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The Proton Is Lighter Than We Thought (sciencemag.org)

Posted by BeauHD on from the weight-loss dept.

sciencehabit writes from a report via Science Magazine: You can't weigh the universe's smallest particles on a bathroom scale. But in a clever new experiment, physicists have found one such particle -- the proton -- is lighter than previously thought. The researchers found the mass to be 1.007276466583 atomic mass units. That's roughly 30 billionths of a percent lower than the average value from past experiments -- a seemingly tiny difference that is actually significant by three standard deviations. The result both creates and clears up mysteries, and could help explain the universe as we know it. The findings have been published in the journal Physical Review Letters.

8 of 143 comments (clear)

  1. No difference by Anonymous Coward · · Score: 2, Interesting

    Standard model doesn't cover gravity so a change in mass means fuck all. Last I remember it couldn't even explain why neutrinos have mass.

    But then what is mass, what actually happens when mass turns to photons? What is energy in photons different from kinetic energy in particles? Why does light travel at C in a vacuum. What's special about C? Even before we get onto the train wreck that is QM.

    1. Re:No difference by Anonymous Coward · · Score: 5, Interesting

      The mass is important. Even in something like the energy levels in hydrogen. The mass of the nucleus is used to calculate the so-called reduced mass of the electron. If a sample of pure protonic hydrogen is used, that means that one is using the mass of a proton in the formula. Although at 30 billionths of a percent difference, I'm guessing the difference can't be seen in spectral lines.

      Mass isn't only used for gravitational effects. It determines the inertia of bodies, so this can conceivably affect coupling constants, depending on how they are defined. Also, in electroweak theory, using the mechanism of spontaneous symmetry breaking, coupling constants are introduced to generate particle masses.

    2. Re:No difference by hord · · Score: 5, Interesting

      The mass doesn't turn into anything. It just turns into photons (or other particles). The photons themselves are energetic disturbances in the electro-magnetic field which carry a momentum. Think of a long, stretchy, string and the photon is just a ripple on it. Does the ripple have mass? It's just a part of the string! But if you touch the string, you'll feel the ripple moving through because the momentum interacts with you and it feels like something is there.

      The speed of light is the same as the speed of sound. What limits sounds waves traveling through a medium? It's governed by the rate at which the particles in the medium can interact. The speed of light is simply the limit at which information can travel through quantum fluctuations. It's not really the speed of light, it's the speed of information propagation, of which light is a very simple example. If it were infinite, all events would be simultaneous. Anything less than infinite allows for units of time and causal order regardless of the overall rate of change because it will now take a non-zero amount of time to move through any given space.

      At least that's how I think about these things...

    3. Re: No difference by Anonymous Coward · · Score: 2, Interesting

      "At least that's how I think about these things..."

      You're thinking well. Yet the question remains, why isn't c faster (*) ? The real fundamental reasons still escape our understanding.

      (*) On the grand scale of things, c is really very, very slow.

  2. Occam's Razor by Anonymous Coward · · Score: 2, Interesting

    The actual value is -
    Just take a value that clears up the most mysteries.
    (cheaper than building another damn super-collider)

  3. Three standard deviations? by Cacadril · · Score: 4, Interesting

    Googling CODATA values:
    proton mass = 1.672 621 898 (21) x 10^-27 kg
    Atomic mass unit = 1.660 539 040 (20) x 10^-27 kg
    Releative standard deviations: 1.25 x 10^-8

    Ratio of codata values: 1.007 276 467 285 (i.e., codata proton mass in terms of atomic units)
    New measurement: 1.007 276 466 583
    Difference: 7.0198469259707963 x 10^-10
    Relative difference: 6.9691362341583399 x 10^-10

    How is this three standard deviations?

    --
    There is no substitute for common sense. Especially, no body of rules will do.
  4. Distance / ?? by Tenebrousedge · · Score: 4, Interesting

    If you think of speed as distance per unit of time, then you could view that as the photon not having any speed at all, since it does not experience time. `c` is not special at all, it just happens to be the speed at which certain massless effects propagate in the universe. It's a limiting condition, sort of inherent to the idea that space and time can be traversed. You might also think of it as the "clock rate" of the universe.

    --
    Those who advocate genocide deserve every protection afforded by law, and none afforded by common human decency.
  5. Re:Frustration by Anonymous Coward · · Score: 4, Interesting

    Perhaps you'd like to read the preprint on the arXiv: https://arxiv.org/abs/1706.06780

    Journals are lousy at publishing confirmation papers, and they have to try to publish important papers because they get academic exposure, and allow the journal to be relevant.

    Well, given that we're talking about PRL, it is perfectly fine at publishing confirmation papers. In general, it will not publish:

    1. Measurements with an uncertainty that is significantly worse than the leading work in the field. Because that's not a confirmation - it's a nothing. It might make an exception if it's a first result from a completely different technique or something.

    2. Marginal incremental updates of relatively mundane parameters. Yes, if you have a ten-year-long experiment, you probably want to publish an updated result every year or two. Unless you're the world leader and you're measuring a very interesting number, don't expect to get your annual "we made the statistical error a bit smaller" paper in to PRL.