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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.

2 of 496 comments (clear)

  1. I actually read the paper... by Peter+T+Ermit · · Score: 5, Informative
    ... and it adds absolutely nothing to the argument over whether there are time-changing constants.

    As other people have pointed out, the fine-structure-constant-is-changing work came out a year ago. The fine structure constant is a function of the speed of light, c, and the charge of the electron, e.

    This particular article argues that e can't change much over time without causing inconsistencies, so they conclude that c must have been changing. No new data, no new support for the constant-is-changing theory. (And the original study was pretty damn flawed. This paper isn't bad.)

  2. Re:questions by Peter+T+Ermit · · Score: 3, Informative
    You shouldn't take popular press versions of science papers literally; often the reporter has no more understanding of physics than you do. That being said...

    The discovery means faster-than-light travel, which is prohibited by the law of relativity, may one day be possible.
    I think this is an error on the reporter's part. I don't see how this is at all related to the paper, unless the reporter thinks: "Speed of light changing therefore Einstein was wrong... Einstein was wrong, therefore we can travel faster than light."

    If the speed of light was close to infinity, immediately after the Big Bang,
    Again, a problem with the reporter here. "Close to infinity" means nothing. What this probably means is that the further back you travel in time, the bigger the speed of light was, and as you approach the Big Bang, the speed of light goes off to infinity. A physicist would say that the speed of light diverges, rather than saying it gets close to infinity.

    The photons [...] interact with the electrons in the gas clouds, charged particles that orbit the nuclei of the metal atoms. This leaves a fingerprint on the light as it arrives on Earth, called the fine structure constant, Murphy explains.
    This is actually close to correct, though it's misleading. The fine structure constant equals 2(pi)e^2/hc (if I recall correctly) where e is the charge of the electron, h is the Planck constant, and c is the speed of light. The value of that constant is related to the electromagnetic force, which, in turn, affects the spacing of the lines in an element's spectrum. Conversely, by looking at the spacing of the lines in elements' spectra, you can figure out the fine structure constant.