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.
A Complicated Prize
While a lot of us in the physics community were fairly certain that the prize was going to Higgs (the particle), it was less clear that it would be awarded to Higgs (the scientist), and if so, who his co-awardees might be. There’s a limit of only three to a prize, but in this case, there are a huge number of people who might rightly feel robbed.
While this isn’t meant to take anything away from Higgs and Englert, there were a lot of contemporaneous researchers who were working on something similar. Phil Anderson (who won the Nobel in 1977 for unrelated work) devised a Higgs-like approach to generating mass two years earlier than Higgs and Englert wrote their theories in 1964. There are at least four other contemporaneous theorists—Robert Brout (Englert’s co-author on the work), Carl Hagen, Gerry Guralnik, and Tom Kibble—who could make legitimate claim. It wasn’t until nearly a decade later that researchers started referring to it as “the Higgs mechanism.”
What’s more, historically prizes have generally gone to the discovery itself, or to a combination of discovery and prediction. For example, in 1964 Arno Penzias and Robert Wilson discovered, largely by accident, that the universe was filled with a low-level radiation—a remnant of the Big Bang. This radiation had been predicted for decades, but it was Penzias and Wilson, and not the theorists who proposed the idea of a background radiation (and definitely not the group led by Robert Dicke, who were scooped while actually trying to detect the background radiation), who won the 1978 Nobel Prize.
Similarly, many in the physics community had reasonable expectations that the Nobel committee would recognize the experimentalists who actually found the particle. This was no easy task. The Large Hadron Collider is a multibillion-dollar international collaboration involving literally thousands of scientists. It involves accelerating protons up to about 99.999996 percent of the speed of light, and it was motivated in no small part on finding the Higgs. While ATLAS and CMS, the two experiments that found the Higgs, more or less simultaneously, may get someday get recognized by the good folks in Sweden, that day is not today.
This is the problem, perhaps, with Big Science. It’s very easy to envision big prizes like the Nobel going to a lone genius or a small team. On the other hand, with giant experiments like the LHC increasingly contributing to groundbreaking science, it’s less clear how credit should be allocated.
What Doesn’t the Higgs Tell Us?
It is easy to overstate the importance of the Higgs discovery. Though the Higgs tells us a great deal about mass, it says absolutely nothing about how gravity works. As one of the fundamental forces of nature, gravity should work the same way as the other forces, with mediators and whatnot. And yet, every attempt to come up with a comprehensive theory of “quantum gravity,” as it’s known, has come up short.
And even with regard to mass, understanding the Higgs doesn’t tell us everything. The recipe of the universe seems to be about 68 percent mysterious “dark energy” that accelerates the expanding universe, about 25 percent incompletely understood “dark matter” that holds together galaxies, and only about 5 percent ordinary stuff—the kind that the Higgs gives mass to.
And even the mass of ordinary matter isn’t entirely explained by the Higgs. Ordinary stuff (e.g., you) is made of protons and neutrons, but those particles are made of even more fundamental particles called quarks. Quarks do, indeed, get their masses from the Higgs, but as it turns out, protons are much more than the sum of their parts; less than 2 percent of the mass of a proton comes directly from the mass of the quarks—and thus, the Higgs. Instead, the vast majority of your mass comes from the fact that everything inside your atomic nuclei is flying around at nearly the speed of light.
The Higgs is important, but when reporters write about it as “the God particle,” they’re overstating the case. The Nobel laureate Leon Lederman coined the term in large part to sell more books, but physicists themselves don’t generally use it at all, except to complain about it as an appellation. And honestly, calling something “the God particle” makes you sound like a mutant in Beneath the Planet of the Apes who worships an unexploded nuclear bomb.
There is a better option. Now that the Nobel committee has given its imprimatur, perhaps it’s time that we start calling it the Englert-Higgs boson. It’s as good a choice as any.
Dave Goldberg is a physics professor at Drexel University and author, most recently, of The Universe in the Rearview Mirror: How Hidden Symmetries Shape Reality.
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