Time travel is kinda tricky. Right now we only know how to travel to the future, and the speeds are terribly slow. It typically takes 24 hours to advance a single day. I'm hopeful that we'll crack backwards time travel to the past soon. I have these here winning lottery numbers that I have to go back to deliver to myself. (Yeah, I would totally cheat at gambling with this power.)
i believe the unknown is unknown, ruling out nothing entirely. i believe in the goodness of the reality of the diversity of the possible. being possible doesn't mean any of us are ever likely to actually see it. this is entirely a separate matter. do i believe it is common? obviously not. now stepping sideways in time, into some parallel quantum universe, seamlessly, invisibly, and believing the slight differences to be memory loss or distortion, this i strongly suspect.
I suppose anything beyond our limited understanding of existence itself---why is there even existence at all---is possible.
Well if Einstein was right about space and time being connected in a 'fabric' called spacetime then why shouldn't we be able to traverse time in a similar manner to moving through space? I imagine if we bent the fabric of spacetime enough we could travel through time. Or we might just end breaking the fabric of spacetime like they did in futurama.
well there's thins thing called entropy. but as long as you didn't try to kill your grandfather you'd probably be ok. you'd either just not be able, or the attempt would shunt you off into some other parallel universe. people have been playing with this thought since before science fiction ever became its own genre. spacetime to stretchy to break, but you could probably tie all sorts of creative knots in it. this is what REALLY happens, when you divide by zero.
people have the wrong idea about impossible. this is not a thing, unless it contradicts itself, and even then, self contradiction can be an illusion. now there are things each of us can't do ourselves, or cause to be done without mechanical or other assistance, but this is not the same thing either. what there is instead of impossible, is some things don't happen often enough for any one of us to ever be very likely to see them. doesn't mean they can't or don't ever happen. it also doesn't mean they have to contradict what science can observe to do so. just what it hasn't observed yet, and perhaps never will in the lifetime of our entire species. 'impossible" things, appearing out of nowhere and dissapearing back again, aren't about what people tell each other to think they know about non-physical beings, gods and things like that. they're just things that have noting to do with any of that, and when they happen, they neither prove nor disprove anything either. usually of course, they only appear to be impossible, because they're being seen from some angle or perspective that distorts their true nature. times arrow is entropy, and while it only points in one direction, but if there were nothing else, no contrary movement, would there be anything at all? why hasn't the universe run down to nothing, waiting for the next big bang to start it all over again. i don't believe the whole answer is some kind of self aware magic. but i do believe the unknown being unknown rules nothing entirely out. what we don't know we don't know, and that is not more nor less. the unknown isn't empty, its just unknown, and owes nothing to what we tell each other.