by Sean Carroll
I was a newly minted postdoc myself at the time, part of the particle theory group at MIT. I remember a somber meeting we held, inviting the entire Boston-area physics community to get together and talk about what we should do next. Some questions were scientific: Is there any other way to attack the questions the SSC was designed to address? Some were more practical: Should we throw our support behind a serious U.S. investment in the LHC, or should we keep fighting a battle that was already lost? Some were even more practical than that: Is there some way we can offer jobs or temporary positions to the scientists who were thrown out of work by the closing of the SSC lab?
At the time of the SSC’s cancellation, $2 billion had already been spent to excavate part of the tunnel and build some of the necessary physical infrastructure. It’s hard to pinpoint a single justification for Congress’s decision to cancel the project, but a frequent complaint was the reluctance of SSC management to institute proper bureaucratic procedures. A 1994 post-cancellation report from a Congressional staff committee, entitled “Out of Control: Lessons from the Superconducting Super Collider,” detailed numerous allegations of mismanagement, including consistently underestimated costs, a failure to carry out mandatory internal reviews, and difficulties in communicating with Congress and the Department of Energy itself. Sometimes the criticisms got silly, as when news stories broke that the laboratory had spent $20,000 on plants (which turned out to include landscaping). The physicists, meanwhile, chafed at what they saw as unnecessary red tape. Roy Schwitters, who was serving as director of the SSC lab, grumbled to a reporter, “Our time and energy are being sapped by bureaucrats and politicians. The SSC is becoming a victim of the revenge of the C students.” In retrospect, that might not have been the most politically astute formulation.
Meanwhile, the physicists were fighting among themselves. While particle physics receives a hefty fraction of research dollars and public attention, it is a distinctly minority pursuit within the larger field of physics. Only 7 percent of the membership of the American Physical Society (APS) are members of the Particles and Fields subdivision; others identify as researchers in condensed matter and materials, atomic and molecular physics, optics, astrophysics, plasma physics, fluid dynamics, biophysics, or other specialties. By the late 1980s and early ’90s, many in these fields were more than a little irked at all the attention and funding that flowed toward particle physics, and to them the SSC was a symbol of priorities that had gone seriously awry.
Bob Park, executive director of the APS’s office of public affairs at the time, said in 1987 that the SSC was “perhaps the most divisive issue ever to confront the physics community.” Philip Anderson of Princeton, a respected condensed matter physicist who won the Nobel Prize in 1977, emphasized “the almost complete irrelevance of the results of particle physics not only to real life but to the rest of science,” and argued that while the SSC was good science, the money could perhaps be better spent elsewhere. James Krumhansl, a materials scientist from Cornell, who was in line to become president of the APS, believed that the project was siphoning away money from more cost-effective areas of research, and that development of a new particle accelerator should wait until superconducting and magnetic technologies had improved. Particle physicists often hurt their own case among their colleagues by trying to claim advances in other fields, such as magnetic resonance imaging, as spinoffs from accelerator development. As Nicolaas Bloembergen, another Nobel Laureate and APS president, testified in 1991, “As one of the pioneers in the field of magnetic resonance, I can assure you that these are spinoffs of small-scale science.”
Somewhat lost in the jostling over bureaucratic control, budget concerns, and disciplinary priority were the larger questions of the meaning of basic research and the importance of discovery for its own sake. In 1993, a new president and many new representatives had been elected, swearing to bring government spending under control. The Berlin Wall had come down and the Soviet Union had collapsed, ending the Cold War and its attendant race for technological superiority. After hitting an apogee with the Manhattan Project during World War II, the influence of high-energy physicists over national policy had been in gradual decline for half a century. Most thoughtful people can agree that the quest to better understand the universe is an important one, but so is finding adequate health care and income security for a nation’s citizens. These are difficult priorities to balance against one another in the best of times.
After the SSC was canceled for good, the land and facilities were turned over to the state of Texas, which tried for a long time to sell them to a private owner. It finally succeeded in 2006, when an Arkansas millionaire named Johnnie Bryan Hunt purchased the site for $6.5 million. Hunt’s idea was to turn the SSC complex into an unprecedentedly secure data storage facility. The laboratory was equipped with power and telecommunications lines, and the site had been carefully chosen to steer clear of earthquakes and floods. But before the end of the year, the seventy-nine-year-old Hunt had slipped on a patch of ice, damaged his skull, and died. Plans for the data center were scrapped, and the SSC site again lay quiet. As of 2012, the complex has been purchased by a chemical manufacturer that hopes to build a new plant, although the neighbors are strenuously objecting. Whatever the ultimate fate of the SSC laboratory, Waxahachie is not playing a major role in the search for the Higgs boson.
As many predicted, the cancellation of the SSC did not lead to increased funding for other areas of science; indeed, the same enthusiastic Congressional budget-cutters went to work on the rest of the research budget with gusto. There was, however, one acknowledged winner in the unfortunate episode: the Large Hadron Collider. Denied their dream of a flagship machine, U.S. physicists successfully lobbied for an increased role in the LHC. The infusion of money from America helped move the LHC forward in scope, keeping alive the prospect that the Higgs wouldn’t stay elusive forever.
FIVE
THE LARGEST MACHINE EVER BUILT
In which we visit the Large Hadron Collider, the triumph of science and technology that has been searching for the Higgs boson.
On September 10, 2008, the Large Hadron Collider came to life. To the cheers of thousands of physicists worldwide, the first protons successfully circulated around the ring. Champagne corks were popped, backs were slapped, speeches were made, and a new era of human discovery had dawned at long last.
Nine days later, it exploded.
Not the entire accelerator, of course. The LHC lives in a circular tunnel 330 feet underground and about seventeen miles in circumference, looping in a circle across the border of Switzerland and France near Geneva. It would take some sort of unimaginable cataclysm for the whole thing to explode. But individual pieces can break.
For the LHC to work, the inside must be kept extremely cold. The machine circulates protons in two different beam pipes: one for moving clockwise, the other counterclockwise, so that the beams can be brought into collision at certain locations where experiments are situated. Both beam pipes travel through superpowerful magnets, whose job it is to curve the protons precisely to stay on their appropriate path.
It’s easy to make magnetic fields: Just run electrical current through a loop of wire. To make strong fields, we need a lot of current. But most materials, even high-quality wires, offer some amount of resistance to the flow of current. The problem then is that the wire will start to heat up and ultimately melt. To combat this problem, the wires are cooled to an incredibly low temperature, so that they become superconductors. A superconductor has no resistance at all, so the wires don’t rise in temperature when current runs through. The LHC is the largest refrigerator in the world (by a wide margin), and the cooling is achieved via liquid helium, kept at minus 456 degrees Fahrenheit, just 3.4 degrees above absolute zero, the coldest temperature possible.
Here is the worry: If the temperature of the helium rises just a bit, the wires in the magnets cease to be superconductors. When that happens, the huge amount of electrical current running thr
ough them meets resistance, and responds by heating up the wires even more. This in turn heats up the helium, and the process runs out of control, with the liquid helium boiling into gas and exploding out of its containers. In operating mode, the LHC magnets are always a hair’s breadth away from disaster.
Such a runaway event is known in the trade as a “quench.” On September 19, 2008, a seemingly minor electrical problem caused a quench in one magnet, and the troubles quickly spread to other magnets nearby. Lyn Evans, head of the LHC at the time, remembers sitting in the personnel office haggling about some fairly trivial thing, when he got a call on his mobile telling him to come immediately—something looked serious. “When I got over there, even on a computer screen I had never seen such carnage. Red everywhere.”
The difficulty was ultimately traced to a faulty connection in a superconducting joint, which caused an electrical arc that pierced a helium vessel. More than fifty magnets had to eventually be replaced out of the 1,232 that work to bend protons around the LHC’s ring. The initial reports out of CERN characterized the incident as a “leak,” but “explosion” is a more accurate description. More than six tons of liquid helium were released into the tunnel in just a few minutes, and the stresses ripped magnets from where they were bolted to the floor. Safety procedures require that no one is allowed in the LHC tunnel when protons are circulating, but at the time of the incident the beam was actually turned off; fortunately the affected area was empty at the time, and nobody was hurt.
Redoubled efforts
At least nobody was hurt physically. Mentally the damage was severe. Robert Aymar, a French physicist, who was the director general of CERN at the time, put out a press release stating, “Coming immediately after the very successful start of LHC operation on 10 September, this is undoubtedly a psychological blow.” After years of hard work, it was deflating to be so close to seeing the LHC running at last, only to be hit by such a jarring setback.
But this is a story with a happy ending. As disappointing as it was, the September 19 explosion galvanized the CERN community around the task of bringing the LHC back to life. Engineers and physicists threw themselves into the task of checking and improving every piece of the machine to make sure it would be able to withstand the unprecedented energies it was expected to tame. This wasn’t just a matter of tightening a few screws: Not only did the damaged equipment have to be repaired, but every other piece of the machine had to be brought up to a higher standard of quality. It was slow and demanding work. Not until over a year later did the accelerator seem ready for prime time once again.
Mike Lamont’s official title is LHC Machine Coordinator, but a Star Trek fan once described him as the “LHC’s Mister Scott.” Having spent more than twenty-three years at CERN, it’s his responsibility to keep the protons coming in the face of seemingly insurmountable obstacles. Tiny glitches happen all the time, of course, but as the day grew closer when the LHC would finally turn on once again, every bump in the road seemed to be magnified to epic-disaster proportions. During tests on November 3, 2009, temperatures on some of the magnets began to rise due to an electrical malfunction in one of the stations on the surface. Lamont explained to curious reporters that the problem had been traced to a tiny piece of bread on a bus bar. Apparently a passing bird had dropped a bit of baguette from overhead. Lamont and the other engineers quickly patched up the problem, and regular operations were restored—but not before reporters’ eyes had grown wide at this bit of news. The Telegraph printed a photograph of the CMS detector next to a photograph of a pigeon, with the caption “The Large Hadron Collider (left) and its arch-nemesis (right).”
On November 20, 2009, protons circulated in the LHC for the first time since the accident. Three days later, the beams were brought together to create the first collisions in the machine. A mere seven days after that, the energies had increased to the point where the LHC was the highest-energy accelerator ever built.
Running on an ordinary schedule, the LHC would shut down during the deep of winter in order to save money during those months when electricity in Geneva is most expensive. But in 2009–2010, everyone was impatient, and the crews doubled their efforts to bring the accelerator up to power. The first physics data (as opposed to “commissioning” data used to test the machine) was taken in early 2010. In March 2010, the LHC reached its provisional energy goal (half of the ultimate target), setting a record for high-energy particle collisions in the process. Champagne flowed once again.
In retrospect, the accident in September 2008 helped the physicists and technicians at the LHC understand their machine much better, and as a result, the physics runs beginning in 2010 were stories of essentially uninterrupted progress. Given that operations didn’t start in earnest until that year, it came as a surprise to almost everybody that the experiments collected and analyzed enough data to discover the Higgs by July 2012. It’s as if you purchased an expensive car that breaks down almost immediately, and you have to spend a while combating some pesky maintenance problems. But once you finally get it on the road and hit the accelerator, the performance takes your breath away.
The Large Hadron Collider is Big Science at its biggest. The number of moving parts—human as well as mechanical—can sometimes be intimidating, or even depressing. In the words of Nobel Laureate Jack Steinberger, “The LHC is a symbol of just how difficult it is these days to make any progress. What a difference when compared to my thesis days, sixty-five years ago, when I, singlehandedly, in half a year, could do an experiment which marked an interesting step forward.” The LHC is the largest and most complicated machine ever built by human beings, and sometimes it’s a surprise that it works at all.
But it does work—spectacularly well. Over and over again, physicists I talked to while writing this book spoke of the awe-inspiring immensity of the operation, but also about how CERN could serve as a model for large-scale international collaboration. Experimentalist Joe Incandela said, “What’s amazing to me is that we have people from seventy countries around the world working—together. Palestinians and Israelis working side by side, Iranians and Iraqi scientists work together—such collaborations in the pursuit of Big Science shouldn’t be overlooked.” Joe Lykken, an American theoretical physicist at Fermilab, wistfully mused, “If only the United Nations could work like CERN, the world would be a much better place.”
If you believe that it’s a worthwhile task to pursue particles like the Higgs boson that require a huge amount of energy to create, Big Science is the only way to go. There is a tremendous amount of fantastic research to be done that can be tackled with relatively inexpensive tabletop experiments, but discovering new massive particles isn’t in that category. Right now the LHC is the only game in town, and its performance is a testimony to human ingenuity and perseverance.
Years of planning
The LHC is a marvel of planning and design. Physicists at CERN had been thinking about a giant proton collider for a while, but the first “official” discussions about what would eventually become the LHC were held at a workshop in Lausanne, Switzerland, in March 1984. The planners knew that the United States was contemplating what would eventually become the Superconducting Super Collider, so they needed to decide whether a European competitor was a sensible use of scarce resources. (They didn’t know, of course, that the SSC would eventually be canceled.) Unlike the SSC, which started from scratch building a new facility, the LHC would be limited in scope by the need to fit inside the already-constructed LEP tunnel. As a result, the target energy was set at 14 TeV, barely more than one-third of the 40 TeV target for the SSC. But the LHC would be able to produce more collisions per second, and was less expensive—and maybe all the good physics would be accessible at 14 TeV, rendering the higher energy of the SSC irrelevant.
Much of the impetus for moving forward with the LHC came from Italian physicist Carlo Rubbia, a brash and influential experimentalist who had collected a Nobel Prize in 1984 for his discovery of the W and Z bosons. Rubbia is a l
arger-than-life figure, as well-known for his forceful personality as for his accomplishments as a scientist (which are considerable). It was he who cajoled CERN into building the first proton-antiproton collider in 1981, a concept that would later be adopted by Fermilab’s Tevatron. (With the LHC we are back to colliding protons on protons, as it is too difficult to make a sufficient number of antiprotons to create the sought-after number of collisions.)
First as the chair of CERN’s Long Range Planning Committee, and later as director general of the lab from 1989 to 1993, Rubbia pushed strongly for the LHC at a time when LEP wasn’t yet finished and the United States was thought to be moving forward with the SSC. Europe was facing its own budgetary woes, especially in Germany, where the costs of reunification were running high. Rubbia was eventually able to convince the European governments that a hadron collider was the logical next step for the lab, regardless of what other countries might be doing. It wasn’t until 1991 that the CERN council adopted a resolution to officially study the LHC proposal, and not until December 1994 (after the SSC was canceled) that the project was finally approved. Lyn Evans was appointed director of the LHC, and the massive task of moving from idea to reality began in earnest.
The architect
In a project stretching over so many years, involving so many people and countries, and with such an intimidating number of significant subprojects, it would be unfair to give too much credit to any single person, downplaying the role of so many others. Nevertheless, if any individual is to be mentioned as having built the LHC, it would be Lyn Evans.
Evans comes across as an unassuming man, gray-haired and distinguished-looking but informal. Born to a mining family in Wales, his first love was chemistry; he took special joy making explosives, perhaps a fitting start for someone who would one day engineer the highest-energy particle collisions humans have ever achieved. In university he switched to physics because “physics was more interesting, and easier.” When the LHC project was approved, CERN needed someone with enough experience to manage the job, but young and energetic enough to see it through to completion. Evans was handed the daunting task of squeezing the highest possible physics return out of a machine with a fixed size, a limited budget, and an array of technological challenges that were unique in the history of experimental science. It was Evans who figured out how to take the original schematic plans for the LHC and modify them into a design that was compatible with financial realities.