The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads Us to the Edge of a New World (2 page)

Jump to July 4, 2012, opening day of the International Conference on High Energy Physics. It’s a biannual gathering, moving from city to city around the world, this year winding up in Melbourne, Australia. Hundreds of particle physicists, Hewett included, have filled the main auditorium to hear a special seminar. All the investment in the LHC, all the anticipation that has built up over the years, is about to pay off.

The presentation itself is beamed to Melbourne from CERN, the laboratory in Geneva that is home to the LHC. There are two talks, which would ordinarily have been presented in Melbourne as part of the conference program. At the last minute, however, the powers that be decided that a moment of this magnitude should be shared with the many people who had helped make the LHC such a success. The sentiment was appreciated—hundreds of physicists at CERN have lined up for hours before the talks were scheduled to begin at nine a.m., Geneva time, camping out overnight with sleeping bags in hopes of getting a good seat.

Rolf Heuer, director general of CERN, introduces the proceedings. There will be talks by American physicist Joe Incandela and Italian physicist Fabiola Gianotti, the spokespersons for the two major experiments that work to collect and analyze LHC data. Both experiments include more than three thousand collaborators each, most of whom are glued to computer monitors scattered around the globe. The event is being live-streamed, not only to Melbourne, but to anyone who wants to hear the results in real-time. It’s an appropriate medium for this celebration of modern Big Science—a high-tech international effort with big stakes and exhilarating rewards.

Traces of nervous energy are evident in both Gianotti’s and Incandela’s talks, but the presentations speak for themselves. They each give heartfelt thanks to the many engineers and scientists who helped make the experiments possible. Then they carefully explain why we should all believe the results they are about to present, demonstrating that they understand how their machines are working and that the analysis of the data is precise and reliable. Only after the stage has been immaculately set do they show us what they’ve found.

And there it is. A handful of graphs that wouldn’t seem like much to the untutored eye, but with a consistent feature: more events (collections of particles streaming from a single collision) than expected with a certain particular energy. All the physicists in the audience know immediately what it means: a new particle. The LHC has glimpsed a part of nature that had heretofore never been seen. Incandela and Gianotti go through the painstaking statistical analysis meant to separate true discoveries from unfortunate statistical fluctuations, and the results in both cases speak without ambiguity: This is something real.

Applause. In Geneva, Melbourne, and around the world. The data are so precise and clear that even scientists who had worked on the experiments for years are taken aback. Welsh physicist Lyn Evans, who more than anyone else was responsible for guiding the LHC through its rocky path to completion, declared himself “gobsmacked” at the exquisite agreement between the two experiments.

I was at CERN myself that day, masquerading as a journalist in a pressroom next to the main auditorium. Journalists aren’t supposed to clap at the news events they cover, but the assembled reporters gave in to the overwhelming emotion of the moment. This wasn’t just a success for CERN, or for physics; this was a success for the human race.

We think we know what’s been found: an elementary particle called the “Higgs boson,” after Scottish physicist Peter Higgs. Higgs himself was in the room for the seminars, eighty-three years old and visibly moved: “I never thought I’d see this happen in my lifetime.” Several other senior physicists who had likewise proposed the same idea back in 1964 were also present; the conventions by which theories are named aren’t always fair, but this was a moment when everyone could join in the celebration.

So what is the Higgs boson? It’s a fundamental particle of nature, of which there aren’t many, and a very special kind of particle to boot. Modern particle physics knows of three kinds of particles. There are particles of matter, like electrons and quarks, that constitute the atoms that make up everything we see. There are the force particles that carry gravity and electromagnetism and the nuclear forces, which hold the matter particles together. And then there is the Higgs, in its own unique category.

The Higgs is important not for what it is but for what it does. The Higgs particle arises from a field pervading space, known as the “Higgs field.” Everything in the known universe, as it travels through space, moves through the Higgs field; it’s always there, lurking invisibly in the background. And it matters: Without the Higgs, electrons and quarks would be massless, just like photons, the particles of light. They would move at the speed of light themselves, and it would be impossible to form atoms and molecules, much less life as we know it. The Higgs field isn’t an active player in the dynamics of ordinary matter, but its presence in the background is crucial. Without it, the world would be an utterly different place. And now we’ve found it.

Some words of caution are in order. What we actually have in hand is evidence for a very Higgs-like particle. It has the right mass, it is produced and decays in roughly the expected ways. But it’s too early in the game to say for sure that what we’ve discovered is definitely the simple Higgs predicted by the original models. It could be something more complicated, or be part of an elaborate web of related particles. But we’ve definitely found some new particle, and it acts like we think a Higgs boson should. For the purposes of this book, I’m going to treat July 4, 2012, as the day the discovery of the Higgs boson was announced. If reality turns out to be more subtle, then all the better for everyone—physicists live for surprises.

Hopes are high that the Higgs discovery represents the beginning of a new age in particle physics. We know that there is more to physics than we currently understand; studying the Higgs offers a new window into worlds yet unseen. Experimenters like Gianotti and Incandela have a new specimen to study; theorists like Hewett have new clues to build better models. Our understanding of the universe has taken a huge, long-anticipated step forward.

This is the story of the people who have devoted their lives to discovering the ultimate nature of reality, of which the Higgs is a crucial component. There are theorists, sitting with pencil and paper, fueled by espresso and heated disputes with colleagues, turning over abstract ideas in their minds. There are engineers, pushing machines and electronics well beyond the limits of existing technology. And most of all there are the experimenters, bringing the machines and the ideas together to discover something new about nature. Modern physics at the cutting edge involves projects that cost billions of dollars and take decades to complete, requiring extraordinary devotion and a willingness to bet high stakes in search of unique rewards. When it all comes together, the world changes.

Life is good. Have another glass of champagne.

ONE

THE POINT

In which we ask why a group of talented and dedicated people would devote their lives to the pursuit of things too small to be seen.

P
article physics is a curious activity. Thousands of people spend billions of dollars building giant machines miles across, whipping around subatomic particles at close to the speed of light and crashing them together, all to discover and study other subatomic particles that have essentially no impact on the daily lives of anyone who is not a particle physicist.

That’s one way of looking at it, anyway. Here’s another way: Particle physics is the purest manifestation of human curiosity about the world in which we live. Human beings have always asked questions, and since the ancient Greeks more than two millennia ago, the impulse to explore has grown into a systematic, worldwide effort to discover the basic rules governing how the universe works. Particle physics arises directly from our restless desire to understand our world; it’s not the particles that motivate us, it’s our human desire to figure out what we don’t understand.

The early years of the twenty-first century are a turning point. The last truly surprising experimental result to emerge from a particle accelerator was in the 1970s, more than thirty-five years ago. (The precise date would depend on your definition of “surprising.”) It’s not because the experimentalists have been asleep at the switch—far from it. The machines have improved by leaps and bounds, reaching into realms that seemed impossibly far away just a short time ago. The problem is that they haven’t seen anything we didn’t already expect them to see. For scientists, who are always hoping to be surprised, that’s extremely annoying.

The problem, in other words, isn’t that the experiments have been inadequate—it’s that the theory has been too good. In the specialized world of modern science, the roles of “experimentalists” and “theorists” have become quite distinct, especially in particle physics. Gone are the days—as recent as the first half of the twentieth century—when a genius like Italian physicist Enrico Fermi could propose a new theory of the weak interactions, then turn around and guide the construction of the first self-sustained artificial nuclear chain reaction. Today, particle theorists scribble equations on blackboards, which ultimately become specific models, which are tested by experimentalists who gather data from exquisitely precise machines. The best theorists keep close tabs on experiments and vice versa, but no one person is a master of both.

The 1970s saw the finishing touches put on our best theory of particle physics, which goes by the fantastically uninspiring name of the “Standard Model.” It’s the Standard Model that describes quarks, gluons, neutrinos, and all the other elementary particles you may have heard of. Like Hollywood celebrities or charismatic politicians, scientific theories are put on a pedestal just so we can tear them down. You don’t become a famous physicist by showing that someone else’s theory is right; you become famous by showing where someone else’s theory goes wrong, or by proposing a better theory.

But the Standard Model is stubborn. For decades now, every experiment that we can do here on earth has duly confirmed its predictions. An entire generation of particle physicists has risen up the academic ladder from students to senior professors, all without having a single new phenomenon that they could discover or explain. The anticipation has been close to unbearable.

All this is changing. The Large Hadron Collider represents a new era in physics, smashing together particles with an energy never before achieved by humankind. And it’s not just higher energy. It’s an energy we’ve been dreaming about for years, in which we expect to find new theoretically predicted particles and hopefully some surprises—the energy where the force known as the “weak interaction” hides its secrets.

The stakes are high. Peering into the unknown for the first time, anything could happen. There are scads of competing theoretical models hoping to anticipate what the LHC will find. You don’t know what you’re going to see until you look. At the center of the speculation lies the Higgs boson, an unassuming particle that represents both the last piece of the Standard Model, and the first glimpse into the world beyond.

A big universe made of little pieces

Near the Pacific coast in Southern California, about an hour-and-a-half drive south of where I live in Los Angeles, there is a magical place where dreams come to life: Legoland. At Dino Island, Fun Town, and other attractions, children marvel at an elaborate world constructed from Legos, tiny plastic blocks that can be fitted together in limitless combinations.

Legoland is a lot like the real world. At any moment, your immediate environment typically contains all sorts of substances: wood, plastic, fabric, glass, metal, air, water, living bodies. Very different kinds of things, with very different properties. But when you look more closely, you discover that these substances aren’t truly distinct from one another. They are simply different arrangements of a small number of fundamental building blocks. These building blocks are the elementary particles. Like the buildings in Legoland, tables and cars and trees and people represent some of the amazing diversity you can achieve by starting with a small number of simple pieces and fitting them together in a variety of ways. An atom is about one-trillionth the size of a Lego block, but the principles are similar.

We take for granted the idea that matter is made of atoms. It’s something we’re taught in school, where we do chemistry experiments in classrooms with the periodic table of the elements hanging on the wall. It’s easy to lose sight of how amazing that fact is. Some things are hard, some are soft; some things are light, some are heavy; some things are liquid, some are solid, some are gas; some things are transparent, some are opaque; some things are alive, some are not. But beneath the surface, all these things are really the same kind of stuff. There are about one hundred atoms listed in the periodic table, and everything around us is just some combination of those atoms.

The hope that we can understand the world in terms of a few basic ingredients is an old idea. In ancient times, a number of different cultures—Babylonians, Greeks, Hindus, and others—invented a remarkably consistent set of five “elements” out of which everything else was made. The ones we are most familiar with are earth, air, fire, and water, but there was also a heavenly fifth element of aether, or quintessence. (Yes, that’s where the movie with Bruce Willis and Milla Jovovich got its name.) Like many ideas, this one was developed into an elaborate system by Aristotle. He suggested that each element sought a particular natural state; for example, earth tends to fall and air tends to rise. By mixing the elements in different combinations, we could account for the different substances we see around us.

Democritus, a Greek philosopher who predated Aristotle, originally suggested that everything we know is made of certain tiny indivisible pieces, which he called “atoms.” It’s an unfortunate accident of history that this terminology was seized upon by John Dalton, a chemist who worked in the early 1800s, to refer to the pieces that define chemical elements. What we now think of as an atom is not indivisible at all—it consists of a nucleus made of protons and neutrons, around which orbit a collection of electrons. Even the protons and neutrons aren’t indivisible; they are made of smaller pieces called “quarks.”