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28th November 2022, 05:43 PM  #161 
Penultimate Amazing
Join Date: Apr 2004
Posts: 14,198

So the spacecrafts begin at t=0,:x=0 and both clocks sychronised. Spacecraft B travels away from spacecraft A at 0.2c
At t = 00:05:00 t'=00:05:57 spacecraft A reads the register and sends a bit at v=10c to spacecraft B. At t=00:05:06 t'= 00:04:59.8 spacecraft B receives the bit, flips it and sends it back to spacecraft A at v'=18.33c. At t=00:04:57 t'=00:05:06 spacecraft A receives the bit and writes it to the register. So if spacecraft A reads and sends a zero, it receives and writes a one to that register 3 seconds earlier. (t is the time on spacecraft A, t' is the time on spacecraft B) I've never been a fan of impossibly long trains and impossibly long platforms. Here is an experiment that should actually be able to be performed if there were such a thing as FTL communication, but clearly it couldn't happen as described. So FTL travel and communication are in the same category as time travel in terms of scientific plausibility. 
29th November 2022, 09:25 PM  #162 
Penultimate Amazing
Join Date: Apr 2004
Posts: 14,198

Correction (doesn't affect outcome):
the spacecrafts begin at t=0,:x=0 and both clocks sychronised. Spacecraft B travels away from spacecraft A at 0.2c At t = 00:05:00 t'=00:05:06 spacecraft A reads the register and sends a bit at v=10c to spacecraft B. At t=00:05:06 t'= 00:04:59.8 spacecraft B receives the bit, flips it and sends it back to spacecraft A at v'=18.33c. At t=00:04:57 t'=00:05:03 spacecraft A receives the bit and writes it to the register. So if spacecraft A reads and sends a zero, it receives and writes a one to that register 3 seconds earlier. (t is the time on spacecraft A, t' is the time on spacecraft B) 
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