Physical time travel to the past

Time Travel is not possible,
for if it was, they would already be here telling us about it.

-- Stephen Hawking

Many of the theories of time travel presume some kind of physical experience, involving some kind of time machine to send travelers to the past or future. These theories are also responsible for the brain twisting confusion that thinking about time travel often causes. Questions about how the same person could exist more than ones, the grandfather paradox and other similar paradoxes and a violation of the causality principle.

If indeed future time machines would allow time travelers to jump back to the past in their original form, then how would we ever be able to reckognize such a time traveler? A few ideas about how we might find out:

• By mistake; the traveler might give away its secrets himself (Whatever that would mean).
• An investigation would reveal clues about his 'non-existing' past.
• People notice that he has extraordinary knowledge about current and future events.
• A renegade time traveler might tell us all about time travel - ha!.

Although there are many films that deal with the physical time travel idea, it is not sure whether it ever happened for real in our history. It seems that there is no proof or evidence that supports this type of time travel experiments. In this respect scientists have said that if time travel would exist, we would already have seen it and noticed. If we can find no proof of possible visits from future travelers, it might tell us that physical time travel is not possible and that we should look for clues in another direction.