Time travel

Time travel is the movement between points in time, analogous to the movement between points in space, in spacetime, typically in four dimensions.

There is time dilation in special relativity and gravitational time dilation in general relativity. The theory of relativity states that the speed of light is the same for all observers in any frame of reference, so time dilation is a direct consequence. A person may use time dilation so that a small amount of proper time passes for them, while a large amount of proper time passes elsewhere, and this can achieve time travel into the future.

General relativity treats the effects of acceleration and the effects of gravity as equivalent, and shows that time dilation also occurs in gravity wells, and it could lead to significant differences in rates of aging for observers at different distances from a large gravity well such as a black hole. An example of this is the black hole Gargantua in the Interstellar Universe.

Traveling to another point and time in spacetime and escaping an instance is associated with technology like a time machine which works with 4d, 5d and 6d.

Travelling to other instances would require megaversal access to 8d via the quantum dimension (7d). It is possible to travel to another instance within a multiverse where if a time paradox event is attempted, you would be thrown into another instance to prevent a causality violation. The effect is that time would decay along this causality line or boundary and all associated matter (including the cause) would follow this decaying timeline.

Traveling to an arbitrary point in the spacetime continuum is connected with wormholes which are natural structures in reality and therefore in 11d. As civilizations get more advanced, they are able to make artificial wormholes and subspace devices that can work with higher dimensions, therefore being able to travel at will to any timeline (instance), for example the TARDIS or tesseract structures.

Beyond 11d it can get weird, as one can travel to before the Big Bang or use subspace conduits or ADs to travel in and out of reality.