The God Particle

by Leon Lederman

  I should probably review the origin of the Higgs idea, since I've been a bit coy about letting the cat out of the bag. It is also called hidden symmetry or "spontaneous symmetry breaking." The idea was introduced into particle physics by Peter Higgs of the University of Edinburgh. It was used by theorists Steven Weinberg and Abdus Salam, working independently, to understand the conversion of a unified and symmetric electroweak force, transmitted by a happy family of four zero-mass messenger particles, into two very different forces: QED with its massless photon and the weak force with massive W+, W−, and Z0's. Weinberg and Salam built on the earlier work of Sheldon Glashow, who, following Julian Schwinger, just knew that there was a consistent, unified electroweak theory but didn't put all the details together. And there were Jeffrey Goldstone and Martinus Veltman and Gerard't Hooft. And there are others who should be mentioned, but that's life. Besides, how many theorists does it take to light up a light bulb?

  Another way of looking at Higgs is from the point of view of symmetry. At high temperatures the symmetry is exposed—regal, pure simplicity. At lower temperatures the symmetry is broken. Time for some more metaphors.

  Consider a magnet. A magnet is a magnet because, at low temperatures, its atomic magnets are aligned. A magnet has a special direction, its north-south axis. Thus it has lost the symmetry of a piece of nonmagnetic iron in which all spatial directions are equivalent. We can "fix" the magnet. By raising the temperature, we go from magnetic iron to nonmagnetic iron. The heat generates molecular agitation, which eventually destroys the alignment, and we have a purer symmetry. Another popular metaphor is the Mexican hat: a symmetric dome surrounded by a symmetric turned-up brim. A marble is perched on the top of the dome. Perfect rotational symmetry, but no stability. When the marble falls to a more stable (lower-energy) position, somewhere on the brim, the symmetry is destroyed even though the basic structure is symmetric.

  In another metaphor we imagine a perfect sphere filled with water vapor at very high temperature. The symmetry is perfect. If we let the system cool, eventually we get a pool of water with some ice floating in it and residual water vapor above. The symmetry has been totally destroyed by the simple act of cooling, which in this metaphor allows the gravitational field to exert itself. However, paradise can be regained by simply heating up the system.

  So: before Higgs, symmetry and boredom; after Higgs, complexity and excitement. When you next look out at the night sky you should be aware that all of space is filled with this mysterious Higgs influence, which is responsible, so this theory holds, for the complexity of the world we know and love.

  Now picture the formulas (ugh!) that give correct predictions and postdictions of the properties of particles and forces we measure at Fermilab and in our accelerator labs of the 1990s. When we plug in reactions to be carried out at much higher energies, the formulas churn out nonsense. Aha, but if we include the Higgs field, then we modify the theory and get a consistent theory even at energies of 1 TeV. Higgs saves the day, saves the standard model with all its virtues. Does all this prove that it is correct? Not at all. It's only the best the theorists can do. Perhaps She is even more clever.

  A DIGRESSION ON NOTHING

  Back in the days of Maxwell, physicists felt that they needed a medium that would pervade all space and through which light and other electromagnetic waves could travel. They called it an aether and established properties so that it could do its job. Aether also provided an absolute coordinate system that enabled measurement of the velocity of light. Einstein's flash of insight showed that aether was an unnecessary burden on space. Here one is tampering with a venerable concept, none other than the "void" invented (or discovered) by Democritus. Today the void, or more precisely, the "vacuum state," is front and center.

  The vacuum state consists of those regions of the universe where all matter has been removed and no energy or momentum exists. It is "nothing at all." James Bjorken, in talking about this state, said that he was tempted to do for particle physics what John Cage did for music: a four-minute-and-twenty-two-second ... nothing. Only fear of the conference chairman dissuaded him. Bjorken, expert as he is on the properties of the vacuum state, doesn't compare to't Hooft, who understands nothing at all much better.

  The sad part of the story is that the pristine absoluteness of the vacuum state (as a concept) has been so polluted (wait until the Sierra Club finds out!) by twentieth-century theorists that it is vastly more complicated than the discarded nineteenth-century aether. What replaces the aether, in addition to all the ghostly virtual particles, is the Higgs field, whose full dimensions we do not yet know. To do its job, there must exist, and experiments must reveal, at least one Higgs particle, electrically neutral. This may be only the tip of the iceberg; a zoo of Higgs boson quanta may be needed to completely describe the new aether. Clearly there are new forces here and new processes. We can summarize the little we know: at least some of the particles that represent the Higgs aether must have zero spin, must be intimately and mysteriously connected to mass, and must manifest themselves at temperatures equivalent to an energy of less than 1 TeV. There is controversy also about the Higgs structure. One school says it's a fundamental particle. Another idea is that it is composed of new, quarklike objects, which could eventually be seen in the laboratory. A third camp is intrigued by the huge mass of the top quark and believes that Higgs is a bound state of top and antitop. Only data will tell. Meanwhile, it's a miracle that we can see the stars at all.

  The new aether is then a reference frame for energy, in this case potential energy. And Higgs alone doesn't explain the other debris and theoretical garbage that is dumped in the vacuum state. The gauge theories deposit their requirements, the cosmologists exploit "false" vacuum energy, and in the evolution of the universe, the vacuum can stretch and expand.

  One longs for a new Einstein who will, in a flash of insight, give us back our lovely nothingness.

  FIND THE HIGGS!

  So Higgs is great. Why, then, hasn't it been universally embraced? Peter Higgs, who loaned his name to the concept (not willingly), works on other things. Veltman, one of the Higgs architects, calls it a rug under which we sweep our ignorance. Glashow is less kind, calling it a toilet in which we flush away the inconsistencies of our present theories. And the other overriding objection is that there isn't a single shred of experimental evidence.

  How does one prove the existence of this field? Higgs, just like QED, QCD, or the weak force, has its own messenger particle, the Higgs boson. Prove Higgs exists? Just find the particle. The standard model is strong enough to tell us that the Higgs particle with the lowest mass (there may be many) must "weigh" less than 1 TeV. Why? If it is more than 1 TeV, the standard model becomes inconsistent, and we have the unitarity crisis.

  The Higgs field, the standard model, and our picture of how God made the universe depend on finding the Higgs boson. There is no accelerator on earth, unfortunately, that has the energy to create a particle as heavy as 1 TeV.

  You could, however, build one.

  THE DESERTRON

  In 1981 we at Fermilab were deeply involved in building the Tevatron and the p-bar/p collider. We were, of course, paying some attention to what was going on in the world and especially to the CERN quest for the W. By late spring of that year we were getting confident that superconducting magnets could work and could be mass-produced with the required stringent specifications. We were convinced, or at least 90 percent convinced, that the 1 TeV mass scale, the terra incognita of particle physics, could be reached at relatively modest cost.

  Thus it made sense to start thinking of the "next machine" (whatever would follow the Tevatron), as an even bigger ring of superconducting magnets. But in 1981 the future of particle research in this country was mortgaged to a machine struggling to survive at the Brookhaven lab. This was the Isabelle project, a proton-proton collider of modest energy that should have been working by 1980 but had been delayed by technical problems. In the interval the physics frontier
had moved on.

  At the annual Fermilab users' meeting in May of 1981, after duly reporting on the State of the Laboratory, I ventured a guess about the future of the field, especially "the energy frontier at 1 TeV." I remarked that Carlo Rubbia, already a dominating influence at CERN, would soon "pave the LEP tunnel with superconducting magnets." The LEP ring, about seventeen miles in circumference, contained conventional magnets for its e+ e− collider. LEP needed that huge radius to reduce the energy lost by the electrons. These radiate energy when they are constrained into a circular orbit by magnets. (The smaller the radius, remember, the more the radiation.) So CERN's LEP machine used weak fields and a large radius. This also made it ideal for accelerating protons, which because of their much larger mass don't radiate very much energy. The farsighted LEP designers surely had this in mind as an eventual application of the big tunnel. Such a machine with superconducting magnets could easily go to about 5 TeV in each ring, or 10 TeV in the collision. And all the United States had to offer in competition beyond the Tevatron at 2 TeV was the ailing Isabelle, a 400 GeV collider (0.8 TeV in total), although it did have a very high collision rate.

  By the summer of 1982, both the Fermilab superconducting-magnet program and the CERN proton-antiproton collider looked as if they would be successful. When American high-energy physicists gathered at Snowmass, Colorado, in August to discuss the status and the future of the field, I made my move. In a talk entitled "The Machine-in-the-Desert," I proposed that the community seriously consider making its number-one priority the building of a huge new accelerator based on the "proven" technology of supermagnets and forge ahead to the 1 TeV mass domain. Let's recall that to produce particles that might have a mass of 1 TeV, the quarks participating in the collision must contribute at least this amount of energy. The protons, carrying the quarks and gluons, must have much higher energy. My guess in 1982 was 10 TeV in each beam. I made a wild guesstimate at the cost and rested my case solidly on the premise that the lure of the Higgs was too attractive to pass up.

  There was a moderately lively debate at Snowmass over the Desertron, as it was initially called. The name was based on the idea that a machine so large could be built only in a place devoid of people and land value and hills and valleys. What was wrong about that idea was that I, a New York City kid, practically raised in the subways, had completely forgotten the power of deep tunneling. History rubbed it in. The German machine HERA goes under the densely populated city of Hamburg. CERN's LEP tunnel burrows under the Jura Mountains.

  I was attempting to forge a coalition of all the American labs to back this idea. SLAC was always looking toward electron acceleration; Brookhaven was struggling to keep Isabelle alive; and a lively and very talented gang at Cornell were trying to upgrade their electron machine to a status they called CESR II. I dubbed my Desertron lab "Slermihaven II" to dramatize the union of all the fiercely competitive labs behind the new venture.

  I won't belabor the politics of science, but after a year full of trauma, the U.S. particle-physics community formally recommended abandoning Isabelle (renamed CBA for Colliding Beam Accelerator) in favor of the Desertron. Now called the Superconducting Super Collider, it was to have 20 TeV in each beam. At the same time—July 1983—Fermilab's new accelerator hit the front pages as a success, accelerating protons to a record of 512 GeV. This was soon followed by further successes, and about a year later the Tevatron went to 900 GeV.

  PRESIDENT REAGAN AND THE SUPER COLLIDER: A TRUE STORY

  By 1986, the SSC proposal was ready to be submitted to President Reagan for approval. As director of Fermilab, I was asked by an assistant secretary of the DOE if we could make a short video for the president. He thought a ten-minute exposure to high-energy physics would be useful when the proposal was discussed at a Cabinet meeting. How do you teach a president high-energy physics in ten minutes? More important, how do you teach this president? After considerable agony, we hit on the idea of having some high school kids visit the lab, be taken on a tour of the machinery, ask a lot of questions, and receive answers designed for them. The president would see and hear all this and maybe get a notion of what high-energy physics is all about. So we invited kids from a nearby school. We coached a few just a bit and let the rest be spontaneous. We filmed about thirty minutes and cut it down to the best fourteen minutes. Our Washington contact warned us: no more than ten minutes! Something about attention span. So we cut more and shipped him ten lucid minutes of high-energy physics for high school sophomores. In a few days we had our reaction. "Way too complicated! Not even close."

  What to do? We redid the soundtrack, wiping out the kids' questions. Some of them, after all, were pretty tough. A voice-over expert then related the kinds of questions the kids might have asked (written out by me), and gave the answers while the action remained the same: the scientist guides pointing, the kids gawking. This time we made it crystal clear and very simple. We tested it on nontechnical people. Then we sent it in. Our DOE guy was getting impatient.

  Again he was underwhelmed. "Well, it's better but it's still too complicated."

  I began to get a little nervous. Not only was the SSC in danger but my job was at stake. That night I awoke at 3 A.M. with a brilliant idea. The next video would go this way: a Mercedes pulls up to the lab entrance, and a distinguished gentleman of fifty-five or so emerges. The voice-over says: "Meet Judge Sylvester Matthews of the Fourteenth Federal District Court, who is visiting a large government research lab." The "judge" explains to his hosts, three handsome young physicists (one female), that he has moved into the neighborhood and drives past the lab on his way to court every day. He reads about our work in the Chicago Tribune, knows we are dealing with "volts" and "atoms," and, since he never studied physics, is curious about what goes on. He enters the building, thanking the physicists for taking time with him this morning.

  My idea was that the president would identify with an intelligent layperson who is self-assured enough to say that he doesn't understand. In the subsequent eight and a half minutes, the judge frequently interrupts the physicists to insist that they go slower and clarify this and that point. At nine-plus minutes, the judge shoots his cuff, looks at his Rolex, and thanks the young scientists graciously. Then, with a shy smile: "You know I really didn't understand most of the things you told me, but I do get a sense of your enthusiasm, of the grandeur of the quest. It somehow reminds me of what it must have been like to explore the West ... man alone on horseback with a vast, unexplored land..." (Yes, I wrote that.)

  When the video got to Washington, the assistant secretary was ecstatic. "You've done it! It's terrific. Just right! It will be shown at Camp David over the weekend."

  Greatly relieved, I went to bed smiling, but I woke up at 4 A.M. in a cold sweat. Something was wrong. Then I knew. I hadn't told the assistant secretary that the "judge" was an actor hired from the Chicago Actors' Bureau. This was around the time the president was having trouble finding a confirmable appointee to the Supreme Court. Suppose he ... I tossed and sweated until it was 8 A.M. in Washington. With my third call I got him.

  "Say, about that video..."

  "I told you it was great."

  "But I have to tell—"

  "It's good, don't worry. It's on its way to Camp David."

  "Wait!" I screamed. "Listen! The judge. It's not a real judge. He's an actor, and the president may want to talk to him, interview him. He looks so intelligent. Suppose he..." [Long pause]

  "The Supreme Court?"

  "Yeah."

  [Pause, then snickering] "Look, if I tell the president he's an actor, he'll surely appoint him to the Supreme Court."

  Not long afterward the president approved the SSC. According to a column by George Will, the discussion about the proposal had been brief. During a Cabinet meeting the president listened to his secretaries, who were about evenly divided on the merits of the SSC. He then quoted a well-known quarterback: "Throw deep." By which everyone assumed he meant "Let's do it." The Super Collider beca
me national policy.

  Over the next year a lively search for a site for the SSC engaged communities all around the nation and in Canada. Something about the project seemed to excite people. Imagine a machine that could cause the mayor of Waxahachie, Texas, to stand up in public and conclude a fiery speech with "And this nation must be the first to find the Higgs scalar boson!" Even "Dallas" featured the Super Collider in a subplot in which J. R. Ewing and others attempted to buy up land around the SSC site.

  When I referred to the mayor's comment at a meeting of the National Conference of Governors, in one of the several million talks I gave while selling the SSC, I was interrupted by the governor of Texas. He corrected my pronunciation of Waxahachie. Apparently I had deviated by more than the normal difference between Texan and New Yorkese. I couldn't resist. "Sir, I really tried," I assured the governor. "I went there, stopped at a restaurant, and asked the waitress to tell me where I was, clearly and distinctly. 'B-U-R-G-E-R—K-I-N-G,' she enunciated." Most of the governors laughed. Not the Texan.

  The year 1987 was the year of three supers. First, there was the supernova that flared in the Large Magellanic Cloud about 160,000 years ago and finally got its signal to our planet so that neutrinos from outside our solar system were detected for the first time. Then there was the discovery of high-temperature superconductivity, which excited the world with its possible technological benefits. Early on there was hope that we would soon have room-temperature superconductors. Visions arose of reduced power costs, levitated trains, a myriad of modern miracles, and, for science, much-reduced costs of building the SSC. Now it's clear that we were too optimistic. In 1993 high-temperature superconductors are still a lively frontier for research and for a deeper understanding of the nature of material, but the commercial and practical applications are still a long way off.