by Sean Carroll
The long-term future of experimental particle physics remains murky. A century or even fifty years ago, it was possible to make a foundational discovery in particle physics with the kind of equipment that could be set up by an individual scientist and a team of students. Those days might be over. If the LHC gives us the Higgs and nothing else, it will be increasingly difficult to convince skeptical governments to allocate even more money to build a next-generation collider.
A machine like the LHC represents an investment of billions of dollars but also of thousands of person-years of effort from dedicated scientists who are devoting their lives to dig just a little bit deeper into nature’s mysteries. People like Lyn Evans, who helped build the LHC, or JoAnne Hewett, who studied countless theoretical models, or Fabiola Gianotti and Joe Incandela, who led their experiments to a historic achievement, have placed an enormous wager. They have gambled that this machine will usher in a new age of discovery, and the stakes they’ve placed are many years of their professional lives. Finding the Higgs is a vindication of all the work they’ve done. But as Hewett says, what we really want is to be surprised—to discover something nobody anticipated. That’s what would really get our minds going.
Historically, nature has been very good at surprising us.
TWO
NEXT TO GODLINESS
In which we explore how the Higgs boson really has nothing to do with God but is nevertheless pretty important.
Leon Lederman has had second thoughts. He knows what he has done, but he can’t take it back. It’s just one of those small things that has enormous unexpected consequences.
We’re speaking, of course, of the “God Particle.” Not the particle itself, which is just the Higgs boson. But the name “God Particle,” for which Lederman is responsible.
One of the world’s great experimental physicists, Lederman won the Nobel Prize in Physics in 1988 for discovering that there is more than one type of neutrino. If he hadn’t won it for that, he has other achievements that would also be Prize-worthy, including the discovery of a new kind of quark. There are only three known neutrinos and six known quarks, so these kinds of achievements aren’t exactly growing on trees. In his spare time he has served as the director of Fermilab and has founded the Illinois Mathematics and Science Academy. Lederman is also a charismatic personality, famous among his colleagues for his humor and storytelling ability. One of his favorite anecdotes relates the time when, as a graduate student, he arranged to bump into Albert Einstein while walking the grounds at the Institute for Advanced Study at Princeton. The great man listened patiently as the eager youngster explained the particle-physics research he was doing at Columbia, and then said with a smile, “That is not interesting.”
But in the public eye, Lederman is better known for something less felicitous: saddling the world with the phrase “God Particle” to refer to the Higgs boson. Indeed, that’s the title of an engaging book on particle physics and the search for the Higgs that he wrote with Dick Teresi. As the authors explain in the first chapter of their book, they chose the phrase in part because “the publisher wouldn’t let us call it the Goddamn Particle, though that might be a more appropriate title, given its villainous nature and the expense it is causing.”
Physicists around the world, a notoriously fractious bunch, will happily agree on one thing: They hate the name God Particle. Peter Higgs, from whom the more traditional name derives, says with a laugh, “I was really rather annoyed about that book. And I think I’m not the only one.”
Meanwhile, journalists around the world, who can be quite contentious in their own right, find unanimity on a single point: They love the name God Particle. One of the safest bets in the world is that if you find an article in the popular press about the Higgs boson, at some point the piece will call it the God Particle.
You can hardly blame the journalists. As names go, God Particle is totally box office, while Higgs boson comes off as a bit inscrutable. But you can’t blame the physicists, either. The Higgs has nothing whatsoever to do with God. It’s just a really important particle, one that’s worth getting excited about, even if that excitement doesn’t quite rise to the level of religious ecstasy. It’s worth understanding why physicists might be tempted to bestow godlike status on this humble elementary particle, even if it’s actually free of any theological implications whatsoever. (Does anyone really think God plays favorites among the particles?)
The mind of God
Physicists have a long and complicated relationship with God. Not just with the hypothetical omnipotent being who created the universe, but with the word “God” itself. When they talk about the universe, physicists will often use the idea of God to express something about the physical world. Einstein was famous for this. Among the most frequently repeated quotes from this eminently quotable scientist are “I want to know God’s thoughts; the rest are details” and, of course, “I am convinced that God does not play dice with the universe.”
Many of us have given into the temptation of following in Einstein’s footsteps. In 1992, a NASA satellite called the Cosmic Background Explorer (COBE) released amazing images of tiny ripples in the background radiation left over from the Big Bang. The significance of the event moved George Smoot, one of the investigators behind COBE, to say, “If you’re religious, it’s like looking at God.” And Stephen Hawking, in the concluding paragraph of his mega-selling A Brief History of Time, doesn’t shy away from using theological language:
However, if we do discover a complete theory, it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people, be able to take part in the discussion of the question of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason—for then we would know the mind of God.
Historically, some of the world’s most influential physicists have been quite religious. Isaac Newton, arguably the greatest scientist of all time, was a devout if somewhat heterodox Christian, who spent as much time studying and interpreting the Bible as he did with physics. In the twentieth century we have the example of Georges Lemaître, a cosmologist who developed the “Primeval Atom” theory—what is now known as the “Big Bang model.” Lemaître was a priest as well as a professor at the Catholic University of Leuven, in Belgium. In the Big Bang model, our observable universe began at a singular moment of infinite density about 13.7 billion years ago; in the Christian account, our universe was created by God at some moment in time. There are obvious parallels between the two stories, but Lemaître was always extremely careful not to mix his religion with science. At one point Pope Pius XII tried to suggest that the Primeval Atom could be identified with “Let there be light” from Genesis, but Lemaître himself persuaded him to drop that line of reasoning.
Today, however, most working physicists are much less likely to believe in God than are members of the general public. When you study the workings of the natural world for a living, you tend to be impressed by how well the universe gets along all by itself, without any supernatural assistance. There are certainly prominent examples of religious physicists, but just as certainly the real work of physics gets along without allowing anything other than the natural world into the equation.
God talk
So if physicists aren’t big believers in God, why do they keep talking about Him? Two reasons, actually: one good, one less so.
The good reason is simply that God provides a very convenient metaphor for talking about the universe. When Einstein says, “I want to know God’s thoughts,” he isn’t thinking of a literal supernatural being that the pope might be imagining. He’s expressing an inner desire to understand the fundamental workings of reality. There is an amazing fact about the universe: It makes sense. We can study what happens to matter under various circumstances, and we find astonishing regularities that never seem to be violated. When these regularities are established as real beyond r
easonable doubt, we call them “laws of nature.”
The actual laws of nature are very interesting, but it’s also interesting that there are laws at all. The laws we’ve discovered to date take the form of precise and elegant mathematical statements. The physicist Eugene Wigner was so moved by this feature of reality that he spoke of “the unreasonable effectiveness of mathematics in physics.” Our universe isn’t simply a hodgepodge of stuff doing random things; it’s a highly orderly and predictable evolution of fixed constituents of matter, an intricately choreographed dance of particles and forces.
When physicists speak metaphorically of God, they are simply giving in to the natural human tendency to anthropomorphize the physical world—to give it a human face. “God’s thoughts” are code for “the underlying laws of nature.” We want to know what those laws are. More ambitiously, we’d like to know if those laws could possibly have been different—are the actual laws of nature just one set among many possible ones, or is there something unique and special about our world? We may or may not be able to answer such a grandiose question, but it’s the kind of thing that lights the imagination of working scientists.
The other reason scientists succumb to God-talk is a bit less lofty: public relations. Calling the Higgs boson the God Particle might be wildly inaccurate, but it’s marketing genius. Physicists react to the God Particle label with horror and disdain. But it draws eyeballs, which is why it will continue to be used, even though every journalist who covers science knows exactly what the physicists think of the term.
“God Particle” gets people to sit up and take notice. Once that phrase has been coined, there’s no way it won’t be used by everyone trying to explain this esoteric concept to a public with other demands on their attention. Say you are looking for the Higgs boson, and many people will change the channel—maybe the Kardashians have done something outrageous. Say you’re looking for the God Particle, and people will at least pay attention when you explain what you mean. The Kardashians will still be acting up tomorrow.
Occasionally this kind of colorful language gets scientists in trouble. In 1993, when the United States was still planning to build a Superconducting Super Collider that would be even more powerful than the LHC, Nobel Laureate Steven Weinberg was testifying before Congress on the virtues of the new machine. At one point the questions took an unexpected turn.
Rep. Harris Fawell (R-IL): I wish sometimes we have some one word that could say it all and that is kind of impossible. I guess perhaps, Dr. Weinberg, you came a little close to it and I’m not sure but I took this down. You said you suspect that it isn’t all an accident that there are rules which govern matter and I jotted down, will this make us find God? I’m sure you didn’t make that claim, but it certainly will enable us to understand so much more about the universe?
Rep. Don Ritter (R-PA): Will the gentleman yield on that? If the gentleman would yield for a moment I would say . . .
Fawell: I’m not sure I want to.
Ritter: If this machine does that I am going to come round and support it.
Weinberg wasn’t so gauche as to refer to the Higgs boson as the God Particle during his Congressional testimony. But the lure of metaphor is strong, and at some point talking about the workings of reality leads one to ask this kind of question.
In case there is any remaining ambiguity: Nothing we might find at the Large Hadron Collider, or might have found at the Superconducting Super Collider, will make us find God. But we will come closer to understanding the ultimate laws of nature.
The final piece
Lederman and Teresi didn’t dub the Higgs boson the God Particle just because they knew it would get attention (although the prospect probably crossed their minds). In the end the flamboyant nomenclature attracted as much bad attention as good. As they put it in the preface to a revised edition of their book: “The title ended up offending two groups: 1) those who believe in God, and 2) those who do not. We were warmly received by those in the middle.”
What they were trying to do was express the importance of the Higgs boson. The book you’re reading right now has a slightly more modest title . . . but only slightly. To be honest, physicists don’t react with unalloyed approval when I tell them about The Particle at the End of the Universe. As far as we know there isn’t any “end” to the universe, either at some location in space or at some future moment in time. And if there were a location where the universe could be said to end, there’s no reason to think you would find a particle there. And if you did, there’s no reason to think it would be the Higgs boson.
But once again, what we’re dealing with here is a metaphor. The Higgs isn’t located at the spatial or temporal “end of the universe”—it’s located at the explanatory end. It’s the final piece of the puzzle of how the ordinary matter that makes up our everyday world works at a deep level. That’s pretty important.
I should quickly rush in with caveats before my fellow physicists get upset again. The Higgs isn’t the missing piece of the puzzle of absolutely everything. Finding the Higgs and measuring its properties leaves plenty of physics still to understand. There’s gravity, for one thing: an entire force of nature that we can’t quite reconcile with the demands of quantum mechanics, and we don’t expect the Higgs to be of any help there. There are also dark matter and dark energy, mysterious substances that pervade the universe and yet have resisted direct detection here on earth. There are other hypothetical exotic particles, the kind theoretical physicists love to invent but for which we currently have no evidence. And then, needless to say, there are all the parts of science that present their own challenges without much crucial input from particle physics at all—from atomic and molecular physics, up through chemistry and biology and geology, all the way to sociology and psychology and economics. The human desire to understand the world will not reach a triumphant conclusion just because we have discovered the Higgs boson.
With all those disclaimers out of the way, let’s get back to emphasizing the singular role of the Higgs: It’s the final part of the Standard Model of particle physics. The Standard Model explains everything we experience in our everyday lives (other than gravity, which is easy enough to tack on). Quarks, neutrinos, and photons; heat, light, and radioactivity; tables, elevators, and airplanes; televisions, computers, and cell phones; bacteria, elephants, and people; asteroids, planets, and stars—all simply applications of the Standard Model in different circumstances. It’s the full theory of immediately discernible reality. And it all fits together beautifully, passing a bewildering variety of experimental tests, as long as there is the Higgs boson. Without the Higgs, or something even more bizarre to take its place, the Standard Model wouldn’t get off the ground.
Figuring out the trick
There’s something fishy about these claims that the Higgs boson is so important. After all, before we actually found it, how did we know it was important at all? What drove us to keep talking about the properties of a hypothetical particle nobody had ever observed?
Imagine you see a performance by a very talented magician, who performs an amazing card trick. The trick involves getting a playing card to mysteriously levitate in the air. You are puzzled by this trick, and you’re absolutely sure that the magician didn’t actually use mystical powers to make the card levitate. You’re also clever and persistent, and after quite a bit of thinking you come up with a way the magician could have done it, involving a thin thread secretly attached to the card. In fact you’re able to come up with other possible schemes involving blowing air and heat pumps, but the thread scenario is both simple and plausible. You even go so far as to reproduce the trick at home, convincing yourself that with the right kind of thread you’re able to do the trick just like the magician did.
But you go back to catch another performance of the magician’s act, where you are able to see the card levitate once again. His version looks just like the one you were able to put together at home—but try as you might, you can’t quite see the threa
d itself.
The Standard Model Higgs boson is like that thread. For a long time we hadn’t seen it directly, but we saw its effects. Or even better, we saw features of the world that make perfect sense if it’s there, and make no sense without it. Without the Higgs boson, particles such as the electron would have zero mass and move at the speed of light; but instead they do have mass and move more slowly. Without the Higgs boson, many elementary particles would appear identical to one another, but instead they are manifestly different, with a variety of masses and lifetimes. With the Higgs, all these features of particle physics make perfect sense.
In circumstances like these, whether we’re thinking about the levitating card or the Higgs boson, there are two options: Our theory is right, or an even more interesting and elaborate theory is right. The effects are there—the card floats, the particles have mass. There must be an explanation. If it’s the simple one we’ll congratulate ourselves on our cleverness; if it’s something more complicated, we’ll have learned something very interesting. Maybe the particle we found at the LHC does part of what the Higgs was proposed to do but not all of it; or maybe the job of the Higgs is played by multiple particles, of which we’ve only found one. We win no matter what, as long as we ultimately succeed in figuring out what’s going on.
Fermions and bosons
Let’s see if we can’t translate this inspirational metaphorical cheerleading about how important the Higgs boson is into a more specific explanation for what it actually is supposed to do.
Particles come in two types: the particles that make up matter, known as “fermions,” and the particles that carry forces, known as “bosons.” The difference between the two is that fermions take up space, while bosons can pile on top of one another. You can’t just take a pile of identical fermions and put them all at the same place; the laws of quantum mechanics won’t allow it. That’s why collections of fermions make up solid objects like tables and planets: The fermions can’t be squeezed on top of one another.