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Special Relativity: Synchronizing Clocks
Michael Fowler
,
UVa Physics 2/29/08
Suppose we want to synchronize two clocks that are some distance apart.
We could stand beside one of them and look at the other through a telescope, but we’d have to
remember in that case that we are seeing the clock
as it was when the light left it
, and correct
accordingly.
Another way to be sure the clocks are synchronized, assuming they are both accurate, is to start
them together. How can we do that? We could, for example, attach a photocell to each clock, so
when a flash of light reaches the clock, it begins running.
If, then, we place a flashbulb at the midpoint of the line joining the two clocks, and flash it, the
light flash will take the same time to reach the two clocks, so they will start at the same time, and
therefore be synchronized.
Let us now put this whole arrangement  the two clocks and the midpoint flashbulb  on a train,
and we suppose the train is moving at some speed
v
to the right, say half the speed of light or so.
Let’s look carefully at the clocksynchronizing operation as seen from the ground. In fact, an
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 Fall '10
 DavidJudd
 Physics, Special Relativity

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