Are we getting close to time travel?

That's only true if "free will" exists, i.e. if its really "changing" the past instead of fulfilling it.

Basically, this limits the very earliest that such backwards going messages can be received to around now-ish.[1]

As a consequence it may not be a paradox anymore, since there will be no point at which we can operate without a suspicion of future interference, thereby reducing the paradox effect, and in fact encouraging it by divining the outcomes of our actions. Of course this divining rapidly loses power anyway, as multiple messages are sent conflicting with one another - it gets messy quick. It gets messier quicker if you choose to go with a "many worlds" interpretation of the universe. Further, there are questions regarding observation: does observing a message from the future cement that future into being, possibly incurring an absurd chain of events but not causing any paradox (the 12 monkeys thing)?

What I am really driving at here is this: Your paradox claims are amusingly simplistic, the real deal here is that we just don't know enough to say.

[1] I am ignoring two big possibilities: 1. that this has been known for some time by, say, evil wall street bankers with secret labs (and their ilk -- governments, supervillians and such). 2. That there aren't aliens at some point in the very distant past whom we get messages to, and convince to do our bidding, who show up at various key stages of history an change everything. This may or may not have happened, depending on what you believe from the history channel (ancient aliens) and Stargate.

Not quite. You're neglecting quantum mechanics.

Very roughly speaking, in quantum field theory, the probability of an event happening is a weighted sum over all the possible ways that it could happen (a path integral), and (again, speaking roughly) the options that seriously violate the various conservation laws tend to have negligible contributions. Presumably the path integral formulation would still hold up even with closed timelike curves (time travel curves).

An inconsistent state, like one where you kill off your own parents, would probably exhibit all sorts of self interference that would make its contribution to the path integral very small, whereas the consistent states would be much better represented, and much more likely to happen. Weird "violations" of physics could quite easily present themselves as the most probable outcomes, especially if the alternative was an inconsistent outcome.

A good way to think about this is in terms of waves on a string, or the "wave" of an electron in orbit around a nucleus - the only vibration frequencies that "survive" are the ones that reinforce themselves, and the rest get cancelled out by interference (in the electron case, because they don't "match up" when they meet themselves after an orbit). If you think of the state of the universe as the electron, and the orbit as a loop through the closed timelike curve, then it's easy enough to imagine quantum mechanics doing all the hard work for us, and making sure that only consistent outcomes are reinforced, while all the other ones are destroyed by interference.

I'll try to put this briefly, without too much technical detail.

General relativity permits (and we've always known this) solutions that involve closed timelike curves (CTCs). Usually, when we look into these solutions in detail, we find that they require strange sorts of matter to sustain themselves, or that they're unstable. Hawking proposed that the universe in some way bans any geometry that would allow these solutions.

The authors here claim that by adding a fifth dimension that's curled up like a circle, and adding a specific sort of curvature to it (the metric contains a periodic cross term between the usual time dimension and the curled dimension), you can get CTCs that are geodesics (i.e. paths that particles will take with no forces on them), and you don't get weird energy conditions or anything like that.

Then they go on about the potential consequences if the universe is actually curved up like this, and so on, but don't offer any particularly compelling reason to believe that it is.

So basically, they claim to have shown that it's possible for the universe to be like this, and that no condition we currently know of prohibits it.

Meh. Could be, if we assume that they're right - it's always, of course, possible that there's some other problem with their solution that wouldn't be covered by the usual energy conditions, I'm not sure, I've been out of the GR circuit for a while so I don't know what people currently consider to be the most reasonable set of constraints that the Real World follows. But even if they're right, there are plenty of solutions to Einstein's equations that could have happened and don't, so there's nothing too revolutionary here, and mentioning a whole lotta shit about branes and the Higgs boson doesn't change that.

This is still quite useful theoretical physics to do, mind you, but it's nowhere near as important as the article makes it out to be.

If it's the latter, you might find sections of RobotRollCall's first comment in this reddit discussion enlightening: http://www.reddit.com/r/askscience/comments/fjwkh/why_exactl...

If it's the former, well, I guess you're probably right. Nobody knows. At least, nobody thinking about it in a purely philosophical/theological context.

I hate to break this to you, but there's no such thing that you can describe as simply as "the present". Since we're talking about time travel here, it's important to remember that relativity is real, and that every single atom in your body exists at a different "present".

Our GPS satellites are time travellers. Their distance away from Earth is so great that we must compensate for their different perception of time, or our reported locations would be way off.

You should not be so absolutist in your views, especially when you don't have an accurate understanding of time.

I also take issue with you suggesting that nothing dangerous should be "bothered" with in research. Look where the Manhattan project got us: We have safe nuclear reactors all over the planet, we have sent a few spaceships outside the solar system (Voyager 1 and 2, for example) that run on nuclear reactors. We know that nuclear research presents great danger, but the rewards are so huge it's worth it.

All knowledge is worth some danger, especially the truly incredible knowledge like finding out that our understanding of physics is incorrect, or building spaceships that leave the solar system.

That being said, understanding time travel (even if it's impossible) is very important for getting a better understanding by what we mean by 'time' in the first place.

Yet in practice it's better to publish that openly, lest the blackhats abuse the vulnerabilities for their purposes unhindered.