31–39 of 39 posts
Why do people bother researching into time travel? Even if it's possible, it's potentially a massively dangerous act. Nobody should have the power to alter events outside of the present in any way, shape or form. Period.
I can't imagine a greater human achievement than time travel.
This is just silly. If time travel were possible, it would have been invented already in the future and our world would be a very different place.
Here's the article that I assume this is referring to: http://arxiv.org/abs/1103.1373 I hate judging based on stupid journalist writeups of stuff like this, so I'll actually look through the article, for once. The first part of the abstract: "We construct a simple class of compactified five-dimensional metrics which admits closed timelike curves (CTCs), and derive the resulting CTCs as analytic solutions to the geode…
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.
>"Because time travel is limited to these special particles, it is not possible for a man to travel back in time and murder one of his parents before he himself is born, for example. However, if scientists could control the production of Higgs singlets, they might be able to send messages to the past or future," This is absurd. If you can send messages back in time, then someone can build a robot that can accept mess…
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.
>"Because time travel is limited to these special particles, it is not possible for a man to travel back in time and murder one of his parents before he himself is born, for example. However, if scientists could control the production of Higgs singlets, they might be able to send messages to the past or future," This is absurd. If you can send messages back in time, then someone can build a robot that can accept mess…
If you can send messages back in time, then someone can build a robot that can accept messages from the future, and kill your parents that way^. Sending information back in time is a paradox. Period 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), an…
Earlier quoted context omitted.
The good thing about time travel is that it would make FTL space travel possible as well.
The implications for computing might be interesting as well... (Charlie Stross mentions this in some of his stories).
This is just silly. If time travel were possible, it would have been invented already in the future and our world would be a very different place.
What about limited forms of time travel such as the one in the film Primer - where they have a device that does indeed allow travel through time but only back to the point where it was turned on and only at the normal rate (i.e. it takes an hour subjectively to go back an hour in time).