The Higgs boson, dark matter and other mysteries of the universe

I work on the Large Hadron Collider, which is the world’s largest particle collider. What it does is simple and brutal. It takes particles called protons and smashes them into one another with lots of energy.

There’s a long tradition in particle physics of these sorts of experiments where you smash particles into one another. The reason for doing this is perhaps not what you would expect. Particle colliders are sometimes described as atom smashers, which conveys the idea that we’re using these machines to smash atoms apart to see what’s inside them. But that’s not really what colliders are for, because we know what’s inside atoms. We discovered that in the 20th century.

The idea that Peter Higgs and several other theorists came up with in the mid-1960s was that mass arises because particles like electrons and quarks interact with a quantum field – an invisible cosmic energy field that fills the whole universe. When particles like electrons or quarks move through this field, it imbues them with the property of mass.

This idea, written in mathematical language, was proposed to solve a particular type of theoretical problem with our understanding of particle physics in the 1960s. The problem was this: you’ve invented this new invisible field. But how do you know it’s there? One way is to hit this field with such force that you make it resonate or ripple, which shows up as a new particle called the Higgs boson.

So, the Higgs boson is really important and interesting because its existence demonstrates that the associated Higgs field is also there. It’s the Higgs field that gives mass to the quarks and electrons that make up our bodies. If it wasn’t there, atoms couldn’t form because electrons and quarks would never bind together to form stable atoms. It plays an absolutely crucial role in shaping all of the ingredients of our universe and making our universe somewhere where things made of atoms like stars and people can exist.

The Higgs boson is so important to our understanding of particle physics that it was hyperbolically referred to as the “God Particle”. This originated in a book by Leon Lederman, a very eminent particle physicist. His story is that his publisher wanted to call the book The God Particle because he knew it would sell more copies. Lederman joked that it should be known as the “The Goddamn Particle” because it was so hard to find.

Most physicists, including myself, don’t really like this association. The Higgs boson has nothing to do with divinity or God or anything like that. On the other hand, it is an incredibly important ingredient of our universe and central to our understanding of particle physics. What’s more, it’s also connected to some of the big outstanding mysteries about the basic building blocks of the universe.

From astronomy, we now suspect that about 85% of the matter in the universe is invisible. It’s what we call dark matter, which is really just a term to cover our ignorance. It’s some kind of substance that’s all around us, but there is no particle that we know about in the Standard Model that can explain what dark matter is.

Another problem with the Standard Model of particle physics is that it tells us that in the very early universe, around a millionth of a second after the Big Bang, all the matter in the universe should have been annihilated in a reaction with its mirror opposite, something called antimatter. Essentially, the theory tells us that the material world should not exist.

These are reasons for thinking there should be new things to discover at the Large Hadron Collider. In a way, the discovery of the Higgs boson closes the story of 20th century physics; it’s the last missing piece of a theory that was developed in the 1960s and 1970s. But it also potentially opens up new avenues for discovery because the Higgs boson is connected to some of the really big problems facing particle physics. The hope is that by studying the Higgs boson very accurately, either at the LHC or some future machine, we will start to get clues about whether there are other ingredients of our universe that we haven’t seen so far.

A lot of the work at the LHC is about finding signs of new particles, forces of nature and phenomena that we’ve never seen. So far, at least, we haven’t seen any of the predicted new particles that we might have hoped to see. This is worrying, of course, though we’ve seen an increasing number of what we call anomalies in the last few years. These are when experimental data subtly disagree with the theory, and it’s looking increasingly likely that we might be seeing the first signs of something altogether new, although it’s too early to say. The next few years will be exciting as we produce more data and learn more about the basic building blocks of our world.

The Large Hadron Collider is an engineering marvel. It’s the biggest scientific instrument ever built. By some measures, it’s the biggest machine ever built.

What we call the experiments at the LHC are basically the detectors, where the particles collide. You can think of these as like gigantic three-dimensional digital cameras made up of millions of precision-engineered components. Their job is to record the particles as they fly out from the collision point.

Each of these experiments has several hundreds, or often thousands, of physicists working on them. My particular experiment is called LHCb, which is one of the four big detectors on the LHC. The “b” in LHCb stands for “beauty”, also sometimes referred to as “bottom”, which is the name of one of the six quarks that we know about. What LHCb does is study these beauty quarks very precisely. We do that because the way these beauty quarks behave can be affected by the existence of new forces of nature or particles that we haven’t yet discovered. By measuring their properties very accurately and comparing that to what our Standard Model tells us should be happening, we can get indirect evidence for the existence of new forces, new particles and so on.

In some sense, the Higgs is the end of one story and the beginning of another. It’s the end of our understanding of 20th century particle physics, the last missing piece of the Standard Model, but it’s also an unusual, unique particle that comes with a whole set of other questions and problems. It’s going to be one of the main areas of study in particle physics for the coming decades.