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The Proton Is Lighter Than We Thought (sciencemag.org)
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.
Don't take it lightly!
Sig?
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.
"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.
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.
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.
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...
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.
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.
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".
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.
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.