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Particle mystery: physicists confirm the muon is more magnetic than predicted

sciencemag.org

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Re: Particle mystery: physicists confirm the muon is more magnetic than predicted

#111

Post by platz »

eloff wrote: post #66
platz wrote: post #46

Earlier quoted context omitted.

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.

> 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.

Which is what I demonstrated the parent poster did.

Re: Particle mystery: physicists confirm the muon is more magnetic than predicted

#112

Post by Strilanc »

hinkley wrote: post #82
chriswarbo wrote: post #65

Earlier quoted context omitted.

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…

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.

It's spacetime 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

Re: Particle mystery: physicists confirm the muon is more magnetic than predicted

#113

Post by whatshisface »

ssivark wrote: post #32
beezle wrote: post #19

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...

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 phy…

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?

Re: Particle mystery: physicists confirm the muon is more magnetic than predicted

#114

Post by podiki »

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.

Re: Particle mystery: physicists confirm the muon is more magnetic than predicted

#115

Post by atty »

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 :)

Re: Particle mystery: physicists confirm the muon is more magnetic than predicted

#116

Post by andi999 »

chriswarbo wrote: post #65
davidivadavid wrote: post #37

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?

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…

Lagrangian mechanics gets a bit ugly if you want to include friction.

Re: Particle mystery: physicists confirm the muon is more magnetic than predicted

#118

Post by zamadatix »

hinkley wrote: post #82
chriswarbo wrote: post #65

Earlier quoted context omitted.

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…

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.

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.

Re: Particle mystery: physicists confirm the muon is more magnetic than predicted

#119

Post by andi999 »

davidivadavid wrote: post #37

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?

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?
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