Now: The Physics of Time

by Richard A. Muller

Ride in an airplane, or in a satellite, and from this effect you will live longer—according to an Earth frame. But you will not experience more time. Time just runs slower when you are moving. Your clock runs slower, but so does your heartbeat and your thinking and your aging. So you won’t notice. That’s the amazing thing about relativity. It isn’t just clocks that run slower; it is everything. That’s why we say that it’s the pace of time that changes.

Large-scale nature is pretty much left-right symmetric (mountains, trees, and humans look just as real in a mirror), but culture isn’t.

(Richard Feynman’s dad used to tease his son about this; he would tell little Richard to keep quiet or he might run out of words and no longer be able to speak.)

Chemists use tables of entropy of common chemicals to determine which chemical reactions will take place and which ones won’t. Unless the calculated entropy of your initial chemicals is less than that of the reaction products, your reaction won’t go.

“drunkard’s walk.” Take lots of steps in random directions and you will wander away from your starting point; your distance from it will increase, on average, by the step size multiplied by the square root of the number of steps.

although entropy continues to increase, the maximum allowed value for the entropy of the universe increases even faster—

To the extent that we consider a human to be a big, complex combination of chemicals responding to external stimuli, no psychological arrow need be postulated.

For want of a nail the shoe was lost. For want of a shoe the horse was lost. For want of a horse the rider was lost. For want of a rider the message was lost. For want of a message the battle was lost. For want of a battle the kingdom was lost. All for the want of a nail.¶

We now think of the vacuum as constantly producing matter and antimatter, which almost as promptly annihilate—except when near a black hole. This feature grew to prominence in Stephen Hawking’s theory of black-hole radiation; a heuristic explanation of the radiation has the intense gravitational field close to the Schwarzschild surface separating the background matter and antimatter pairs before they annihilate, sucking one into the black hole and emitting the other to infinity.

Maybe someday someone will organize a religion based on Wheeler’s idea. Your soul, when you die, moves backward in time, scatters, and becomes a forward-moving soul, a different person. This happens many times. Maybe there is, indeed, only one soul in the universe. A nice aspect of this religion is that it doesn’t require us to postulate the Golden Rule. In fact, the Golden Rule is an inevitable consequence. Whatever you do unto others, you are in fact doing unto yourself.

The Exploratorium museum in San Francisco has a wonderful room that simulates a colorless environment.

Mathematics investigates truths not by experimental tests, but only by self-consistency.