Higgs theory Explained

Greetings from chilly Toronto, where I’m briefly in town to participate in a public event about the Higgs boson tonight. Should be a good time, especially because it’s not just me giving a talk; I will spend 20 minutes explaining the theoretical motivation behind the Higgs, after which experimentalists Pierre Savard and William Trischuk will talk about the actual experiments.

Which raises the question: how does one explain the theoretical motivation behind the Higgs, given a small number of minutes and a motivated-but-nonexpert audience? It’s something I should have figured out by now, having written a book and all. But I’ve been fishing around, and I think I’ve finally settled on a favorite approach to doing it.

A couple of preliminary notes. I don’t think there is a good explanation of the Higgs boson at the sound bite level, say 15 seconds or less. That’s because you need to explain two distinct things: first, that there is a Higgs field filling space that interacts with the particles moving through it and giving some of them mass; and second, that the Higgs boson is the particle we observe when we interact with a vibration in that field. Both of these ideas are part of quantum field theory, which we generally don’t try to explain in physics popularizations, so it’s more than a few seconds of work to get them across. But I don’t think there is a shortcut: if you want to explain the Higgs at all, you have to explain the Higgs field.

With that in mind, the biggest stumbling block to providing a convincing popular-level motivation for the Higgs field is that we immediately leap to the idea that the role of the Higgs is to “give particles mass, ” where by “particles” we really mean “quarks, charged leptons, and the W & Z bosons.” This raises a couple of problems. First, why do we need some mechanism to give particles mass? Why can’t they just have mass? Of course some particles can just have mass — like the Higgs itself. So you’re starting off by moving backwards, bringing up the need to explain why different symmetries apparently prevent particles from having mass, which is actually harder to explain than the Higgs mechanism. And second, most of the mass in real objects comes from QCD, not from the Higgs mechanism at all, so you are almost inevitably giving people the wrong idea. You see why it’s a tricky situation.