[HN Gopher] Particle mystery: physicists confirm the muon is mor...
___________________________________________________________________
Particle mystery: physicists confirm the muon is more magnetic than
predicted
Author : furcyd
Score : 367 points
Date : 2021-04-07 15:26 UTC (7 hours ago)
(HTM) web link (www.sciencemag.org)
(TXT) w3m dump (www.sciencemag.org)
| gus_massa wrote:
| Only 4.2 sigmas. ;)
|
| That is really a lot. It's less than the official arbitrary
| threshold of 5 sigmas to proclaim a discovery, but it's a lot.
|
| In the past, experiments with 2 or 3 sigmas were later classified
| as flukes, but AFAIK no experiment with 4 sigmas has
| "disappeared" later.
| sgt101 wrote:
| Oh sweet summer physicist, what do you know of reality? Reality
| is for the markets, lovely mathey person, when a one in a
| million chance comes every month, and investment portfolios lie
| scattered over the floor like the corpses on a battlefield.
| Reality is for when your mortgage and the kid's school fees are
| riding on it, and quantitative strategies are borne and die
| with the fads of last summers interns pet projects.
|
| In some domains 7 sigma events come and go - statistics is not
| something to be used to determine possibility in the absence of
| theory. If you go shopping you _will_ buy a dress, just because
| it 's a pretty one doesn't mean that it was made for you.
| comboy wrote:
| Neutrinos faster than light had 6 sigma.
|
| It just shows probabilistic significance. Confirmation by
| independent research teams helps eliminate calculation and
| execution errors.
| thepangolino wrote:
| This is the second separate experiment giving similar value.
| XorNot wrote:
| The use of a secret frequency source not known to the
| experimenters is also a very good way to deal with
| potential bias.
| Robotbeat wrote:
| That does help a lot!
|
| Of course, this is still not good enough. But the nice
| thing about things that are real is they eventually stand
| up to increasing levels of self-doubt and 3rd party
| verification... it's an extraordinary result (because, of
| course, the Standard Model seems to be sufficient for just
| about everything else... so any verified deviation is
| extraordinary), and so funding shouldn't be a problem.
|
| A decent heuristic: Real effects are those that get bigger
| the more careful your experiment is (and the more times it
| is replicated by careful outsiders), not smaller.
| [deleted]
| davrosthedalek wrote:
| "Separate" for slightly small values of separate. It's the
| same measurement approach, and using many components from
| the first experiment, so there could be correlated errors.
| But they made many fundamental improvements to the
| experiment, so it's great to see that the effect hasn't
| gone away.
| ISL wrote:
| The primary shared component is the ring/yoke. I worked
| in the same lab as a substantial team of g-2 scientists
| for the last decade and watched them come to this result.
| The level of re-characterization of the properties of the
| entire instrument was extremely extensive. If anything,
| one should regard the lessons that they have learned
| along the way as providing extra insight into the
| properties of the original BNL measurement.
|
| To use a car analogy: This is as if you took someone's
| prize-winning race car, kept the moderately-priceless
| chassis, installed upgraded components in essentially
| every other sense (remove the piston engine, install a
| jet engine, remove the entire cockpit and replace with
| modern avionics, install entirely new outer shell,
| replace the tires with new materials that are two-decades
| newer...), put the car through the most extensive testing
| program anyone has ever performed on a race car, filled
| the gas tank with rocket fuel, and took it back to Le
| Mans.
|
| I believe that the likelihood of a meaningful ring-
| correlated systematic, while still possible, is quite low
| in this case. The magnetic-field mapping, shimming, and
| monitoring campaigns, in particular, should give people
| confidence that any run-to-run correlated impact of the
| ring ought to be very small.
| selectodude wrote:
| Ideally they have all their fiber optic cables screwed on
| tight at Fermilab.
| gizmo686 wrote:
| As I recall, FTL neutrinos were the result of experimental
| error, not chance; and so are outside the scope of what sigma
| screen for.
| theptip wrote:
| In scope for the context of this thread though; your GP
| claimed that 4 sigmas means "it'll probably pan out as
| being real", your parent provided a 6-sigma counter
| example.
| kbelder wrote:
| "It's 99.99% significant, if we assume the 10% case that
| we haven't fucked up somewhere."
| [deleted]
| ianai wrote:
| Or the title of this topic as it is right now is
| misleading. It says they've confirmed the stronger
| magnetic field. Ie it was either predicted elsewhere or
| seen elsewhere. The later would build confidence in the
| testing apparatus.
| lamontcg wrote:
| That's the point.
|
| At the time it was very significant results, just like this
| one.
|
| Turned out someone hadn't plugged a piece of equipment in
| right and it was very precisely measuring that flaw in the
| experiment.
|
| You can't look at any 8 sigma result and just state that it
| must necessarily be true. Your theory may be flawed or you
| may not understand your experiment and you just have highly
| precise data as to how you've messed something else up.
| mhh__ wrote:
| It's probably worth saying that even "chance" is still a
| little misleading in the sense that the quantification of
| that chance is still done by the physicists and therefore
| can be biased
| tompagenet2 wrote:
| Genuine question from ignorance. Is this related to this work at
| CERN? https://www.theguardian.com/science/2021/mar/23/large-
| hadron...
| dukwon wrote:
| Maybe. There are plenty of attempts to explain g-2 and LFUV in
| B decays in one go.
|
| But really there's no way to know for sure yet.
| yk wrote:
| Yes and no. It is two very different experimental situations,
| the magnetic moment is at rest (well, in an accelerator but the
| rest frame is defined by the muon) and the R_k anomaly is in an
| collision. On the other hand, as a theorists the immediate
| thing one thinks about is lepton universality, that the only
| difference between a electron and a muon is its mass, is
| violated. So there will be a lot of work this year on trying to
| explain both results at the same time.
| davidivadavid wrote:
| Physics noob question: is there any physical framework that does
| away with the concept of "force"?
|
| I know a bit about how it is reconceptualized as space-time
| deformation in the context of general relativity, but that's
| about it.
|
| It just seems like one of those inherently anthropocentric
| concepts that (potentially) holds us back from exploring
| something different?
| BlueTemplar wrote:
| I'd have to brush up on my quantum mechanics, but IIRC they
| don't have the concept of "force" ?
|
| (F=ma being replaced by Schrodinger's equation.)
| dkersten wrote:
| Isn't quantum field theory kinda like that in that "forces" are
| actually just the effects of the fields interacting? (Not a
| physicist, so...)
| dogma1138 wrote:
| Gravity isn't a force in general relativity.
|
| However other forces such as the strong nuclear and the
| electroweak are forces in theories such as the standard model.
|
| Grand Unification theories often are trying to turn gravity
| into a force this is where mediating particles such as the
| graviton come into play but these aren't very successful yet.
|
| It may be that gravity isn't a force at all and is just an
| emergent phenomenon from the geometric properties of space
| time, or it could be both basically two distinct phenomena that
| cause attraction between massive objects where on a larger
| scale it's primarily dominated by the geometry of space time
| and on the quantum scales by a mediated force with its own
| field and quanta (particles).
| jessermeyer wrote:
| > Gravity isn't a force in general relativity.
|
| More importantly, GR has nothing to say about forces at all.
| chriswarbo wrote:
| Lagrangian mechanics is equivalent to Newtonian mechanics, but
| doesn't involve force
| https://en.wikipedia.org/wiki/Lagrangian_mechanics
|
| The idea of replacing a 'gravitational force' with spacetime
| curvature gave us General Relativity; extending this same idea
| to electromagnetism gives us Kaluza-Klein theory
| https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory
|
| The current state of the art is Quantum Field Theory (of which
| the Standard Model is an example)
| https://en.wikipedia.org/wiki/Quantum_field_theory
|
| In QFT, "particles" and "forces" are emergent phenomena (waves
| of excitation in the underlying fields, and the
| couplings/interactions/symmetries of those fields). QFT tends
| to be modelled using Lagrangian mechanics too.
| andi999 wrote:
| Lagrangian mechanics gets a bit ugly if you want to include
| friction.
| hinkley wrote:
| I still need someone to ELI5 to me how space curvature model
| explains the attraction between two bodies that have a
| delta-v of 0.
| zamalek wrote:
| A common framework for explaining spacetime gravitation is
| the rubber sheet with a heavy ball, showing that other
| objects on the sheet fall towards the ball. This is really
| flawed because it explains gravity using gravity.
|
| Instead, you keep the rubber sheet and the single ball.
| Instead of placing other objects on the curved rubber,
| project (using a projector if you want) a straight line
| (from a flat surface) down onto the rubber. If you trace
| the projection of the line onto the rubber, you'll notice
| that it is no longer straight - it curves with the rubber
| (especially if you subsequently flatten the rubber out).
| That's a world line[1]. That's the direction of movement
| that an object would see as its "momentum" - but it
| wouldn't actually follow the world line, as the world line
| changes when the object moves.
|
| To build a geodesic (the actual orbit/movement of the
| object), you need to move along the world line and then
| build a new one, repeatedly. I haven't completely figured
| out the instructions to build a geodesic in this analogy,
| but seeing/imagining the curved world line should be
| enlightening:
|
| There is no attraction.
|
| [1]: https://en.wikipedia.org/wiki/World_line#World_lines_i
| n_gene...
| stan_rogers wrote:
| They don't. You're only thinking in three (spatial)
| dimensions. Time is more fundamental than you think.
| zamadatix wrote:
| An attempt at a true ELI5 is the bodies exist in what we
| know as spacetime, not as separate independent concepts of
| space and time which we perceive from our day to day
| experience, so we have to know a bit about the difference.
| Chiefly in spacetime everything always travels the same
| "speed" (c, the universal speed limit) and it's just a
| matter of how much of that speed appears as "traveling
| through space" and how much appears as "traveling through
| time". When 2 bodies warp spacetime it causes changes in
| the way each body's spacetime speed is distributed causing
| them to accelerate towards each other.
|
| The ELI15 version is think about vectors in our normal
| concept of 3D space first, if I told you a body was always
| moving at 100 meters per second and it was 100% in the
| horizontal direction you'd say there was 0 meters per
| second in the vertical direction. Now say something curves
| this geometry a little bit, the body will still be
| traveling at 100 meters per second but now a tiny bit of
| that speed may appear to manifest in the vertical direction
| and a tiny bit less appear to manifest in the horizontal
| direction. Same general story with spacetime except the
| math is a lot more complex leading to some nuance in how
| things actually change.
|
| The ELI20 version should you want to understand how to
| calculate the effects yourself is probably best left to
| this 8 part mini series rather than me
| https://youtu.be/xodtfM1r9FA and the 8th episode recap
| actually has a challenge problem to calculate what causes a
| stationary satellite to fall to the sun (in an idealized
| example) that exactly matches your question.
| bencollier49 wrote:
| That's the best explanation I've ever heard. I'd like to
| know if it really is mathematically rigorous. If so,
| bravo.
| taylodl wrote:
| This is a good video explaining just that!
| https://www.youtube.com/watch?v=wrwgIjBUYVc
| zcrackerz wrote:
| Think of your velocity vector as having a time component.
| The magnitude of this vector is c, so when you are at rest,
| you're moving full speed through time. When you accelerate,
| you shift some of this speed into the spatial dimensions.
| This is also why time passes more slowly for moving
| objects. Gravity also has this effect because not only is
| space curved, but space-time is curved. This means what
| would normally be a straight path through time is partially
| warped into the spatial dimensions when you encounter such
| a curvature.
| Strilanc wrote:
| It's space _time_ curvature. This is an important
| distinction, because although you can zero out the spatial
| component of your 4-vector you can 't also zero out the
| time component.
|
| Apparently you can think of the gravitational force as
| arising from time gradients [1]. Time flows slower closer
| to the planet, so if your arm is pointing towards the
| planet then your arm is advancing slightly slower in a
| particular way and this creates a situation where your arm
| wants to pull away from you; an apparent force.
|
| 1: https://www.youtube.com/watch?v=UKxQTvqcpSg
| Andrew_nenakhov wrote:
| Imagine a 2d sheet that is weiged by steel balls. It'll be
| curved because of weights. Now, put a sand on it and it'll
| start rolling according to sheet's curvature. That's
| attraction between bodies for you.
| andi999 wrote:
| Why is it an anthropocentric concept, did you never place
| anything on a scale? Or have a wire rip from a weight hanging
| on it?
| davidivadavid wrote:
| Of course. The point is that _interpreting that_ as a
| "force" is anthropomorphization ("this physical thing is
| "pushing"/"pulling" this").
| alephu5 wrote:
| It's a good question.
|
| One thing you find in modern physics is that ideas are often
| named according to some mathematical analogue to classical
| physics. You start thinking about forces by imagining a ball
| being kicked, and after boiling away the conceptual baggage you
| realise it's all about the exchange of energy.
|
| It turns out that energy exchange is one of the most
| fundamental mechanisms that drives nature so it makes sense
| that this same mathematics appears in deeper theories. Unlike
| classical physics the symbols in quantum equations don't
| represent simple numbers, they're usually quite complicated and
| subtle actually but remarkably these equations share many
| properties with their classical counterparts. To be fair this
| could just be that phenomena that differ completely from
| classical physics are incomprehensible to us.
|
| So an electron "spin", at least mathematically, is governed by
| equations that are remarkable similar to classical equations of
| angular momentum and so on. Force is in the same category and
| really just means "fundamental interaction".
| fctorial wrote:
| string theory?
| BlueTemplar wrote:
| Somewhat tangential, but Newton has been made fun of because he
| suggested the apparently "magical" idea that forces could act
| at a distance...
| outworlder wrote:
| > It just seems like one of those inherently anthropocentric
| concepts that (potentially) holds us back from exploring
| something different?
|
| This is something I struggle with.
|
| I know that physics originated from an experimental framework.
| We observe phenomena, then we try to come up with explanations
| for said phenomena, formulate hypothesis, then test them. That
| is fine.
|
| But this breaks down when the 'fundamental forces' are
| involved. What _is_ a force? All the explanations I've ever
| seen (apart from gravity) seem to treat a 'force' as an atomic
| concept. They will describe what a force 'does', but not what
| it 'is'. Maybe that's something unknowable, but it bothers me.
|
| F* magnets, how do they work.
| l33tman wrote:
| At its essence, in the modern understanding, a force is an
| emergent phenomena arising out of the fact that a world (a
| spacetime filled with your particles) where two particles of
| opposite charge seem to move towards each other is more
| probable than a world where they don't.
|
| This sounds silly but it's exactly the root cause in the
| current understanding and shoehorning in the word "force" in
| "force-carrying particles" is a stretch and causes this
| confusion. It's true that there would be no electromagnetic
| force without the photons. But photons and their likes are
| not the only way a "force" arises. For example, the Pauli
| exclusion principle can be seen as a "force" and it arises
| without photons with just electrons.
| ajkjk wrote:
| Yes, very much so. Forces are not really a thing in the
| Standard Model. There are symmetry groups attached to spacetime
| which lead to exchanges of gauge bosons which 'create' forces.
| dogma1138 wrote:
| Aren't forces in the standard model just fields which their
| quanta is gauge bosons (force carrying particles)?
| nyc640 wrote:
| There was a nice explanation of the finding in comic format from
| APS & PhD Comics: https://physics.aps.org/articles/v14/47
| lgrebe wrote:
| This sound like the hypothesized ,,subtle-matter" as proposed
| by Dr. Klaus Volkamer [1]?
|
| - still looking for a better link than the Book... I'll update
| this later
|
| [1] https://amzn.to/3mvvsWW
| gct wrote:
| lol
| dan-robertson wrote:
| But if muons are inanimate, why would they be affected by
| this hypothesised "subtle matter" which makes up the soul of
| living things?
| danellis wrote:
| What's the symbol that looks like a b fell over?
| monocasa wrote:
| Lowercase Sigma
| nyc640 wrote:
| Just to expand a bit, the sigma symbol is a standard symbol
| used to indicate the standard deviation of a measurement,
| and standard deviation is roughly a measure of how much
| variation there is within a data set (and consequently how
| confident you can be in your measurement). So when they say
| that the theoretical result is now 4.2 sigma (units of
| standard deviation) away from the experimental result
| instead of 2.7 sigma, that is because the new experiment
| provided more precise data that scientists could use to
| lower the perceived variance.
|
| Assuming that there were no experimental errors, you can
| use the measure of standard deviation to express roughly
| what % chance a measurement is due to a statistical anomaly
| vs. a real indication that something is wrong.
|
| To put some numbers to this, a measurement 1 sigma from the
| prediction would mean that there is roughly a 84% chance
| that the measurement represented a deviation from the
| prediction and a 16% chance that it was just a statistical
| anomaly. Similarly:
|
| > 2 sigma = 97.7%/2.3% chance of deviation/anomaly
|
| > 3 sigma = 99.9%/0.1% chance of deviation/anomaly
|
| > 4.2 sigma = 99.9987%/0.0013% chance of deviation/anomaly
|
| Which is why this is potentially big news since there is a
| very small chance that the disagreements between
| measurement and prediction are due to a statistical
| anomaly, and a higher chance that there are some
| fundamental physics going on that we don't understand and
| thus cannot predict.
|
| edit: Again, this assumes both that there were no errors
| made in the experiment (it inspires confidence that they
| were able to reproduce this result twice in different
| settings) and that there were no mistakes made in the
| predicition itself, which as another commenter mentions
| eleswhere, is a nontrivial task in and of itself.
| BlueTemplar wrote:
| Oh, so it's a bit like electron screening, but with virtual
| particles ? Fine structurally neat !
| Fiahil wrote:
| why did they move the magnet from Brookhaven to Chicago?
| nyc640 wrote:
| From what I understand the Magnet is extremely specialized
| and it would cost millions more to manufacture a second one
| rather than ship the existing one. As to why Fermilab,
| scientists had exhausted the capabilities of the particle
| accelerator at Brookhaven and Fermilab already possessed the
| equipment to generate more intense muon beams.
| kazinator wrote:
| They mystery here is why that comic image that is inlined into
| the page loads so slowly, but if you click on it while it is
| loading, you get a pop-up which shows the whole darn thing
| almost instantly, at what looks like the same resolution, even
| as the in-line one is still loading.
|
| Spooky quantum effect, there!
| jhoutromundo wrote:
| Let me say that this is the best thing that I ever saw in
| science: people using art to explain extremely complex findings
| that might change the future in a bit. I laughed a bit on 'I
| don't know you anymore'.
|
| When I was younger, I remember to read cyberpunk comics quite a
| lot. They explain a vision of the future that is improbable,
| but in many ways it get stuff right. Imagine aligning this with
| real word science. Imagine hearing from a superhero how his
| powers came to him. Imagine having a scientist name on the
| movie credits.
|
| It doesn't need to make everything scientifically accurate, but
| explaining the fundamentals can engage more people to enter
| science.
|
| Yesterday I was watching a new movie from Netflix called
| 'hacker'. The movie is awful, but it starts showing how Stuxnet
| should work, and that is pretty awesome. This is cool because I
| know the fundamentals of Stuxnet.
|
| If they break the 4th wall and show something that could happen
| for real, it could bring more emotions to the movie.
| gct wrote:
| I used to read the Cartoon Guide to... books as a kid:
| https://www.amazon.com/Cartoon-Guide-Physics/dp/0062731009.
| They were great.
| ipnon wrote:
| Nature seems to have this interesting property of always
| increasing in perceived complexity.
| whimsicalism wrote:
| We're evolutionarily optimized for understanding slow, macro-
| scale, somewhat low-energy things.
|
| Of course we'll perceive things as complex when we move outside
| of that regime.
| oscardssmith wrote:
| The less mysterious reformulation is that humans are better at
| finding less mysterious relationships.
| dokem wrote:
| Sometimes I think about this half-baked theory where physical
| laws don't exist until they are discovered. Once you catch
| physics with it's pants down it now must maintain those
| constraints or have it's bluff called.
| SuoDuanDao wrote:
| sounds a lot like Sheldrake's theory of 'physical habits' -
| he describes it as things being quite random the first time
| and becoming more likely to follow the same patterns the more
| often they're followed.
| f6v wrote:
| I wonder where's the limit to what our minds can comprehend.
| It's fascinating we went this far, since brain didn't evolve to
| study physics.
| nahuel0x wrote:
| Maybe there aren't anything like "fundamental laws" and all are
| emergent patterns, like we are, and in other places in the
| Universe the "fundamental laws" are completely different. In
| that case, the hermetics had a point when they talked about
| infinite divisibility.
| BiteCode_dev wrote:
| Wouldn't that be amazing if the universe developed more and
| more characteristics as you look for them? Or even, that it's
| pushed to create something when you do?
|
| Infinite playground.
| BlueTemplar wrote:
| Godel kind of proved that about Mathematics.
| schmorptron wrote:
| That sounds wild, do you have a link where I can read more
| about this, or is wikipedia fine to learn about it?
| jl6 wrote:
| Axioms are the foundational assumptions from which formal
| systems of mathematics are built. Some systems of axioms
| are unable to prove the truth or falsity of some
| statements within that system. But you can add such
| statements to your set of axioms to form a new, larger
| formal system, which in turn has _other_ indeterminate
| statements, and so on, thus building, in GP's terms, an
| infinite playground of mathematics.
|
| Book recommendation: Godel, Escher, Bach by Douglas
| Hofstadter.
| ArnoVW wrote:
| https://en.m.wikipedia.org/wiki/G%C3%B6del%27s_incomplete
| nes...
|
| TLDR: you can have a mathematics that always gives true
| answers (but that cannot answer everything). Or you can
| have a mathematics that can answer every possible
| question (but some answers are wrong, you do not know
| which). Choose.
|
| This dispaired mathematicians of the early 20th century,
| who had hoped to create 'one mathematics to rule them
| all'. Of course you can have _several_ disjunct
| mathematics, each one for the problem you like.
| ffhhj wrote:
| If there was a single force in the beginning, there might be
| more forces branching out in the future of the universe, who
| knows.
| lolthishuman wrote:
| It's simple. The universe is electromagnetic. The Bose-Einstein
| condensate is the aether in most dense form. Everything
| evaporates into lower densities by means of rotation via the
| torus and vortices. Everything is pressure finding equilibrium
| spread throughout densities in fluid. Easy to reason about. The
| sun is hollow and incompressible aether inside, which is why it's
| cold. The surface is electromagnetic activated by the currents
| spread throughout the galaxy. Every sun is like a lamp. Every sun
| is a plasmoid. Outer space is least dense form of the aether.
| Sound makes matter.
|
| Fun!
| zbendefy wrote:
| Is this the same thing that this 2016 article is about? Or is it
| a new finding with a similiar conclusion?
|
| https://www.nature.com/news/has-a-hungarian-physics-lab-foun...
| dukwon wrote:
| It's unrelated
| aaomidi wrote:
| Everytime I see news like this, it just reminds me of the three
| body problem and the extremely unique Sophons in them.
| atty wrote:
| Alexey Petrov, quoted in the article, subbed in to teach one day
| in my quantum mechanics class :) It was the first day we were
| being introduced to the theory of scattering, and I will never
| forget his intro. He asked the class, "what is scattering?",
| waited a moment, and then threw a whiteboard marker against the
| wall, and answered his own question: "that's scattering". Lots of
| times, physics classes can be so heavy on math that it's hard to
| even remember that you're trying to describe the real world
| sometimes, and moments like that were always very memorable to
| me, because it helped remind me I wasn't just solving equations
| for the hell of it :)
| dylan604 wrote:
| would have been even more impressive example with a dusty
| chalkboard eraser to be able to see the scattering
| dang wrote:
| That article is https://www.bbc.com/news/56643677.
|
| (The comment was posted to
| https://news.ycombinator.com/item?id=26726981 before we merged
| the threads.)
| kache_ wrote:
| An old professor of mine loved the "Throw something at the
| blackboard" technique. Great way to get the class potheads to
| wake up
| forgotmysn wrote:
| how many potheads did you have in your quantum mechanics
| class?
| xzel wrote:
| Hmm probably about a third of my graduate level QED class
| and considerably less in my undergraduate QM but you'd be
| surprised at the cross over between potheads and high level
| physics.
| mhh__ wrote:
| The joke I have heard is that Physics students are either
| shut-ins or party animals, either way they're both
| microdosing something or other...
| dplavery92 wrote:
| Personally I had grown out of that habit a semester or two
| before undergrad QM (though "Modern Physics" and
| "Experimental Physics" were another story...) but there
| were still some hangers on. Maybe 1-3 in a class of 20-25?
| Neither the norm nor unheard of. From that point on the
| statistics were probably about the same in grad school.
| jefft255 wrote:
| Is this trying to imply that it would be surprising for a
| pothead to take a quantum mechanics class? Cause, having
| hung out with plenty of physicists, that wouldn't surprise
| me too much... :P
| kache_ wrote:
| It was an algorithms class. But I'm 100% certain there was
| at least one ;)
| snissn wrote:
| that's super cool! i've always been able to connect the work in
| physics class to some physical system except for when i studied
| quantum mechanical density matrices. still have no idea what
| those are about :)
| ISL wrote:
| My favorite example of this was during a lecture on waveguides,
| when Michael Schick picked up the section of cylindrical metal
| pipe he was using to motivate the cylindrical-waveguide problem
| at hand, looked at the class through the pipe, and said,
| "clearly, it admits higher-order modes."
|
| That little episode brought great joy to this experimentalist's
| heart.
| geniium wrote:
| I love that kind of practical example.
| lifeisstillgood wrote:
| I have a theory about how well educated the mass of humans are,
| could be and should be.
|
| Bear with me.
|
| Roughly 2000 years ago, the number of people who could do
| arithmetic and writing was < 1% of the population. By 200 years
| ago it was maybe what 10%?
|
| Now it is 95% of the world population, and 99.9% of 'Western'
| world.
|
| Lets say that Alexey Petrov is about as highly educated and
| trained as any human so far. (A Physics PhD represents pretty
| much 25 years of full-time full-on education). But most of us
| stop earlier, say 20 years, and many have less full-on
| education, perhaps not doing an hour a day of revision or
| whatever.
|
| But imagine we could build the computing resources, the smaller
| class sizes, the gamification, whatever, that meant that each
| child was pushed as far as they could get (maybe some kind of
| Mastery learning approach ) - not as far as they can get if the
| teacher is dealing with 30 other unruly kids, but actually as
| far as their brain will take them.
|
| Will Alexey be that much far ahead when we do this? Is Alexey
| as far ahead as any human can be? Or can we go further - how
| much further? And if every kid leaving university is as well
| trained as an Astronaut, is capable of calculus and vector
| multiplication, will that make a difference in the world today?
| ryan93 wrote:
| Most people demonstrate pretty clearly that they don't have
| the aptitude for serious physics. A substantial number of
| people can't get passed freshman classes and that's true even
| for the top few% of high school students.
| plebianRube wrote:
| I agree wholeheartedly. We would live in an exceptional
| world. The obstacle preventing this is greed and exploitation
| of people who are born into low income situations. Rising out
| is the exception, not the rule. Affording many years of
| education is simply not an option for some. I wish it were,
| but this is another issue.
| centimeter wrote:
| The evidence is quite clear that going to college doesn't
| actually improve life outcomes very much at all. We
| mistakenly thought it did for a while, but what was
| actually happening is the people who were going to college
| were smart and very likely to succeed anyway.
| dieortin wrote:
| Everyone being as trained as an astronaut would definitely
| make a difference, if only because they would appreciate the
| importance of science, technology, innovation... And not
| believe stupid conspiracy theories about vaccines.
| JohnBooty wrote:
| You can't really manufacture geniuses, right?
|
| I'm "smart" relative to the general population, but you could
| have thrown all the education in the world at me and I'd
| never have become Alexey Petrov.
|
| I have a hunch that the Alexey Petrovs -- the upper 0.001% or
| whatever -- of the world do tend to get recognized and/or
| carve out their own space.
|
| I think the ones who'd benefit from your plan would be...
| well, folks like me. I mean, _I_ did fine I guess, but surely
| there are millions as smart as me and smarter than me who
| fell through the cracks in one way or another.
|
| I suspect fairly quickly we'd run into some interesting
| limits.
|
| For example, how many particle physicists can the world
| actually _support?_ There are already more aspiring particle
| physicists than jobs or academic positions. Throwing more
| candidates at these positions would raise the bar for
| acceptance, but it 's not like we'd actually get... hordes of
| additional practicing particle physicists than we have now.
| We'd also have to invest in more LHC-style experimental
| opportunities, more doctorate programs, and so on.
|
| Obviously, you can replace "particle physicist" with other
| cutting-edge big-brain vocation. How many top-tier
| semiconductor engineers can the world support? I mean, there
| are only so many cutting-edge semiconductor fabs, and the
| availability of top-tier semiconductor engineers is not the
| limiting factor preventing us from making more.
|
| There are also cultural issues. A lot of people just don't
| trust the whole "establishment" for science and learning
| these days. Anti-intellectualism is a thing. You can't throw
| education at that problem when education itself is seen as
| the problem.
| diegoperini wrote:
| > ...will that make a difference in the world today?
|
| It will make a huge difference, and no difference at all. It
| will probably help us solve all of our current problems. And
| then it will also introduce a whole new brand of problems
| which will be sources of crises that generation will deal
| with. What you read on news will change, but the human
| emotional response to those news will be very similar to
| today's.
| surfsvammel wrote:
| I have the opposite experience. Physics classes where always
| the most interactive and practical. But then again, I only ever
| studied up to undergrad level physics.
| yaya69 wrote:
| And the gluon is the opposite
| gautamcgoel wrote:
| Honestly feel sorry for particle physicists... Their entire gig
| is spending billions on fancy equipment, and _hoping_ that
| observe something unexpected. If they see exactly what they
| expected to see, all that effort was basically wasted. Also, a
| lot of "discoveries" turn out to be equipment miscalibration -
| remember those particles which supposedly moved faster than light
| a few years back? Always struck me as an odd way to do science.
| arbitrage wrote:
| Remember, you can't solve the halting problem.
|
| This is progress. Sometimes science takes two steps back and
| one step forward. Sometimes that one step is bigger than you
| realized. And it wasn't backwards, it was projecting into a
| different spacial dimension. Or something.
|
| The point is, this is probably good news, honestly.
| yetihehe wrote:
| Two steps back, but the new step forward is in better
| direction.
| potatoman22 wrote:
| Could you explain what you mean by halting problem in this
| context?
| tootie wrote:
| The Structure of Scientific Revolutions by Thomas Kuhn lays all
| this out pretty clearly. The work of "normal science" is to
| make predictions based on established models and test them
| until you find something that breaks, then you have a "paradigm
| shift" that creates a new model.
|
| https://en.wikipedia.org/wiki/The_Structure_of_Scientific_Re...
| astrophysician wrote:
| From a physicists standpoint, not seeing something unexpected
| is not a waste at all.
| gautamcgoel wrote:
| Can you expand on that? I was under the impression that many
| thought of it as a waste (Sabine Hossenfelder comes to mind,
| for example).
| aqme28 wrote:
| Theorizing a phenomenon and having experimental evidence of
| a phenomenon are very different things.
| CrazyDave wrote:
| I assume it helps trim off the branches of research that
| become unviable with the new evidence.
| astrophysician wrote:
| Yea, some people are disappointed; some of the more
| interesting and exciting moments in physics are when we
| find out we're wrong, but not always. E.g. I will never
| forget the time and place I heard about the preliminary
| detection of primordial B-modes by BICEP (which turned out
| to be dust contamination) -- that was a predicted detection
| from canonical inflation models, as the Higgs was a
| standard prediction from the standard model (also a pretty
| exciting moment).
|
| Not seeing something when we "expect" to not see anything
| (from the perspective of certain models) might be more
| boring, but it's definitely not a "waste" (again speaking
| purely from a physicist's standpoint).
|
| We _know_ the standard model is incomplete, but where and
| how are not well known. Not seeing evidence for new physics
| rules out certain models, and places upper /lower limits on
| others. It's progress either way.
| bluGill wrote:
| Some do I'm sure. However if we see something unexpected
| and it turns out to be true that means our ideas of physics
| are fundamentally wrong. While it is long term good to
| correct our understanding, in the mean time a lot of the
| real world depends on us being right, and so until we
| correct the theory who knows what will work. I'd hate to
| find our margin of safety on nuclear bombs was too small
| and it is only luck that they haven't all blown up in their
| silos over the years.
| whimsicalism wrote:
| > Sabine Hossenfelder
|
| Hossenfelder has a lot of... unique takes in the physics
| world, I don't think she should be used as a general
| barometer of the field.
| BrandoElFollito wrote:
| From a physicist's standpoint, always being right is
| disheartening.
|
| I think that every physicist hopes to see something that does
| not match and then a fantastic work begins.
|
| I did not see anything like this during my studies, PhD and
| short career and moved to industry. I terribly miss the
| teaching, though.
| mooneater wrote:
| Is there a way you can continue to teach in some capacity?
| BrandoElFollito wrote:
| This is something I have in mind for some time. I have a
| great job, but it takes all my "professional" time, the
| rest if for my family and hobbies.
|
| I am still 10-12 years away from official retirement and
| until then I doubt to have the time. Taken into account
| the seniority of my position, I am quite confident that I
| could teach afterwards at a good school, something I
| would do even for free.
| [deleted]
| m463 wrote:
| I think learning to observe anything at such small scales as a
| routine matter will increase understanding of all kinds of
| other things we look at. There are folks riding on their
| coattails, and folks riding on _their_ coattails.
|
| But yeah, it's the long game.
| gher-shyu3i wrote:
| > If they see exactly what they expected to see
|
| Why? Validating a hypothesis is quite valuable.
| renewiltord wrote:
| It's actually not at all. Or more precisely, no one treats it
| as valuable. If you fail to reject H0 repeatedly your career
| is doomed to mediocrity.
| pxhb wrote:
| > Honestly feel sorry for particle physicists... Their entire
| gig is spending billions on fancy equipment, and hoping that
| observe something unexpected.
|
| This isn't the way I would frame it. No one will fund billions
| on fancy equipment for unexpected results, and no one is
| flipping a coin expecting something other than heads/tails. The
| usual course is that there is some theoretical
| expectation/justification of a result, however we then need to
| build the experimental capacity to see if it is true.
| wrnr wrote:
| Live from the Fermilab:
| https://www.youtube.com/watch?v=81PfYnpuOPA
| glofish wrote:
| Amusingly - fittingly for our times - in the same issue of the
| exact same journal (Nature) another paper has been published that
| indicates that the prior, so much "hyped" discrepancy might be
| due to the theory having being applied inaccurately in the past.
| When computed with the new method, the experimental and
| theoretical models align far more accurately.
|
| So now all that matters is what kind of article do your want to
| write. A sensationalist one to get eyeballs or a realistic one
| that is far less exciting. Thus the exact same discovery can be
| presented via two radically different headlines:
|
| BBC goes with " _Muons: 'Strong' evidence found for a new force
| of nature_" https://www.bbc.com/news/56643677
|
| > "Now, physicists say they have found possible signs of a fifth
| fundamental force of nature"
|
| ScienceDaily says: " _The muon 's magnetic moment fits just
| fine_"
| https://www.sciencedaily.com/releases/2021/04/210407114159.h...
|
| > "A new estimate of the strength of the sub-atomic particle's
| magnetic field aligns with the standard model of particle
| physics."
|
| There you have it, the mainstream media is not credible even when
| they attempt to write about a physics experiment ...
| atty wrote:
| As someone who has worked in fields that use lattice
| calculations (on the experimental side), the new calculation is
| interesting, but I would not say it's particularly convincing
| yet. Lattice calculations are VERY difficult, and are not
| always stable. I am not questioning whether they did their work
| well or not, just pointing out that in high energy physics and
| high energy nuclear physics, many times our experimental
| results are significantly better constrained and also undergo
| significantly more testing via reproduction of results by other
| experiments than our theory counterparts' work. Is it possible
| that all of our previous experiments have had some sort of
| correlated systematic error in them? Unlikely, but yes. Is it
| more likely that this lattice calculation may be
| underestimating its errors? Much more likely. Another
| interesting option is that one of the theoretical calculations
| was actually done slightly wrong. My first guess would be the
| lattice result, since it's newer, but both procedures are
| complicated, so it could be either.
| glofish wrote:
| I am not sure I follow the logic. The new computation aligns
| with the experiment.
|
| Why is it more likely for it to be wrong than the calculation
| that shows the theory deviating from experiment.
| atty wrote:
| The old calculation relies on older experimental results
| that have been verified by multiple experiments - so if the
| older value is wrong, it means either the calculation was
| done wrong (possible), or the experiments all have had a
| significant correlated systematic error that has never been
| caught (also possible). However, I'd say both of those
| things are relatively unlikely, when compared to the
| probability of some small error in a new paper that was
| just released that uses a new method that involves lattice
| calculations. This is all a balance of probabilities
| argument, but from my experience in the field, I'd say it's
| more likely that any errors in calculation or missed
| systematics would be in the new paper.
|
| However, I'm an experimentalist who has worked close to a
| lot of this stuff, not an actual theorist, so I'd love to
| get a theorists interpretation as well.
| Anon84 wrote:
| I'm getting a "faster than light neutrinos" feeling about this
| one
| [deleted]
| cambalache wrote:
| https://www.math.columbia.edu/~woit/wordpress/?p=12292
|
| This just PR fluff, with the paper published today in Nature
| there is no discrepancy with the SM. Mother Nature loves Ockham's
| razor.
| mkaic wrote:
| I highly recommend the YouTube channel PBS Space Time's coverage
| of this, it's informative, well organized, and accessible even to
| someone like me who doesn't have any background in physics.
| wnevets wrote:
| I can't wait for PBS Spacetime to tell me what to think about
| this.
| blue_cadet_3 wrote:
| Fermilab has a channel as well describing it.
| https://www.youtube.com/watch?v=ZjnK5exNhZ0
| terramex wrote:
| They already did, 15 minutes ago:
| https://www.youtube.com/watch?v=O4Ko7NW2yQo
|
| For those who do not know - PBS Spacetime is YouTube channel
| hosted by astrophysics Ph.D Matt O'Dowd, aimed at casual
| physics enthusiasts without oversimplifying underlying physics
| too much.
| MperorM wrote:
| Am I the only one who barely understands anything from that
| show?
|
| Every episode I hear a dozen barely explained confusing terms
| with quantum this and higgs-field that.
|
| I feel like they care more about impressing me with how
| complicated this stuff is than they do about actually teaching
| me much. Maybe I'm just not the target audience :(
| wnevets wrote:
| There are a lot of quantum mechanics episodes from 1-2 years
| ago that cause my eyes to just glaze over from all of the
| math and technical terms. However I feel like the newer
| episodes are much better at explaining things to the casual
| viewer rather than math nerds.
| gonational wrote:
| Science is a never ending series of incorrect observations, each
| disqualifying the penultimate while asserting the ultimate is
| axiomatic.
|
| When you're young you get excited each time a new breakthrough is
| happening. If you manage to grow up, you get tired of the
| pattern, and the signal to noise ratio starts to look like a good
| statistical P value.
| goatcode wrote:
| >the strong force and the weak force.
|
| Is there a reason we're leaving "nuclear" off these forces' names
| now?
| quchen wrote:
| I think this would be misleading once you dive deeper into
| particle physics. The strong interaction is really >>the
| interaction mediated by gluons between color-charged things<<.
|
| * Gluons interact with gluons, without the need for quarks.
|
| * Many (almost all) bound quark states are not found in nuclei,
| only uud (protons) and udd (neutrons) are. But there are also
| all the mesons (e.g. the pion), and a whole lot of other
| baryons (xis and sigmas and what have you) exist.
|
| To put this into perspective, it feels a bit like calling
| electromagnetic interaction the >>chemical interaction<<,
| because chemistry is explained for the most part by the
| interaction of electrons. But that would leave out a lot of
| different ways matter can interact, like Bremsstrahlung,
| positrons, proton/proton repulsion, and all that.
| fctorial wrote:
| They aren't tied to the nucleus of the atom in any way. It's
| just that they were discovered in phenomena involving atom
| nucleus.
| rocqua wrote:
| I have indeed often seen the names referred to without the term
| "nuclear".
| goatcode wrote:
| Weird. This must have changed in the past 10 years or so,
| since I've been out of college.
| dylan604 wrote:
| It's something you never get used to. As you get older,
| this will just keep happening. We used to put commas before
| the last item in a list back in like the stone ages when I
| was in school. My SAT score looked really lame for a bit of
| time when those suddenly changed.
| goatcode wrote:
| I understand the grumpy old person archetype now. I feel
| like I've been one for a long time, but it's really
| hitting home over the past decade.
| dukwon wrote:
| This (very important) paper from 1967 calls them "weak
| interaction" and "strong interaction": https://journals.aps
| .org/prl/abstract/10.1103/PhysRevLett.19...
|
| Putting the word "nuclear" in the middle seems to just be
| done in textbooks and classrooms.
| uhtred wrote:
| Can anyone explain in layman's terms why this is important?
| Jeff_Brown wrote:
| From another comment, there's this PBS Space Time video on
| Youtube.
|
| https://www.youtube.com/watch?v=O4Ko7NW2yQo
| 1-6 wrote:
| 3D point clouds and x-rays! More research can be done on low-
| cost devices. It puts LiDAR to shame but there are also great
| privacy implications. Muon tomography:
| https://en.wikipedia.org/wiki/Muon_tomography
| whatshisface wrote:
| Extremely precise measurements of the muon magnetic moment
| are not going to be useful for those applications.
| whatshisface wrote:
| If you take the current sum of all human knowledge and
| calculate something called g, and then subtract two, you get
| something different from the the real value of g-2. Therefore,
| we have identified something that lies beyond the sum of all
| human knowledge. That's kind of the whole idea behind being a
| physicist so understandably anyone remotely related to the area
| this belongs to is pretty excited.
|
| If you are wondering, "why does this one single number matter
| so much, who cares if we didn't know it before," it is because
| it hints at a great new theory that could change everything.
| Nobody knows what theory, but in the past small discrepancies
| in fundamental measurements have been the seeds of great
| theories.
| gus_massa wrote:
| The electrons and the muons are very similar. We can measure
| the magnetic moment and make some calculations and calculate a
| number g. If they were perfectly ideal particles, then g must
| be exactly 2, so it's interesting to measure g-2.
|
| The real particles have a lot of virtual particles that appear
| around them and are impossible to detect directly. It's like a
| cloud of more electrons, positrons, photons, and other
| particles.
|
| They are impossible to detect directly, but they affect
| slightly the result of the experiments, so when you go to a lab
| and measure g, you don't get exactly 2.
|
| We have a very good model for all the virtual particles that
| appear around them, i.e. the electrons, positrons, photons, and
| other particles. It's call the "Standard Model". (But I don't
| like the name.)
|
| We can use the "Standard Model" to calculate the correction of
| g of an electron, and the theoretical calculation agree with
| the experiments up to the current precision level.
|
| We[1] can use the "Standard Model" to calculate the correction
| of g of a muon, and the theoretical calculation does not agree
| with the experiments!!!
|
| The disagreement is very small, and there is still a small
| chance that the disagreement is a fluke, but people is
| optimistic and think that it they continue measuring they can
| be confident enough that it is not a fluke.
|
| [1] Actually not me, this is not my research area, but I know a
| few persons that can.
|
| ---
|
| Back to your question:
|
| > *Why is this important?
|
| If the theoretical calculation and the experimental value
| disagree, it means that the "Standard Model" is wrong.
| Physicist would be very happy to prove that it is wrong,
| because they can study variants of this experiment and try to
| improve the model. (And be famous, and get a Nobel prize.)
|
| Physicist are very worried because they are afraid that the
| "Standard Model" is so good that to prove it is wrong they need
| to build a device that is as big as the Solar system. (And they
| can't be famous, and the Nobel prize will go that work in other
| areas.)
|
| If this result is "confirmed", the idea is to add a new
| particle to the "Standard Model" and get the "Standard Model
| II". (IIRC it already has a few corrections, so we will call
| the new version the "Standard Model".)
|
| It's difficult because the new particle must change the
| predictions for this experiment, but not change too much the
| predictions for other experiments. It may take a few years or
| decades to find the new theoretical particle that match the
| experiments.
|
| If you are pessimistic, the new particle will be useful only to
| explain a small correction that is only relevant in very
| accurate experiments in the lab, or inside a big star, or other
| unusual events.
|
| If you are optimistic, in 100 year every moron on Earth will
| have in the pocket a device that will use this new particle for
| something amazing.
|
| Or perhaps something in between. Nobody has any clue about
| this.
| misiti3780 wrote:
| What is everyones favorite book on quantum mechanics (I would
| love understand more of the 3 generations of matter)?
| HellDunkel wrote:
| As a layperson i really enjoyed Brian Greenes Fabric of the
| Cosmos. It is a great read and the chapters on quantum
| mechanics are captivating.
| andrepd wrote:
| Cohen-Tannoudji, Sakurai.
| panda-giddiness wrote:
| As others have noted, it sounds like what you're really
| interested in is particle physics. In that case, I'd recommend
| Griffiths's "Introduction to Elementary Particles", which would
| be accessible to someone with an undergraduate level knowledge
| of physics. But you could probably get away with knowing less,
| depending on your background.
| martincmartin wrote:
| Quantum Mechanics and the three generations of matter are
| slightly different. Quantum Mechanics is like Newton's laws at
| small scales, in that if you know what things are like at time
| t, and you know all the potentials (forces), it tells you how
| they evolve. It also tells you what states are physically
| allowed (e.g. only certain energies for electrons orbiting an
| atom). You can study QM for years without any real look at the
| standard model, which is where the three generations come from.
|
| If you want an undergraduate class in QM, edX has MIT's classes
| on line:
|
| https://learning.edx.org/course/course-v1:MITx+8.04.1x+3T201...
|
| If you want a textbook, Griffth's "Introduction to Quantum
| Mechanics" is the standard answer. It's very much a "shut up
| and calculate" book, you'll learn how to compute expected
| values of commutators without much intuition for what they
| mean.
|
| Update: Others point out Griffth's "Introduction to Elementary
| Particles", read their recommendations, sounds like the way to
| go.
|
| If don't want to spend 12 hours a week for 3 months and still
| not have learned much about the 3 generations, then ... I don't
| know, maybe QED: The Strange Theory of Light and Matter? I
| don't know if it has the 3 generations, but it only assumes
| high school math, yet gets into the quantum version of
| electricity and magnetism.
| misiti3780 wrote:
| thx
| ianai wrote:
| Did you want a QM text or a text on the Standard Model?
| misiti3780 wrote:
| QM
| AnimalMuppet wrote:
| I seem to recall that Feynman said that we don't understand why
| there are three generations, and that it's embarrassing that we
| don't. It means we don't really know what's going on.
| Koshkin wrote:
| This one is just what you need:
|
| Sudbery, A. (1986): Quantum Mechanics and the Particles of
| Nature: An Outline for Mathematicians.
| mhh__ wrote:
| Bellentine's book is a good introduction to a lot of quantum
| physics (you will need mathematics), and to really understand
| particle physics you need even more mathematics
| andi999 wrote:
| Actually just for High Energy Physics you do not really need
| Quantum mechanics, I think Griffith 'Introduction to Elementary
| Particles' was pretty good. You might want to look more into
| special relativity first.
| wwarner wrote:
| A great intro is Sean Carroll's youtube series "The Biggest
| Ideas in the Universe".
| https://www.youtube.com/playlist?list=PLrxfgDEc2NxZJcWcrxH3j...
| bodhiandphysics wrote:
| How much physics do you know? How much math? Griffins
| introduction to elementary particles is the standard model at
| an undergrad level... and is great. To understand the three
| generations at a higher level you need a lot of math (you need
| to know what a Lie algebra is and Noether's theorem)
| misiti3780 wrote:
| I do not use math or physics on a daily basis, but have an MS
| in Applied Math, and a lot of classes in EE.
| beezle wrote:
| You might also check on Perkins Intro to High Energy
| Physics which also links to experimental techniques.
| bodhiandphysics wrote:
| Griffin is a good book then (as well as his intro to qm)
| thisiscorrect wrote:
| Mine is Sakurai's "Modern Quantum Mechanics." But it sounds
| like you're really asking which book would be good for you to
| learn about quantum mechanics and also the Standard Model of
| particle physics.
| selimthegrim wrote:
| I would not just throw someone into Sakurai starting from
| scratch.
| cozzyd wrote:
| Sakurai, but it won't help you understand the 3 generations of
| matter because we don't understand why there are 3 generations
| at all. If you just want to learn particle physics, you can do
| worse than just reading the review sections of the PDG
| (pdg.lbl.gov)
|
| And it's probably not a great beginner's text, even though it's
| really good.
| whimsicalism wrote:
| I would not start Sakurai without at least doing some of an
| undergrad book first, to get the basic concepts.
| cozzyd wrote:
| Sakurai is very clear, IMO, but requires a better
| understanding of linear algebra than a typical
| undergraduate text. But if you know linear algebra well, QM
| is pretty straightforward...
| eevilspock wrote:
| > _" The concordance shows the old result was neither a
| statistical fluke nor the product of some undetected flaw in the
| experiment, says Chris Polly, a Fermilab physicist and co-
| spokesperson for the g-2 team. "Because I was a graduate student
| on the Brookhaven experiment, it was certainly an overwhelming
| sense of relief for me," he says."_
|
| A committed scientist should worry about having such feelings,
| even though it is very human. It represents a possible source of
| non-independence of tests and of scientific bias.
| Arjuna144 wrote:
| hahah all this for some what? 10^(-6) or 10^(-5) discrepancy?!
| What about this age old 10^120 discrepancy that eveyone seems to
| be just fine about...
| https://en.wikipedia.org/wiki/Cosmological_constant_problem
| podiki wrote:
| People aren't "just fine" about dark energy. It is an entire
| field of study in physics/astronomy. A problem there is that we
| are quite stuck; some future experiments might tell us
| something (if it has changed over time for instance), but
| theoretically there aren't any stand out answers or ones that
| can see experimental confirmation soon.
| nimish wrote:
| It'll be a huge victory for lattice-QCD if the computational
| result is true.
| zzzeek wrote:
| bottom line this for me.
|
| can we have levitating cars or not ?
| 1-6 wrote:
| Must be background radiation day at HN.
| whatshisface wrote:
| This is not a collider experiment, so it doesn't have that
| particular failure mode.
| mjevans wrote:
| I read the release written by the lab.
|
| https://news.fnal.gov/2021/04/first-results-from-fermilabs-m...
| treyh wrote:
| With 19 free parameters in the standard model, can't they fit any
| experimental result by adjusting a "constant"?
| PeterisP wrote:
| Sure they can fit any experimental result that way, they can
| probably fit any 19 experimental results that way, but in
| general if you would freely adjust a constant to fit one
| experiment then it would stop fitting other experiments.
| tW4r wrote:
| Do we need TDD for particle physics so CI could run tests on
| what experiments break when merging a theory
| tux3 wrote:
| Are you volunteering to write the YAML for it? =) Should be
| pretty much trivial! Exercise left to the reader.
| whatshisface wrote:
| That's done by hand. I guess you could automate it. Maybe
| we'll see that some time in the next century.
| treyh wrote:
| My understanding is that with the lagrangian approach then
| the free parameters are not all interacting with each other
| because they are part of different terms. This means a change
| to a free parameter doesn't necessarily break experiments.
| atty wrote:
| The point is that there are now 10s-100s of experiments
| that have been reported to very good precision (obviously
| not all to the extra-ordinary precision of this
| measurement). There are no longer any "free parameters" in
| the SM, in the sense that each one has been constrained by
| at least one experiment by now. Also, in complicated
| processes like this one, multiple parameters could make an
| effect on the observed value, such as the fermion masses.
| (Not saying the fermion masses actually affect g-2, it's
| been a few years since I've done any QED, so my memory is a
| little cloudy :) )
| treyh wrote:
| ah, well it will be interesting to see how the theorists
| resolve this!
| layoutIfNeeded wrote:
| "With four parameters I can fit an elephant, and with five I
| can make him wiggle his trunk." - John von Neumann
| aworkerbee wrote:
| Can anyone recommend any pop-sci books? I haven't taken a science
| class since high school, and that is barely remembered. Mostly
| interested in getting philosophically up to date with the state
| of matter(?), it's different types, how these objects interact.
| throw1234651234 wrote:
| The only update that I got since was high school was that
| electrons aren't on concrete orbitals around the nucleus, but
| that there is a probability distribution saying that they are
| likely somewhere around the area where the concrete "orbital"
| concept is usually drawn.
|
| That and quantum shenanigans, but that comes down to "we can't
| transport information faster than light."
| keanebean86 wrote:
| Just mention pilot wave theory and someone on this site might
| reply with a very detailed explanation of quantum mechanics.
|
| https://en.wikipedia.org/wiki/Pilot_wave_theory
| sdedovic wrote:
| My personal favorite:
|
| - Thirty Years that Shook Physics: The Story of Quantum Theory
|
| Other great books:
|
| - The Theory Of Everything
|
| - The Quark and the Jaguar
|
| - Six Easy Pieces
| Zanni wrote:
| Recommended up thread, but Feynman's QED: The Strange Theory of
| Light and Matter [0] is fantastic and very accessible. It's not
| particularly "up to date" (dating back to 1985), but it's not
| obsolete.
|
| [0]
| https://en.wikipedia.org/wiki/QED:_The_Strange_Theory_of_Lig...
| podiki wrote:
| As a particle physicist (no longer working in the field, sadly),
| this is one of the more exciting results in a long time. Muon g-2
| has been there, in some form of another for debate and model
| building, for many years (taken somewhat seriously for 15+?),
| waiting for better statistics and confirmation. At over 4 sigma
| this is much more compelling than it has ever been, and the best
| potential sign of new (non-Standard Model) physics.
|
| I'm not current on what models people like to explain this
| result, but it has been factored in (or ignored if you didn't
| trust it) in particle physics model building and phenomenology
| for years. This result makes it much more serious and something I
| imagine all new physics models (say for dark matter or other
| collider predictions or tensions in data) will be using.
|
| Whether or not anything interesting is predicted, theoretically,
| from this remains to be seen. I don't know off hand if it signals
| anything in particular, as the big ideas, like supersymmetry, are
| a bit removed from current collider experiments and aren't
| necessarily tied to g-2 if I remember correctly.
| beezle wrote:
| The Quanta write up is a bit more neutral on this announcement.
| There is a computational result that was not included in the
| theoretical value used to bench the test against. Once reviewed,
| this difference may yet go back to oblivion.
|
| https://www.quantamagazine.org/muon-g-2-experiment-at-fermil...
| elliekelly wrote:
| In the Scientific American article also currently linked on the
| front page a scientist & professor* at an Italian university is
| quoted as saying something along the lines of "this is probably
| an error in the theoretical calculation". Would this be what
| the professor was referring to?
|
| Edit: I'm not entirely sure whether they're a professor, but
| here's the exact quote
|
| > "My feeling is that there's nothing new under the sun," says
| Tommaso Dorigo, an experimental physicist at the University of
| Padua in Italy, who was also not involved with the new study.
| "I think that this is still more likely to be a theoretical
| miscalculation.... But it is certainly the most important thing
| that we have to look into presently."
| T-A wrote:
| https://www.science20.com/tommaso_dorigo/new_muon_g2_results.
| ..
| ssivark wrote:
| To clarify, for those not familiar with this topic, this
| experiment is making measurements at such exquisite precision
| that even the calculations for the theoretical prediction are
| extremely non-trivial and require careful estimation of many
| many pieces which are then combined. Which is to say that
| debugging the theoretical prediction is (almost) as hard as
| debugging the experiment. So I would expect the particle
| physics community to be extremely circumspect while the details
| get ironed out.
|
| The Quanta article explains it quite nicely. To quote their
| example of what has happened in the past:
|
| > _"A year after Brookhaven's headline-making measurement,
| theorists spotted a mistake in the prediction. A formula
| representing one group of the tens of thousands of quantum
| fluctuations that muons can engage in contained a rogue minus
| sign; fixing it in the calculation reduced the difference
| between theory and experiment to just two sigma. That's nothing
| to get excited about."_
| platz wrote:
| it's not good to cherry-pick paragraphs from the whole
| artile.
|
| > But as the Brookhaven team accrued 10 times more data,
| their measurement of the muon's g-factor stayed the same
| while the error bars around the measurement shrank. The
| discrepancy with theory grew back to three sigma by the time
| of the experiment's final report in 2006.
| ssivark wrote:
| No, the essence of my point is that the number of sigmas is
| meaningless when you have a systematic error -- in either
| the experiment or the theoretical estimate -- all that the
| sigmas tell you is that the two are mismatched. If a
| mistake could happen once, a similar mistake could easily
| happen again, so we need to be extremely wary of taking the
| sigmas at face value. (Eg: the DAMA experiment reports dark
| matter detections with over 40sigma significance, but the
| community doesn't take their validity too seriously)
|
| Any change in the theoretical estimates could in principle
| drastically change the number of sigmas mismatch with
| experiment in either direction (but as the scientific
| endeavor is human after all, typically each helps debug the
| other and the two converge over time).
| gfodor wrote:
| "A similar mistake could happen again"
|
| "Similar" is doing a lot of work there - what constitutes
| similar basically dictates if error correction has any
| future proofing benefits or none at all.
| ephimetheus wrote:
| The systematic errors enter the sigma calculation,
| doesn't it?
| ssivark wrote:
| Cannot, because here we're talking about "unknown
| unknowns".
| eloff wrote:
| > it's not good to cherry-pick paragraphs from the whole
| artile
|
| Isn't that exactly what you just did?
|
| There's nothing wrong with showing only small quotes, the
| problem would be cherry picking them in a way that leads
| people to draw incorrect conclusions about the whole.
| platz wrote:
| Which is what I demonstrated the parent poster did.
| shock-value wrote:
| They were using a quote from the article to support their
| own point, not stating that it represented the article's
| overall conclusion.
| whatshisface wrote:
| If the theoretical prediction can't be calculated until the
| experiment is done that motivates the choices of what and
| what not to approximate, is it really a prediction?
| 6gvONxR4sf7o wrote:
| Sometimes it's like unit tests, where you might get the
| test itself wrong at first, but that still helps you get
| closer and write better tests.
| raincom wrote:
| That's what Duhem-Quine thesis in the philosophy of
| sciences is. The thesis is that "it is impossible to test a
| hypothesis in isolation, because an empirical of the
| hypothesis requires one or more auxiliary/background
| assumptions/hypotheses".
| whatshisface wrote:
| Not exactly. Analytic solutions to simple problems will
| produce as many predictions as you want from them, and
| you can test them in a year, two years, or a century from
| then. These highly approximated calculations, in
| contrast, will come out one way or the other, depending
| on how many of which terms you add (this is especially
| common in quantum chemistry) - and nobody will decide on
| the "right" way to choose terms until they have an
| experiment to compare it against. That means that they
| aren't predicting outcomes, they're rationalizing
| outcomes.
| raincom wrote:
| Of course, that's how two rival paradigms(research
| programs) 'rationalize' their own testing/outcomes.
| btilly wrote:
| _If the theoretical prediction can 't be calculated until
| the experiment is done that motivates the choices of what
| and what not to approximate, is it really a prediction?_
|
| Let me make that more meta.
|
| If a theory is unable to predict a particular key value, is
| it still a theory?
|
| This is not a hypothetical question. The theory being
| tested here is the Standard Model. The Standard Model in
| principle is entirely symmetric with regards to a whole
| variety of things that we don't see symmetry in. For
| example the relative mass of the electron and the proton.
|
| But, you ask, how can it be that those things are
| different? Well, for the same reason that we find pencils
| lying on their side rather than perfectly balanced around
| the point of symmetry on the tip. Namely that the point of
| perfect symmetry is unstable, and there are fields setting
| the value of each asymmetry that we actually see. Each
| field is carried by a particle. Each particle's properties
| reflect the value of the field. And therefore the theory
| has a number of free parameters that can only be determined
| by experiment, not theory.
|
| In fact there are 19 such parameters. https://en.wikipedia.
| org/wiki/Standard_Model#Theoretical_asp... has a table with
| the complete list. And for a measurement as precise as this
| experiment requires, the uncertainty of the values of those
| parameters is highly relevant to the measurement itself.
| jack_riminton wrote:
| That was beautifully explained thank you
| ssivark wrote:
| That's a good (and profound) question, not deserving of
| downvotes.
|
| It turns out that the simplified paradigmatic "scientific
| method" is a very bad caricature of what actually happens
| on the cutting edge when we're pushing the boundaries of
| what we understand (not just theory, but also experimental
| design). Even on the theoretical front, the _principles_
| might be well-understood, but making predictions requires
| accurately modeling all the aspects that contribute to the
| actual experimental measurement (and not just the simple
| principled part). In that sense, the border between theory
| and experiment is very fuzzy, and the two inevitably end-up
| influencing each other, and it is fundamentally
| unavoidable.
|
| Unfortunately, it would require more effort on my part to
| articulate this, and all I can spare right now is a drive-
| by comment. Steven Weinberg has some very insightful
| thoughts on the topic, both generally and specifically in
| the context of particle physics, in his book "Dreams of a
| final theory" (chapter 5).
|
| If you don't have access to the book, in a pinch, you could
| peruse some slides that I made for a discussion:
| https://speakerdeck.com/sivark/walking-through-weinbergs-
| dre...
| beezle wrote:
| On the BMW collaboration with the lattice qcd computational
| estimate -
|
| This is a pre-print https://arxiv.org/abs/2002.12347
|
| This is the link to the Nature publication:
| https://www.nature.com/articles/s41586-021-03418-1
| jessriedel wrote:
| That new alternative approach is considered substantially less
| reliable by most experts.
|
| https://mobile.twitter.com/dangaristo/status/137982536595107...
|
| From Gordan Krnjaic at Fermilab:
|
| > if the lattice result [new approach] is mathematically sound
| then there would have to be some as yet unknown correlated
| systematic error in many decades worth of experiments that have
| studied e+e- annihilation to hadrons
|
| > alternatively, it could mean that the theoretical techniques
| that map the experimental data onto the g-2 prediction could be
| subtly wrong for currently unknown reasons, but I have not
| heard of anyone making this argument in the literature
|
| https://mobile.twitter.com/GordanKrnjaic/status/137984412453...
| j4yav wrote:
| There is a nice video explanation from PBS at
| https://youtu.be/O4Ko7NW2yQo
| seventytwo wrote:
| PBS, man. Just steadily and reliably educating everyone for
| years now. Good shit.
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