I have a little confusion in my head when I want to imagine time. Time is a bit more abstract then space dimensions for me. So I began from definition of time, and it is defined through motion of electrons in Cs atom. Therefore, I thought if the Universe was so simple, such that there are only two particles (without any internal constituents), weather described with quantum or classical mechanics. And if we have motion of those two particles we could define time in that way. But in case that those two particles stand still, there is no motion in that Universe, so my question would be: what happens with time in that case? Does it pass? Or stand still? My opinion is that time is artificially introduced concept, and that it doesn't really exist. I think that it is simply consequence of motion of particles and therefore I would say that velocity is more fundamental than time. With this thinking, there is no possibility of time travelling because everywhere exist only now (if that is correct choice of words).