No Proton Decay Means Grand Unification Must Wait

The talk of simple geometry reminds me of the Ptolemaic universe for some reason. Layman's comment, I know, but I just couldn't resist.

Study math now! With reverse ageing in the future you could potentially become one of the best in the field. There is time.

What coincidences?

Why assume we are blind?

Complex numbers are an underlying structure that has unified wide ranging physical phenomena

The modeling and the maths allow us to make concrete, precise predictions of how nature behaves, that are testable by experiment.

I sometimes wonder if there is a way to automate the generation of mathematical abstractions and reporting the ones that have physical relevance. I guess one of the big problems then (besides tractability) is how to feed it with experimental data. Even if it is not feasible, then it would still be interesting to read how mathematical physicists would theoretically approach this problem (and even how they would define it).

Quanta Magazine has also a good reputation among many theoretical physicists including myself. They of course do suffer from the occasional misconception, but as a whole the accuracy of their reporting is leaps and bounds above many other popular science sites or blogs.

If it were solely to detect proton decay, yes, I agree it would be very impressive. The reality is a bit more prosaic though, as the article suggests in passing:

"In the meantime, a Nobel Prize has been won for a different discovery in the cathedral-esque water tank pertaining to particles called neutrinos."

Hyper-K is a dual-purpose detector, a neutrino detector as well as a proton decay detector. Substantial part of Hyper-K funding should be interpreted as investment to a neutrino detector.

At a guess, probability.

You can't have a single virtual particle appearing, it's always two, due to conservation of momentum, charge etc

So it'd be a quark-antiquark pair popping up.

The proton is the lightest Baryon (3 quark particle), there is no lighter Baryon it could decay into. The decay products have to be lighter than the original proton, by at least the mass of the virtual quark pair, to repay the energy 'borrowed' from the vacuum to create the virtual quark pair (because energy is always conserved). So the proton remains unaffected by the virtual particles popping in and out of existence around it. The virtual particles have no choice but to effectively to annihilate with one another and disappear, to pay back the energy debt.

Heavier Baryons (Sigmas, Lambdas) are indeed destabilized by virtual quark pairs, that is the mechanism by which they decay, almost instantaneously, on their own.

You could have an up-anti up quark pair that pops up close to the up quark of the proton, the up quarks could 'swap places', and then the up of the proton annihilates with the anti up of the virtual quark pair, but the the result is still a proton.

Virtual particles are not are ordinary particles that pop in and out of existence. Virtual particles are a particular way to model quantum interactions. Some argue virtual particles are "real" in an ontological way, and pop science tends to lean toward that view, but they're certainly not real the way regular particles are real.

It's required that quantum interactions obey conservation laws, and any non-conserving "virtual configuration" must be short-lived, only existing to the extent it might affect interactions with "real", physically allowed configurations. There's no quantum interaction that lets a proton turn into something else while obeying conservation laws. In particular, normal interactions can't change the number of quarks in a given configuration, and the proton is the lowest energy configuration of 3 quarks. So it can't "tunnel" via a virtual configuration into some other real configuration.

Grand unified theories usually introduce additional mechanisms that can turn quarks into leptons, so proton decay is a test of those theories.

The symmetry breaking should be thought of as a phase transition that occurs as the temperature of the universe changes, like liquid freezing and becoming ice. The universe was initially very hot, but rapidly cooled down as it expanded and went through phase transitions when it passed the "freezing temperature", i.e the temperature at which the laws of physics prefer to spontaneously break the symmetry.

You're implying that there is some way to write such an article that simply explains particle physics to the layman with out causing any confusion.

Symmetry breaking just means when I look at an object at a certain range (energy range, size, whatever), it looks identical to another object. But then when I widen my view suddenly it diverges from that other object and act different.

So there is a search for why.

For example an up and down quark look virtually identical, because they are quite similar. But at a certain point something differs in an experiment, and you realize it's because their masses are not identical, and in a certain situation the symmetry is broken and you can see the different masses.

I think in an effort to understand exactly how the mechanics of the big bang worked and how you can go from an infinitesimal point of incredible energy to an enormous and expansive universe with the diverse laws we observe today.

From the article:

> If the forces were indeed one during the “grand unification epoch” of the universe’s first trillionth of a trillionth of a trillionth of a second, then particles that now have distinct responses to the three forces would then have been symmetric and interchangeable, like facets of a crystal. As the universe cooled, these symmetries would have broken, like a crystal shattering, introducing distinct particles and the complexity seen in the universe today.

Because, even in the simplest case both would involve changes energy/enthalpy and therefore would interact with each other. In particular reactions in one might drive the equilibrium populations in the other and vice versa.

One problem with simply combing the current General Relativity and Standard Model theories is local vs non-local determination. That is moderately complex to explain... perhaps someone has a better source than Wikipedia:

https://en.wikipedia.org/wiki/Principle_of_locality

Because, on one side, we've been able to deduce, in principle, all such interactions (and there are maaaaany) from just two. So it'd be surprising. On the other hand, these two interactions, General Relativity and the Standard Model, talk about the exact same things (the same "statements" in your example). While in many energy ranges the effects of one or the other are too small to be noticed, there definitely is an energy range in which both should have strong effects. Yet they aren't compatible. If we performed experiments in those ranges, the theory that describes what we measure would need to be compatible with both, an extension; the unified theory.

> Why do we assume the theories are unifiable?

I think it's a great question. Maybe the universe itself is the attempt to unify these theories. Greg Egan style.

A neutrino interaction with the electrons or nuclei of water can produce a charged particle that moves faster than the speed of light in water (not to be confused with exceeding the speed of light in a vacuum). This creates a cone of light known as Cherenkov radiation, which is the optical equivalent to a sonic boom. The Cherenkov light is projected as a ring on the wall of the detector and recorded . . .

From: https://en.wikipedia.org/wiki/Super-Kamiokande#Description