Question: is there any scientific basis for time travel?

Edward Banks answered on 19 Mar 2020:

Actually yes! One of the fundamentals of Einstein’s theory of relativity is that light has a finite (but very fast) speed, and this puts a speed limit on everything else in the universe. However, we also know that no matter how fast you are going, light always looks like it is going the same speed. Now after some complicated maths, we find that this means the faster you are going, the slower you experience time- time will pass differently for people going slowly.
So take the classic thought experiment of a pair of twins. One of them stays on Earth, and the other goes off in a spaceship, which accelerates to close to the speed of light- travels for a few years, and then comes back. Because of the previously mentioned relativity, the one on the spaceship will have experienced less time, and have aged less!

Now lets take this a step further, imagine we somehow manage to set up a stable wormhole. A wormhole is a theoretical object that cuts a shortcut through space-time; even though they may be separated by hundreds, thousands of light-years, if you go through the wormhole you can get from one end to the other instantaneously. Imagine we had two ends of a wormhole, and again we kept one on Earth, and sent the other off on a spaceship close to the speed of light. As we said before, the one travelling at near the speed of light will have experienced less passage of time than the one on Earth. But if you then bring them back close to each other, this means the end of the wormhole that went on the journey is actually in the past compared to the one that didn’t move! So you could go into the past by stepping through the wormhole.

So this is all mathematically plausible; it falls out of the solutions to general relativity. But we haven’t found any stable wormholes yet in real life, so who knows if they are actually possible or not.