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My question is

Let's say you have an object moving through space locally at less than the speed of light. Is it possible to watch that object playing backwards like a record spinning the wrong direction according to the following version of general relativity? One where space doesn't exist in spots that would take an infinite amount of time to compute how it goes directly from causation in the direction of the future light cone such as where there would be closed time like curves. That is, could you watch an object playing backwards from something like light from that object bending around a fast moving black hole then bending around another fast moving black hole before it reaches you.

If the answer is yes, then that probably means it's also possible to produce something like the sonic boom but with light. I know that a an object travelling in a time contraction track fast enough while still being below the speed of light within the track could produce a luminous boom. So a really distant object that normally would be extremely dim could have a flash of appearing much brighter than usual. Having 2 images of a galaxy behind another galaxy from gravitational lensing doesn't count. I know that if you look at the one from more recently then the one from longer ago, you are observing one event first then another event that's in its past light cone. However, in each image, you are watching it playing forwards.

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  • $\begingroup$ @josephh I said general relativity, not special relativity. Absolutely, special relativity predicts that it's impossible to have an object appear to be playing backwards. However, I don't see how to prove general relativity predicts it. Space time is curved in general relativity. $\endgroup$ – Timothy Mar 8 at 5:18
  • $\begingroup$ why don't you read the article in wikipedia It says there exist special solutions,en.wikipedia.org/wiki/Time_travel $\endgroup$ – anna v Mar 8 at 5:21
  • $\begingroup$ @annav I fixed up the question. $\endgroup$ – Timothy Mar 8 at 6:13
  • $\begingroup$ Well, with gravitational lensing, you can get several images of a distant galaxy, with each image having a different time delay due to the light path length differences. But of course time flows forward in each image, so I guess that's not quite what your question is asking about. $\endgroup$ – PM 2Ring Mar 8 at 6:41
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There are certain spacetimes which allow for closed timelike loops. For example, the Misner or Goedel universes.

To my mind, it suggests an aporia in General Relativity mainly because its difficult to make any physical sense of this. Until they are actually observed (!) or shown to have some physical sense, they remain curiosities of the formalism of GR.

(It could also mean that there is an opportunity to invent a theory that transcends GR, in the sense that it has no such solutions. Though, of course, it would need more than this to qualify as a contender against GR).

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  • $\begingroup$ I realized my question was actually whether it can happen according to a version of general relativity where the space in the future light cone of any point that's part of a closed timelike curve doesn't exist. $\endgroup$ – Timothy Mar 8 at 18:25

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