we could say it is logically possible but very very unlikely. Entropy is usually cited as the reason. Entropy is disorder and it increases over time in a closed system. We have all witnessed this in our own lives. Things wear out, fall apart, and become messy over time. It takes energy from outside to put them back together again.
One kind of time travel is not only theoretically possible but experimentally proven. I can go forward in your time but not in mine. If I travel at close to the speed of light I will age more slowly than you age so if one twin journeyed away from the earth at near the speed of light and returned, he would be noticeably younger than the other twin. Time travel to the past, however, creates the so-called grandfather problem. Going back into the past and killing your grandfather is inconsistent with your birth. What about going back into the past without changing it? This seems logically possible. Some physicists believe the universe is like a giant fruitcake where the past, present and future all exist simultaneously, the so-called block universe. Time for you depends on how you slice it but so far this stubborn fact remains: We can go forward in time some of us at different rates depending on gravity and speed but no one yet has figured out how to go backward in time. Time is fundamentally different from the three spacial dimensions.
The past is intricately related to observation and memory. Proust (In Search of Lost Time) pointed out that unprompted awakenings of memory triggered by something illogical and unforeseen (such as a madeleine cookie) could invoke the past in its entirety. In a new book (On the Origen of Time) by Thomas Hertog who collaborated with Stephen Hawking, a theory of time based on quantum mechanics is developed where we create the universe as it creates us. Hertog points out the similarities to Darwin’s theory of evolution. In quantum mechanics the microscopic particles that make up the universe as we know it do not have a specified position. They exist in a “superposition” of many (maybe infinite) states and do not assume a particular state until they are observed.
There are other theories. Physicist Carlo Rovelli in his book The Order of Time argues that events are the building blocks of reality and that time emerges from relationships between events.
Why does time race by for some of us and drag out seemingly forever for others? Virginia Wolfe writes in The Moment and Other Essays: In a sense, to live in the moment is always to live against time. Yet what composed the present moment? If you are young, the future lies upon the present, like a piece of glass, making it tremble and quiver. If you are old, the past lies upon the present, like a thick glass, making it waver, distorting it. All the same, everybody believes that the present is something, seeks out the different elements in this situation in order to compose the truth of it, the whole of it. Or, as physicist Janna Levin says: When there is a lot of change relative to your overall experience psychologically, you will consider time to be moving more quickly. If you’re a child and you’re having an experience, your overall body of experience is so small that actually, psychologically, your perception of time is kind of slower. And as you get older, that same experience you might share with a child, seems to you that time is passing faster—because your overall body of experience is larger relative to the amount of change you’re perceiving. (Time Management Tips From The Universe by Becca Rashid and Ian Bogost).
Levin goes on to connect time to who we are a human beings.
Intuitively, we have a great deal of anxiety about the idea that we might not exist in the future. But we’re completely okay with the idea that we did not exist prior to some point in the past. That asymmetry is just built into us.
To know time has passed, I have to experience some change.
We do, yes, measure time through change.
I think it’s really going to sound quite difficult, but the physicist is likely to go as far as to say, there really is no self. You are a collection of quantum particles and interactions, and they change. And we see this all the time. I certainly could take a chemical that would completely change my chemistry and completely change my personality. In what sense am I still me?
We are just a collection of particles. And one day we will go back into the galaxy. That sounds about right to me.
One of my life long heroes, William Blake, said: “I see the past, present, and future, existing all at once before me.” (I See The Four-Fold Man). You might not associate Blake with our modern physicists but they share the the most important ingredient of understanding: imagination. (See Imagination and Reason in the Time of Tragedy: Lao Tzu, Voltaire, Blake, Camus and Marquez)
So, what time is it? We are still imagining time. The answer’s out there somewhere waiting to be found.