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Science

The Proton Is Lighter Than We Thought (sciencemag.org) 143

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.
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The Proton Is Lighter Than We Thought

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  • Heavy news! (Score:5, Funny)

    by pahles ( 701275 ) on Friday July 21, 2017 @02:03AM (#54850987)
    Don't take it lightly!
  • by Anonymous Coward

    Sounds like one of the programmers decided to slightly tweak one of the global constants on our program perhaps to make it possible to build a really cool hyperspace wormhole ride.

  • by NoNonAlphaCharsHere ( 2201864 ) on Friday July 21, 2017 @02:28AM (#54851031)
    That's just astonishing. Get the Nobel committee on the phone. It'll be interesting to see what tweaks to the Standard Model come about as a result of this -- one of its 72 unexplained empirical "constants" has suddenly been (drastically) updated.
    • No difference (Score:2, Interesting)

      by Anonymous Coward

      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.

      • Re:No difference (Score:5, Interesting)

        by Anonymous Coward on Friday July 21, 2017 @05:20AM (#54851369)

        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.

      • Re:No difference (Score:5, Interesting)

        by hord ( 5016115 ) <jhord@carbon.cc> on Friday July 21, 2017 @08:06AM (#54851697)

        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...

        • Re: No difference (Score:2, Interesting)

          by Anonymous Coward

          "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.

          • Re: No difference (Score:5, Insightful)

            by slack_justyb ( 862874 ) on Friday July 21, 2017 @10:43AM (#54852437)

            Yet the question remains, why isn't c faster

            Well there's some that say physical constants have the value that they have because we happen to live in a universe where that is the value. In other words, it could be that the values of constants c (speed of light), G (gravitational constant), h (Planck's constant), and so on are just random values. It just happens that you exist to ask the question with the values c, G, h, and so on being what they are.

            A good parallel would be "Why are we the third planet?" Why couldn't there have been some extra planet in between Venus and Earth, and thus make us the forth planet/Venus not exist and Earth be the second planet? The answer is, there's nothing that "forced" Earth to be the third planet, it's just how things lined up. As we've studied exoplanets we've come to understand that being the "third" planet isn't related to being in the habitable zone. Some stars have their first planet within the habitable zone, some don't. Three just isn't some magical number that assures you'll land in the habitable zone of a star.

            But the real answer to, "Why the constants are what they are" is, "We just don't know for sure". We're not at that point and while there are some ideas out there that try to explain it, none of them have been shown to be demonstrably correct. That's not to say they are incorrect, just that they're still at best an educated guess and we lack the ability to really be able to test some of them. One day that may change, but it could be that none of us are currently living in an era where humanity will be able to reach any conclusive answer on those questions. I'm okay with that, because I can only imagine how absolutely frustrated Newton was with being unable to explain Venus' orbit then having to die never knowing the answer.

            However, I'll say this, even if the values of constants are randomly chosen at Big Bang for a universe, it still means that order comes from those selected values and that, that order is observable and can be modeled. Just because the Standard Model has gaps doesn't mean it lacks value. The periodic chart had gaps in its early days too, but it gave us insight into what we knew and where to look for the gaps that did exist. The Standard Model in it's current form came about mid-1970s and since then it's had amazing predictive power. Heck I distinctly remember when the first top quark was discovered in 1995 and that was massive because up till then it was just this particle that we assumed existed on paper. So it might be tempting to shout this is a train wreck because it lacks so much, but it is the model we have right now and the model we have has shown to be demonstrably correct. Trying to forward models that we just don't have the ability to test to anything within the domain of "fact" or "scientifically accurate" makes science no better than people who think the universe began by a cosmic unicorn fart. I think people get angry at that notion that "look here's a model that explains way much more! Forward it as fact and I can at least die knowing that I knew everything." We have to move at the pace we're currently at and any faster we might as well just stick a religion flag in it. So yeah, there's holes in our understanding of the Universe, but that doesn't mean what we have is a "train wreck" and it should not tempt us to adopt models that haven't been shown to be correct "string theory".

        • by Tablizer ( 95088 )

          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.

          "String theory" is already taken ;-)

      • Distance / ?? (Score:5, Interesting)

        by Tenebrousedge ( 1226584 ) <tenebrousedge AT gmail DOT com> on Friday July 21, 2017 @10:37AM (#54852391)

        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.

      • Standard model doesn't cover gravity

        Right. I don't think the theory of evolution does much with it either. A theory or model will cover certain things and not other.

        Last I remember it couldn't even explain why neutrinos have mass.

        Neutrinos change type over distance, which means that they aren't going at C (if they were, it would always be "now", and there would be no time for any change to occur). They do have momentum. Hence, they have mass. If you're looking for why any part of the Standard Model

        • by lgw ( 121541 )

          They do have momentum. Hence, they have mass

          That's backwards. Everything with mass has momentum when it moves, but most things that have momentum are massless particles.

          • Sure, but massless particles travel at C, and anything else that has momentum has mass.

            • by lgw ( 121541 )

              You know, I'm not sure that's strictly true, but a counter-example doesn't spring to mind. Anyhow, my point was that it's better to think of energy, not mass, as the source of gravity, momentum, and so on. It's only for historical/traditional reasons that we would think of energy as "having mass", rather than the more useful idea of mass as "a kind of energy".

      • lol...Mass exists independent from gravity!
      • > Standard model doesn't cover gravity ... it couldn't even explain why neutrinos have mass.

        It also doesn't cover consciousness.

        It is a woefully incomplete model.

  • by Anonymous Coward on Friday July 21, 2017 @02:39AM (#54851047)

    "You can't weigh the universe's smallest particles on a bathroom scale"
    Of course you can, duh. You get a bucket full of them (say, 10 trillion), weigh it on the bathroom scale then subtract the weight of the bucket and divide what's left by 10 trillion. Voila, the weight of 1 proton. Silly scientists, do I have to think of everything?
    OTOH, weighing a labrador who doesn't want to stand still on the bathroom scale - now, that's the REAL Nobel-worthy challenge.

    • by aliquis ( 678370 )

      OTOH, weighing a labrador who doesn't want to stand still on the bathroom scale - now, that's the REAL Nobel-worthy challenge.

      Ask the Chinese!
      They seem to be doing very well with solving the worlds problems these days!

      • by abies ( 607076 )

        OTOH, weighing a labrador who doesn't want to stand still on the bathroom scale - now, that's the REAL Nobel-worthy challenge.

        Ask the Chinese![...]

        We are talking about live labrador, not one being prepared for dinner...

    • Re:They're wrong (Score:4, Insightful)

      by ShanghaiBill ( 739463 ) on Friday July 21, 2017 @04:10AM (#54851241)

      You get a bucket full of them (say, 10 trillion), weigh it on the bathroom scale ...

      10 trillion protons would weigh a few picograms. You will need about 10 quadrillion picograms to fill a bucket.

      Even then, the protons would be contaminated with electrons, gluons, neutrons, etc. It will be much harder to fill a bucket with pure protons.

      • by quenda ( 644621 )

        It will be much harder to fill a bucket with pure protons.

        Given their mutual repulsion, I'd say getting even a picogram of pure protons into a sealed bucket will be quite a challenge.
        Even Dr. Egon Spengler never achieved it.

      • Even then, the protons would be contaminated with electrons, gluons, neutrons, etc. It will be much harder to fill a bucket with pure protons.

        I was going to mod this funny, but then I thought "No, nobody will understand the joke..." Much harder, snort mrrf, har har har.

      • Aren't the gluons part of the protons?

    • You get a bucket full of them (say, 10 trillion), weigh it on the bathroom scale then subtract the weight of the bucket and divide what's left by 10 trillion. Voila, the weight of 1 proton.

      A bathroom scale is only accurate at several kg+, and a kilo of protons is closer to 10 trillion buckets of 10 trillion protons each. The hard part is counting them.

    • Weigh yourself, then weigh yourself holding the dog. Can i have my nobel prize now?

    • You just need to feed it enough protons. Trust me, it won't move when its belly's full.

    • by idji ( 984038 )
      1.Weight yourself.
      2.Pick up your dog.
      3.Weigh yourself and the dog.
      4.Profit
    • Would the weight of the Labrador help solve the mysteries of the universe?
  • by Anonymous Coward

    From now on the proton cancer treatments will be 30 billionths of a percent cheaper! And the future proton rifles 30 billionths of a percent lighter.

  • systemic error (Score:5, Insightful)

    by Anonymous Coward on Friday July 21, 2017 @03:11AM (#54851145)

    In physics, we're limited by our environment. I've seen ridiculous things like the sprinklers coming on disrupt gravity constant measurements. Air conditioning, doors opening and closing, trains running a block away... there are so many things that can screw up these kinds of measurements.

    A precise measurement is not the same thing as an accurate measurement. These guys went to great lengths to be as accurate as possible, but in situations like this, it's not reasonable to try to use a single apparatus to definitively contradict what people have measured for the last 5-10 years.

    So... the mass of the proton isn't changing (by this honestly insignificant amount) until a couple of other groups independently verify this measurement.

    • That's exactly what the last paragraph is about, and the researchers want to have other group try to reproduce it.

      Problem is that if this is the only technique that is capable of this level of accuracy and/or precision, then other groups reproducing the result using the same measurement technique will improve the precision of the value (by making the same measurement many times) but not necessarily improve the accuracy. If there's an inherent bias in the method leading to the different answer then it will b

      • Re: systemic error (Score:4, Insightful)

        by Kjella ( 173770 ) on Friday July 21, 2017 @09:03AM (#54851899) Homepage

        You are talking about two different things, a disturbance in the environment can be tested by trying in another environment. If the flaw is inherent to the technique that's a different problem, but then at least you have two studies coming to the same result. That's a much stronger result than one experiment, which could be flawed in a million ways you can't even imagine. Even if it's wrong, knowing that the experiments must share a common flaw narrows down the search immensely.

        • Agreed that environmental variability gets washed out when someone else does it. My issue is that any bias in the experiment by design gets repeated as well. So if they come to the same result, you're still left with the question of whether this method is simply more precise but biased, or actually more accurate and the old method was biased.

          Another way of saying it is that we should be concerned that the new result is not within error of the old result. One possibility is that there was a bias in the old m

  • Great news! How's the photon doing?

  • Occam's Razor (Score:2, Interesting)

    by Anonymous Coward

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

  • by Cacadril ( 866218 ) on Friday July 21, 2017 @08:20AM (#54851743)
    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?
    • by Shimbo ( 100005 )

      How is this three standard deviations?

      It is if you believe their stated accuracy as it's much higher than previous work.

    • Re: (Score:2, Insightful)

      by Anonymous Coward

      Because the big uncertainties you quote on the CODATA 2014 proton mass and amu are 100% correlated - they're the uncertainty on the kilogram.

      The CODATA 2014 uncertainty on the ratio of the proton mass to the amu is much smaller - look at figure 5 in the PRL.

      • Thanks, that resolves it. Of course, comparing a proton to a carbon atom is very different from comparing it to a kilogram prototype.I failed to google and find a codata value for m_p/amu (mass of proton/atomic mass unit), and I did not think deeper about the uncertainty in the kg prototype.

        Now the computation becomes p_m(codata) minus p_m(new measurement), compared to uncertainty in p_m(codata).
        The difference is 296 x 10^-12,
        the uncertainty is 91 x 10^-12,
        the ratio 296/91 = 3.25.
        The new value is more

  • Was it Russian or American proton?

  • Does this mean all of my Periodic Tables are wrong???
    • by Tablizer ( 95088 )

      Does this mean all of my Periodic Tables are wrong?

      Yip, they are no longer "periodic". You can throw it out with your old Solar System model that had Pluto as a planet. (It doesn't balance right if you just tear off one ex-planet.) When Planet 9 is discovered, you'll need a new one again.

      Physics is becoming like web dev stacks: you have to replace them every 4 years to keep up with the Joneses.

  • Proton packs now lighter.

  • You know, cutting down on carbs, drinking water, a little exercise? That'll make a difference....

  • don't worry (Score:5, Insightful)

    by slashmydots ( 2189826 ) on Friday July 21, 2017 @11:49AM (#54852843)
    But don't worry, they've got the estimate of mass in the universe 100% flawlessly calculated based on observations and dark matter is totally real and not a math mistake.
    • Observed mass would have increase by an order of magnitude to eliminate the calculated "missing mass". This change is 13.5 orders of magnitude smaller than that.

  • Still costs the same, though.

    I blame that metric system. Toilet rolls, 68p for two. That's over a pound each in the old money.

  • by Verdatum ( 1257828 ) on Friday July 21, 2017 @12:29PM (#54853155)
    This is one of the most interesting things I've heard in quite awhile. I'm interested in learning more about this, but when I look into tracking down the primary-source, peer-reviewed publication [aps.org], I am dismayed to find that it would cost $25 to read it. I understand that running a science journal costs money, and I'd be happy to pay a fee to read something like this. I understand that most physics journal publications have a limited audience, and I understand that professional physicists are generally tied to an entity such as a university or laboratory that provide them with a costly-but-worthwhile subscription service, meaning they don't need to purchase papers a la carte. Still, I am confused by this pricing model. I feel as though one would generate far more revenue by lowering the cost for a single article. The actual cost per download, obviously, is so low as to be immeasurable. So the only thing defining the price charged per download is that it needs to cost more to purchase more than a handful of articles than it does to subscribe, thus incentivizing subscriptions. So I looked into it: depending on the state of your academic career, this translates to $85 for undergrad students to $213 for established professionals per year. This gets you 51 issues, containing around 7 featured "editor's picks" papers each. That means, in the most expensive group, it's presuming that you are only going to find actual interest and satisfaction out of 213/25 = 8.5 papers a year. Now technically, the subscription is only $60, the rest is cost for membership in the American Physical Society. If you go by that number, then it's implying that you're going to get significant interest out of around 2 papers a year. These numbers just do not make any sense to me.

    I understand that there's a good chance that I'm able to access this source for free though one of my state's local libraries, and that's wonderful. I tried and failed to access it through one library card. I still feel as though more this entity would generate more net revenue and have the side effect of more people able to speak intelligently on the subject if the cost of a single paper was $2-$5 each.

    In writing out this frustration, I think I'm beginning to understand, and I'm wondering if I might have a possible solution. I believe the average paper out of a scolarly journal produces effectively zero interest from the general public. They are too niche or too complicated or the findings are too unsurprising. For these papers, it doesn't matter if it costs $25 dollars or if it costs $1, you're still selling about the same number of copies. So it makes sense to charge the higher price. Every month or so, a decent journal such as this manages to publish an article that some science-news entity thinks is interesting enough to post a writeup. Every few months, they publish something that interests a number of science-writers, and manages to hit the slashdot level of interest. Once or twice a year, they publish something that gets mainstream attention and shows up on the level of something like SciShow (one of the few entities that makes science friendly and digestible, but also fact-checks and doesn't constantly get details plain wrong like so many other pop-sci media sources). The lower pricing would only make sense on those higher tiers, where greater demand for the original paper is generated. So now I'm wondering, why don't journals re-actively price accordingly? When a paper gets wider attention, slash the price. I suppose the response to this is that this isn't done for fear of it generating bias in publication selection. And I get that; greed is the enemy of integrity; it's why MTV stopped playing music videos long before the days where we could just stream them, it's why History channel and Discovery Networks bailed on quality educational programming. You don't want your academic journals vying to go viral; so you isolate yourself from that business. But in rea

    • Re:Frustration (Score:4, Interesting)

      by Anonymous Coward on Friday July 21, 2017 @01:03PM (#54853389)

      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.

    • Speaking as someone who has written several dozen scientific papers and has gone through this process many times, the journal system has become something of a racket.

      In an age before computers, they used to have to type set your submitted articles. This involved often retyping the manuscript and physical cutting the text to fit within the scope as needed. This was time consuming and the cost of the journal was real. (this was before my time admittedly.) Since no digital data bases existed, there was also
  • Typing out 1.007276466583 is going to be a real pain. Lets just say an amu is the weight of a proton and not 1/12 the weight of carbon or 1/16 of oxygen.

    https://en.wikipedia.org/wiki/... [wikipedia.org]

    • It's easier for labs to accurately weigh out carbon or oxygen than it is for them to weigh out a proton. You want standards that are easy for others to reproduce, not standards based on an brand new experiment.

  • Wouldn't a change in our understanding a proton's mass also impact our theories about potential proton decay?
    (I hope they don't decay, and we mostly think they don't but we're not totally sure)

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