If you could travel back in time would you know before you did it

Question

i mean how do we know we have not already done it , perhaps this is not the first time we have been here , but that we have come back to stop sonething from happining , but if it does not happen how will we know to stop it

Answer 1

According to current, conventional, theoretical physics - time travel into the past is impossible. I'll try to explain!

Einstein published his Theory of General Relativity in 1915 but it was not until the late nineteen forties that, the Austrian mathematician, Kurt Godel found a time travel possibility within a solution to some relativistic equations. He found, that if the universe is rotating then time travel in both directions should be possible. By both directions, I mean, into the past and back or into the future and back. Alas, recent observational work used to study the cosmic back-ground radiation has indicated that the universe has not rotated significantly since its creation. Hence, time travel into the past would appear to be impossible.

However, Einstein's theory of Special Relativity allows 'time-dilated' travel into the future. If an astronaut sets off on a journey travelling at a high percentage of the speed of light, then his on board clock will run more slowly than an equivalent clock here on Earth. Thus, when the high speed traveller returns after a few years of his elapsed time; here on Earth many hundreds of years may have elapsed. The time dilation equation is given below: -

t(Earth) = t(traveller)

..............._________

...............√(1 - (v/c)²)

Where 'c' is the speed of light and 'v' the traveller's velocity, which may be expressed as a percentage of the speed of light ((say) 0.99999c).

There also exists an oddity called a ‘Kerr metric’. Within the ergo-sphere (an elliptical region just outside of the spherical event horizon) of a rotating Black Hole, a traveller would travel through closed time loops as they were dragged along by the angular momentum of the hole. This metric is a measure of how space-like coordinates become time-like in a region of dragged rotating space-time! However, closed time-like loops do not permit retrograde time travel and, furthermore, it is impossible to escape from the ergo-sphere of a rotating Black Hole.  

So, to summarise, the answer appears to be that you cannot travel through time into the past but you can travel into the future - at least theoretically!

Answer 2

Once we had created the time machine, we cannot go any further back in time than the moment we created it. It's the laws of probability or something like that.

Answer 3

I thought I answered this question last October.

Answer 4

Good question. The only way you would know is if you were not in an identical state before and during the time displacement. For example, if you were seated in an isolated room when the displacement occurs, you probably could not tell that it occurred because you would have no frame of reference. On the other hand if you were in the room but eating a popsicle, you would know you went back in time because the popsicle would be bigger than before.

Hope this helps.  

Answer 5

Time is an interval between two events and does not 'flow', i.e time does not exist and is only a device we use to measure the interval- in whatever units you choose. So you can't travel back or forward in time. So the question has no meaning