Around the time of reports last year about the discovery of the Higgs particle at the LHC (Large Hadron Collider), reader Anthony in a private email to me asked a good question. The Higgs particle is repeatedly referred to as the means by which all other particles get their mass. If not for the Higgs, elementary particles like the electron, muon, and the like would be massless and like all massless particles would be zipping around at the speed of light. At present, there is no explanation for why these particles have mass at all let alone the actual values that they do have. According to current theory, it is the Higgs phenomenon that gives all the other particles their mass. So how does that happen?
In many popular explanations, a metaphor is used. It asserted that these Higgs particles permeate all space and act as a kind of viscous fluid that ‘slows’ the other particles down, which is equivalent to giving them mass. But this raises the question of how the Higgs particle gets its own mass. Surely it cannot be slowing itself down? This is the good question that Anthony raised, and rather than give a short and glib answer, I thought that the scientifically-minded readers of this blog might like more solid information about the much-ballyhooed discovery of this particle last July. The catch is that this will turn out to be one of my dreaded multi-part series, so buckle up, it’s going to be a bumpy ride*. To make it easy to refer back to the other posts in this series, I will present the material in bite-sized chunks every weekday so that people have time to digest it before moving on to the next part. I have created a new category so that the entire series will be in one place for easy reference.
Although the discovery of the Higgs is by now somewhat old news, I hope to provide more solid information than the hyperventilating popular media accounts that tend to go along the lines of how ‘the god particle’ will unlock the secrets of the universe. At the same time I will avoid the difficult mathematics. This series of posts will try to explain why the search was pursued with such intensity, some of the basic physics underlying it, and why the entire process was so difficult and costly. This will involve plenty of hand-waving arguments using metaphors and analogies at various points because the theory is pretty mathematical and complicated. Also, this is not my area so I am not going to claim 100% accuracy for everything that follows but it should be pretty close.
It would be helpful to rectify three popular misconceptions right at the beginning.
The first is that there are three related phenomena associated with the name Higgs: two of them refer to specific entities and are the Higgs field and the Higgs particle (also called a boson for technical reasons that I won’t be going into), while the third is the Higgs mechanism, which represents a process involving those two. Although it was the discovery of the Higgs particle that made the headlines, the other two are as important. The Higgs particle derives its significance from the fact that it provides concrete evidence that we are on the right track in postulating the existence of the Higgs field and the Higgs mechanism that follows from it. If the Higgs particle had not been found, it would have cast serious doubt on what has been called the Standard Model of particle physics that has been so successful so far in explaining the properties of fundamental particles. The discovery of the Higgs does not mean that there are no more unanswered questions. But it is an important part of the structure.
The second thing to note is that although the name Higgs is the one that has stuck to all three phenomena, there were actually six people in three groups working independently who in 1964 published papers contributing to the eventual theory: Robert Brout and Francois Englert; Peter Higgs (working alone); and Carl Richard Hagen, Gerald Guralnik, and Tom Kibble. So why does only Higgs get his name attached to this? The way things get named in physics is often an accident and the first easily remembered and plausible name that comes along tends to get fixed in people’s minds. In the spirit of sharing credit more appropriately, some have tried to have the label BEHHGK (pronounced ‘beck’) replace Higgs but it hasn’t caught on.
The third popular misconception is that although it is often asserted that the Higgs particle gives mass to everything, this statement has to be modified in two ways: one is that it is the Higgs field, via the Higgs mechanism, that gives rise to mass; and the second is that it gives mass only to the elementary particles, not to all the objects in the universe that have mass.
Next: How ordinary matter is made.
(* I know that this allusion is to a common misquote of the original line from the classic 1950 film All About Eve but the misquote is more generally serviceable than the correct “Fasten your seat belts. It’s going to be a bumpy night“, which may be why it has caught on. Too bad that line wasn’t from that other classic 1957 film The Three Faces of Eve to better fit with the title of this post.)