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This question related to the Grandfather Paradox.

Assume that time travel to the past is a reality. What experiment/test could the time traveler perform in order to determine if he is in his own timeline or an alternate timeline/universe?

If the time traveler was in his own timeline and kills his grandfather, that means he would have never been born -- and thus cannot travel back in time to kill his grandfather. If his grandfather was not killed, that means he would have been born -- and thus could travel back in time to kill his grandfather. And so on ...

At the moment the time traveler kills his grandfather, what would happen if the time traveler was in his own timeline/universe? Would it be any different if the time traveler was in a different timeline/universe? How could the time traveler know for sure if he is in his own timeline/universe or not?

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He can try to kill the grandfather. If he is in the same time line as initially, he will not be able to kill the grandfather. – Chris Jan 19 at 3:21
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See the FAQ section on questions that aren't appropriate here, in particular the section "Questions about fictional physics". – John Rennie Jan 19 at 7:22

closed as off topic by John Rennie, David Zaslavsky♦ Jan 19 at 7:49

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The initial assumption of accepting time travel is incorrect. If you start with the wrong assumption then all other observations that flow from that assumption are also wrong. Forget the grandfather. Suppose you travel back and set fire to an oilfield. If the oil is burned how can you burn the same molecules again in your time. Time travel is made impossible by the Second Law of Thermodynamics that states that entropy overall must always increase with the flow of time.

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The assumption was to be accepted as true for the hypothetical situation. – PhysicsNewbie Jan 19 at 5:03

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