The Higgs Boson in Context [Uncertain Principles]
I ran across this recently while looking for something else, and was reminded of it by this discussion of jargon. It’s an attempt to explain the general historical context of the whole Higgs Boson thing, and why it’s important. I improvised this in response to somebody’s question about how I would explain that, drawing mostly on my recollection of a couple of history-of-field-theory books. I kept it in case I needed to bust it out when they discovered the Higgs, but that fell during the time when I wasn’t able to blog, so I never used it. I’m never going to use it for anything else, though, so I might as well throw it up here to be mocked and reviled for my ignorance of theoretical physics.
If you want to understand the importance of the Higgs, you really need to go back to the start of quantum physics, when people started to think seriously about how to treat electromagnetic interactions. Classically, you just sort of assert that particles have charges, and as long as you don’t think too much about that, it works reasonably well– you can do a very good job of calculating the spectrum of light emitted by simple atoms, for example. If you start to look closely, though, there are some big problems. Specifically, if you try to calculate things like the energy of a single electron by itself, you get utter nonsense– the simple calculation gives you an infinite answer. The problem is, basically, that you’re trying to pack a finite amount of charge into an infinitesimally small space, and it ought to take an infinite amount of energy to do that. On the experimental side, there are some problems as well– the simple calculation for the energies of an electron inside a hydrogen atom is very, very good, but doesn’t quite get everything. In particular, there’s a thing called the “Lamb shift,” a slight difference in the energy of a particular state that nobody could explain.
This was a big crisis for theoretical physics, and some very smart people spent a lot of time beating on it. Eventually, nearly simultaneously on different sides of the planet, Richard Feynman, Julian Schwinger, and Shin-Ichiro Tomonaga hit on the solution, the theory that’s now called “quantum electro-dynamics,” or QED for short. The new theory had some surprising elements, in particular the fact that empty space is no longer empty– it’s filled with a fluctuating electromagnetic field, that can manifest as “virtual particles” popping out of nowhere, then disappearing again. This is deeply weird, but fixes the problems with the simplest models– having these virtual particles pop into existence tends to sort of smear out the charge of the electron, so it’s not packed so tightly, which lets you get rid of the infinite energy for an electron by itself. And the interaction between electrons in an atom and these particles popping out of empty space has a tiny but measurable effect on the energy of those electrons, which shows up in things like the Lamb shift.
So, QED fixes the problems with putting electromagnetism into quantum mechanics by filling empty space with virtual particles. This sounds bizarre, but it’s fantastically successful– for one particular property, the “g-factor” of the electron, which determines the energy of an electron interacting with a magnetic field, the QED prediction and the experimental measurement agree with each other to about 14 decimal places. It’s probably the best tested theory in the history of testable theories.
The next big problem to face physics was the need to incorporate some new forces, in particular the “weak nuclear force,” which is called that because it mostly acts on particles found in the nucleus of an atom, and it’s not as strong as the “strong nuclear force.” Physicists suck at names. when you try to add the weak force into the theory, you once again find yourself getting nonsensical results– particles that ought to exist don’t, or particles that do exist shouldn’t.
Once again, the solution is to change the nature of empty space. Where QED took empty space and filled it with virtual particles acting through the electromagnetic field, incorporating the weak force into the picture adds another field permeating all of space. A bunch of different people came up with the idea at around the same time, but for various reasons Peter Higgs’s name has gotten attached to this thing, so they call it the “Higgs field.” Like the virtual particles from QED, this can occasionally pop up as a particle from nowhere, which is the Higgs boson.
As with QED, filling empty space with a whole new thing seems pretty weird, but it works very well to get rid of the nonsensical answers. In particular, it interacts with some particles in a way that makes them behave as if they have mass, when the simplest attempt at a theory of the weak force says they shouldn’t.
This “Higgs mechanism” is one of the central elements of the Standard Model of particle physics. Again, physicists suck at names. It manages to successfully incorporate the weak force into quantum mechanics, and sets the basic parameters for all the particles making up that theory. every one of them has been found, with the exception of the Higgs boson itself, which has proven trickier to track down than people would’ve liked. Once they find that– and nobody seriously doubts that they will– the Standard Model will be complete, which is why it’s a big deal.
(The “featured image” is a picture of Feynman, Schwinger, and Tomonaga, because I already had it, and it was easy to add to the post, and these things look better with an image of some sort. If you’re reading via RSS, you’re not missing much.)