Another thing to note is, if time travel is possible (let's say backwards), then why aren't we seeing anyone from the future yet? This comes down to a belief of multiple universes OR that time travel is simply not possible. Cause think about it, if a fully functioning time machine is ever invented in the future, say, in year 3000, then why haven't we seen anyone from the future? Clearly they would have impact a great deal of our history by now. Could it be that they're in another universe?