Slashdot Mirror
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.
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.
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.
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.
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.
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.