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About Time

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Time is monumentally confusing and, like almost everyone (including most physicists), Barry Evans, in this column of May 18 ("It's About Time"), has it all wrong when he says that "... yet one-way time moves irredeemably from past to future."

He's correct in that physical events only change from past to future (the broken egg will never unbreak) but this is really about a sequence of physical events. The second law of thermodynamics says that a sequence of events can only increase in entropy, can only become more random as the system ages, but time itself has no direction.

You can measure a sequence of events with a clock but you cannot measure the flow of time in some direction or how its rate of flow changes. Would you say that time is passing from left to right or at one second per second? This just doesn't make any sense but that's exactly what's being implied by using the term "arrow of time." It implies that time, like an arrow, is moving and moving in some direction. This is quite wrong. Time has no direction. Time has no motion. There is no arrow of time.

And, just to be thoroughly contrary here, time is not "merely" just another dimension like the three spatial dimensions. Most physicists, if pressed on the matter, would consider time as something quite different. You can move backward or forward through any of the spatial dimensions but not so with time. It's a different sort of creature; we can change position in space but we can only experience the ever-present now (never the past nor the future).

Finally, as implied (incorrectly) in the well-known "twins paradox," time is not affected by speed. True, the twin who travels near the speed of light ages more slowly then his twin at home but it's not the speed that's doing it. His clocks are affected by changes in speed; in other words, clocks are changed by acceleration (or gravity, which is equivalent) but not by speed.

Douglas George, Eureka


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