I remember reading an interview with a leading developer of an invisibility jacket, when asked whether he thought time travel would be possible in the future he responded "of course", when they proceeded to ask him that if that were the case, why have we not yet met any time travlers? He replied "Because they will most likely have developed perfect invisibility by then".
I just thought I'd share that, I remember it really made me think about the future, and also caused me to do a search of my room for any cloaked time travelers, this stuff excites me.