| MadSci Network: Physics |
Hello, Nine years old is sure a young age to start teaching someone relativity! But if he can understand it, more power to him... Anyway, the answer is "noon plus one second". In the reference frame of the two clocks, it takes you one second to reach the second clock, so the second clock shows "noon plus one second" at the instant that the tram passes it. Although simultaneity is not in general preserved under special relativity, in this case it is (as is intuitively evident), so that in the reference frame of the tram, it is also true that the second clock shows "noon plus one second" at the instant that the tram passes it. However, the "instants" are not the same: although the observer in the clock frame sees one second pass as the tram moves from clock one to clock two, the observer in the tram actually sees no time pass at all (according to his own pocketwatch). To him, the outside world has become strangely contracted, so that there is actually no distance at all between the two clocks. I hope this helps a little in shedding light on an often inscrutable topic... -Aaron
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