Time Machines

In sci-fi movies or cartoons, the main characters can always travel back through time. We have discussed how time slows down before, however, we never know if time could be reversed. We can find the answer with the Time Dilation formula.

This time, instead of substituting v=c, we will substitute v=(√2)c. By doing that, we obtain:

Here iΔt is know as imaginary time. Imaginary time is different from regular time. If we imagine "regular time" as a horizontal line running between "past" in one direction and "future" in the other, then imaginary time would run perpendicular to this line as the imaginary numbers run perpendicular to the real numbers in the complex plane. However, imaginary time is not imaginary in the sense that it is unreal or made-up — it simply runs in a direction different from the type of time we experience. In essence, imaginary time is a way of looking at the time dimension as if it were a dimension of space: you can move forward and backward along imaginary time, just like you can move right and left in space.


To conclude, travelling back to past is not possible. There's no way something can travel faster than the speed of light. Even if a thing really did it, you still can't travel back to the past, as you will be travelling on a different "time line". So, we can just forget the dreams of reversing time.