The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads Us to the Edge of a New World (30 page)

But interest has been immense. The development office at Johns Hopkins showed a clip to the university’s board of directors, one of whom made an investment on the spot. The National Science Foundation, which supports much of the basic research in the United States and is constantly haranguing scientists to get more involved in public outreach, was thrilled to find out that one of their researchers was taking outreach seriously, and offered substantial support. Walter Murch, a highly respected Hollywood editor who has worked with George Lucas and Francis Ford Coppola and won multiple Academy Awards, became fascinated by the film and offered his services at well below his usual fee.

Throughout the process, Kaplan’s goal has been to capture some of the quixotic fervor that pushes scientists to understand the universe just a tiny bit better than anyone has understood it before. The emotional stakes are high; physics is an experimental science, and the most brilliant theorists in the world get little credit if the theory they propose turns out not to be the path nature has chosen. In Kaplan’s words,

In the end, it’s an incredibly heroic exercise. And it is filled with different egos, and intensity, and overconfidence maybe. But what you understand is that people fool themselves. Scientists create a world in their brain, in order to get themselves to work as hard as they do and to keep going, knowing that it could be a complete failure. Their entire career could just be in the toilet as totally irrelevant.

As of mid-2012,
Particle Fever
is nearing completion, and the team is hoping to get chosen for the Sundance Film Festival in January 2013. Fittingly, they are wildly ambitious, hoping for an eventual wide theatrical release that will truly bring the LHC to the masses. Whether that succeeds, they will certainly have created a singular document that will stand as a testament to both the excitement and the nervousness of physicists at the dawn of the LHC era.

And David Kaplan will be able to devote himself to physics full-time once again. As interesting and novel as the process was, there’s no danger he will be changing jobs anytime soon:

Making a movie is just a terrible experience. It’s so illogical, and there’s ego, and people making arguments in ways that just don’t make any sense. I hate it . . . I love physics.

ELEVEN

NOBEL DREAMS

In which we relate the fascinating tale of how the “Higgs” mechanism was invented and think about how history will remember it.

I
t was 1940, and Germany had just invaded Denmark. Niels Bohr, one of the founders of quantum mechanics and director of the Institute for Theoretical Physics in Copenhagen, was in possession of valuable pieces of contraband he needed to keep hidden from the Nazis at all costs: two gold medals that accompanied winning the Nobel Prize. How could he keep them away from the approaching army?

Bohr had won the Nobel in 1922, but neither of the medals belonged to him; he had previously auctioned off his prize medal to help support resistance forces in Finland. They belonged to Max von Laue and James Franck, two German physicists, who had illegally smuggled their medals (which were engraved with their names) out of the country to keep them away from the Nazis. Bohr turned to his friend, the chemist George de Hevesy, who hit upon a brilliant idea: They would dissolve the medals in acid. Gold doesn’t dissolve easily, so the scientists turned to aqua regia, a highly corrosive mixture of nitric acid and hydrochloric acid, renowned for its ability to tear down “noble” metals. Placed in the aqua regia, over the course of an afternoon, the Nobel medals gradually dissociated into their individual atoms, which remained suspended in the solution. Any soldiers that would come poking around looking for suspicious hidden treasure would find nothing but a couple of innocuous flasks of chemicals hidden among hundreds of similar-looking containers.

The ruse worked. After the war, scientists were able to recover the gold by precipitating the atoms out of de Hevesy’s solution. Bohr delivered the metal back to the Royal Swedish Academy of Sciences in Stockholm, which was able to recast von Laue’s and Franck’s Nobel medals. De Hevesy himself, who fled to Sweden in 1943, won the Nobel Prize in Chemistry in 1944—not for discovering new techniques in hiding contraband, but for the use of isotopes in tracing chemical reactions.

In case it wasn’t obvious, people take Nobel Prizes very seriously. At the end of the nineteenth century, chemist Alfred Nobel, the inventor of dynamite, established prizes in Physics, Chemistry, Physiology or Medicine, Literature, and Peace, which have been awarded each year since 1901. (The Economics prize, begun in 1968, is run by a different organization.) Nobel passed away in 1896, and the executors of his will were surprised to find that he had donated 94 percent of his considerable fortune to the establishment of the prizes.

In the years since, the Nobel Prizes have become universally recognized as the pinnacle of scientific recognition. That isn’t quite the same as scientific “achievement”—the Nobels have quite specific criteria, and there are endless arguments about how well the prizes match up with the truly important scientific discoveries. Nobel’s original will aimed the prizes at “those who, during the preceding year, shall have conferred the greatest benefit on mankind,” and the Physics prize in particular “to the person who shall have made the most important ‘discovery’ or ‘invention’ within the field of physics.” To some extent these instructions are simply ignored; after a few early prizes were given to findings that later turned out to be in error, nobody pretends anymore that the prizes recognize work done in the preceding year. Crucially, making a “discovery” is not the same as being recognized as one of the world’s leading scientists. Some discoveries are made somewhat by accident, by people who later leave the field. And some scientists do fantastic work over the course of a lifetime, but don’t quite have a single world-changing discovery that rises to the level of a Nobel.

There are other criteria that highly constrain the Nobel choices. Prizes are not awarded posthumously, although if a laureate passes away between the time when the decision is made and when it is announced, the prize is still given to them. Most important for physics, the prize is not given to more than three people in any one year. Unlike the Peace prize, for example, the Physics prize isn’t given to an organization or a collaboration; it is given to three or fewer individuals. That poses something of a challenge in the Big Science era.

When it comes to theoretical contributions, it’s not enough to be smart, or even to be right; you have to be right, and your theory has to be confirmed by experiment. Stephen Hawking’s most important contribution to science is the realization that black holes give off radiation due to the effects of quantum mechanics. The large majority of physicists believe he is right, but at this point it’s a purely theoretical result; we haven’t observed any evaporating black holes, and we don’t have any promising way of doing so with current technologies. It’s quite possible that Hawking will never win the Nobel Prize, despite his incredibly impressive contributions.

To outsiders, it can sometimes seem like the whole point of doing research is to win the Nobel Prize. That’s not the case; the Nobel captures important moments in science, but scientists themselves recognize there is a rich tapestry of progress that includes many contributions, great and small, which build on one another over the years. Still—let’s admit it—winning the Nobel is a big deal, and physicists certainly keep track of which discoveries might someday qualify.

There is no question that discovering the Higgs boson is the kind of achievement that is certainly worthy of the Nobel Prize. For that matter, inventing the theory that predicted the Higgs in the first place is undoubtedly prize-worthy. But that doesn’t necessarily imply that any prizes are actually going to be given. Who might win them? Ultimately it’s not prizes that matter, it’s the science; but we have a good excuse for looking at the fascinating history of the ideas behind the Higgs boson and how physicists set about searching for it. The goal of this chapter is not to provide a definitive history nor to adjudicate who deserves what prize. Quite the opposite: By looking at how the ideas developed over time, it should become clear that the Higgs mechanism, like many great ideas in science, involved many crucial steps to the final answer. Attempting to draw a bright line between three (or fewer) people who deserve a prize and the many others who don’t necessarily does great violence to the reality of the development, even if it does make for good news copy.

In this chapter we’re going to try to get the history right, although such a brief account will necessarily be incomplete. For history, however, the details often matter. Therefore, compared with the rest of the book, this chapter will go a little bit more into technical details. Feel free to skip over it, if you don’t mind missing out on some fascinating physics and compelling human drama.

Superconductivity

In Chapter Eight we explored the deep connection between symmetries and forces of nature. If we have a “local” or “gauge” symmetry—one that operates independently at each point in space—it necessarily comes with a connection field, and connection fields give rise to forces. This is how gravity and electromagnetism both work, and in the 1950s, Yang and Mills suggested a way to extend the idea to other forces of nature. The problem, as Wolfgang Pauli forcibly pointed out, is that the underlying symmetry always comes associated with massless boson particles. That’s part of the power of symmetries: They imply stringent restrictions on the properties that particles can have. The symmetry underlying electromagnetism, for example, implies that electric charge is exactly conserved.

But forces mediated by massless particles—as far as anyone knew at the time—stretch over infinite distances and should be very easy to detect. Gravity and electromagnetism are the obvious examples, while the nuclear forces seem very different. Today we recognize that the strong and weak interactions are also Yang-Mills-type forces, with the massless particles hidden from us for different reasons: In the strong force the gluons are massless but confined inside hadrons, while in the weak force the W and Z bosons become massive because of spontaneous symmetry breaking.

Back in 1949, American physicist Julian Schwinger had put forward an argument that forces based on symmetries would always be carried by massless particles. He kept thinking about the problem, however, and in 1961, he realized that his argument was not airtight: There was a loophole that allowed for the gauge bosons to get a mass. He wasn’t quite sure how it might actually happen, but he wrote a paper that pointed out his previous mistake. Schwinger was famously elegant and precise in his personal style as well as his physics research. He stood in contrast with Richard Feynman, with whom he and Sin-Itiro Tomonaga shared the Nobel Prize in 1965. Feynman was known for his boisterously informal personality and deeply intuitive approach to physics, while Schwinger was unfailingly meticulous and proper. When he wrote a paper pointing out a flaw in a well-accepted piece of conventional wisdom, people took him seriously.

The question remained: What could cause the force-carrying bosons to get a mass? The answer came from a slightly unexpected source: not particle physics but condensed matter physics, the study of materials and their properties. In particular, insights borrowed from the theory of superconductors—materials with no resistance to electricity, such as those that power the giant magnets in the LHC.

Electrical current is the flow of electrons through a medium. In an ordinary conductor, the electrons keep bumping into atoms and other electrons, providing resistance to the flow. Superconductors are materials in which, when the temperature is low enough, current can flow through unimpeded. The first good theory of superconductors was put forward by Soviet physicists Vitaly Ginzburg and Lev Landau in 1950. They suggested that a special kind of field permeates the superconductor, which acts to give a mass to the ordinarily massless photon. They weren’t necessarily thinking of a new fundamental field of nature, but a collective motion of electrons, atoms, and electromagnetic fields—much like a sound wave doesn’t come from vibrations of a fundamental field, but from the collective motion of atoms in the air bumping into one another.

Although Landau and Ginzburg proposed that some kind of field was responsible for superconductivity, they didn’t specify what that field actually was. That step was carried out by American physicists John Bardeen, Leon Cooper, and Robert Schrieffer, who invented what’s called the “BCS theory” of superconductivity in 1957. The BCS theory is one of the milestones of twentieth-century physics, and certainly deserves a book of its own. (This isn’t that book.)

BCS borrowed an idea of Cooper’s, that pairs of particles could team up at very low temperatures. It’s these “Cooper pairs” that make up the mysterious field suggested by Landau and Ginzburg. While a single electron would continually meet resistance by bumping into the atoms around it, a Cooper pair can combine in a clever way so that every nudge that pushes on one electron exerts an equal and opposite pull on the other one (and vice versa). As a result, the paired electrons glide through the superconductor unimpeded.

This is directly related to the fact that photons are effectively massive inside the superconductor. When particles are massless, their energy is directly proportional to their velocity and can range from zero up to any number you imagine. Massive particles, by contrast, come with the minimum energy they can possibly have: their rest energy, given by
E = mc
²
. When moving electrons are jostled by atoms and other electrons in a material, their electric field gently shakes, which creates very low-energy photons you would hardly ever notice. It’s that continual emission of photons that lets the electrons lose energy and slow down, diluting the current. Because photons obtain a mass in the Landau-Ginzburg and BCS theories, there is a certain minimum energy required to make them. Electrons that don’t have enough energy can’t make any photons, and therefore can’t lose energy: The Cooper pairs flow through the material with zero resistance.