Muons do not rotate as predicted by the best physics model. Why not? It could be due to completely unknown subatomic particles entering and disappearing from quantum foam.
This is not a kind of SF technobabble. This comes from fairly real experimental results, and it might very well be that the Universe tells us that we still don’t understand everything about it.
These extremely interesting and possibly game-changing results come from Fermilab, a high-energy particle acceleration lab in Illinois. There I do a lot of different types of experiments there, and one is called Muon g-2 (literally, “g minus 2”), which examines a subatomic particle called muon.
Muons are similar to electrons – for example, they have a negative charge and the same rotation (a fundamental property of particles, which will become important in an instant), although they are 200 times more massive.
Using everything we know about subatomic particles (called the standard model), physicists can predict a lot about the behavior of a muon. For example, a rotating charged particle has a magnetic property associated with it called a time, which is a measure of the strength of its magnetic field and its orientation. If you put a muon in a magnetic field, it will undergo a called oscillation precession; this is physically similar to a toy tip that sways as it spins on a table.
The models predict this precession extremely accurately. Extremely. Physicists give it a value called factor g, and is very close to, but not exactly equal to 2.
Here things are fun: On our macroscopic scale, we like to believe that space is smooth and continuous. But on a quantum scale, an incredibly small scale (like 10-35 meters!) quantum mechanics implies that space is not continuous and smooth, and instead may appear in discrete units, such as check marks on a graph. This means that, at that scale, the space may not be empty, but instead boils and foams with energy.
Sometimes this energy will spontaneously create a pair of subatomic particles (because mass and energy are the two sides of the same coin, E being equal to mc2 and all this). These particles may appear in existence, but the same laws of quantum reality require that the particles interact immediately and become energy again, going back into the energy of the vacuum. It’s called (and I like that) quantum foam.
A muon that rotates in a magnetic field is affected by quantum foam. If there were no foam, the value of the g-factor would be very close to 2. But the particles that appear in and out of existence affect the oscillation of the muon. This is called abnormal magnetic moment, deviation from normal value.
The standard model predicts the value of this anomalous moment by examining everything that is known about forces and particles. It should be very precise. However, it’s always nice to make sure and that’s what the Muon g-2 experiment does. It injects muons into a very stable magnetic field and measure oscillation, which can then be compared with the prediction. If I agree, then yes, we will understand how the quantum mechanical universe behaves.
If not … well. That would be interesting, wouldn’t it?
The standard model predicts the abnormal value of the muon’s magnetic moment 0.00116591810 (± 0.0000000004343; as I said, very accurate).
The new experiment is worth 0.00116592061 (± 0.00000000041).
These are different. The difference is small, of course, only 0.0002%. But still, they should be equal. And I’m not.
This small difference means a lot. It means that there are forces and / or particles that act on the quantum scale that we do not know about!
May be. Here’s the key monkey: The results are not Fairly to the statistical snuff. It is very unlikely that they will be caused by a random chance. It’s like throwing a coin: if heads appear three times in a row, you might think the coin is rigged, but there’s a one in eight chance that it will happen at random. The more times you turn it over and it gets up, the less likely it is to be random.
Scientists use a term called sigma to measure this chance. The gold standard in particle physics experiments is when an experiment is in the five-sigma range, which means that it has a random chance of about one million out of three or, if you prefer, a 99.99997% chance of either real is about 68%, two is 95%, three is 97% and so on, crawling closer and closer to 100%). The results of the Muon G factor experiment are only 4.2 sigma, which means that they still have a 1 in 38,000 chance of being due to random noise.
However, this is a 99.997% chance of being real, and that’s pretty good*. It is simply not enough for physicists to declare victory. The good news is, they’re not done yet. The experiment has been performed three times so far, makes a fourth and a fifth is planned. The scientists examined the data from the first tests, but this amounts to only about 6% of the total amount of data they expect from the experiment. To use the above analogy, it is as if they overturned the coin a few times and got strange results, but will continue to turn it over many times to be sure.
If the rest of the data aligns with what they’ve seen so far, the five-sign certainty will pass. And if that happens, it certainly means that the Universe is weirder and more mysterious than even the quantum mechanics we know about tells us … and that’s already he told us that the universe is damn weird.
If you want all this in comic form, then Jorge Cham covers you:
So this is potentially very interesting. The standard model is quite successful (for example, predicted the existence of the Higgs boson, which was first found a few years ago), but we know that there are cracks in it, things that do not predict as well. In this case, the muons that float and spin and sway in a magnetic field signal us to go further down that path, causing us to move on to more physics that we still don’t understand, or don’t even know anything about. .
And this is the dream of every particle physicist. When the experiments check the theory, that’s nice, because it’s like showing that the road behind us is smoothly paved.
But what’s next?
[Correction (16:00 UTC on April 8, 2021): I originally calculated the percentages incorrectly on those chances, adding an extra two 9s in the decimal point (in other words I had written them as straight odds, not percentages, like a 0.01 chance is 1%). Arg! The numbers are now fixed.]