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    • CommentTimeJul 26th 2011
    The hopes of going back in time and visiting the jurassic era escape a T-Rex and warping into the future to save the world from Skynet will never happen. Chinese physicists have just proved that time traveling is out of the realm of possibility (at least in this universe).

    In a published study, Shengwang Du and his team of physicists at the Hong Kong University of Technology and Science stated that single photons can't travel faster than the speed of light.

    By result, the possibilities of time traveling have been debunked in one fell swoop because it was previously believed that if a single photon could travel faster than the speed of light, it could "teleport" information to another time.

    • CommentTimeJul 26th 2011
    Still leaves the possibility of using wormholes for time travel.
    • CommentTimeJul 26th 2011
    One day they will travel back in time to eat those words.
  1.  (10075.4)
    Now, to be fair, their findings indicate that photons can't go faster than the speed of light. While it's true that we've never detected anything that moves faster than a photon, there is a theoretical particle familiar to anyone who has ever seen Star Trek, the tachyon, which is a particle that moves faster than the speed of light from its creation, and can never be slowed down to less than the speed of light.

    Of course, there is no evidence that tachyons exist.

    Another way to think of the speed of light is not as the "speed that photons move in a vacuum," since scientists recently were able to slow down a photon to the speed of sound, but as "the rate at which a theoretically detectable change can occur" (I say theoretically detectable because we don't have instruments accurate enough to get anywhere near the scales we're talking about). Photons, then, are just fast little buggers that change their position that quickly. So what's significant about their findings is actually that the speed of light might well be the "universal speed limit."

    Anyway, yes, forget accelerating beyond light-speed. Focus on folding space instead.
  2.  (10075.5)
    Sure. A couple of months ago, they all but ban the depiction of time travel in their culture, and now they declare the concept impossible. It's almost as if they were a government uncomfortable with the idea of history being changed.
      CommentAuthorAlan Tyson
    • CommentTimeJul 26th 2011
    Huh... well, now that you put it that way, this article takes on a whole new layer of ODD.
    • CommentAuthorOxbrow
    • CommentTimeJul 26th 2011
    Especially considering some of the revisionist history during and since the Cultural Revolution...
    • CommentAuthorOddcult
    • CommentTimeJul 26th 2011
    Okay, n00b question I've always wondered about that I may as well ask here.

    Why is the Speed of Light the speed of light?
  3.  (10075.9)
    i want to believe that the chinese people are angry about the train crash cover up because its REALLY covering up some bizarre time travel horror.
  4.  (10075.10)
    @oddcult - the flip answer... "because that's how fast light goes."

    I don't remember my semester as a chemistry student well enough to break down e=mc^2 for you, but that's a big part. I'm sure someone will be more than happy to correct my sleep deprived, worked all day brain, but c is the universal constant, which is also the speed of light. If it wasn't that speed (in a vacuum) then the math behind pretty much all of Einsteinian physics wouldn't work. Which means that the laws of physics would literally be different. So the more sophisticated answer is "because that's how fast light goes."
    • CommentAuthorOddcult
    • CommentTimeJul 26th 2011
    Okay, but what I really mean, I suppose, is; why is that the sweet spot at which energy propels mass? Why can't you just add a bit more energy and deal with a bit more mass? I mean... to use a crap analogy, sticking a turbo on a car makes it go faster, or a bigger engine, or a richer fuel, but there's a point at which aerodynamics and weight mean there's nothing more to add that will help it go faster and not slow it down instead. What's happening either to light or photons that mean that C is that point?
  5.  (10075.12)
    I have no scientific background at all, as you know, but this is what I understand:

    Photons are massless. C, the speed of light, is the limit because a hair over C would require an infinite amount of energy to drive it. C is therefore the available energy in the universe working against the properties of vacuum. That's basically the best you can do with one massless photon.

    "Why can't you just add a bit more energy and deal with a bit more mass?"

    The curves involved are asymptotic. And you can't carve more mass off something classically massless.

    Also consider: in a certain sense, C is also the velocity of time.

    I am probably wrong about all of this.
    • CommentAuthorOddcult
    • CommentTimeJul 26th 2011
    Okay, understood, but surely the E=MC2 equation works backwards as well? A photon at the speed of light has, or is, energy, so therefore that's it's equivalent mass?

    If photons didn't move, then you'd get a zero sum in the equation, sure, but as far as I'm aware they can't not move, and so therefore must have some kind of mass.

    I am also probably wrong and going on a basic understanding of simple equations rather than advanced physics.

    The issue I'm curious about is that photons move at the speed of light without anything close to an infinite amount of energy, because there are lots of photons and there seems to be a vast difference between the energy that's required to power a simple torch, the filament of which gives of photons at the speed of light, and all of the energy in the universe ever. That's what I can't get my head around.
  6.  (10075.14)
    Okay, how about this: the properties of vacuum allow a photon to move at C. For it to move faster, you'd have to change the properties of vacuum. Changing anything else wouldn't do it, because it still has to move through vacuum, and right now nobody knows how you'd have to change hard vacuum to make light travel through it faster. Does that help?
    • CommentAuthorOddcult
    • CommentTimeJul 26th 2011
    Yeah, I get that bit of it, I'm just amazed at the difference in the amount of energy it would take to move the photon that bit faster, when barely takes anything to get it there in the first place.

    Vaccum is by definition, frictionless and resistance-less though, so changing that can't be done, sure, but I can't help thinking along the lines of travelators or firing guns from aircraft, or all of the simple things that add velocity to movement. Why isn't a light shone from a spacecraft travelling faster than from one at rest, as you'd have added the energy then? The light is C from both, but one is (let's say) 1/2 C. So why don't the photons from the spacecraft at 1/2C travelling at C+1/2C when the energy requirements for this are present? If we're just talking about the properties of vacuum, then this means a resistance free state, so it comes back down to propellant, surely?

    There probably is a simple answer to this and I'm missing something obvious, of course.
  7.  (10075.16)
    You're missing the concept of relative speed. Someone explain that while I go out drinking.
  8.  (10075.17)
    Well, maybe the photon is moving instantly, and so time doesn't happen to it, and the speed of light is just where the clock has stopped on the rest of us when you point at it in another location, in other words the photon's journey is a line that doesn't have time in it, but can't prevent the universe from aging

    If it makes me feel better, that's sciencey enough
    • CommentTimeJul 26th 2011
    Saying photons can't go faster than light is a tautology. Photons are light, or rather, light is photons. A = A.
    • CommentTimeJul 26th 2011
    I just want to derail this serious conversation to interject that all we would need to do is capture a TARDIS. Ok, continue.
  9.  (10075.20)
    Yeah, I don't trust most governments... particularly the PRC. And I seem to remember a very well respected "theoretical physicist" saying on the Science Channel that the phenomenon could be possible via bent space, not more-than light speed. He was folding a piece of paper with two points marked on it, saying that time travel is completely possible if space could be bent. Which is where black holes and the string theory and all the rest come into play.

    I think.