A lot of these things aren't as far-fetched as people seem to think. You know, I think they've already built a magnetrain in Europe somewhere (a really fast train suspended over the tracks by powerful electromagnets).
I wouldn't be surprised if we have nuclear fusion, antigravity, etc. by 2050. Even cold fusion. It's our generation -- people born between 1985 and 2000 -- that's probably going to invent most of these things. Just because we don't all drive flying cars like they predicted in the '80s doesn't mean we haven't made technological advances -- just look at cybertechnology. People didn't have personal computers and the www back then. And a generation before that, they didn't have TV. And two generations before that, they didn't have radios. And so on, and so on. So what will our generation's contributions to technology be...?