Time travel is the magic of the modern age, I think. A hypothetical goalpost based in nonphysical possibilities and wild guesses. Which is interesting, as the flow of time is a logical, rather than physical, construct as well. I would conjecture that the only place where one could "rewind the record" would be from outside the universe itself - and that we'll never get there. One might simulate it, hypothetically, by constructing a new universe with a structure identical to that of a short time back - but to do so would require literally more matter than exists in the universe, just as a hypothetical simulation of the entire universe would.
But that's just my opinion.
Whether or not Stephen Hawking thinks it's possible makes small difference - he's a man. An intelligent man, sure, but just a man, and he is fallible.
And the argument of "a thousand years ago X was thought impossible" is logically flawed - it could be paired with any desired result with the same chance of occurring - for instance, "Will it be possible someday to transform all humanity simultaneously into polka-dotted ligers?"
...only in Scribblenauts. Which, come to think of it, also applies to time travel. And Cthulhu.
