A new experiment casts doubt on the leading theory of the nucleus
quantamagazine.org
quantamagazine.org
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.
are they trying to clickbait jim simons
Whether or not you consider that to be part of their job is in the eyes of the reader.
Because I expect a news article on the topic to clearly contextualize that answer. That is a core component of their job.
Quanta magazine is pretty good in most things I read, but I feel like they drop this particular ball pretty often. I suppose that concession to clickbaitery is the bare minimum anyone can survive with nowadays. But they are still several cuts above most things I read.
My take from reading the article (not a physicist) is the physics of the nucleus (i.e. the protons and neutrons and strong nuclear force) are treated as emergent phenomena from the quantum theories about fundamental particles (e.g. quarks, leptons & gluons).
Per the article, such leading theory of the nucleus is "chiral effective theory," which seems to be quite inaccurate at making predictions for the experiment in question.
I'm not sure how much more accurate the headline could be, unless chiral effective theory is not in fact the ex ante leading theory of the nucleus.
I think you're reacting to things the paper doesn't say - they never claim any new physics. EFT is a simpler model than what you'd derive from QCD and it makes sense it'll be wrong in some limits. The paper finds such a limit. That's all? The paper title and abstract seem to be pretty accurate? Or are you objecting to the characterization of EFT as "theory"?
If so, then how about planet formation theory, or solid state physics? Are those also not theories, because they're ultimately just limits of the standard model?
BTW, This is not about Quanta which I find is a really good resource. Although, there might indeed be some click-baitiness not with the motive of profit(you could describe it as a charity run by Jim Simons), but in the sense of someone trying to get students interested with a provocative title for a science talk.
The challenge is to strike the right balance between making content appealing and keeping it accurate and valuable, especially crucial with scientific publications, where the accuracy and trustworthiness of information is paramount.
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 popular now.
I think that's why elegance goes a long way in theories: a simple and concise description is harder to overfit.
Gell-Mann and other proposed a unifying principle in the 60s, and as far as I know that's been broadly successful and ultimately led to the standard model. https://en.wikipedia.org/wiki/Eightfold_way_(physics)
We are not now discovering any new unexpected particles (or any theoretically expected ones, since the Higgs), which is a bit unfortunate in terms of giving theorists something to work with.
[1] https://en.m.wikipedia.org/wiki/Standard_Model#Construction_...
[2] https://www.preposterousuniverse.com/blog/2010/09/23/the-law...
[3] https://physics.stackexchange.com/questions/128374/evidence-....
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.
And I guess less formally there's also the problem of complexity: condensed matter physics exists because trying to solve the standard model for a solid directly is both incredibly infeasible (think "cost of flipping bits in the calculation far extends that of all matter in the observable universe") and fails to capture the emergent phenomena in a natural way.
If no inflation, then no Big Bang, so our Visible Universe is much older.
If our Universe is much older, then life evolved multiple times already. Red stars are shallow gravity wells, so they are primary target of an expansive civilization, because it easy to enter/exit them, so they are colonized first and their light is captured fully.
Note that the 'laws' of physics are no better than normal scientific theories, scientists just had more hubris back then.
It’s a much much bigger problem if the universe significantly older than we think it is… if we were to believe the Wikipedia article on this[0], we’d only expect stars to exist at all for about 100 trillion years, but given that the distribution of hydrogen availability is likely to follow an inverse exponential decay curve of some sort, we’d probably see much lower amounts of hydrogen much earlier than that.
[0] https://en.wikipedia.org/wiki/Future_of_an_expanding_univers...
(Not a native speaker).
Most galaxies in our galaxy cluster are moving away from us because of coincidence: Shappley attractor makes accretion disk by attracting mater from Dipole Repeller void[0], so our local group of galaxies is stretched along the way. At scale of our local galaxy cluster, Doppler Shift is responsible for majority of Red Shift.
At cosmic scale, Red Shift cannot be explained by Doppler Shift alone. If we take into account gravitational waves, then at least part of Red Shift can be explained by gravitational noise: gravitational waves are slowing down light a bit, so photon loses tiny bit of energy with every such interaction, which causes major part of Red Shift at cosmic scale.
> where fresh hydrogen for stars comes from in an ancient universe,
This is though question which is hard to answer. If elementary particles are bubbles, then they are popping up because something is stretching our Universe, i.e. our Universe is inflating ... oh, fck.
> where the cosmic background radiation comes from
[If inflation theory is false, no Big Bang, and visible Universe is much older, then] Cosmic microwave background is just light from distant galaxies with large Red Shift z=1000 (light was stretched about 1000 times from galaxies in range of about 4 trillion light years).
> why the distant universe appears 'younger'...
James Webb infra-red telescope is proving that this assumption is false right now. Read the news.
It is possible and I would judge even likely that some other value is conserved; that conservation of energy can be broken doesn't mean all chaos is unleashed and the Patent Office should revoke their ban on perpetual motion machines. When it is finally worked out, we may even pick up our "energy" label and move it to this new quantity. Depends on a lot of details we don't currently know. But what we today call energy is not necessarily conserved at large scales.
Saying that the universe can't do X because it violates conservation of energy is a circular argument; the precise definition of "conservation of energy" used by physics today is derived from our belief that the universe can't do X, but we also know our beliefs are incomplete. Very good approximations. Don't quit your day job to build a perpetual motion machine. But we are not in a position yet to even claim that our description of the universe is complete and we know the exact thing being conserved.
Energy is in general only conserved locally. More precisely, the covariant derivative of the stress-energy tensor `\nabla_{\mu}T^{\mu \nu}` is zero, but this can only be put into integral form in a few special cases.
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 Model in any sense.
This isn’t some exotic phenomena only found in deep space!
We have a long way to go before we can par ourselves on the back and claim to truly understand what’s going on.
No one disagrees, but if it were that easy to just jump straight to the final theory we would have done it long ago. For now, effective theories are all we've got.
> 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.
Yes, it does. You don't need GR for mass-energy equivalence, just special relativity. And the Standard Model is fully special-relativistic.
No one is claiming to "truly" understand anything and your cynicism is misplaced.
I could understand the atoms sharing electrons, but just want to make sure I'm understanding you correctly, because you said it's unexplained.
" 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."
I really don't see what's controversial about what I've said that's riled up people so much...
It may be stated as such, and added in to equations as an external piece of knowledge from relativity, but this is cheating a bit.
Essentially, when we state that H2O has less mass than H+H+O, what we actually mean is that H2O bends spacetime a little bit less than the three atoms individually that made it up. There's no accepted variant of QM or the Standard Model that explains this. The dynamics of spacetime curvature rearranging as the photon is emitted as the hydrogen atoms burn is not explained by modern science. This is fundamentally the "QM is incompatible with GR" issue.
My point was that it isn't just near black holes that a GR-compatible microscopic theory is relevant.
It's relevant even in the flame of a candle. It's a small effect, but it's there. The inconsistency in the theories occurs at all scales.
Even in pure QM, the water molecule will have less inertia than unbonded hydrogen and oxygen atoms. This should in principle be measurable by applying a known force to the water molecule and to the three atoms, and measuring their acceleration. The difference should perfectly match the inertial difference predicted by SR and GR.
GR adds the observation that, if the water molecule has less inertia, it should also bend space-time less, and it is this bending of space time that can't be explained by QM.
Though I should add that I've had a reply to a different comment once that explained that QM is actually compatible with the flat-ish but not perfectly flat space times that GR predicts anywhere not very close to a black hole. They were claiming that in fact modern QFTs can even predict things like the gravitational lensing produced by our sun, and that they only break down when near the event horizon of a black hole.
I'm not sure this is correct. It bends spacetime less simply because it's in a lower energy state. It's correct to say that the Standard Model doesn't explain spacetime curvature, but the curvature in GR is implied by the energy which is explained.
> 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
Is highly imprecise at best, and misleading at worst.
It is true that the mass of the water molecule is slightly less than that of the oxygen and hydrogen atoms combined. It is not true that this excess mass is converted into "binding energy", binding energy is negative in stable molecules. That is the binding energy measures how much energy you would have to add to break up the molecule, or conversely, how much energy is lost (as heat/light/whatever) to the environment when the molecule is formed.
The mass is lower because it has been converted into heat in the environment, not because it has been converted into binding energy.
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I would call this an instance of the language model producing convincing sounding nonsense (something that they do quite often when asked about technical stuff).
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.
The chemical energy in the electron orbitals is far lower by comparison (infrared as opposed to gamma radiation).
You don't need to weigh individual atoms or molecules to take measurement!
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.
Not sure I follow your direction here. Seems to be a conflation of three separate things, not necessarily compatible with each other. In classical physics mass and charge (of a particle) are different properties. One defines how particle behaves in response to forces, the other how it interacts with em fields. That's one. The other, if we go into relativistic physics, there's mass-energy equivalence (as stated by einstein)... however, charge itself isn't a form of energy, BUT charged particles can have energy associated with their electric fields that would contribute, in a sense, to the overall mass-energy of a system (which is usually ignored unless we're talking sub-atomic particles or high-energy physics). That's two. And then there's binding (not bounding) energy which represents the amount of energy required to split a system of particles into its non-interacting components (such as, in context of nuclear physics, splitting a nucleus into protons and neutrons).. or you've meant electron binding energy which represents amount of energy needed to remove an electron from an atom.. that'd be a third.
Not OP, but burning hydrogen in oxygen is exothermic. It makes intuitive sense that the energy from that reaction no longer contributes to the mass of its products.
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.
Suggest a better theory so you can pat yourself on the back then.
This is a misconception of scientific endeavour in general and of physics in particular. All models are approximations of reality. We have a theory that is consistent with experimental observations, then we make observations with which the theory is not consistent anymore and we develop a new theory that explains those new observations as well, and so on. We will never have an "exact" model, whatever that even means. But we have models that have limitations that are far beyond what's relevant for most people's life.
At many points in time, we could pat ourselves on the back. The heliocentric model. Newtons model. General Relativity. The Standard Model. All these models were important steps forward and led us to where we are today, which is absolutely astonishing. No, we don't have a full theory explaining everything, but we never will.
Your are correct that there is a (strong) conflict between general relativity and quantum field theory, and this is a major problem for theorists, but it does not pose problems for using mass-energy equivalence in quantum field theories (since it comes from SR not GR).
There are real, physical, examples where the GR/QFT conflict is more problematic. For example in quantum physics labs around the world it is possible to put things which have mass in superpositions of being in two different places. This is usually done with very small objects, but it happens. We have absolutely no idea what is happening to space-time when we do this.
...except, isn't it true that the galaxy that contains the earth wouldn't exist were it not for dark matter?
In contrast, there are phenomenon which we know standard particle physics and quantum mechanics gives the wrong answere (despite getting so much else right).
If you do not possess that curiously then so be it, but others are still motivated by it.
And then of course as there are complex emergent effects of multiparticle systems that are difficult to calculate accurately.
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.
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.
That could be a call to stop bothering with exploring the domain entirely as infeasible. But I don't understand why string theory gets singled out for finger waggling when any other theory must run into the same problem.
"I remember my friend Johnny von Neumann used to say, with four parameters I can fit an elephant, and with five I can make him wiggle his trunk." [1]
"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-...
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.
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.
We can do it analytically for single-electron atoms. We can solve it numerically for much larger systems.
Feynman diagrams are a visual way of representing a boatload of very complex equations and the worse part is that they work! But maybe it's a failure of math more than physics
It sounds like the setup to a joke, the punchline being that you tell it there's cake in the dining room, but I am honestly curious?
Laser bombardment? Running it through a particle accelerator? Pointing out the girl helium over at the bar looked at it?
Ok, sure, they shot electrons at it, but why would that have any real, measurable effect on the nucleus?
What are the conditions that qualify as "excited" for a helium nucleus? Is it just the "balooning", or is there some real meaning to the term?
I have so many questions.
I bet on more terms.
> 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.
• 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...