We'll never be able to travel back in time.
That's not to say we won't be able to "look" back in time, just not physically go there.
If we could ever go back in time, we would have done it, and we would surely know about it.
Yeah yeah that whole "keep it secret" & "doon't mess up the past" thing. But from the moment traveling back in time is invented, till the end of time, is a pretty long time (I would think). The odds that someone, or even something, would come back and time and mess up something, or let its time travel be know, are pretty high I think.
Of course I would want me to bring me the results of every sports event and every lottery drawing. I also want me to bring me accounts of every major natural disaster. THEN i'd be set.