"In 1949, the mathematician Kurt Godel - a friend of Einstein's and a colleague at Princeton University's Institute for Advanced Study - decided to tackle a situation where the whole universe is rotating. In Godel's solutions, time travel was actually allowed by the equations ... if the universe were rotating. A rotating universe could itself function as a time machine.

Now, if the universe were rotating, there would be ways to detect it (light beams would bend, for example, if the whole universe were rotating), and so far the evidence is overwhelmingly strong that there is no sort of universal rotation. So again, time travel is ruled out by this particular set of results. But the fact is that things in the universe do rotate, and that again opens up the possibility."

"In 1949, when his good friend Kurt Gödel showed that a rotating universe allowed for time travel, he was deeply worried.

Gödel, in fact, would pester astronomers visiting Princeton and ask if there was any sign that the universe was rotating. In Einstein’s writings, he finally concluded that time travel might be inherent in his equations, but they can be dismissed "on physical grounds," i.e., they could not form using known physical mechanisms. In other words, the universe expanded, not rotated. So if the universe did rotate, then time travel might be an everyday occurrence. This argument holds even today. There are a large class of solutions of Einstein’s equations, but many can be dismissed "on physical grounds." For example, in 1937, W.J. Van Stockum showed that a spinning cylinder that was infinitely long could satisfy all of Einstein’s equations. Decades later, it was shown that the Stockum solution actually allowed for time travel. If you danced around this cosmic Maypole fast enough, you could come back before you left. But again, "on physical grounds," one can argue that cylinders can never be infinitely long, so this was just a mathematical curiosity."

Then you have Black Holes, 'stabilized' worm holes clad with 'exotic (negative) matter/energy' etc. So the math seems to allow it, but I don't think it will work in reality.

Time travel Physics. ==

I think of it like this. Assume that there is a universal 'same clock'. Let's use light as that clock. You are born and now it start ticking for you, I'm born and it starts ticking for me. But those clocks, although having the same exact durations, as we will find whn being in the same 'frame of reference' is also uniquely our own as shown by a 'time dilation'. Two synchronized clocks on a table, move one to the floor, see their durations start to differ with gravity's influence.

If you travel near light the universe might pass forward at furious pace time wise as far as you are concerned, but your rate of durations do not change, you do not become in 'slow motion' and the arrow still only have one way, for all involved. There is a symmetry in that. But there is no symmetry in assuming that your 'arrow of time' both can point forward. at the same time as it points 'backwards' to me as in backwards time travel. How would it do that?

The clocks we have is uniquely our own, although belonging to a same conceptual common 'ground state' as I see it. To assume that the rest of the universe would be the one ticking backwards becomes just as confusing, as if you share their frame surely would find only one arrow, pointing in one direction, same as always.