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The English science fiction writer H.G. Wells wrote the book 'Time Machine' in 1895. As far as I know, this is the only book about time travel written before Einstein's special theory of relativity of 1905. H. G. Wells could have influence Einstein but Einstein did not assert that time travel is possible. What Einstein did say is that space and time are linked into a four dimensional continuum.

The theory of space-time says that space and time can only change as a group. Time cannot change by itself and same with space. If one change the space, time also change. The universal expansion of space can also imply that time change as indicated by the increase of entropy.

but what happens if the universe is contracting? We can say that the entropy is then decreasing, just the reverse of expansion. If the increase in entropy is one direction of time then the decrease in entropy is the other direction of time. Both directions are related to what is happening to space. One case is that space is expanding and the other is that space is contracting.

But light in the form of a photon does not change in space-time. Photon (unit of light) is always constant in the space-time continuum. So if we really want to travel in time, we must become a photon then we can move in the space-time continuum without getting older or getting younger. We live forever and go anywhere, we are then moving constantly at the speed of light. The key is that our mass have to be zero like the photon.

Antonio