Time Travel

This has been bothering me for a while, mainly due to my obsession with the Japanese cartoon Doraemon, in which the main character Nobita has a time machine in the drawer of his desk.

Time travel is possible if one can travel faster than the speed of light. Suppose it is achieved one day in the future. Why don't we see future time travelers in our current world?

There is a discussion by Stephen Hawking in his famous book, A Brief History of Time. I didn't study enough Physics to comment on Hawking's suggestion, but let me state what my worries are.

If future time travelers can indeed go back in time, here's a couple potential explanations of why we don't see any of them now.

1. Our current world is not interesting enough to warrant them a visit.
2. They are here, but
a) They cannot reveal their identity; or
b) They are invisible to us.

If 1 is true, then we will probably see some of these travelers in the future, which I think is more intimidating than seeing aliens. 2a is possible since they might not be able to act upon their free will, as the past is fixed and they can only be quiet spectators. But the question now is: who are they? Scientists? Homeless people on the streets? Or you and me?

2b offers an explanation to why we don't identify them, but this is even more unpleasant. If this is true, you and I and everyone else have the chance of being watched by these future travelers, and we can't even tell if they are here. However, this poses more questions as well: How do they survive in our world? What makes them invisible to us?

Given the large amount of debate generated when cloning was invented, time travel will certainly be controversial. I hope this technique will never exist (or at least time travel is only confined to going to the future). Even God cannot go back in time, so shouldn't people.