Sometimes, a major discovery is exactly what you were hoping not to find. That’s the case with a team at Penn State who seem to have recently closed the door on any new physics stemming from a longstanding discrepency in the magnetic moment of the muon. It turns out, the model was fine, and we just needed better calculations.
The Muon is a heavier cousin to the electron. Like the electron, it has an intrinsic magnetic moment, but the traditional methods to calculate it did not quite match experiments, which was very exciting because it made us hope our models could be improved. Rather than try the traditional approximation methods for the unsolvable equations, the group at Penn State set up what you can think of as the Quantum Chromodynamic equivalent of a Finite Element Model (FEM) simulation–a grid of discrete steps in space and time. Tiny ones, of course, because the muon, like the electron, is a point-like particle with no lower size limit. In any case, according to their paper in Nature, after a decade of refinement and increasingly expensive supercomputer runs, the mystery can be put to bed. Instead of the discrepancy that so exited physicists 25 years ago when it was first found, theory and experiment now match to 11 digits, or a 0.5 sigma discrepancy, if you prefer.
Statistically, the Standard Model works– and that kind of sucks. It sucks, because it’s the gaps in the model where new physics are possible, and everyone has been pushing at those few gaps for the last 50 years to try and find what might be behind the standard model. Even [Zoltan Fodor], the principle investigator behind this project, is sad to see it work out. Sure, it’s a feather in his cap to get the calculations right at last–but ask anybody in the field, and they’d rather keep the door open to new physics than be right. We were certainly hoping it was something novel, last time the topic came up.
You might think muons are the last thing a hacker would ever encounter, but since there’s a steady rain of them from the sky in the form of cosmic rays, it’s not only easy to interact with them, you can actually put them to practical use– like muon tomography, or navigation indoors and underground.
Header Image Credit: Dani Zemba / Penn State
I guess the author meant “principal investigator” (PI) instead of “principle investigator”. Nice article!
To be fair, I’ve seen actual prospective PIs make the same error. In grant applications even. Embarrassing.
It seems they make them younger and less literate every year. Or maybe I’m just getting older and less tolerant.
=X I made this mistake recently on a proposal presentation. Spelled principal right in 5 different places, then on the very last slide I spelled it wrong. I caught it as I was presenting, but I don’t think anyone noticed, so that embarrassment was contained. At least I know I’ll never make that mistake again.
all that alliteration broke my brain.
11 digits would be 6.5 sigma, wouldn’t it? 11 digits is the eye of a needle compared to the barn door of 0.5 sigma
You’ll have to step us through that leap of logic how you got “11 digits = 6.5 sigma”
There’s a bit of nuance lost in the retelling by this author. The original article states their calculations (and the errors in the measurements that go into the calculations) differ from the model prediction by only 0.5 standard deviations. The fact that it takes 11 digits to write the number with sufficient precision sounds impressive but isn’t really relevant.
I feel bad for all the theorists who built on the gap but I am happy for humans in general. We understand something new.
The standard model seems to be disliked. Even when they were building it out people seemed upset about it. I get that it’s a big sprawling mess but isn’t that kind of awesome?
“Disliked” I think is overstating it. The standard model one of the most successful theories ever created by humans and is indeed awesome. The problem is that it’s so successful that it’s a bit “boring” now and yet still doesn’t explain everything we observe. It means there’s a lot we don’t understand about the universe. Any hint of a discrepancy excites people because it’s a hint that the path to more discoveries may be there.
People want anti-gravity—if the Standard Model is wrong–they figure the univers3 might let us have sci-fi tech when it isn’t looking
Woke gravity, then we can deny it and do…whatever.
Deny woke gravity = FAFO like Mike Hughes.
But seriously, I don’t believe the Standard Model prohibits anti-gravity yet. My sci-fi hopes persist.
Black holes would be a lot more interesting if it did.
Im not convinced this isnt data massaging of the highest order, feels like they just used a bunch of admissible error modifiers to make the math work. Like a brute force solution rather than an elegant one. Im hoping combining electro magnetic lattice compute and 4 valence point mesh theories will find a better solution