[Erin Pavlina]

I think your logic is flawed because of your assumptions. You're assuming that if a time traveler were wandering around in the past he or she would announce it to the general public, "Hey ya'll, I'll just be a sec... gotta assasinate someone and then I'll get out of your way," and that probably isn't likely. So if someone were time traveling they would probably take pains to guard this knowledge from others.

And secondly, you're assuming that just because a time traveler has never made himself aware to YOU that he hasn't made himself aware to anyone.

Not saying you're wrong, not saying time travel is possible, but just commenting on your logic.

As for time travel, I have a feeling it's possible though I don't understand the physics well enough to even begin to discuss it.