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Speed of Light Inconstant?

Posted by michael on from the still-can-count-on-death-and-taxes dept.

DHR writes "Australian scientists have discovered that light isn't quite as fast as it used to be." We've done previous stories on these findings. Those of you with subscriptions to Nature can read the actual paper, the rest of us will just have to suffer.

11 of 496 comments (clear)

  1. Entropy and the collapsing universe theory. by GodInHell · · Score: 3, Interesting

    Would this perhaps be linked to the idea that there's a limited amount of energy in the universe, which is more and more being turned into kinnetic potential as objects get further and further from the center point?

    Or perhaps we're just setting aside another 'unbreakable' barrier.

    -GiH

  2. E=mc^2? by InsaneCats · · Score: 2, Interesting

    So if the speed of light is slowing down, could we convert matter to energy, wait millions of years for the speed of light to change, and then convert it back - violating the conservation of energy laws?

    1. Re:E=mc^2? by rknop · · Score: 3, Interesting

      So if the speed of light is slowing down, could we convert matter to energy, wait millions of years for the speed of light to change, and then convert it back - violating the conservation of energy laws?

      Good question, but I would think probably not. E=mc^2 doesn't really tell you about some remarkable physical process that lets you convert between two differen things "mass" and "energy". Mass is just another form of energy, and that equation tells you how much energy you have in (say) one kilogram of mass.

      I'd have to think harder whether or not there is a problem with conservation of energy here. Here's the challenge: come up with a thought experiment that lets you get "something for nothing" from a changing speed of light. Just counting the energy in the universe isn't good enough (see below); what you need is some way of increasing (say) the stored energy in a localized object or particle *without* introducing any energy or work from outside. I can't think of a way to do it, but maybe somebody else might. (I haven't really posed my thought experiment well; can somebody suggest a better way to pose it?)

      The reason that just talking about the total energy in the universe isn't good enough is that in fact General Relativity already does *not* have a global law of conservation of energy! There is a *local* conservation of energy, which is expressed in terms of derivatives of the stress-energy tensor. However, the fact that there is no single global inertial reference frame for the whole universe makes it difficult to say what is the "energy of the universe".

      You can come up with things that look like they violate conservation of energy with plain vanilla GR and cosmology right now. For instance, the cosmological redshift. Start with a universe that has one photon in it. The universe expands, and the photon redshifts. Now the photon has less energy. What happened to conservation of energy? Similarly, if you have a cosmological constant (vacuum energy), and your universe gets bigger, you have more vacuum, thus more energy. What happened to the conservation of energy? With an infinite universe you can always say that you're pushing work out to further and further reaches of the universe, and since you never reach an "edge" you don't have to worry about somebody ever having to absorb all that work. (With a closed universe, I believe that formally some of the energy goes into the curvature.) But, really, conservation of energy is a local concept in a GR rather than a universe-wide concept.

      -Rob

  3. Warp Speed [was Re:ObTrek Reference] by Heraklit · · Score: 2, Interesting
    Not necessarily... depends on the frame of reference, whether the Klingons or the Romulans are watching. But did you know that physicists are actually working on a warp drive (at least theoretically)? :-)

    Even constantly improving the model!

  4. Possibilities? by yeoua · · Score: 5, Interesting

    One possibility, though, is that the structure of the vacuum in space has changed. This is where we get into the rather spooky world of quantum physics. When light travels through a medium other than a vacuum, such as glass or water, it slows down. A vacuum, far from being empty, is teeming with quantum "virtual" particles that flit in and out of existence.

    Sometimes those particles become real, such as under a strong electric charge, Lineweaver says. If the vacuum of space is changing uniformly across the universe, just as the universe is expanding uniformly, it could affect the speed of light.

    Well... this was the hypothesis that was given in the article... and from the looks of this, it seems that there is a possibility that light didn't slow down at all. Here he explains that it is the medium that light is travelling in that is slowing it down. So light's top speed in a vacuum may still be the same... c, but the medium, the universe, is changing. Who knows.

    But if light is slowing down, then that faster than light travel maybe possible. However, how the hell do you see anything when your going faster than any signal? Well... maybe you can communicate with the spooky particles and get instant communication while travelling at faster than light speeds. Of course you'd best be sure your data arrived promptly, as you'll never see the planet you just rammed.

  5. Dr. Walt Brown agrees with the idea by danpbrowning · · Score: 3, Interesting

    This is exactly the case put forward by Dr. Walt Brown (Ph. D.).

    --
    Daniel
  6. Re:Makes no sense. by Anonymous Coward · · Score: 1, Interesting

    as far as I can tell, in the case where the
    elastic modulus of a medium is essentially
    infinite, elastic waves propagate at an
    essentially infinite rate.

    So the speed of sound is practically the same
    as the speed of light in the perfectly elastic
    gob that was the ur-universe.

  7. Why is entropy untouchable? by dark-nl · · Score: 2, Interesting

    The second law of thermodynamics is just a statistical consequence of more fundamental laws of physics. I don't see why breaking it is automatically "illegal", while messing with the speed of light is fair game. You get temporal paradoxes if the speed of light is not the same everywhere[1], and that bothers me far more than cups of coffee getting hotter.

    [1] General relativity rules out the concept of "everywhere at the same time", so if the speed of light changes, it can't change uniformly, because there's no uniform.

  8. Re:Independent analysis by Anonymous Coward · · Score: 1, Interesting
    It's that same group saying the same thing again. Although I haven't reviewed their latest paper, I remember that I wasn't impressed with the statistical analysis of their data, as of the previous paper.

    Why should we care what someone with a hotmail account, a geocities web page, and a journal ranting about the moderation system thinks about this? You're probably fifteen.

  9. Re:Independent analysis by God!+Awful · · Score: 3, Interesting


    It's that same group saying the same thing again.
    Well, you are the same guy posting the same thing again, although I notice you have a different username than last time. Please tell me you didn't honestly go back to the previous story, pick a random message that got modded up to +5, and repost it here... that would be the ultimate in karma whoring.

    -a

    --
    How to rationalize theft.
  10. Creationist have been saying this since the 80's.. by Anonymous Coward · · Score: 1, Interesting

    ... but since they believe in creation, and not the dogma of darwinian evolution(which still can't explain the consistant, SUDDEN appearance of species throughout the fossil record), they're not taken seriously.

    If light is slowing down, then I'd wager money that other "constants" are too.