Time travel is not possible.

[A0523]

I don't think that time travel is possible.

For time travel to be possible, all the past, and present, and future should exist somewhere in material (physical / tangible) form.

This means that the state of earth 5 seconds ago should be existing somewhere in material form. This also means that the state of earth 15 minutes into the future should also exist somewhere in material form.

If we assume the least count of 1 second, then given the age of earth as 4.543 billion years, there should exist 143 quadrillion (past) earths somewhere in material form.

But there is no evidence that another earth exists somewhere in material form, forget about 143 quadrillion earths existing simultaneously.

Same goes for future, if earth will remain around for another 4.543 billion years, then there should exist 143 quadrillion (future) earths somewhere in material form but there is no proof of this also.

Same theory can be applied to universe and it can be said that quadrillion of past/future universes should be existing somewhere in material form but there is no proof of that.

One theory is that when you start time travel then "that earth" to which you are time traveling to will come into existence but there is no proof of this.

So, I think that time travel is not possible.

 

[non sequitur]

The coexistent multiverse theory (hugh everett many worlds interpretation) is a valid theory that can explain the theoretic system, as can the Heisenberg Uncertainty Principle. However none can explain the past nor future, but only the present. Your question of a world 5 seconds ago or 5 seconds from now, both theories state that every possible outcome at this exact moment has occurred, essentially relying on the collapse of waveform function and in the case of Schrödinger's Cat thought Experiment - your own interaction simple by being an observer. Time travel in the future is very real. Easiest way is to accelerate to a speed just under the speed of light and then decelerate. If you travel at the speed of light there is no way to slow down so it's a hopeless cause, a little slower will do the trick. Going back, I have no idea but can only guess if you can 'go back' it's actually not your own past but a divergent world and therefore not a past per se.

 

[Dizzie]

As non sequitur described, time dilation is a real and observed method of time travel into the future. Theories of the Higgs Singlet and Closed Timelike Curves point to the possibility of sending particles and/ or information to the past.