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...
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…
Particle mystery: physicists confirm the muon is more magnetic than predicted
141–150 of 301 posts
Re: Particle mystery: physicists confirm the muon is more magnetic than predicted
#142Earlier quoted context omitted.
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?
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...
Re: Particle mystery: physicists confirm the muon is more magnetic than predicted
#143I read the release written by the lab.
https://news.fnal.gov/2021/04/first-results-from-fermilabs-m...
Re: Particle mystery: physicists confirm the muon is more magnetic than predicted
#144Earlier quoted context omitted.
This is the second separate experiment giving similar value.
"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.
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.
Re: Particle mystery: physicists confirm the muon is more magnetic than predicted
#145Earlier quoted context omitted.
An old professor of mine loved the "Throw something at the blackboard" technique. Great way to get the class potheads to wake up
how many potheads did you have in your quantum mechanics class?
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
Re: Particle mystery: physicists confirm the muon is more magnetic than predicted
#146There is a nice video explanation from PBS at https://youtu.be/O4Ko7NW2yQo
Re: Particle mystery: physicists confirm the muon is more magnetic than predicted
#147As 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.
Re: Particle mystery: physicists confirm the muon is more magnetic than predicted
#148Only 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.
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.
Re: Particle mystery: physicists confirm the muon is more magnetic than predicted
#149Science 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.
Re: Particle mystery: physicists confirm the muon is more magnetic than predicted
#150Earlier quoted context omitted.
An old professor of mine loved the "Throw something at the blackboard" technique. Great way to get the class potheads to wake up
how many potheads did you have in your quantum mechanics class?
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.