Fri Jan 30, 2004 6:22 am
wow, i founded something about tachyon...
read this link
The entire "FTL implies time travel" meme has to do with what's sometimes called "failure of simultaneity at a distance".
Here's a spacetime diagram of a referee (O3) and two duelists (O1 and O2). Space is up/down, time is left/right, in the diagram.
The paths O1 and O2 take through spacetime are the colorcoded arrowed lines. The events in spacetime that each considers "simultaneous" and "8 seconds after the start" are along the thinner, non-arrowed colorcoded lines. So we see that, each of the three observers thinks the other two have slow clocks, and that if we are allowed to move faster than a lightcone, we'll end up going "pastward" in somebody's reckoning.
We can trace out the shots on this diagram, also. Step through it one more time: if green shoots at 8 seconds out, the shot will go along the green "line of simultaneity", and hit blue at 4 seconds elapsed. If blue returns fire from there, it will return along a line paralel to the blue "line of simultaneity", and catch green napping at 2 seconds elapsed.
_________________
Spamius Threadius
read this link
The entire "FTL implies time travel" meme has to do with what's sometimes called "failure of simultaneity at a distance".
Here's a spacetime diagram of a referee (O3) and two duelists (O1 and O2). Space is up/down, time is left/right, in the diagram.
The paths O1 and O2 take through spacetime are the colorcoded arrowed lines. The events in spacetime that each considers "simultaneous" and "8 seconds after the start" are along the thinner, non-arrowed colorcoded lines. So we see that, each of the three observers thinks the other two have slow clocks, and that if we are allowed to move faster than a lightcone, we'll end up going "pastward" in somebody's reckoning.
We can trace out the shots on this diagram, also. Step through it one more time: if green shoots at 8 seconds out, the shot will go along the green "line of simultaneity", and hit blue at 4 seconds elapsed. If blue returns fire from there, it will return along a line paralel to the blue "line of simultaneity", and catch green napping at 2 seconds elapsed.
_________________
Spamius Threadius
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