A Time experiment

[Roboramma]

Time dilation really is nothing more than changing the orientation of your worldline in spacetime, in a way that is analagous to changing the orientation of an object in space. For instance:

The two sticks in the first image have the same height.

In the second image on the other hand, one of those sticks has been turned at an angle, and they have different heights. The height of the red line is only that of the black line, and is significantly less than the height of the blue line. But they are the same sticks! What happened to that height? It became width: which we see has increased by the length of the green line. The conversion factor is the pythagorean theorem.

 

[JJM 777]

if I have two wrist watches that I carry with me at all times (...), I can't get them to disagree with each other.
(...)
I agree, but don't really understand why you think it's interesting to point this out.
(...)
That the percieved flow of time doesn't change is no more interesting than the fact that I can't change my state of motion relative to myself.

These notions are of interest if anyone wonders what kind of time travel might be theoretically possible, as the OP asks. These notions give the answer that you cannot travel into your own biological history or future, time travel is not an answer to becoming younger or living forever, visiting a moment when you are grey and old, then coming back to being a teenager again.

With careful, but much more complex, analysis we would come to the conclusion that time travel is not an answer to visiting anyone else´s past either, beyond the biological moment which the person in question has already passed wherever he now is.

 

[Roboramma]

While I agree that time travel to the past is very likely impossible, I don't agree that it follows from any of those "notions".