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Mystery of the Shrunken Proton 171

ananyo writes "The proton, a fundamental constituent of the atomic nucleus, seems to be smaller than was previously thought. And despite three years of careful analysis and reanalysis of numerous experiments, nobody can figure out why. An new experiment published in Science only deepens the mystery. The proton's problems started in 2010, when research using hydrogen made with muons seemed to show that the particle was 4% smaller than originally thought. The measurement, published in Nature, differed from those obtained by two other methods by 4%, or 0.03 femtometers. That's a tiny amount but is still significantly larger than the error bars on either of the other measurements. The latest experiment also used muonic hydrogen, but probed a different set of energy levels in the atom. It yielded the same result as the Nature paper — a proton radius of 0.84 fm — but is still in disagreement with the earlier two measurements. So what's the problem? There could be a problem with the models used to estimate the proton size from the measurements, but so far, none has been identified. The unlikely but tantalizing alternative is that this is a hint of new physics."
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Mystery of the Shrunken Proton

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  • by whoda ( 569082 ) on Friday January 25, 2013 @11:40AM (#42691107) Homepage

    It's old physics that we haven't figured out yet, but thought we had.

  • Re:easy (Score:5, Insightful)

    by Anonymous Coward on Friday January 25, 2013 @11:47AM (#42691191)

    uh sure, if the prior method for measuring was also showing the reduced size, but it's not ... so how does "the universe expanding" explain two simultaneously different measurements? besides, if the universe were expanding and protons weren't, i don't think our meter sticks would be expanding.

    how the hell did this get +5 anyway ... brainless mods

  • Re:easy (Score:5, Insightful)

    by mrsquid0 ( 1335303 ) on Friday January 25, 2013 @12:10PM (#42691493) Homepage

    It does not work that way. Things like metre sticks are held together by the electromagnetic force, which is decoupled from the expansion of the Universe. This means that objects in the Universe do not expand, they just move along with the expansion. If everything in the Universe expanded with the Hubble flow then we would never be able to detect the Hubble flow. Only spacetime expands, not what is sitting around in spacetime.

    The explanation for the unexpected small size of the proton is probably something to do with the way that muons interact with protons. We assume that electrons and muons interact with protons in exactly the same way, but this is a hypothesis. There is very little observational evidence supporting the idea that electrons and muons behave in exactly the same way when they are bound to an atomic nucleus. The problem with this idea is that it requires that particle physics be extended beyond the standard model. It is also possible that the problem is something much more mundane, like a faulty connection somewhere in the experimental setup. We need an independent verification of this result before we start rewriting the textbooks.

  • by jalvarez13 ( 1321457 ) on Friday January 25, 2013 @12:28PM (#42691821)

    It reminds me of the Michelson-Morley experiment. Back then no one understood why an experiment that should have given different results for the speed of a ray of light failed to do so. As we know today, the constant speed of light is the basis for Einstein's relativity theory and has been proved right many times.

    Could this be one of those moments?

  • Re:Global warming (Score:4, Insightful)

    by FatdogHaiku ( 978357 ) on Friday January 25, 2013 @02:05PM (#42693049)
    You'd shrink too... it's cold out there in the aether.
    Well, that's what he's telling the other particles...
  • Re:easy (Score:5, Insightful)

    by rasmusbr ( 2186518 ) on Friday January 25, 2013 @02:31PM (#42693397)

    how the hell did this get +5 anyway ... brainless mods

    Anyone's who's read an amateur physics forum knows that the expanding scale universe "model" is reinvented several times a year by isolated eager guys armed with high school diplomas, apocryphal tales about Einstein and quotes by Galileo. It's one of those ideas that seem obviously true for several seconds until you actually think about it.

    Here's a tip: The age of simple discoveries in mature sciences is over. That's why they're called mature. Unless you've spent years studying physics intensely while getting frequent feedback from experienced physicists, your chances of making minor contributions to physics are infinitesimally close to zero. Any idea that you quickly stumble upon based on your high school or college Physics 101 understanding has literally been thought, tried and discarded a thousand times before by physicists.

Space is to place as eternity is to time. -- Joseph Joubert