Well actually my theory on how to travel back and forth in time.
Some caveats first, obviously I don't know what I am talking about. I struggle to understand how to build an Ikea bookcase let alone how the universe and all things work.
So feel free to laugh at the following as a piece of nonsense
The one thing I can say is that science does not fully understand how the universe got here, how the expansion is contained, what's at the edge of the universe, how quantum physics allows particles to be in multiple places at once, black holes, is there a multiverse etc.
And even if scientists could explain all that I am sure that I would not understand it.
But that does not stop me from wondering though.
So what is time, my theory is that time is movement. Everything in the universe is moving constantly, even when we are sat still, all the particles that make our form as well as everything around us are constantly moving.
If they all stopped then I believe there would be no time, i.e. nothing would ever change it would always be the same.
Now if that is true then if we speeded up the movement of these particles then effectively things would change more quickly and therefore time would go forward more quickly. If we slowed these particles down then things would change more slowly and effectively slow down time. Now what if we could reverse those particles, would that mean that time would go backwards?
If that is true and we had a machine that could achieve that then we would effectively be able to go back and forth in time.
Now of course we don't have such a machine and we would have to move the universe as a whole back and forth at the same time so not much use for nipping forward getting the horse racing results and then nipping back to make a big win. Or leaping back 63 million years to see what really happened to the dinosaurs. Additionally our bodies would also change back and forth at the same time and therefore not exist 63 million years ago so we would have to isolate ourselves from this change.
But I think its an interesting although maybe stupid concept. Scientists tell us that the singularity that forms a black hole will warp space and time so who knows, I obviously don't!