- #1

Sorcerer

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- 52

**Leading clocks lag**

So, if two clocks are fixed to a the ends of a barn, and they are set off with light pulses from the midpoint, in the frame of the barn the clocks start simultaneously.

Now a rod moves to in the +x direction at speed v relative to the barn. To the observer on rod, the "leading clock" is the clock on the -x side (when the observer at the midpoint of the rod hits the origin of the barn). The pulses, which are shot when the origins coincide, will hit at different times according to the rod observer, notably, the -x side clock will be struck later from the rod observer's perspective, and so will be "lagging" behind the trailing clock (which is on the +x side of the barn).

Is that correct on how that works?

**Twin paradox**

If so, what about the situation with the twin paradox, where light from an approaching clock results in the

*appearance*of the clock moving faster (is that right?).

**Twin paradox with returning twin with two clocks, one in the front of the spaceship and one in the back.**

So now consider the standard twin paradox scenario, and we're on the return trip, except the returning twin has two clocks, one in the front of his spaceship (nearest the earth twin) and one in the back of the spaceship. Now we have a situation where, from the earth's frame, light from the nearest clock (the "leading" clock) will actually reach earth first, won't it? So each tick would take less time to be seen, so wouldn't in this case the leading clock appear to run faster?

Clearly I still have some confusion about what clocks actually measure and what distant clocks appear to measure, but can anyone help me clear up this confusion? Thanks.