6 ms·

Can 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,

by mabbo 9y ago

Can 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 ago
No 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 ago
The 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 ago
  Just 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 ago
    Yeah, 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 ago
      Not just self-interact, but self-interact strongly. Photons can self-interact too, through intermediate charged particles, but do so much less often.
      - QAPereo 9y ago
        To 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 ago
  I'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 ago
    I 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 ago
    It'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 ago
As 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 ago
  If 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 ago
    I'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 ago
So 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 ago
No, 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 ago
The "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.

by mabbo 9y ago

moomin 9y ago

No 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 ago

The 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 ago
Just 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 ago
  Yeah, 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 ago
    Not just self-interact, but self-interact strongly. Photons can self-interact too, through intermediate charged particles, but do so much less often.
    - QAPereo 9y ago
      To 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 ago
I'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 ago
  I 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 ago
  It'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 ago

As 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 ago
If 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 ago
  I'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 ago

So 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 ago

No, 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 ago

The "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.