This morning, to the nearly universal expectations of the physics community, the 2013 Nobel Prize in physics was awarded to François Englert and Peter Higgs for the theoretical prediction of what has come to be known as the Higgs boson. Nobel Prizes (at least in the sciences) are almost always given out for a discovery rather than a prediction, so it wasn’t until last year, when two independent groups at the Large Hadron Collider detected the eponymous particle, that Englert and Higgs were even in contention. This year’s announcement represents an incredibly quick turnaround for a committee that has generally been fairly conservative in its awards. Einstein had to wait 16 years for his.
I’d like to share some cocktail party chatter on why the Higgs is such a big deal, what it means for the future of Big Science, and perhaps most importantly, why you should, under no circumstances, call it “the God particle.”
The Big Idea
As it’s normally described in the press, the Higgs boson gives mass to other particles, but it’s much more than that. The “Standard Model of Physics” is a mathematical description of every fundamental particle and interaction of nature (except gravity—so far, only Einstein’s theory of general relativity manages to get gravity right). The Higgs is the last piece of a puzzle, the final particle to be discovered in the Standard Model—and with the right sort of properties that we’d predicted from the start.
The Higgs boson is also the answer to a riddle: Why is the weak nuclear interaction, the interaction that controls (among much else) the fusion in the interior of the sun, so weak? Some forces, like electricity and magnetism, can extend over vast distances—your compass, for instance, responds to magnetic fields on a global scale—but the weak force is confined to the nuclei of atoms.
The weakness of the weak force is more than just a byproduct of the name. For the last half-century, we’ve understood the fundamental interactions of physics to arise when two particles exchange a “mediator,” basically a messenger particle that tells two electrons (for example) whether they should attract or repel one another. For electricity, the mediator is known as a photon, the particle of light. The photon is completely massless, which is why it’s able to travel so fast and so far. Indeed, a fundamental feature of the Standard Model is that all of the mediators are supposed to massless.
For electromagnetism and the “strong force” that holds protons and neutrons together, the mediators are massless, but the weak interaction is very different. In the weak interaction, the mediator particles are known, a tad unimaginatively, as the W and Z bosons, and when they were discovered 40 years ago, they were found to have a mass roughly a hundred times as much as a proton. In the particle physics world, this is huge—although marginally lighter than the Higgs boson itself. The relative bulkiness of the Ws and Zs is what ultimately confines them to atomic nuclei.
The “Higgs mechanism” aims to explain where all of that mass comes from.
How does the Higgs give mass? There is no shortage of analogies. Some have likened it to water that saturates sponges to make them heavier, or to a cosmic pool of molasses that slows down all particles that move through it, or to a celebrity thronged by admirers as she enters a room (the Higgs bosons are the admirers). All of these approaches aim to describe mass in terms of its consequences: Massive things, all things being equal, travel slower than massless things. Peter Higgs himself has described the mechanism as slowing down particles in the same way that a beam of light is slowed as it travels through a piece of glass.
Pick your analogy; they’re all imperfect. If the Higgs really were like molasses, then particles would not only slow down, they’d keep slowing until they came to a stop. But as Newton taught us, objects in motion stay in motion.
So skip the analogies and instead think of the Higgs as just another mediator particle, but with a twist: It allows the W and Z particles to interact with themselves rather than with another particle. To a physicist, an interaction is just a fancy way of introducing energy to the equation. And that equation is the most famous one in all of physics: E=mc2.
Einstein’s equation says a lot. For instance, by taking hydrogen and converting it to helium (as happens in the sun), there’s a reduction in mass, and that deficit produces a huge amount of energy.
The process works in reverse as well. Introduce enough energy (and you need a lot to make a difference), and the energy behaves the same as ordinary mass. In fact, this is where you came from. In the early universe, there was so much energy flying around in the form of massless photons that when they collided with one another, they were able to produce fundamental particles like electrons and quarks from whole cloth.
The Higgs doesn’t just pump up the mass for W and Z bosons. All fundamental particles should naturally be massless according to the Standard Model, but they aren’t. The Higgs is ultimately responsible for not only the mass of the W and Z particles, but all of the electrons and quarks in your being.
And that is a very big deal.