Theoretical Uncertainty and Uncertain Theory
Here’s a discussion of the status of the latest measurements of (g-2) versus theory. This kind of problem is not confined to particle physics. It also happens in cosmology that we have problems making accurate predictions to compare with observations, especially when using galaxies to trace large-scale structure. There’s a lot of messy astrophysics to be accounted for.
Yesterday, Fermilab’s Muon g-2 experiment announced a new measurement of the magnetic moment of the muon, a number which describes how muons interact with magnetic fields. For what might seem like a small technical detail, physicists have been very excited about this measurement because it’s a small technical detail that the Standard Model seems to get wrong, making it a potential hint of new undiscovered particles. Quanta magazine has a great piece on the announcement, which explains more than I will here, but the upshot is that there are two different calculations on the market that attempt to predict the magnetic moment of the muon. One of them, using older methods, disagrees with the experiment. The other, with a new approach, agrees. The question then becomes, which calculation was wrong? And why?
What does it mean for a prediction to match an experimental result? The simple, wrong, answer is…
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In the Dark 
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