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A new experiment casts doubt on the leading theory of the nucleus

quantamagazine.org

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Re: A new experiment casts doubt on the leading theory of the nucleus

#21

Post by cwillu »

rpz wrote: post #13

I am not a physicist but if I were to take a stab at simplifying things I’d assume that a neutron is probably just a proton and an electron… isn’t that what a neutron decays to once it has been ejected from a nucleus anyways?

“The complexity of the proton and of the neutron seems to be real, and not due to a lack of knowledge on the part of physicists. We have equations that we use for describing quarks, anti-quarks and gluons, and the strong nuclear forces that they exert on one another. [These equations are called “QCD”, short for “quantum chromodynamics”.] We can check the accuracy of those equations through many different measurements, including the rates for producing various types of particles at the LHC. And when we put the QCD equations into a big computer, and make the computer calculate the properties of protons and neutrons, and other similar particles (collectively called “hadrons”), the computer’s predictions for the properties of these particles closely resemble what we see in the real world. So we do have good reason to believe that the QCD equations are right, and that our knowledge of the proton and neutron is based on the right equations. Yet having the right equations isn’t enough by itself, because

• simple equations can have very complicated solutions, and

• sometimes it is impossible to describe complicated solutions in a simple way.

As far as we can tell, that is the situation with nucleons: they are complicated solutions to the relatively simple equations of QCD, and there seems to be no way to describe them in a few words or pictures.”

-- https://profmattstrassler.com/articles-and-posts/particle-ph...

Probably the most straightforward and stark demonstration of why a neutron can't be just a proton, electron and neutrino all stuck together is that it entirely fails to explain where all the rest of the particles come from when you have a jet: https://profmattstrassler.com/articles-and-posts/particle-ph...

Re: A new experiment casts doubt on the leading theory of the nucleus

#22

Post by vaidhy »

jiggawatts wrote: post #16
jfengel wrote: post #9

Earlier quoted context omitted.

But relativity explains GPS. And the two theories together explain practically everything to insane levels of precision. The only time they go wrong is when they both operate at once, in a narrow range around black holes or the very earliest universe.

General Relativity doesn’t end just above the atmosphere and quantum mechanics ought to apply to everything, not just experiments. The current microscopic models don’t even attempt to explain how a molecule of water is lighter than the oxygen and two hydrogen atoms that went into making it. Oh sure, we can wave our hands at it and invoke the mass-energy relation from GR, but this doesn’t “pop out” of the Standard Mod…

Nothing says mass-energy equivalence cannot be applied to small particles. We have a good explanation of a very large set of physical phenomena. Yes, there are always things that are unknown and more you know, the more there is to know at the edges.

No one is claiming to "truly" understand anything and your cynicism is misplaced.

Re: A new experiment casts doubt on the leading theory of the nucleus

#23

Post by jepler »

rpz wrote: post #13

I am not a physicist but if I were to take a stab at simplifying things I’d assume that a neutron is probably just a proton and an electron… isn’t that what a neutron decays to once it has been ejected from a nucleus anyways?

I mean, it's not a bad theory. The wikipedia article on neutrons discusses how this was an assumption somewhat like this about 100 years ago ("nuclear electrons") and the lines of reasoning that led to abandonment of the idea: https://en.wikipedia.org/wiki/Neutron#Discovery -- it has to do with the observable quantity called "spin"; the spin of a neutron is not the sum of the spin of an electron and a proton, so it must be something else.

Re: A new experiment casts doubt on the leading theory of the nucleus

#24

Post by andrewflnr »

AnimalMuppet wrote: post #11

I am far from an expert. But from the article, it seems to me to be more likely that it casts doubt on the approximations they're using to do the calculations.

Well yes, but our understanding of what approximations should work is not really separable from the theory itself. E.g. from the article,

> Van Kolck contends that some of the parts deemed less important and routinely ignored are in fact very important.

So it's still good science IMO.

Re: A new experiment casts doubt on the leading theory of the nucleus

#25

Post by houston_Euler »

jiggawatts wrote: post #16
jfengel wrote: post #9

Earlier quoted context omitted.

But relativity explains GPS. And the two theories together explain practically everything to insane levels of precision. The only time they go wrong is when they both operate at once, in a narrow range around black holes or the very earliest universe.

General Relativity doesn’t end just above the atmosphere and quantum mechanics ought to apply to everything, not just experiments. The current microscopic models don’t even attempt to explain how a molecule of water is lighter than the oxygen and two hydrogen atoms that went into making it. Oh sure, we can wave our hands at it and invoke the mass-energy relation from GR, but this doesn’t “pop out” of the Standard Mod…

Can you point to some evidence for the claim that "a molecule of water is lighter than the oxygen and two hydrogen atoms that went into making it?"

I could understand the atoms sharing electrons, but just want to make sure I'm understanding you correctly, because you said it's unexplained.

Re: A new experiment casts doubt on the leading theory of the nucleus

#26

Post by 8bitsrule »

This is great news, if it holds up. There hasn't been a lot of remarkable advancement in physics since the Standard Model.

"Another topic that comes up is simplicity. According to Feynman, nature is usually much simpler than our thoughts. Therefore, when trying to explain phenomena, we tend to overcomplicate things. Often, in the end, reality can be explained by much simpler terms. We just need to look at it from another point of view."

- https://cassandradispatch.org/richard-feynman-on-looking-at-...

Re: A new experiment casts doubt on the leading theory of the nucleus

#27

Post by godelski »

version_five wrote: post #2

> Instead, at these scales, a new effective force emerges — the strong nuclear force, transmitted between nucleons by the exchange of pions. I'm admittedly ignorant, but I'm not convinced that a lot of theoretical physics is basically curve fitting where you've got a model with enough flexibility that you can make it fit the data. String theory always seemed like an egregious version of this, I think it's less popula…

Experimental physics works a bit differently than most people think. While string theory was/is popular, very few hold it as certainty. From the very beginning the discussions around it were that it was a non-testable theory. While out-group conversations around physics are "physicists believe" in-group conversations are more "the leading theory is". Uncertainty is deeply ingrained in the study and the focus is more around making our knowledge less wrong rather than proving something correct/making our knowledge correct. Subtle, but notably different. It is the reason you always see quotes with qualifiers like "should" or "we think" and rarely certainty (easy to miss if you aren't looking).

These distinctions matter when you create experiments and interpret results. They generally don't matter to the layman, since an authoritative answer is good enough. But they do matter if you need to do any form of evaluation, as essentially what I'm talking about is the importance of including error and uncertainty. Which btw, particle physics often has a uniquely tight bound: 5 sigma. You'll even notice CERN's blog post about 5 sigma has lots of qualifiers, does not suggest it claims certainty, how it isn't alone enough, and even references that there are good arguments for even higher bars. It's a different language than people are used to.

https://home.cern/resources/faqs/five-sigma

Re: A new experiment casts doubt on the leading theory of the nucleus

#28

Post by jxy »

The fundamental theories we have is Quantum Electrodynamics and Quantum Chromodynamics.

This new experiment tells you that "modern nuclear forces, including those derived within chiral effective field theory" break down and cannot be used to describe what they observed. Here is the arxiv: https://arxiv.org/abs/2112.10582

It just tells you that their effective theory is no longer effective in these circumstances. Unless you actually observe something contradicts QED+QCD calculations, nothing fundamental is wrong.

I can't believe they pick such a clickbaity title for a serious publication and let quanta magazine publish an even more clickbaity article about it. Well, I guess they need more funding.

[EDIT] PS. The science is sound and suggests that nuclear physicists must refine their theories to match observations. This also encourages those working on QED+QCD, as increased computational power may enable precise form factor calculations for comparison with experiments.

Re: A new experiment casts doubt on the leading theory of the nucleus

#29

Post by canjobear »

8bitsrule wrote: post #26

This is great news, if it holds up. There hasn't been a lot of remarkable advancement in physics since the Standard Model. "Another topic that comes up is simplicity. According to Feynman, nature is usually much simpler than our thoughts. Therefore, when trying to explain phenomena, we tend to overcomplicate things. Often, in the end, reality can be explained by much simpler terms. We just need to look at it from ano…

It doesn’t sound like this is necessarily a challenge to the Standard Model, only to one of the ways of approximately deriving predictions about the strong force.

Re: A new experiment casts doubt on the leading theory of the nucleus

#30

Post by jdkee »

houston_Euler wrote: post #25
jiggawatts wrote: post #16

Earlier quoted context omitted.

General Relativity doesn’t end just above the atmosphere and quantum mechanics ought to apply to everything, not just experiments. The current microscopic models don’t even attempt to explain how a molecule of water is lighter than the oxygen and two hydrogen atoms that went into making it. Oh sure, we can wave our hands at it and invoke the mass-energy relation from GR, but this doesn’t “pop out” of the Standard Mod…

Can you point to some evidence for the claim that "a molecule of water is lighter than the oxygen and two hydrogen atoms that went into making it?" I could understand the atoms sharing electrons, but just want to make sure I'm understanding you correctly, because you said it's unexplained.

Per our new electronic friend:

" The weight of a molecule of water (H2O) is the sum of the weights of the two hydrogen atoms and one oxygen atom that compose it. Here are the atomic weights of these elements:

Hydrogen (H): Approximately 1 atomic mass unit (amu) Oxygen (O): Approximately 16 amu So for a molecule of water:

2 Hydrogen atoms: 2 * 1 amu = 2 amu 1 Oxygen atom: 16 amu Adding these together gives a total of 18 amu for a molecule of water.

This means that a molecule of water has the same weight as the sum of the weights of the two hydrogen atoms and one oxygen atom that compose it, because the molecule is simply a combination of these atoms. There's no loss or gain in weight when the atoms combine to form the molecule.

However, this does not take into account the minor decrease in mass that occurs during the formation of a water molecule due to the conversion of some mass into binding energy according to Einstein's equation E=mc^2. This decrease is incredibly small and generally not considered in standard atomic weight calculations, but it does technically make the water molecule ever so slightly lighter than the sum of its constituent atoms."

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