Unfortunately,
time travel in a way that affects this universe is
impossible. No generalization here - it will never happen, no matter how advanced humanity becomes before the
heat death of the universe. Oh, perhaps you could look back in time - but you can't move or communicate anything. Perhaps you can split new
alternative timelines from ours - but other than the lack of your presence, nothing in the reality that we currently exist in will change. Time travel as portrayed in books and movies and as understood in the popular conception is impossible.
Why?Because if it was possible, I would snap my fingers right now...
*snap*
And my future self would appear. He would come bearing technology so advanced that it made anything modern scientists could understand look like alchemy. Being me, he would share it with me and I would become unto a God - immortal, omnipotent, omniscient. I would become posthuman in a way never thought of. Conquest of Earth? Che, who needs to - but nations that did not agree to certain moral guidelines would exist without my technology, while those who did agree with me would flourish. Human pain and suffering would cease to exist beyond the everyday tribulations of life inherent to the human condition. A united humanity would begin the exploration of the two last frontiers - deep underwater, and deep interstellar space. And some unimaginable time later, when humanity is spread among the galaxies and barely recognizable to the homo sapiens of the year 2000, I would step back into the past when I snapped my fingers, bestow my gift upon myself, and return.
If time travel was possible in any real sense, I would have already bootstrapped myself into the future. Any possible obstacles could be circumnavigated through information from a future self to a past self.
The very fact that I write these words here on E2 proves that time travel is impossible.
Update: Yeah, yeah, we're all travelling through time a second a second. Not quite what I'm talking about here.