Someone asked me to explain the Higgs Boson. This will be the last question I answer in a while. I’ll let the ask function stay open, but I’ll be collecting the questions and answering some of them at a later date. To clarify my earlier post, I do not consider any of the questions I answered to be dumb. The comment about dumb questions was intended to discourage people from asking me to help them with their schoolwork. I have no interest in that. But if you have a question about science inspired by genuine interest and curiosity, that is the sort of question I am interested in answering on this blog. This blog isn’t just about Q and A, though: more posts about science inspired by my own curiosity are forthcoming.
So, the elusive and mysterious Higgs boson. On this subject I am hopelessly out of my depth, as acquiring a good understanding of it requires a background in mathematical physics which neither I nor most of my readers possess. I will try to defer to better informed authorities. Here is John Baez, a mathematical physicist I really admire for this productivity both in producing cutting-edge theoretical science and also cranking out one educational piece after the other. This was written before CERN confirmed that the particle they detected in 2012 was indeed a Higgs boson:
The Standard Model predicts the existence of a spin-0 particle called the Higgs boson, which comes in two isospin states, one with charge +1 and one neutral. (It also predicts that this particle has an antiparticle.) According to the Standard Model, the interaction of the Higgs boson with the electroweak force is responsible for a “spontaneous symmetry breaking” process that makes this force act like two very different forces: the electromagnetic force and the weak force. Moreover, it is primarily the interaction of the Higgs boson with the other particles in the Standard Model that endows them with their masses! The Higgs boson is very mysterious, because in addition to doing all these important things, it stands alone, very different from all the other particles. For example, it is the only spin-0 particle in the Standard Model. To add to the mystery, it is the only particle in the Standard Model that has not yet been directly detected! [ed. note: how it has]
On the 4th of July, 2012, two experimental teams looking for the Higgs boson at the Large Hadron Collider (LHC) announced the discovery of a previously unknown boson with mass of roughly 125-126 GeV/c2. Using the combined analysis of two interaction types, these experiments reached a statistical significance of 5 sigma, meaning that if no such boson existed, the chance of seeing what they was less than 1 in a million.
However, it has not yet been confirmed that this boson behaves as the Standard Model predicts of the Higgs [ed. note: at this point, many signs point to the particle behaving roughly as predicted]. Some particle physicists hope that the Higgs boson, when seen, will work a bit differently than the Standard Model predicts. For example, some variants of the Standard Model predict more than one type of Higgs boson. LHC may also discover other new phenomena when it starts colliding particles at energies higher than ever before explored. For example, it could find evidence for supersymmetry, providing indirect support for superstring theory.
So what is up with this boson, anyway? Bosons are a kind of elementary particles, the other kind being fermions. You may have heard about the Pauli exclusion principle, which says that no two particles (such as neutrons) can occupy the exact same quantum state. Fermions are particles that obey this principle, as well as other laws found by Paul Dirac and Enrico Fermi (principal discoverer of the neutron). Bosons do not, however, obey these laws. The Higgs particle is a boson.
As mentioned above, the Higgs is important for several reasons. For one, it is the missing piece in the Standard Model of physics. This is the model that constitutes what is colloquially only known as quantum physics. Using a variety of laws operating on a variety of particles, it explains three of the fundamental forces of nature: the electromagnetic force, and the weak and strong nuclear forces. Einstein’s General Relativity explains the last force, gravitation, and famously we have yet to find a good theory of quantum gravity, a theory that can explain all four forces in a common framework. Finding the Higgs, predicted more than forty years ago, goes a long way towards confirming the standard model.
But its most publicized property is its ability to give (certain) particles mass; without the so-called Higgs mechanism, we don’t know how to explain the mass of some particles. As it turns out, if you look closely, by which I mean at the subatomic level—like the researchers at the Large Hadron Collider—you find that the electromagnetic and weak nuclear forces can be unified to one force. But why then do they behave as if they were two, how come this one force seems to act like one force in certain circumstances and another under different circumstances? This is where the Higgs boson comes in. It “spontaneously breaks symmetry” and cleaves the electroweak force into the weak and electromagnetic forces. Interacting with the Higgs field, a field that can be described by four numbers that permeates space—so the theory goes—also endows the W and Z bosons, carriers of the weak nuclear force, with a mass they would otherwise not have. Thus we have in principle four particles involved with the electroweak force, produced by the Higgs symmetry breaking: the positively charged W+ boson, its antiparticle the negative W- boson, the electroneutral Z boson, and finally the familiar, massless photon.
This symmetry breaking, the cleaving of one force into two apparent ones, can only be seen at very large energies, hence the need to build the expensive particle accelerator at CERN.
Various analogies have been proposed to explain how particles gain mass by interacting with the Higgs field, but none of them really hit the mark; all of them, while partially accurate, are prone to misinterpretation. In reality, what goes on in the quantum realm has no easily explainable analog in the macroscopic world we live in. I won’t even pretend to make an analogy. To fully understand it, you need a physics background.
This has been a layman’s attempt at explaining the Higgs boson. It is undoubtedly not wholly accurate, precisely because I lack the necessary scientific background. Those of you who are physicists will likely object to some of what I’ve said, and that is fine. I am perfectly aware that I am not entirely qualified to speak about this, but for the sake of my own understanding and that of my readers, I’ve given it a shot. If someone reblogs this with a better, more accurate explanation that is nevertheless accessible to the layman, I’ll share it. Maybe a physicist among you would like to do a guest post? I haven’t forgotten the early days when this was a group blog.
Anyway, the takeaway, which is one thing I am fairly certain is entirely accurate, is this: the discovery of the Higgs boson is very important in that it presents strong confirmation of what we already suspected based on previous evidence, namely that the Standard Model is, while not perfect, a very good description of reality at the subatomic level, as good as any we have today. The Higgs mechanism also solves important problems with the Standard Model involving how certain particles gain mass, particles which without this mechanism would be massless—and we know from experiments that they do have mass.