Take Fig. 2 from this earlier article about the known particles [which I recommend you read first, if you haven’t already.] This figure shows the known elementary particles of nature (plus the conjectured Higgs of the Standard Model) and the lines indicate which particles directly affect one another. You see three of the four known forces of nature (gravity is left off to avoid clutter): the strong nuclear force (with gluons as force carriers), electromagnetism (whose force carrier is the photon) and the weak nuclear force (with W’s and Z as force carriers). And you see that the neutrinos, charged leptons and quarks do not interact directly with one another; they are directly affected only by the force carriers. And finally, the Higgs field, which is non-zero in our universe [you might want to look at these video clips for more info], and is indicated by the green swath, affects all of the known massive elementary particles, and in fact is responsible for making them massive.
Now compare this with Fig. 3, which shows what the world of particles would be like if the Higgs field were zero. Look closely. You’ll see many differences! [In a little while we’ll see where some of them come from.]
- Instead of the electromagnetic and weak nuclear force present in our world, with its non-zero-Higgs-field, a zero-Higgs-field world has these forces scrambled and rearranged. The rearranged forces are called hypercharge and isospin (for historical reasons; the names are just that, names, without other significance.)
- As part of this scrambling, the force carrier particles are changed; there are 3 W particles and an X particle, and the Z0 and photon are missing. And the W and X particles are all massless now.
- The force carriers are now simpler in another sense. The photon affects the W+ and W– particles directly; you can see that in Fig. 2, where they are connected by a purple line. But the X particle does not directly affect any of the three W particles. The gluons affect themselves as before (the red curved line); the W’s affect themselves too; but the X particle affects no force carriers at all.
- For every matter particle (except neutrinos) there are now two particles with the same name. But they’re different, as different as Arnold Palmer and Arnold Schwarzenegger. Physicists (for complicated reasons) have several naming schemes for them, but a top quark by any name would smell as sweet — so for current purposes I’ve indicated them as different by rotating one to the left and one to the right. We can call them top-left and top-right. [This happens in fact to be one of the naming schemes physicists use and it does have a bit of an underlying meaning, but it’s best to just view these as names.]
- Notice that the left-particles all come in pairs, one pair for each generation, and are affected by the isospin force. The electron comes with the neutrino-e (or “electron-neutrino”), the up quark comes with the down-quark, etc.
- But the right-particles come singly, one for each generation, and are not affected by the isospin force.
- There are only neutrino-lefts; there are no neutrino-rights.
- In Figure 1, I used the labeling neutrino-1, neutrino-2 and neutrino-3 for the neutrinos, but in Figure 2 I use labels that correspond to the names “electron-neutrino”, “muon-neutrino”, and “tau-neutrino”. This is a subtlety you can ignore unless you are really interested in it, in which case you should read this article.
- All of the particles shown are massless — except for the Higgs particles, of which there are four! (That’s a minimum; the Standard Model, in which one assumes the simplest possible Higgs fields, has four, but the full story could be more complicated.)