Oh boy does this topic cause debates, it's hard to know if us humans will ever be able to actually travel in time. For me, after watching BTTF, I was puzzled with questions about time travel.
Before we head into a debate, lets read the wiki, http://en.wikipedia.org/wiki/Time_travel
I believe Time Travel is a possibility, but there can be a chance that we will never find out. Or for my life span that is, maybe in the future, but right now its a topic that's still being discovered and debated.