When you write about time travel (as people have done since the era of H.G. Wells, and in some measure, even before), you want your readers to be able to suspend disbelief long enough to tell your story.

So it’s a good idea to stay abreast of the science of the subject. To be honest, though, it isn’t there. Yet.

The theory of relativity concludes it’s possible, though unlikely. For some versions of it, negative mass and energy are required. Or a shortcut that bypasses gravity. Or make-up-your-own, which is what theoretical physicists and science fiction writers are left to do — at least until the technology for handling the physics of the problem is available to us!

My character Stan, in the People of the Water Cycle novels, is one of those folks who goes his own way.

If the subject interests you, here’s a summary from Scientific American that I found accessible to my rather primitive and unscientific mind:

https://www.scientificamerican.com/article/is-time-travel-possible/