Einstein & clocks

The Clocks That Shaped Einstein's Leap in Time, New York Times, by Dennis Overbye, 6/24/03

What does it mean, Albert Einstein asked in 1905, to say that a train arrives someplace--in Paris, say--at 7 o'clock?

You might not think you need to know something as deep as relativity to answer such a question. But Einstein needed to answer the question to invent his theory of relativity, the breakthrough that wrenched science into a new century and enshrined the equivalence of matter and energy.
In his last step, after a decade of pondering the mysteries of light and motion, Einstein concluded that there was no such thing as absolute time, envisioned by scientists since Newton, ticking uniformly through the cosmos. Rather there were only the times measured by individual clocks. To talk about times and measurements at different places, the clocks have to be synchronized, he said. And the way to do that is to flash light signals between them, correcting for the time it takes for the signal to travel from one clock to another.

A simple prescription. Yet when Einstein followed it, he found that clocks moving with respect to one another would not run at the same speed. The modern age was born.

So begins a fascinating article.
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