I'm no physicist. I just want to be clear on that. The subject does come up with some fascinating things though. If I'd been better at mathematics, I'd have been interested in taking that route.
This week, New Scientist talks about time travel. Again, you can't see all of it unless you subscribe or get hold of a copy but here's the gist of it (based on my limited understanding).
In 2008, the Large Hadron Collider starts up. I don't know for sure what a hadron is or how big it is, but the LHC is very big indeed. It will accelerate tiny particles to enormous speeds and smash them into each other. This is what happens when you let child-geeks play marbles, you realise. They can't just stick with the little glass balls. They have to develop the theme - to make it harder they use subatomic particles and massive magnets to accelerate them. It does sound like enormous fun. I wonder if 'Hadron' is Greek for 'marble'?
The thing is, this LHC sends particles so fast that their collisions could rip a hole in space-time and form a wormhole to the future. A very little wormhole, only big enough for subatomic particles to pass through, but it would nonetheless be the first definite transport of an object through time.
The article says that 'time travel, if it's possible at all, would only be possible as far back as the invention of the first time machine'. I didn't (and still don't fully) understand why this would be but I suspect it's to do with the wormhole idea. A wormhole created in the future would have to link to one in the past. We've never created a wormhole yet. Until we do, the future people can't link to it. Something like that. I think. If the calculations of physics are right, we could be on the verge of the time travel era but only as far back as now. That's great for people in the future but not a lot of use to us.
One of the biggest and most convincing arguments against time travel is this: If people in the future manage to invent time travel, why have none of them come back to see us?
It's always been a flawed argument. Anyone who claims to have come from the future ends up in the rubber room. So maybe some have come back. Anyone with sense would come back in time armed with horse-racing and football results and some winning lottery numbers. They'd keep a low profile, gradually build up a fortune and retire. They would not announce they were from the future, because their history books will tell them that in the 2000's, anyone claiming to be a time traveller ended up in a rubber room. They might be here. They're probably not. According to the theory of wormholes, they can't be--but they might be once the LHC starts up. Don't bother saving the lottery results until after that happens. Then save them all. Your great-great-grandchildren will make a fortune with that information. Perhaps they already have.
There is, of course, the pessimistic view that states that nobody from the future has come back to see us for a much simpler reason.
There isn't one.