Time, Clocks, and Reference Frames
As happens sometimes, a moment
settled and hovered and remained for
much more than a moment. And sound
stopped and movement stopped for
much, much more than a moment.
Then gradually time awakened again
and moved sluggishly on.
These lines from Steinbeck’s novel cap Tture the experience we have all had of the varying l ow of personal time. Our subjective experience of time can be affected by many things: catching the fly ball that wins the game, winning the race, illness, drugs, or a traumatic experience. It is well known that drugs, such as marijuana and LSD, can change—sometimes profoundly in the latter case—the human perception of time. People who have been in car crashes report the feeling of time slowing down, with seconds seeming like minutes. The windshield appears to crack in slow motion due to the trauma of the accident. If our subjective experience of time is so l uid, we might ask, “Well then, what is time . . . really?” Most of us can give no better answer than Saint Augustine in the Confessions: “What then is time? If no one asks of me, I know; if I wish to explain to him who asks, I know not.” Augustine’s answer some what anticipates Supreme Court justice Potter Stewart’s well-known definition of obscenity, delivered from the bench: “I know it when I see it.”
In this book we are concerned with measures of time that do not depend on the variations and vagaries of human perception. Physicists do not at all discount the importance of the problem of the human cognition of time, but it is,
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