[The physics and philosophy article “Is Time an Illusion?” by Craig Callender appears in the June 2010 edition of Scientific American (pp. 58-65). Online article here.]
Does Time exist, or is Time an illusion? Craig Callender assures us that many physicists believe in the latter and far more bizarre theory. They believe that time is not an intrinsic property of the universe, but rather, an artificial convenience for human beings.
It is a mind-boggling theory. The point is that we can imagine the universe as three dimensions of space and one distinct dimension of time, for a total of four dimensions of spacetime. And our brains have the capacity to handle three dimensions. Normally these are the three dimensions of space, as we leave the effects of the remaining dimension—time—to prediction; that is, if we have one 3D frame, we can predict the next 3D frame in time.
But what if we were to visualize three dimensions again, only this time, we do so for two dimensions of space and one dimensions of time? This 3D frame would tell us exactly what happened in a 2D plane for all time, including the future. This makes much less intuitive sense for a human.
So what evidence do physicists have for casting away time? Here is an excerpt from the article on canonical quantum gravity:
Canonical quantum gravity emerged in the 1950s and 1960s, when physicists rewrote Einstein’s equations for gravity in the same form as the equations for electromagnetism [….] When physicists John Wheeler and Bryce DeWitt attempted this procedure in the late 1960s, they arrived at a very strange result. The equations (dubbed the Wheeler-DeWitt equation) utterly lacked a time variable. The symbol t denoting time had simply vanished.
In other words, time has within this context no intrinsic meaning.
Here is the analogy. Callender compares time to money, saying that it is only a common currency that aimed to simplify a barter system. The article supposes that a cup of coffee is worth $2, a pair of shoes $100, and a used car $2000. Then we can exchange 50 cups of coffee for a pair of shoes, or 1000 cups for a used car.
Then it supposes that light goes 300,000 km per second, the heart has 75 beats per minute, and the Earth has 1 rotation per day. These three processes—the speed of light, a heartbeat, and the Earth’s rotation—can now be described without using time. We may simply start at the base unit of a heartbeat, and say that light travels 240,000 km per beat, while the Earth rotates at 108,000 beats per rotation. A diagram in the print version of the article makes this more clear.
To sum it up: “The concepts of time and change may emerge from a universe that, at root, is utterly static.”
(By the way, according to the article “[the author] assures us that his lifelong interest in time has nothing to do with his last name.” :P)