[HN Gopher] Muon G-2 Experiment at Fermilab Finds Hint of New Pa...
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Muon G-2 Experiment at Fermilab Finds Hint of New Particles
Author : gmays
Score : 95 points
Date : 2021-04-08 14:19 UTC (8 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| quantum_mcts wrote:
| Check out this phyics.stackexchange answer:
| https://physics.stackexchange.com/a/627852/386 I've been involved
| in one of the light-by-light theory groups a long time ago. The
| situation with theoretical prediction is not as clear.
| dang wrote:
| Discussed yesterday:
|
| _Particle mystery: physicists confirm the muon is more magnetic
| than predicted_ - https://news.ycombinator.com/item?id=26726269 -
| April 2021 (282 comments)
| DrBazza wrote:
| Regardless of whether this is a real result, I always had trouble
| "trusting" the "Standard Model" when I was at university. There
| are too many knobs to twiddle, and levers to pull in order to get
| the results. The mathematics is non-trivial. Just reading the
| article gives you an idea of how difficult it is to make
| predictions from the model.
|
| Compare it to this comment about General Relativity:
|
| "Widely acknowledged as a theory of extraordinary beauty, general
| relativity has often been described as the most beautiful of all
| existing physical theories." (via wikipedia - Landau & Lifshitz
| 1975, p. 228).
|
| (ignoring the cosmological constant, of course).
|
| Compared to most, or all, other physical theories, the Standard
| Model feels like there's something much simpler set of equations
| underneath waiting to be discovered.
| coliveira wrote:
| Despite its complexity, the model has been remarkably
| successful during the last decades.
| whimsicalism wrote:
| It doesn't seem obvious that the fundamental models of reality
| would just happen to match up with the mathematical constructs
| that we humans have come up with.
| idolaspecus wrote:
| On the flip side, it wouldn't be entirely surprising if
| mathematical constructs that we have thought of are in fact
| very good models of fundamental reality. We should remember
| that, after all, nothing exists outside of fundamental
| reality, and if certain basic patterns can be encoded such
| that the encoding is both high-fidelity and simple, that
| won't be shocking. It might be awe-inspiring, but not really
| surprising.
| CarelessExpert wrote:
| This is a deep philosophical debate: Is mathematics invented
| or discovered?
|
| https://www.pbs.org/wgbh/nova/article/great-math-mystery/
| whimsicalism wrote:
| I think it's a bit less deep than that. It's more, "is the
| language we use to describe mathematics invented or
| discovered", which I would put myself (and most people)
| firmly in the invented camp.
| [deleted]
| willis936 wrote:
| Nature doesn't care how complicated it is. A bias towards
| beauty is a trap that any serious scientist will not fall for.
|
| https://www.youtube.com/watch?v=xFKgIOX8IRE
| whimsicalism wrote:
| A bias towards "beauty" or simplicity of some form is
| inevitable and part of good science.
|
| For every theory, you can generate a more complicated theory
| with more moving parts that generates the exact same
| predictions. For instance, my theory of gravity is the same
| as general relativity, except that at 3 PM April 9th, 2021,
| all gravity will be reversed.
|
| You have to appeal to some principle to sort out such
| theories from good descriptions of how the world works.
| CarelessExpert wrote:
| > You have to appeal to some principle to sort out such
| theories from good descriptions of how the world works.
|
| Yes: testable predictions followed by experimental
| evidence.
|
| Beyond that I don't see how what you're talking about is
| anything other than an appeal to aesthetics.
| whimsicalism wrote:
| > Yes: testable predictions followed by experimental
| evidence.
|
| But there are an infinite number of theories matching the
| current evidence. Some predictions of the theories might
| not be testable, what do you do then?
| willis936 wrote:
| Simple: you label them as fiction rather than science.
| The scientific method has experimental feedback built
| into the loop.
| [deleted]
| lumost wrote:
| Most of the standar model complexity comes from the variety of
| particles, forces, and aggregations thereof that need to be
| contended with.
|
| GR likewise becomes a brutal computational mess with these many
| body problems.
|
| What will be interesting in these new experimental results is
| whether we're reaching the limits where determining the
| correctness of our approximations becomes impractical.
| haxiomic wrote:
| If its turtles all the way down, and physics goes on forever
| like a fractal, you'll find domains where you can approximate
| with relatively simple mathematics ("beautiful") and domains
| that require much more mathematical machinery to describe
| spekcular wrote:
| On this point, you might enjoy "A Fortunate Universe (Life in a
| Finely Tuned Cosmos)" by Lewis and Barnes. It discusses this
| "fine-tuning" problem in a detailed and up-to-date way, and
| avoids the theological speculation found in some other
| treatments. (That is, fine-tuning is sometimes presented as
| evidence for God.)
| mseepgood wrote:
| Why does it take physicists so long to find the complete
| foundation of the universe? I want an answer in my lifetime.
| ganzuul wrote:
| Hilbert's tomb: Wir mussen wissen Wir werden wissen
|
| You should not be downvoted. Spare the world a little cruelty
| where we can.
| vecter wrote:
| He/she is being downvoted for demanding an answer, as if
| they're entitled to one but all the physicists out there are
| just too dumb to figure it out or refuse to give them what
| they are owed.
|
| Perhaps that is not how this person actually feels. If so, a
| little humility and empathy in their communication would go a
| long way to rectify that.
| ganzuul wrote:
| Hilbert demanded an answer too. Godel showed that his
| effort would never reach its goal. We are all still reeling
| from the blow.
| rrss wrote:
| The tomb next to hilbert:
|
| "I must know. Why do the mathematicians take so long to
| find out?"
| xxpor wrote:
| 120 years ago, we had no model of the atom, no quantum theory,
| no relativity, and only the first hints of figuring out
| radioactivity. Yet we were able to split the atom in 1942,
| create the MOSFET in 1959, and started launching the first GPS
| satellites in 1978.
|
| It's hard to express how much progress we've made in such a
| small amount of time relative to the rest of history. It's a
| god damn miracle.
| Iwan-Zotow wrote:
| screwed up half of biosphere as well...
| sto_hristo wrote:
| It's theories galore out there that aim to describe everything.
| Proving them right/wrong via experiments is the hard part.
| ISL wrote:
| Physicist here:
|
| 1. One should be rather specific about what 'the complete
| foundation' might comprise. The depth of questions one can ask
| is infinite, but some questions are more important than others.
| The g-2 experiment is asking a specific question: "Does the
| anomalous magnetic moment of the muon open a door to
| discoveries that are inaccessible with modern colliders?"
|
| It is tempting to regard fundamental physics as a study of "Why
| are we here?", but it is really a study of "How are we here?"
| The difference is subtle but substantial. If "Why?" is what
| you're seeking, you are more likely to find that answer within,
| rather than within the study of physics.
|
| 2. Physicists can do a lot more in these directions with
| greater institutional support. With great sadness, I recently
| departed a lab, where colleagues next-door were working on this
| very experiment, precisely because a collision between funding
| rules and administrative priorities made further progress
| within my specialty unsustainable. I was the third postdoc in a
| row to do the same; not for lack of scientific promise nor
| ability to attract grants.
| mseepgood wrote:
| > It is tempting to regard fundamental physics as a study of
| "Why are we here?", but it is really a study of "How are we
| here?" The difference is subtle but substantial. If "Why?" is
| what you're seeking, you are more likely to find that answer
| within, rather than within the study of physics.
|
| I don't want to know why, I just want to know the complete
| set of rules at the lowest level.
| ISL wrote:
| It is unlikely that we will ever grasp the complete set of
| rules at the lowest level. I don't say this to be
| defeatist, but rather as a statement of pragmatism.
|
| To do so would be to have a convincing grasp of Planck-
| scale physics -- a detailed understanding of physics at and
| above energy-densities reached in the Big Bang. Some
| precision experiments and astrophysical measurements _do_
| constrain certain Planck-scale models, but a true test of
| whether or not we understand early-universe physics is
| likely to necessitate creating a few Big Bangs ourselves.
| Doing so, with known technology, seems impossible. If it
| were possible, doing so would seem fraught with actual
| risk.
|
| (N.B. for the non-expert reader: there are cosmic rays that
| strike the Sun at least once every five minutes (and Earth,
| at least once a month) with energies 10,000,000 times
| greater than anything humans have ever achieved. Those
| collisions, over the last 4,500,000,000 years, have not yet
| resulted in the disruption of spacetime or the formation of
| a black hole. You are very, very, very safe from physicists
| breaking the universe as you know it. :).)
|
| _Edit to add: You, mseepgood, aren 't alone in your desire
| for knowledge. One Stephen Hawking once stated, "My goal is
| simple. It is a complete understanding of the universe, why
| it is as it is and why it exists at all."_
| refulgentis wrote:
| dumb q I was never smart enough to ask when I was doing a
| physics degree: how do we know the big bang required
| enormous energy and thus is impossible? in the few peeks
| we got at grad school physics, I walked with away with
| the likely erroneous impression that the best guess was
| the big bang happened due to "quantum fluctuations in a
| vacuum" which sounded suspiciously close to "at random" -
| and I won't lie, since, I've just assumed that at any
| point there could be another big bang and we'd be blown
| away!
| ISL wrote:
| I think the safest answer regarding the Big Bang is that
| we don't really understand the mechanism. In particular,
| anything regarding inflation stands on truly dubious
| ground (It gets the necessary outcomes right, but we have
| _no_ presently-testable theory regarding the mechanism.
| Any mechanism that does must defy the laws of physics as
| we know them).
|
| I can't pretend to be an expert here, but the quantum-
| fluctuations in a vacuum that we all experience at all
| times do, over longer times ("long" here is generally
| unfathomably short), need to satisfy energy-conservation.
| To do otherwise requires paying an overwhelming
| probabilistic cost (a much bigger nigh-infinity than your
| garden-variety nigh-infinity). If you're worried about
| unexpected instantaneous death from the universe, I would
| argue that one should be far more concerned with, say, a
| gamma-ray burst nearby from within the galaxy (or, far
| more likely yet, a nuclear war) than being overrun by a
| Big-Bang-like event.
|
| For that same reason (energy conservation), perhaps the
| central question one might ask of the Big Bang theory is,
| "How did it come to pass that all of that energy wound up
| in such a tiny volume?" There are plenty of theories out
| there, the best of which attempt to confront inflation at
| the same time, but I am unaware of a clear leader.
|
| I don't mean to entirely disregard the importance of
| quantum fluctuations in cosmology. Indeed, the large-
| scale structure of the cosmic-microwave background is
| very consistent with pure quantum fluctuation, as if the
| fluctuations of a tiny volume of space had been magnified
| to cosmic scale. It is simply this experimentalist's
| opinion that there is probably substantially more to the
| story than the universe having won the lottery of all
| lotteries in order to exist at all.
| spekcular wrote:
| What do you feeling is wrong with "the universe having
| won the lottery of all lotteries in order to exist at
| all"? Our existence seems consistent with some multiverse
| picture where we just end up observing one out of many
| universes that was capable of supporting life. After all,
| if any of a number of fundamental constants gets tweaked
| by a small amount, then we end up in situations like e.g.
| hydrogen being the only naturally occurring element.
|
| (I'm purposely being a bit provocative here because I
| haven't heard an explanation for fine-tuning that doesn't
| rely on multiverses or divine intervention.)
| gbpz wrote:
| I blame the mathematicians anf the engineers.
| mhh__ wrote:
| So far we're struggling to reverse engineer all the perl it was
| hacked together with
| collinvandyck76 wrote:
| the container that runs the simulation is extremely hard to
| escape from
| MichaelApproved wrote:
| I know you're joking around but does the universe seem hacked
| together to you?
|
| I feel like it's incredibly elegant. All these low level
| rules are able to create such complex structures with
| beautiful order to it.
|
| It's so orderly, we can play things backwards billions of
| years. We can look back to how things were just a fraction of
| a second after this version of the universe began.
|
| It's astonishing.
| criddell wrote:
| But can we explain just what exactly quantum mechanics
| _is_?
| xxpor wrote:
| It's too bad we'll almost certainly never be able to answer
| the meta question of how or why we ended up with the rules
| we did.
| whimsicalism wrote:
| These questions are more metaphysics than science.
|
| I, personally, am partial to the idea that the anthropic
| principle has a pretty big role to play, at least in
| terms of the fundamental constants.
| mhh__ wrote:
| Maybe. The fact that a treatment of particle physics based
| on Symmetry groups works so well is rather odd, but equally
| why should it be that way? Elegance is subjective,
| mathematical elegance even more so.
| libraryofbabel wrote:
| There have been a bunch of articles near the top of HN on this
| result, but I found this one from Quanta magazine to be one of
| the best non-technical explanations.
|
| Particularly interesting was the focus on an alternative
| _theoretical_ calculation for the muon magnetic moment: the "BMW"
| approach, which uses a numerical lattice model and produces a
| number much closer to the Fermilab experiment.
|
| For an outsider, one of the surprising things here must be just
| _how hard the theoretical calculation actually is_ , especially
| as you get deeper into the decimal places and have to include the
| vacuum effects on the muon of basically all particles in the
| standard model, including hadrons which means trying to calculate
| the Strong Force. Back when I studied quantum field theory in
| college we never got anywhere near actually producing numbers for
| strong force effects; the equations weren't soluble with the
| usual perturbation theory techniques. But it's interesting to
| read about how it is possible to get useful numbers with these
| different cutting-edge theoretical/computational methods - but
| with some uncertainty about whether _they're actually right_!
|
| Curious to hear any practicing physicists on HN weigh in on the
| BMW calculation versus the orthodox theoretical approach that
| everyone's comparing the Fermilab result against.
| whatshisface wrote:
| The class of integrals that QCD solutions belong to is known to
| be NP-hard. It is not known specifically that QCD itself is NP-
| hard but it is suspected to be by many.
| tobmlt wrote:
| Can't upvote you enough. This is driving me crazy-curious. It
| must be eating at the HEP folks... unless it isn't, hah.
|
| If this becomes a quagmire nested with the muon quagmire within
| the new physics quagmire. I will surely have to find a way to
| renormalize my self energy.
| podiki wrote:
| Someone linked to this Twitter thread in the other discussion,
| from a theorist (one I happen to know a very little, from back
| in the day):
| https://mobile.twitter.com/GordanKrnjaic/status/137983430884...
|
| Not a lattice theorist, but I can tell you lattice stuff is
| very hard, and also very cool to be calculating such bare bones
| nature on a computer. Lattice results can be hard to parse for
| the outsiders, and I know there is often debate over how
| trustworthy the results are when it is so hard to check (you
| don't just build and perform another experiment). That's not to
| say the people doing it aren't very smart and capable, but it
| is an unbelievably difficult problem to do, and just like
| experiments have problems and errors, so to does lattice
| calculations. Treating them like almost another form of
| experiment is perhaps best (how does it fit in with other
| experiments? with theory expectations? how can we know if it is
| correct or not and correlate with other results? etc.). In
| other words, theorists and model makers (like work I used to
| do), may or may not include lattice results based on how they
| feel about some result (or what it does to their own
| model....).
| nickthegreek wrote:
| PBS Spacetime just released a video on this experiment.
| https://www.youtube.com/watch?v=O4Ko7NW2yQo
| MichaelApproved wrote:
| So did Fermilab ;) https://youtu.be/ZjnK5exNhZ0
|
| Definitely worth checking out the rest of the videos on both
| those channels.
|
| While we're at it, check out 60 Symbols' channel for great
| physics discussions that hardly ever (thanks Brady!) include
| equations https://youtube.com/user/sixtysymbols
| peter303 wrote:
| The muon was the first non-standard matter particle and second
| transient particle discovered in 1937. It lead to much new
| physics in mid-20th century. And continues to suggest new
| physics.
| fasteddie31003 wrote:
| Question for physicists: Are the G-2 results more groundbreaking
| than discovering the Higgs particle to moving physics forward?
| peteradio wrote:
| If physics is climbing a mountain.
|
| G-2 result is seeing the next hand hold (hoping its not a
| mirage).
|
| Higgs discovery and its subsequent precision measurement is
| resting your toe into a hold and flexing your calf upwards.
| Diederich wrote:
| I'm not a physicist, I just pay some attention to these things.
|
| The Higgs particle was expected, and so finding it within
| expected ranges was confirmation of the standard model.
|
| The G-2 results are showing deviations from the expected ranges
| from the standard model.
|
| In the former case, Higgs, the standard was further, strongly
| confirmed. In the latter case, G-2, there's a strong indication
| that the standard model is fundamentally missing something.
|
| I think that's pretty exciting!
| quantum_mcts wrote:
| Physicist. Some people in the community are quite excited
| because it hints at something beyond SM. The problem is that
| the quoted theoretical prediction for g-2 is not a settled
| issue and is a subject of a long controversy between various
| groups of theorists.
| https://physics.stackexchange.com/a/627852/386
| podiki wrote:
| I would agree with the other commenters. g-2 has been a debate
| for a long time, but fundamentally points to something new if
| the result holds. The Higgs was expected, and given the mass
| and properties we've seen, doesn't point to anything new. "New"
| meaning not the Standard Model.
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