Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

quantamagazine.org

Post reply on HN
Print view View original

31–40 of 120 posts

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

#31

Post by JKCalhoun »

vaidhy wrote: post #17
JKCalhoun wrote: post #12

Earlier quoted context omitted.

Historically, haven't the more "elegant" models been shown to be correct? The various explanations for planetary motion come to mind as an example.

No.. In fact by the standards of the day, an circular orbit is more elegant. Think about circles within circles and the entire universe revolving around you. To some extent, models that made less assumptions tend to be more correct.. but I think those are few and far between. We are now trying to explain very small discrepancies (by human scale) and the models are necessarily more complex.

I was thinking of the epicycle in fact. Kind of a hack, I think.

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

#32

Post by JKCalhoun »

dexwiz wrote: post #18
JKCalhoun wrote: post #12

Earlier quoted context omitted.

Historically, haven't the more "elegant" models been shown to be correct? The various explanations for planetary motion come to mind as an example.

Elegance is matter of perspective. Epicycles are a very elegant way to explain planetary orbits from a geocentric view point, but they are very wrong.

I would agree epicycles are elegant — if they worked. :-)

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

#33

Post by marcosdumay »

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.

You mean experimental evidence? I don't think our mass measurements are that precise.

Just to be clear, that statement is very well accepted physics, and we have plenty of evidence of bounding energy changing the mass of things on the more energetic reactions (the nuclear ones). It would be incredibly surprising (in "redo all of physics" surprising) if it didn't hold for chemical reactions too, but I don't think anybody has evidence.

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

#34

Post by jjtheblunt »

andreareina wrote: post #7
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…

The standard model has a number of free parameters [1] but the results of calculations are pretty sensitive to them, and this is what predicted (not just explained post-hoc) the Higgs. It's not incorrect to say there's curve fitting involved, but it severely understates the magnitude of the achievement that is the standard model, and its success in explaining everything that underpins everyday life[2], as well as mos…

If it explains everything then why are experiments still ongoing? What is left to explain?

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

#35

Post by cyberax »

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…

The problem with the nucleus is that the internal dynamics there are impossible to describe with any reasonable precision.

If for the electron shell we can calculate pretty much anything we want from the first principles (energy spectra, the half-lives of unstable and metastable states, etc.), we can't do anything similar for the nucleus.

For example, we can't compute half-lives of unstable nuclear isotopes. The best models are on the level of "imagine that a nucleus is a drop of water" or "assume that a nucleus is a potential well that contains an alpha particle".

And no, this is not a fundamental theory issue. We can describe the behavior of individual nuclear particles just fine at the energies that exist within the nucleus. It's their interaction that is completely baffling.

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

#36

Post by yongjik »

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…

> 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 Model in any sense.

Mass-energy equivalence, a.k.a. E=mc^2, is special relativity. It's fundamentally linked with our understanding of electromagnetism. Physics students generally learn about special relativity before they get to quantum mechanics.

This is undergraduate physics level material.

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

#37

Post by ftxbro »

jxy wrote: post #28

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. Unle…

> "Well, I guess they need more funding."

are they trying to clickbait jim simons

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

#38

Post by XorNot »

marcosdumay wrote: post #33
houston_Euler wrote: post #25

Earlier quoted context omitted.

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.

You mean experimental evidence? I don't think our mass measurements are that precise. Just to be clear, that statement is very well accepted physics, and we have plenty of evidence of bounding energy changing the mass of things on the more energetic reactions (the nuclear ones). It would be incredibly surprising (in "redo all of physics" surprising) if it didn't hold for chemical reactions too, but I don't think anyb…

Well yes but the energy scale involved is tiny. We notice these things with nuclear reactions because the energies are much higher.

The chemical energy in the electron orbitals is far lower by comparison (infrared as opposed to gamma radiation).

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

#39

Post by jcranmer »

cyberax wrote: post #35
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…

The problem with the nucleus is that the internal dynamics there are impossible to describe with any reasonable precision. If for the electron shell we can calculate pretty much anything we want from the first principles (energy spectra, the half-lives of unstable and metastable states, etc.), we can't do anything similar for the nucleus. For example, we can't compute half-lives of unstable nuclear isotopes. The best…

> If for the electron shell we can calculate pretty much anything we want from the first principles (energy spectra, the half-lives of unstable and metastable states, etc.), we can't do anything similar for the nucleus.

As I understand it, we can only really do that for a single-electron atoms. Multi-electron interactions get the same problem as inside the nucleus.

Post reply on HN