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Mysteries the Standard Model can’t explain
- azalemeth 5y agoOne other mystery not mentioned is the problem of fine tuning. The standard model requires certain parameters (like alpha, the fine structure constant) to have their current values accurate to many orders of magnitude for the universe as we know it to exist. There are two philosophical schools of thought about that -- (a) we're in the universe we're in, so by definition it must exist and there's a selection bias there; or (b) there is an underlying detailed structure that gives the values of supposed 'fundamental' quantities their shape as an emergent property of something more beautiful – and thus they're not "free" at all. This is one of the things that SUSY was supposed to solve – but it's been experimentally found to not really exist by the LHC. A good introduction about this (in the context of the Higgs mass, where the need for fine tuning is really apparent) is here: https://www.physicsmatt.com/blog/2016/11/17/paper-explainer-precision-corrections-to-fine-tuning-in-susy https://www.physicsmatt.com/blog/2016/11/17/paper-explainer-...
- Ginden 5y ago> (a) we're in the universe we're in, so by definition it must exist and there's a selection bias there; This has basically 3 possible explanations - insane coincidence, multiverse (with many versions of constants; certain forms of mathematicism also provide such "multiverse") or "reason" (simulation admin/God).
- pfortuny 5y agoThanks for this detailed explanation. Did not know about the fine-tuning problem.
- andrewgleave 5y agoYou may find this an interesting read: https://www.bretthall.org/fine-structure.html https://www.bretthall.org/fine-structure.html
- jessermeyer 5y agoIt's only framed as a problem when it is assumed that the values could be other than what they are. But we have no reason to suspect that they could be different. We have no idea how unlikely the current selection is given our observation is a single observable. For all we know, it's certain. 'What really interests me is whether God had any choice in creation' - Albert Einstein
- brink 5y ago> It's only framed as a problem when it is assumed that the values could be other than what they are. Well then your problem would be "What fixed those values to what they are?", which I don't think is the lesser of a problem.
- jessermeyer 5y agoThat's not really a problem in the sense that it doesn't align with expectations. That's a genuine unknown.
- WithinReason 5y agoThe article has some more instances of pysicists naming things: "The partner of the Higgs, the higgsino." "The partner of the top quark, the stop squark."
- steerablesafe 5y agoMandatory SMBC: https://www.smbc-comics.com/?id=1452#comic https://www.smbc-comics.com/?id=1452#comic
- wongarsu 5y agoThe stop squark is one of the sfermions (the superpartner particles of their associated fermions). As such they are all sparticles. Some of the other sfermions would be the sup squark, the scharm squark, the sstrange squark, the selectron or the stau. [1] In my opinion physicists are great at naming things :D 1: https://en.wikipedia.org/wiki/Sfermion https://en.wikipedia.org/wiki/Sfermion
- saalweachter 5y agoIt seems kind of seems hipster. "I'll name the particles something that I can later disavow as a joke if people don't like it, so I'm not risking myself."
- mbg721 5y agoI mean, you only get to use "Particle McParticleFace" once.
- Taniwha 5y agoPretty sure it's its own anti-particle
- whatshisface 5y agoWhat alternative would you propose? Greek naming? Latin?
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- Mizza 5y ago“This is rather as if you imagine a puddle waking up one morning and thinking, 'This is an interesting world I find myself in — an interesting hole I find myself in — fits me rather neatly, doesn't it? In fact it fits me staggeringly well, must have been made to have me in it!' This is such a powerful idea that as the sun rises in the sky and the air heats up and as, gradually, the puddle gets smaller and smaller, frantically hanging on to the notion that everything's going to be alright, because this world was meant to have him in it, was built to have him in it; so the moment he disappears catches him rather by surprise. I think this may be something we need to be on the watch out for.” --Douglas Adams
- AnIdiotOnTheNet 5y agoTo me the fine tuning problem is a bit like saying "circles wouldn't exist without π being exactly the value it is" and wondering why π has that value specifically and not any other value. I don't think A and B are mutually exclusive. The values seem perfectly tuned for our universe because we exist in our universe, and they are probably emergent from a more fundamental parameter, possibly something like the particular Calabi-Yau manifold topology that happens to correspond to our universe (in the case of superstring theory). If we lived in a different CY topology that was capable of supporting intelligent life then we'd wonder why that one's constants are so precisely tuned for us. But then, I'm and idiot who just watches PBS Space Time and nods his head, not a physicist.
- dogma1138 5y agoThat’s not that great analogy for fine tuning. The quantized representative value of Pi is arbitrary based our numerical system, the relationship that derives it is fixed if the relationship would change circles indeed would not exist. Let’s move the analogy to triangles a triangle has 180 degrees but that only holds true when it’s on a flat surface if you have a curvature it can have more or less than 180 degrees. So this isn’t a fine tuning problem on its own, if you would lived in a universe where triangles have less or more than 180 degrees it would represent a universe with negative or positive curvature. The issue with fine tuning is that the curvature of the universe is directly tied to the mass/energy density and any deviation from an extremely narrow range which our universe seems to sit in out of all possible values would not just produce a universe with triangles with fewer or more degrees than 180 but would either produce a universe that would collapse on itself within a blink of an eye or expand so fast that gravity would never be strong enough to cause even the most basic structures to form. So the issue really is that to produce a universe which will form galaxies and stars and survive long enough to produce life you need a lot of parameters at a certain very specific value even the smallest of deviations would not produce a universe that would ever support life, yet alone an intelligent life. What’s even stranger iirc is that the values have to be really what they are now you can’t simply 2X all of them to maintain the proportions and get the same result. And this is really what people are looking to solve, yes the androcentric is a solution if they were anything than what they are now we wouldn’t be here to discuss why, but the issue is that out of all other possible combinations you don’t seem to find another stable state and that is the true mystery.
- coremoff 5y agosomewhat related, I think, is the enormous disparity between the strength of the strong/week/electromagnetic forces and gravity (30 or 40 orders of magnitude); possible indication that there's something missing
- tsimionescu 5y agoWhy is this a problem? If the other three forces were perfectly equal, or in regular intervals, maybe this would have meant something, but the other three forces' strength varies by x, y, z between them. Other than human intuition, there is nothing inherently different between x = 2 and x = 10^30-40.
- throwawaylinux 5y agoIsn't the whole thing made up to fit observation though? Why is that any more arbitrary than, say, electromagnetism existing?
- TheOtherHobbes 5y agoIt's an explanatory theory with a lot - a lot - of gaps. It has been extended with some nice predictions like the Higgs. But basically it's a Franken-patchwork of math glued together quite awkwardly. Because that is what it is. Literally. It was developed by thousands of grad students and their supervisors throwing math at the wall and keeping anything that matched observations. So there was a lot of random searching involved. What's missing is a central guiding metaphor. Relativity has one. In comparison, the Standard Model is very epicycle-ish tool for calculating Lagrangians with plenty of "Yes but" and "Except when".
- throwawaylinux 5y agoI'm not sure I quite explained myself, although I do appreciate the reply. See, I also don't see how one central guiding metaphor would be any less arbitrary than none, or ten metaphors. What I am asking is why would α = 0.0072973525693 be more of a problem than electromagnetism or the speed of light being constant or e=mc^2? If the fine structure constant was exactly 1 would that make it better? Why is 1 less arbitrary or more good? I understand the beauty in simplicity, fewer concepts or ideas, smaller formulas explaining more things, 1 being "nicer" than other numbers, etc. So I understand that aspect of goodness, so it is the connection to underlying observable reality I'm asking about. Because isn't it also arbitrary to think that if we could explain things in more beautiful ways then it would be a deeper understanding or closer to the truth?
- abrichr 5y agoIt sounds like you're asking why parsimony is desirable in science. From https://aeon.co/essays/are-scientific-theories-really-better-when-they-are-simpler https://aeon.co/essays/are-scientific-theories-really-better...: > The upshot is that there are three parsimony paradigms that explain how the simplicity of a theory can be relevant to saying what the world is like: > Paradigm 1: sometimes simpler theories have higher probabilities. > Paradigm 2: sometimes simpler theories are better supported by the observations. > Paradigm 3: sometimes the simplicity of a model is relevant to estimating its predictive accuracy. > These three paradigms have something important in common. Whether a given problem fits into any of them depends on empirical assumptions about the problem. Those assumptions might be true of some problems, but false of others. Although parsimony is demonstrably relevant to forming judgments about what the world is like, there is in the end no unconditional and presuppositionless justification for Ockham’s Razor.
- blackhaz 5y agoCan wave-particle duality be considered as part of the riddle?
- jonquark 5y agoNot really in the same way. The Standard Model is built out of quantum field theories that take as a given our experiment results that matter on quantum scales is unlike the "large scale" matter we see around us. The problems described in the articles are unexpected results that we see in our experiments compared to the Standard Model, "weird/nonintuitive" aspects of modern particle physics would be a separate article.
- mikhailfranco 5y agoNo, it's quite clear in QFT that elementary entities: - travel as unitary time-reversible non-local waves (propagate, interfere, entangle) - interact as non-unitary time-irreversible local particle events (position, time, exchange, create, destroy) Your interpretation of quantum mechanics will determine how you imagine the two views connect (Born Law, Many Worlds, ...)
- ajkjk 5y agoI don't think it's correct to say that they interact as particle events, because off-shell interactions are a thing, and interacting strictly as particles would prohibit that, no?
- casparvitch 5y agoNo, physicists are pretty comfortable with that one. It isn't immediately intuitive, but the models we have are powerful and predictive. There is of course a somewhat open question as to the interpretation of quantum mechanics. That question is almost metaphysics, whereas the problems quoted in the article are more holes in our present theory.
- hdjjhhvvhga 5y agoWell, they're comfortable because the phenomenon is well-studied, we have very good models and can with good accuracy predict what will happen. What we don't know is why exactly it behaves in this way.
- b-x 5y agoWhat about the existence of magnetic monopoles?
- aardvark179 5y agoWell the standard model doesn’t predict them, and apart from one detection that has never been reproduced we’ve never detected any pre-existing ones or any created in a particle accelerator.
- deleted 5y ago[deleted]
- b-x 5y agoThe standard model doesn't predict the graviton neither, nonetheless, they mentioned it in the article. Does the SM theorize about the impossibility of the monopoles' existence?
- galcerte 5y agoWe have detected the effects of gravitons (...if it's gravitons and not something else) at macroscopic scales, however we have not done the same with monopoles. So that comparison is not apples to apples. I have not heard anything about the SM predicting them being impossible, but I assume it does given that I haven't heard anything about the subject. Source: I have a master's in physics and a friend of mine did his bachelor's thesis in monopoles in classical electrodynamics (albeit modified) and his master's in quantum ones, so he would've told me if he knew. However, if any GUT theory we have come up with is correct (because a few exist), then that does imply the existence of monopoles.
- auntienomen 5y agoGravitons are a universal prediction, so one doesn't get any credit for predicting them. _Any_ low-energy quantum field theory approximation to gravity will have them, so long as it looks like GR at large enough distance scales.
- cjfd 5y agoThe neutrino mass thing is much less a surprise than the rest. Neutrino mass always was quite possible as an optional add-on. Basically, the situation for the quarks, where all six have mass, can be copied to apply to the leptons as well.
- morelandjs 5y agoI’d add to this, that we know very little about the spatial distribution of nuclear matter at and below the scale of a nucleus. The standard model excels at understanding the salient characteristics of asymptotic states before and after an interaction, things like spin, lepton number, etc. But we still can’t tell you how gluons are distributed inside the proton.
- indutny 5y agoNor can we tell why proton is a spin 1/2 particle because the gluon soup and particle-antiparticle pairs make this complicated.
- evanb 5y agoWe're not all the way there yet, but this is a hot and rapidly-advancing topic. See, eg. https://arxiv.org/abs/2111.06948 https://arxiv.org/abs/2111.06948 and sources therein.
- akomtu 5y agoI'd speculate it's platonic solids, highly complex and dynamic, but resembling those solids from outside.
- T-A 5y agoI am so tired of seeing massless neutrinos being described as a "prediction" of the Standard Model, and finite neutrino masses as beyond-Standard Model physics or even a "mystery". This is especially disappointing coming from a supposedly serious magazine like Symmetry. Neutrinos were originally hypothesized in order to solve a problem which did not require them to have mass, and for a long time after they were actually observed, their measured masses remained within error bars straddling zero. It therefore made perfect sense to model them as massless. But to actually include neutrino masses in the Standard Model is trivial, and was done long ago. The most straightforward way to do it is to give them quark-like mass terms. This requires introducing a right-handed partner for each known (left-handed) neutrino, which some people don't like because right-handed particles don't partake in weak interactions, and weak interactions are the only (known) neutrino interactions (apart from gravity), so you end up with undetectable particles. The main alternative is to use Majorana mass terms, making neutrinos their own anti-particles, which some people don't like because it deviates from the pattern of all other fermions in the Standard Model. A third way is to say "it's both", typically involving the seesaw mechanism, which some people don't like because it requires unfashionable GUT-style beyond-Standard Model physics. Point is, there is neither a failed "prediction" nor a great "mystery" here. There is uncertainty about which kind of mass term we should use for neutrinos, because the experimentally observable differences between the alternatives are really, really tiny.
- nxpnsv 5y agoThe mystery part is: what is the correct way to include the mass term.
- T-A 5y agoNo mystery at all, you add it to the massless part of the Standard Model Lagrangian. :)
- supergarfield 5y ago> This requires introducing a right-handed partner for each known (left-handed) neutrino, which some people don't like because right-handed particles don't partake in weak interactions, and weak interactions are the only (known) neutrino interactions (apart from gravity), so you end up with undetectable particles. I'd be curious to hear more about this. What mechanism forces you to add right-handed partners? Is it some conservation property? Are calculations too difficult without them? Maybe it's also not clear if there really is a difference between saying "right-handed neutrinos exist but are undetectable" and "right-handed neutrinos are fake particles added for ease of modeling". Edit: Wikipedia also says > The neutral-current Z^0 interaction can cause any two fermions in the standard model to deflect: Either particles or anti-particles, with any electric charge, and both left- and right-chirality, although the strength of the interaction differs. So could right-handed neutrinos be detected this way?
- streamofdigits 5y agoThe problem is that from an experimental / observational technologies perspective we have been for many decades now in some sort of "evidence desert" that pushes against fundamental technology boundaries and that is not conducive to solving big "mysteries". Unifications, re-interpretations, new conceptualizations (new forces etc) are the mental tools through which we solve previous "mysteries" (and create new ones). Right now there are alive more physicists than ever and even a tiny piece of important news could lead to a revolution - in like a couple of years. But what you really want is a firehose of new data points, "a new window". This has not happened and it may not happen for generations (for the attentive reader: gravitational waves are at the very, very edge of the detectable). As Feynman might say, the Universe doesn't owe us a continuous stream of gee-wow moments But if I had to bet where the breakthrough might come from I'd say it would probably be cosmology rather than elementary particles...
- jjk166 5y agoI've recently heard a rather interesting and optimistic take on this. Since we have had so many brilliant minds looking in so many places for new physics and still have not seen evidence of it, that suggests whenever we do find new physics, it will have to be so bafflingly strange that all these brilliant people could never imagine it. It may very well be a bigger paradigm shift than the jump from classical to modern physics.
- snowwrestler 5y agoIt seems crazy to say that we have not seen evidence for new physics when the size estimates of dark matter and dark energy account for about 95% of known energy in the observable universe. How is that not evidence for new physics? If our physical theories cover only about ~5% of what we observe… that seems like a bit of an issue, no matter how accurately they model that 5%.
- jjk166 5y agoNeither dark matter nor dark energy are new physics. We don't know exactly what particle or combination of particles is responsible for dark matter, but there's not yet evidence that dark matter actually is composed of something outside the standard model. Dark energy is, despite the name, well explained by general relativity. When people talk about new physics, they're referring to things that change our understanding of how the universe works on a fundamental level. By comparison to biology, these are like newly discovered species - of course they're interesting but our understanding of nature is unchallenged.
- mellosouls 5y ago(2018) though I don't expect much has changed...
- bmitc 5y agoThe standard model and particle physics has become basically a religion for some scientists. > “As for the question ‘What are we?’ the Standard Model has the answer,” says Saúl Ramos, a researcher at the National Autonomous University of Mexico (UNAM). “It tells us that every object in the universe is not independent, and that every particle is there for a reason.” Because this makes no sense unless you're operating under some sort of belief system.
- dwheeler 5y agoI would add, why do certain particles decay into other particles? For example, the tau particle contains nothing else, as far as we can tell, yet it decays into certain other particles (and not the same ones every time). More generally, the standard model records a lot of particles and things that happen, but not why those instead of others. I suspect there's a simple model underneath, but I have no idea what it is.
- tsimionescu 5y agoCoincidentally, Sabine Hossenfelder (a theoretical physicist) had just had a piece on this topic: http://backreaction.blogspot.com/2021/11/why-can-elementary-particles-decay.html?m=1 http://backreaction.blogspot.com/2021/11/why-can-elementary-...
- evanb 5y agoAs a physicist I'd say these things are well understood. - Why do certain particles decay into other particles? Quantum mechanics is totalitarian: what ever is not forbidden is mandatory. Forbidden: excluded by some symmetry principle (violation of a conserved quantity, like energy, angular momentum, ...) - The tau decays into certain other particles (and not the same ones every time). Tau carries electric charge, fermion number, angular momentum. The decay products' total quantum numbers match that of the tau. But the quantum-mechanical totalitarian principle says that every possible combination that satisfies that constraint happens with some amplitude. - The standard model records a lot of particles and things that happen, but not why those instead of others. I suspect there's a simple model underneath, but I have no idea what it is. If by 'those' and 'others' you mean all the varied observed phenomena, then yes, there is a simple model underneath and it IS the standard model. If by 'those' and 'others' you mean 'why is the SM the way it is', that's (likely) an out-of-bounds question for the SM in the first place. But a modern perspective on the SM is to think of it as a low-energy effective field theory anyway.
- umvi 5y agoIs there any evidence of "dark matter" or "dark energy" actually existing? I find it more likely that we just don't understand the real mechanisms behind galaxy rotation and universe expansion and so we just made up unfalsifiable stopgaps to make the numbers work out.
- JudasGoat 5y agoI always find it curious that both dark matter and dark energy aren't available locally to study.
- AnIdiotOnTheNet 5y agoIt likely is, we just can't detect it on such small scales. It would be a form of matter that interacts pretty much only via gravity, and since gravity is already 40 orders of magnitude weaker than the electromagnetic force we usually use to detect things, it's understandable that it is kinda hard to see.
- AnimalMuppet 5y agoThey might be, but only in very small quantities. The amount of dark matter that we would need to "fix" the galaxy rotation problem... would it affect the orbits of things in the solar system at all? (OK, yes, it would, but observably?) I haven't done the math, but I strongly suspect that the answer is "no".
- dahfizz 5y agoDark matter is especially dubious to me. Is it possible its literally matter which is dark? i.e. there are more planets and asteroids and mass than we can see because it is not illuminated? How can we be confident in our prediction of the mass of distant galaxies? Maybe that is what is meant when a physicist says dark matter, and its the media that mysticizes it.
- jasonwatkinspdx 5y agoSo dark matter doesn't just mean "not illuminated" it means it doesn't interact with the EM field at all. However it does interact gravitationally, and this has a measurable impact on matter we can see with our telescopes, the cosmic microwave background, etc. Cosmology today is, in general, very sophisticated. I mean no offense but armchair contrarian takes here are very much just coming from a place of ignorance. Any criticism we can imagine as lay people has already been plumbed to a depth and detail we will never be capable of in our lives. One can point out that there's always some degree of uncertainty in absolute terms, but I think the appropriate understanding is Bayesian, and I'd sooner bet on getting hit in the head by an astroid walking through my neighborhood than that cosmologists have this all fundamentally wrong. The wikipedia page does a reasonably good job of going through the multiple independent lines of evidence we have for dark matter. Sean Carrol has some great posts / videos in this topic area as well. The reason we're so confident of the current state of knowledge is not somehow that physicists and cosmologists suffer from hubris that blinds them to sophomoric criticisms, though sadly there's a number of people who continue to grind that grift.
- sesm 5y ago2, 3 and 4 are not Standard Model problems, but cosmological problems. There are cosmological theories that explain them by using only General Relativity without any changes to particle physics. For example, you can check out Nick Gorkavyi's cosmological papers: https://pos.sissa.it/335/039/ https://pos.sissa.it/335/039/ https://academic.oup.com/mnras/article/476/1/1384/4848298 https://academic.oup.com/mnras/article/476/1/1384/4848298 https://academic.oup.com/mnras/article/461/3/2929/2608669 https://academic.oup.com/mnras/article/461/3/2929/2608669 https://arxiv.org/abs/2110.10218 https://arxiv.org/abs/2110.10218 https://www.sao.ru/Doc-k8/Science/Public/Bulletin/Vol76/N3/ASPB285.pdf https://www.sao.ru/Doc-k8/Science/Public/Bulletin/Vol76/N3/A... (this one is available only in Russian for now)
- kloch 5y agoThey forgot at least one mystery: What determines the fermion mass spectrum and specific mass vlaues? Why do these particle masses take such seemingly random values? Related: Why are these masses so much smaller than the Planck mass? For comparison, the electric charge is sqrt(alpha_em) or ~1/11th the value of the Planck charge.
- redis_mlc 5y ago> Five mysteries the Standard Model can’t explain And a good thing, too. Otherwise those juicy big-science grants would disappear!