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Proton-size puzzle deepens
- mabbo 9y agoCan someone who is more well-studied in physics tell me: what are the implications of this? Is it a curiosity, but of no practical matter? Or is it "Oh my god, a 4% smaller proton could mean cold fusion and jetpacks"?
- moomin 9y agoNo idea, but I find it amazingly cool that even today with our modern technology, we're finding there's more to be learned about the stuff of high-school physics.
- davrosthedalek 9y agoThe proton is very fundamental. Almost all of the visible matter around us is either protons or neutrons, and their mass is almost completely generated dynamically from QCD (forget Higgs). Its size and mass are cornerstones. Being able to calculate them from first principles would be an enormous achievement. For me, it's mainly interesting because two different fields of physics meet, nuclear physics (electron scattering) experiments, and atomic physics (spectroscopy). Otherwise, it's the same as with all basic science. We don't know what it is "good for" until somebody figures out how to cure cancer with it. The paper this article refers to is in particular interesting, because it finds a value not in agreement with earlier measurements of the /same/ type. The indicated 3.3 sigma shift in the Rydberg constant, one of the most exact measured quantities in existence, is a little bit worrying, but such shifts happen more often than they should.
- QAPereo 9y agoJust to add for GP’s benefit, QCD is monstrously complex, like electric charge x 3, which explains why the achievement would be so enormous.
- davrosthedalek 9y agoYeah, the real problem is that the theory is mostly non-perturbative, i.e. it's hard to phrase the theory as a power series. The underlying reason is that gluons can self-interact.
- jessriedel 9y agoNot just self-interact, but self-interact strongly. Photons can self-interact too, through intermediate charged particles, but do so much less often.
- QAPereo 9y agoTo be fair, the photon self-interaction is usually negligible (barring the right medium and high energies), while for gluons it’s most of the story. Unless you’re looking at exotic situations, photons are well behaved, but gluons are many flavors of pain.
- killjoywashere 9y agoI'm a physics major, and still in science 20 years later, cancer research. I originally came here to ask, in general, why would anyone care about this result? Since you asserted an answer to the question before I managed to ask, I'm happy to subordinate my question. But I will also suggest your specific answer, cure cancer, won't work. I need to kill cells, which requires a cascade of large molecules interacting at energies on the order of a fraction of an eV, or massive amounts of high energy radiation. I can kill cells directly with high energy radiation, however, the energies for this investigation, the hydrogen 2s-4p transition, (1,2) are trivial (486 nm is visible light). Also, radiotherapy isn't really good at interrogating cell type, the current standard for new cancer therapies (immunotherapy). (1) http://science.sciencemag.org/content/358/6359/79 http://science.sciencemag.org/content/358/6359/79 (2) https://indico.mitp.uni-mainz.de/event/14/contribution/11/material/slides/0.pdf https://indico.mitp.uni-mainz.de/event/14/contribution/11/ma...
- TheSpiceIsLife 9y agoI don't think the parent comment meant that literally. Sometimes we don't know what new knowledge will enable us to do until the PhDs, engineers, and technicians get their hands on it.
- miemo 9y agoIt's like finding out your friend since childhood is 3 years older than you always thought. People care because it's jarring that something so 'known' and basic might be different. And yeah the cancer part was more a 'holy grail' thing. replace it with 'cures poverty' and his point still stands
- eesmith 9y agoAs far as I can tell, on your axis it's a curiosity with no Mr. Fusion coming to a DeLorean near you. If the proton and muon sizes were different, then a bunch of physicists would be chomping away at being able to replace the Standard Model and get the Nobel Prize. As it stands, it looks like there's a question of why the old measurements were off, and that's about it.
- danbruc 9y agoIf the proton and muon sizes were different [...] They are different, in fact the muon is believed to be a point particle and not to have any internal structure like, for example, the proton. Nonetheless one can assign a non-zero radius to the muon in specific contexts due to its interaction with the vacuum.
- eesmith 9y agoI'm sorry, I completely misread that. It replaced the electron with a muon, not a proton with a muon. Thank you for your correction.
- mattheww 9y agoSo there's no obvious practical application (right now). Also, the proton is not 4% smaller. Protons are obviously whatever size they are. The discrepancy comes from the fact there are two techniques to measure the proton size. Both experiments do their thing and then there's a way to interpret the results that would tell you the size of the proton (look up proton form factors). However, when you do the interpretations, which depend on some theoretical calculations, you get different results. The general thinking around this result, because nobody has found any issue with the experimental results, is that there are some additional interactions that are stronger than expected that need to be accounted for (there are some unknown quantities that allow this). One of the interactions would only affect the muonic hydrogen measurement - basically there are some different interactions between muons and protons than between electrons and protons because of the muon's mass and those might be different than originally thought. The other is a type of interaction that could affect both normal and muonic hydrogen. This new measurement shows that the interactions that affect both has to play an important role in understanding this discrepancy. There are other measurements trying to measure this effect independently (not using hydrogen at all).
- andrepd 9y agoNo, the radius of the proton being smaller than previously thought does not directly lead to any technological developments. However... It does raise curious questions, namely what is it that we missed that lead us to believe the previous results. If the proton is indeed so much smaller, what is it that was skewing the results of the previous experiments? Perhaps this signals new physics and strange new effects. And that may eventually lead to cold fusion and jetpacs :)
- tim333 9y agoThe "Oh my god" is more that the laws of physics as we have them could be wrong. Might not mean much but experiments like Michelson–Morley not agreeing with the understandings of the time have had big effects.
- andy_ppp 9y agoSlightly off topic but I strongly recommend subscribing to this amazing YouTube channel: PBS Space Time. It'll give a bit of background and I've enjoyed learning it. https://youtu.be/z3rgl-_a5C0 https://youtu.be/z3rgl-_a5C0
- Koshkin 9y agoThe article keeps talking about "the size of the proton", its "radius", etc., but I would like to point out that the proton is not a sphere and does not, in fact, have a size in the normal sense, being an aggregate of three other particles; so in this case the notion of "size" itself must be defined in some pragmatic fashion before any meaningful statements about it can be made.
- SAI_Peregrinus 9y agoI feel it necessary to point out that the proton is only an aggregate of three other particles on average. It's three quarks, plus several gluons mediating interactions between the quarks, and lots of virtual quark-antiquark pairs.
- Koshkin 9y ago... and the muon that "spends more time inside the nucleus", according to the article. (You direct your sarcasm at an easy target; it is also too easy to turn a blind eye to all the glaring omissions and gross misrepresentations - i.e., effectively, lies - purposefully made in popular texts for the sake of making the material more "accessible" for the general reader.)
- davrosthedalek 9y agoWell, it's not so far off. Every time you "look", the wavefunction of the lepton collapses to a point. For the muon, that point is more often inside.
- ggm 9y agoIf the muon is 400x more massive, then is there not a f(400x) error rate, which has to be imputed to the radius of the proton, influenced by the significantly larger mass being made to act as an electron in orbit around it? Radius being understood to be somewhat metaphorical here.
- idlewords 9y agoI don't understand this question. Why would the muon's mass change the error rate?
- ggm 9y agobecause the imputed 'radius' of the proton in normal matter is a function of its interactions with electrons in orbit and its own properties. If you replace an electron with a Muon which orbits but is 400x more massive, then some element of distortion has to come into play. Its radii is now a function of its innate properties and an orbiting body 400x more massive than normal. Therefore, I posit (plausibly wrongly btw, I am not a physicist)_ that there is some measurement inaccuracy which stems from this, which is a function of this 400x size difference.
- monochromatic 9y agoWhy would the error be linear in the mass of the electron or muon? I mean, maybe it is... but it’s not at all obvious to me why that would be so.
- SubiculumCode 9y agoAre the old measurement method still being used today? What a wonderful oddity it would be if those measurements changed as well.
- comnetxr 9y agoMy interpretation of this is that the muon measured radius of the proton is the correct one. This rules out the speculation that the muon measurement was accessing some sort of new physics which caused it to be 4% off. The key quote is here: "Some researchers speculated that perhaps some previously unknown physics could make muons act differently than electrons. This would have required a revision of the standard model of particle physics, which predicts that muons and electrons should be identical in every way except for their masses — and might have pointed to the existence of yet-to-be-discovered elementary particles." This is the reason for this precision research: it could give you the hint for where to look for new physics. This result, far from "deepening the proton-size puzzle", says that muons do not have any new physics. In other words, it's a null result.