Comments by "zenith parsec" (@zenithparsec) on "The Spaceships Paradox - Can You Solve It?" video.

  1. Be careful: at relativistic speeds, the space weather might break not only the string, but your spaceship too. (I think the problem is that "common sense" physics words are being used loosely. What do you mean by "identically accelerate"? Acceleration is the the 2nd derivative of position; all you have to do is make sure the relative acceleration is stays zero between the two ships while they follow the same path. There will be a proper acceleration curve which prevents the string from breaking, by keeping the length constant. Although both ships might have different "gas pedal" settings, they will maintain the same distance, and as their relative positions as measured by any ruler they happen to carry (like the thread, for example) will stay constant, they obviously have accelerated identically. The argument is basically "if it breaks because you were too slow, either speed up or have the other guy slow down, if the string is getting slack, then slow down or have the other guy speed up. You can work out when these things, as well as all the other relativistic effects that make it tricky, are going to happen in advance so you don't need to worry about coordinating at the time." start by guessing some acceleration curves for each ship, and then: do all this: check the math on your curves; did the thread break? tweak one ship's the acceleration curve to make it fail at a later time. do all this again; otherwise: we're done. we have a curve where the thread won't break!
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