It is technically possible to travel forward in time, but there is no reason or law that has made travelling into the past even remotely possible, as of yet. Personally, I can see skipping over some time, as in a wormhole theory or close-to-light-speed-orbit around Earth or whatever, but never going back to a point to where two of the same beings could exist on the same plane of existence. To put it bluntly, travelling back into the past is more preposterous than finding a way to travel into the future. Oh, and whoever says that "time doesn't exist," needs to read less hogwash from the object/concept religion that is found on today's Internet... Personally, my imagination does enough time travel as it is; cheers!