That is true. And it is possible, in principle, that some new revelations will come along and completely rewrite our understanding of physics, and allow for FTL travel, time travel, transport to "parallel universes" (ala Fringe), etc. But there are good reasons to not expect that, in that the places where our understanding is incomplete mostly deal with "edge" cases - extremes of scale (quantum mechanics), time (origins of the universe / big bang), gravity (insides of black holes), etc. But the physics we have today is otherwise very well tested, and makes incredibly precise and accurate predictions that match extremely well with observed phenomena.

Given that, I think a strong measure of skepticism in this regard is fairly well supported. But, a good scientist should always be willing to change their position if the evidence dictates such, and new evidence can always come along. See: The Problem of Induction.

>Statistics makes the claim that aliens are more likely to exist than not.

"There exists alien somewhere in the universe" doesn't imply "there are aliens visiting us right now", though.