I agree with everything except with the time travel things.
Considering that the time is infinite, so with an infinite number of lives in the universe, in which you would find an infinite number of scientific societies, I can see only two hypotheses:
1) time travel is possible: with what I pointed above, we should see those machine everywhere in our actual time (not saying in an infinity of please in our actual time, which would be harder to imagine)
2) as it's not the case, I see only two possible conclusions:
2a) the time itself is not infinite (or something will happen after which there will be no more life in the universe)
2b) or, what I personally believe in, past travel is simply not possible...