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(August 31, 2014 at 9:30 pm)KUSA Wrote: The arrow of time only goes forward. The entropy of the universe can't be undone.
Going back I time does not imply entropy is undone. If you were to go for time B back to time A and change subsequent history, it seems entirely plausible that how you can change subsequent history is constricted by laws of physics to maintaining precisely the same amount of entropy increase in the new progression of time from A to B as in the original progression from A to B.
One possible explanation that has been advanced for why there are no traveler from the future in the present is the same time machine one uses to travel back in time must have already been operating at the destination time in order for time travel to be possible at all. a ie, a time machine can only transport you to any time in history after the time machine itself has already been built and turned on. If no time machine has been invented yet, then your will see no time traveler from the future because time travel to before the first time machine began operation is impossible.
But once the first time machine has been invented, built, and switched on, then time travelers for during the life span of the time machine may freely go back and forth to any time period when this machine has continuously operated.
So, if there is a discontinuity in the operation of the machine, would time travelers forward of that discontinuity be able to travel further past that that discontinuity, or only back to the discontinuity?
