If time travel were indeed possible, we probably could not go into the past, but only the future. I see no real indication that shows that we can go backward, unless it includes us going to an alternate universe. In which case, that's really not time travel at all.
I think Hawking feels the...
If it were true that things pass through the wormholes, then we are capable of the same.
But alas! it does not happen with us, at least not under normal circumstances, and so nothing passes from the other way all the same.
Now what happens in a black hole is rather arguable, however. My idea...
A very simple answer:
There has yet to be a complete observed symmetry between them, if one does in fact exist. They work on their own scales, but when integrating them, they fail for the most part.
Such is why elegant ideas such as string theory come out the woodwork. Some believe that...
String theory has evolved into compiled systems floating in an even higher dimensional space. Or the last I checked, anyways (I haven't stayed current with it).
M-theory is what they call it, which gave rise to the 11th dimension (just when you though there was too many lol). But, the theory is...