I've heard this quote before, and I don't get it. This article fails to show me just how complicated that is. When I think "complicated," I think of a multiplicity of interconnected chemical molecular processes like what must happen in the cell, or layers of recursively connected neurons in the brain. Not some mindless cloud of gluons. What they've described seems less "complicated" and more "confusing." "We don't understand this (yet?)" is a lot different than "it's possible to understand this, if your brain is really big."
It's complex in a physicist's sense of the word: the equations are hopelessly complicated to solve even in very simple cases. This means it's hard to build intuition or describe in simple terms.
Quantum chromodynamics is actually pretty similar to Maxwell's equations of electromagnetism. The big difference is that unlike photos, gluons interact with each other. This means goodbye to linear equations and simple planewave solutions. One can't even solve the equations in empty space, and only recently have supercomputers become powerful enough to make good, quantitative predictions about things like the proton mass.
I wonder if it is inherently complex in an information-theory framework, or that we simply haven’t yet found its “natural” basis under which its description is most succinct?
My non-physicist but curious-about-the-topic take is similar. Things at the quantum level are not "complex" in the systems-theory sense. They couldn't be, I think, since we're dealing with the most basic constituents of the universe. They are mysterious, confusing, wildly counterintuitive... but they are fundamental. The most basic stuff there is.
The study of these things, on the other hand, is genuinely complex and difficult. But that's epistemology, not ontology.
> The results suggested that in even higher-energy collisions, the proton would appear as a cloud made up almost entirely of gluons. The gluon dandelion is exactly what QCD predicts.
I find the proton as a gluon dandelion cloud enthralling
Non-physicst here. Hopefully someone can correct me or elaborate. My understanding is that what's being described is smaller scale decoherence inside the proton. Normally, the universe only asks protons the question: "are you a proton?" and it's like "Yep I'm a proton." (What's your baryon number? What's your charge? etc)
When we blast it with higher and higher energies, we're asking new questions: "What are the momenta of your quarks? What's your color field arrangement?" There are many possible answers to those questions and we're now starting to see the landscape of them.
So having different answers based on how you look is really answering different questions, just like asking an electron: What's your momentum? What's your location?
This has a specific meaning and is not a word I would use here. For something to be "decoherent" the particle phases would need to be "uncorrelated" or "random", but given the internal wavelengths, masses, and strength of the interaction of the particles involved against the spatial dimension of the proton this is not the case under quantum field theory.
In some ways the problem of this being "complicated" is because it's intractably coherent with a fluctuating large number of particles interacting via three "colors" of self-interacting charge (very different from electric charge and not just "three" independent charges) to consider. I'd put money on any decoherence would likely simplify the problem.
> Normally, the universe only asks protons the question: "are you a proton?" and it's like "Yep I'm a proton." (What's your baryon number? What's your charge? etc)
Protons have internal structure (the quarks and gluons) and size. Those are relevant to its interactions. To consider a proton "by itself" and just reduced to quantum numbers is not "normal" if by "normal" you mean "protons at a scale in nature you deal with every day". Those protons are bound in nuclei and are modified by the fact they are bound. These effects have been explicitly measured and documented, the EMC effect being one of them. The "new questions" you are referring to are in fact relevant questions at low energies and are not "new". They are a large active area of research typically referred to as "medium energy" (despite the fact it extends into "low" energy traditional nuclear physics and high energy QCD physics).
Even in a hydrogen atom, the internal structure of the proton modifies the chemistry by small changes in the electronic shell energies, in particular contributions to the lamb shift which has been used to measure the radius of the proton.
Maybe most directly, if what you described were the case you wouldn't have so many decimals in atomic mass numbers of nuclei.
> So having different answers based on how you look is really answering different questions, just like asking an electron: What's your momentum? What's your location?
The problems of looking at quarks and gluons at different energy scales are also endemic to other forces (e.g. electromagnetic) and all particles (for example, look up the running of coupling constants and renormalization theory). Saying they are "different" questions is more akin to comparing questions of skyscraper engineering and concrete dust mechanics. They are not orthogonal as I would consider momentum and location. They're questions of scale and things like emergent effects at different scales.
There are orthogonal questions of internal structure to be considered, though. Deep inelastic scattering processes at high energies tend to ask the "what are the momentum" questions. Elastic nucleon form factors ask more the "location". They both exist in a unified framework of "generalized parton distributions".
When I was a physics student, there were four forces: strong, weak, EM, and gravity. That picture seemed neat and clean. Strong kept the nucleus together, EM kept molecules and atoms together (or broke them apart), gravity kept astronomical bodies together, weak was some kind of momentum-accounting device.
Recently, GPT informed me that the strong force is really a tiny after-effect of the "QCD force" (in the same way that the Van der Waals forces are after-effect of EM). Also, more and more questions about "dark matter" seem to be building up, suggesting that the standard Newton-Einstein story of gravity is far from the complete picture.
25 years ago it seemed like physics was mostly complete, and the only remaining work was exploring the corner cases and polishing out all the imperfections. It doesn't feel that way anymore! The confusing part is that modern physics is so unbelievably successful and useful for technology - if the underlying theory was way off, how could the tech work?
> 25 years ago it seemed like physics was mostly complete, and the only remaining work was exploring the corner cases and polishing out all the imperfections
Around 125 years ago, many thought the same about physics, that physics is mostly complete and it just explaining and finishing some edge cases and polishing all our measurements. There was just two things that were a little bit puzzling, the "looming clouds" over physics (per Kelvin description) will later lead to both Quantum Theory and Theory of relativity (Black body radiation and Michelson–Morley experiment) and the fundamental change of our understanding for physics after that.
So I would not take this position. Does this mean we are in a similar moment? maybe, who knows?
> Recently, GPT informed me that the strong force is really a tiny after-effect of the "QCD force"
Maybe you should not take everything GPT tells you at face value? I have no idea what this QCD force is supposed to be. The strong force is _the_ force of QCD.
The Standard Model still considers the electromagnetic, weak and strong force. The description of the weak and EM force can be unified into the electroweak force and there are theories that try to also unify it with the strong force and even gravity, but there are issues on the theory side and no clear evidence on the experimental side as to which direction is the correct one.
The Standard Model and General Relativity are still our most successful theories. It is clear that they don't tell the whole picture, but (annoyingly?) it is not clear at all where this is going.
Just for dark matter there are probably a dozen proposed hypothetical particles, but so far we have found none. But maybe it's something completely different...
> 25 years ago it seemed like physics was mostly complete, and the only remaining work was exploring the corner cases and polishing out all the imperfections. It doesn't feel that way anymore!
Physicists thought the same thing c. 1900, but then one of the "corner cases" turned into the ultraviolet catastrophe[1]. The consequences of the solution to that problem kept the whole field busy for a good part of the 20th century.
I'm highly skeptical of the idea that physics is anywhere near complete. The relative success of our technology gives us the illusory impression that we're almost done, but it's not obvious that physics even has a single, complete description that we can describe. We assume it does for convenience, in the same way that we assume the laws are constant everywhere in spacetime. I view this as both exciting and terrifying, but mostly exciting.
"QCD force" is the same thing as the "strong" force. There is no reason whatsoever to invent any new name.
There are several hierarchical levels at which the strong interaction and the electromagnetic interaction bind the components of matter.
The electromagnetic interaction attempts to neutralize the electric charge. To a first approximation this is achieved in atoms. The residual forces caused by imperfect neutralization bind atoms in molecules. Even between molecules there remain some even weaker residual attraction forces, which are the Van der Waals forces, which are thus at the third hierarchical level.
For the strong interaction, there are only 2 hierarchical levels, approximate charge neutralization is achieved in nucleons, which are bound by residual attractive forces into nuclei.
So the forces between the nucleons of a nucleus correspond to the inter-atomic forces from inside a molecule, not to the Van der Waals forces between molecules.
> Recently, GPT informed me that the strong force is really a tiny after-effect of the "QCD force"
This is kind of just semantics. QCD describes both the force binding quarks inside protons and neutrons, and the residual force binding protons and neutrons. This is all part of the Standard Model, which has been essentially unchanged for the last 50 years. The big theoretical challenge is to incorporate gravity into this picture, but this is an almost impossible thing to explore experimentally because gravity is very weak compared to the other 3 forces. That's why the Standard Model is so successful, even though it doesn't incorporated gravity.
> The confusing part is that modern physics is so unbelievably successful and useful for technology - if the underlying theory was way off, how could the tech work?
Who says "way" off? It's not complete to explain everything, but it explains a lot correctly enough to use it for calculations, predictions and practical effects. Same way Newton was and remains useful, and how people have been using maths and technology to solve problems for a long time since before Newton was born.
So if we understand the internal differences between protons and neutrons, what’s the practical application? Turning neutrons into protons with low energies - alchemy?
Neutrons turn spontaneously into protons, which is called beta decay, and which happens in any nucleus with too many neutrons. This includes the free neutrons, which decay into protons in minutes.
Neutrons and protons differ in their composition, a neutron being made of 2 d quarks + 1 u quark, while a proton is made of 1 d quark + 2 u quarks, much in the same way as a nucleus of tritium differs from a nucleus of helium 3, the former being made of 2 neutrons + 1 proton, while the latter is made of 1 neutron + 2 protons.
For the strong interactions, nucleons (i.e. protons and neutrons) and nuclei are analogous to what atoms and molecules are for the electromagnetic interaction.
The strong interaction attempts to neutralize the hadronic charge (a.k.a. color charge), while the electromagnetic interaction attempts to neutralize the electric charge.
To a first approximation, the hadronic charge is neutralized in nucleons and the electric charge is neutralized in atoms.
However, because of the movement of the quarks inside of a nucleon and of the electrons inside an atom, the neutralization of the charge is imperfect and there remain some residual forces of attraction, respectively strong and electromagnetic, which bind the nucleons into nuclei and the atoms into molecules. Because they are just residual forces, the binding forces between nucleons in a nucleus are much weaker than those between quarks in a nucleon, similarly to how the binding forces between atoms in a molecule are much weaker than those that bind most of the electrons to the nucleus in an atom.
because the article says that it is a haze of probabilities that only takes concrete form when observed, could it be a part of a larger neural network?
I get what you’re saying, but the measurements are real. In some sense they are the truth.
In the article this refers to the finding that the quark is more complex than three valence quarks.
The measurements indicating that the three-quark-model is incomplete are overwhelmingly conclusive, so some degree of certainty in the language is warranted in my view.
Your personal insult aside, resonance is a fundamental term in physics and harmonic oscillators are fundamental to quantum field theory and modern physics. Music was a metaphor- this isn’t Nature.
Waves don’t come from pressure. Pressure comes from constrained waves… constraints prevent oscillatory relations from freely satisfying their phases. Pressure is a local manifestation of the same idea behind gravity. When many interacting modes lock into a persistent configuration, they impose constraints on nearby modes. To us on the inside it looks like curvature and attraction. But the comment section on HN is a bloodsport…
I’m sharing not arguing. This is the comment section of a website. I sold my autonomy for a wage doing other things, but I happily accept my affliction of contemplating the universe. Maybe it will spark something in the imagination of someone. Amateurs thinking is what led humanity to this point. I clearly stated my lack of domain expertise- but I reserve my right to unprofessionally question foundations and reject treating silence about first principles as intellectual virtue. I also accept, with grumbling, the downvotes.
If i remember correctly Feynman said in one of his lectures that we know the mass of the electron with much greater precision than the proton, which may mean that it electrons are easier to study. I don't know if this is still true though.
Spallation generation: High-energy protons (~800 MeV) hit a heavy target, releasing a wide spectrum of fast neutrons up to hundreds of MeV. These are then moderated down to useful energies for experiments.
It’s not the LHC, sure. But I don’t see any reason (apart from “why bother”) why they can’t do spallation in Geneva. OK maybe there’s a cooling problem…
Well my point is that the energy of the spallation neutrons is monotonically related to the energy of the protons hitting the Tungsten target ... although somewhat lower. I would consider these 100s MeV partiles to be (quite) high energy in contrast to the thermal neutrons alluded to elsewhere. Sure the spallation is lossy, but the result is still pretty high. And the physics is somewhat different with neutron experiments vs. protons... iiuc
There absolutely are direct neutron experiments, but they are much lower energy and have a different focus, partly because neutrons being neutral means they’re very hard to accelerate.
There’s an ultra cold neutron source at Paul Scherrer that is used to measure if the neutron has an electric dipole moment. This is complementary to high energy experiments.
Neutrons are not that different from protons. The decay from neutrons to protons is pretty well understood, and there’s no reason to think that the nature of quark/gluon interactions in a neutron are significantly different from those in a proton. What kind of new physics are you imagining we’d get?
Of course more experimental data is a good thing, but in this case it doesn’t seem obvious that it would lead to anything really new.
I think they mean that what happens when a neutron decays is well understood. One of the neutron's down quarks change to an up quark, facilitated by a virtual W boson with negative charge. The W boson is very unstable and immediately decays into an electron and an electron anti-neutrino, both of which are ejected leaving behind the former neutrino which is now a proton because of that quark change.
When that happens is less understood, hence the discrepancies you mentioned.
The same QCD theory that's used to model the proton models the neutron. Theoretically, our understanding of both is on the same footing.
The comment I replied to talked about "new physics". That's a term that's used in physics to describe physics beyond the Standard Model. Better experimental data about neutron internals could certainly help constrain the neutron lifetime, but that would be likely to be experimental constraints on existing physics, not new physics in the sense that the term is normally used.
Where are you getting that implication? I didn't see anything in the article suggesting that neutrons were simple and I would share your skepticism if someone claimed they were. The fact that neutrons can spontaneously decay into protons (plus other stuff) suggests otherwise.
If you saw an article titled “My Nana is the nicest person you could possibly meet”, would you interpret that to be a statement that your own grandmother is considerably less nice?
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