If time travel was posible wouldn't we be living the final version of events effected by time travel? So even if we discover time travel what ever we change by going back in time has already been changed?
Well, a number of things might be suggested, most obviously that time travel into the past is unlikely because of the number of paradoxes it would create as well as the lack of time travelers we've seen. Some have argued that a Multiverse composed of branching, parallel universes would make reverse time travel possible because, in such a system, universes and events would be more plastic and alterable. Time travel to the past would open up a new, nearly congruent universe, though with some differences. You may also be interested in reading about the grandfather paradox. Time travel to the future, meanwhile, is something allowed by the theory of relativity, and goes into effect as one entity moves closer to the speed of light relative to another object, resulting in the two experiencing time passing at different rates. When the "faster" object slows, it finds that less time has passed for its than for its immobile counterpart. Back to Wikipedia for more about the basis of forward time travel. This isn't my field, though.
Yeah, the lack of people walking amongst us from a future date, with future technologies and cool futuristic hairstyles might mean it will never happen. Which could either mean it is not possible or that we never made it far enough as a species to discover it.
Or you can believe that time travel only works by creating parallel worlds. Whenever anyone goes back in time a new branch forms so that the time line they are leaving is preserved. You then have to accept that we are in either the original timeline (un-likely), that the timeline we were in was changed in a way that we can percieve (for example someone went back in time, creating a new timeline, and then was immediately eaten by a dinosaur, causing no lasting effects that we could notice), or that time travel isn't possible. http://en.wikipedia.org/wiki/Many-worlds_interpretation#Time...
That's one of the things Steven Hawking has been known to say: the lack of time travelers among us suggests there is no way to time travel, at least not into the past. Apparently, what he said was "I gave a party for time-travellers, but I didn't send out the invitations until after the party. I sat there a long time, but no one came."
Maybe time travelers don't think we are interesting.
I think the problem with time travel is that is you went back in to to kill say Hitler.
Killing him would negate your reason for going back in time and cancel your trip. Accidental changes in history might not cancel trips but also might not be noticed for the same reason. History might at least seem immutable and hence the Travelers only have reason to observe not interact.