Peter Galison on Time

PETER GALISON ON TIME

Posted November 10, 2011

In a way physics has departed from our everyday understanding of what time is. For us nothing is more important than the finitude of time, than the fact that we're mortal. We don't see time as reversible. We get older, we die, we see things break, we see glasses fall off of counters and shatter into pieces on the floor. We don't see these gather up and become a perfectly formed glass on the shelf again. We don't see people getting younger. We see trees grow and crack and die. We see a direction to the movement of things, and that directionality—that flow towards our own personal ends—is very different from what physics takes time to be.

There are some rare processes in physics that can occur in one direction but not in the other. But for most of physics it can go both ways, and we think of time insofar as we're thinking as physicists, as processes that are governed by a clock, by repetitive phenomena, by something that occurs over and over again. In the early days it might be the rise of the sun, the turning of the Earth on its axis, or the rotation of the Earth around the sun. We're always looking for things that repeat over and over again, and that repetition, that cycle of things, forms a relative way of understanding the advance of time. That's all time becomes is some repetitive process.

It's very different from the everyday human experience, and so time as measured by clocks, by these back-and-forth or up-and-down motions, these cyclical processes, comes to be what time is in a sense. It's the measure of things in physics, and time as a measured quantity becomes the central aspect of what time is as opposed to something purely metaphysical, something beyond anything that we could possibly measure.

AUDIO

Produced by

David Levin

Original interview by

Randy MacLowery

IMAGE

(Peter Galison)

© WGBH Educational Foundation 2011

Major funding for "The Fabric of the Cosmos" is provided by the National Science Foundation and the Alfred P. Sloan Foundation.

Additional funding for this program is provided by the Arthur Vining Davis Foundations.