One of my favourites. Although it’s not widely accepted, the theory is that time travel is possible, although we don’t have the technology to build what is required, yet.
Basically it would require a HUGE hadron collider, much bigger than the one built undernearth France and Switzerland - in fact, it would need to be built in space.
The Hadron Collider would need to shoot atoms at each other consistantly for a while, then be stabilised by technology we don’t quite have yet.
Time is basically a variable, meaning it can change. For example time doesn’t exist within a black hole, and even Satellites need to consider that time is going at a different rate than time on the ground. Variables are number that can change. To the more extreme, if in your time you travelled 365 times faster than somebody in another time, every year that they experience is only a day to you.
Some also believe the Hadron Collider will implode the galaxy, but I’m not a pessimist.