The anticipated cost of the project when it was canceled had risen from $4.4 billion at its inception in 1987 to about $12 billion in 1993. While this was, and still is, a large amount of money, one can debate the merits of killing the project. Two billion dollars had already been spent on it, and twenty-four kilometers of tunnel had been completed.
The decision to kill the project was not black-and-white, but a number of things could have played a bigger role in considerations—from the opportunity costs of losing a fair fraction of the talented accelerator physicists and particle physics experimentalists in the country to the many new breakthroughs that might have resulted from the expenditures on high-tech development that would have contributed to our economy. Moreover, had the SSC been built and functioned as planned, we may have had answers more than a decade ago to experimental questions we are still addressing. Would knowing the answers have changed anything we might have done in the meantime? We’ll probably never know.
The $12 billion would have been spent over some ten to fifteen years during construction and the commencement of operations, which makes the cost in the range of $1 billion per year. In the federal budget this is not a large amount. My own political views are well known, so it may not be surprising for me to suggest, for example, that the United States would have been just as secure had it cut the bloated US defense budget by this amount, far less than 1 percent of its total each year. Moreover, the entire cost of the SSC would have probably been comparable to the air-conditioning and transportation costs of the disastrous 2003 Iraq invasion, which decreased our net security and well-being. I can’t help referring once again to Robert Wilson’s testimony before Congress regarding the Fermilab accelerator: “It has nothing to do directly with defending our country except to help make it worth defending.”
These are political questions, however, not scientific ones, and in a democracy, Congress, representing the public, has the right and responsibility to oversee priorities for expenditures on large public projects. The particle physics community, perhaps too used to a secure inflow of money during the Cold War, did not do an adequate job of informing the public and Congress what the project was all about. It is not surprising that in hard economic times the first thing to be cut would be something that seemed so esoteric. I wondered at the time why it was necessary to kill the project, rather than suspend funding until the economy improved or until technological developments might have reduced its cost. Neither the tunnel (now filling with water) nor the laboratory buildings (now occupied by a chemical company) were going anywhere.
Despite these developments in the United States, CERN was moving forward with a new machine, the Large Electron-Positron (LEP) Collider, designed to explore in detail the physics of the W and the Z particles, at the urging of its newest Nobel laureate, the indomitable Carlo Rubbia. He became the laboratory’s director in 1989, the same year the new machine came online.
A twenty-seven-kilometer-long circular tunnel was dug about a hundred meters underground around the old SPS machine, which was now used to inject electrons and positrons into the bigger ring, where they were further accelerated to huge energies. Located on the outskirts of Geneva, the new machine was large enough to cross under the Jura Mountains into France. European nations are more familiar with building tunnels than the United States is, and when the tunnel was completed, the two ends met up to within one centimeter. Moreover CERN, as an international collaboration of many countries, did not significantly eat into the GDP of any one country.
The new machine ran successfully for more than a decade, and after the demise of the SSC in the United States, the huge LEP tunnel was considered for the creation of a miniversion of the SSC—not quite as powerful but still energetic enough to explore much of the parameter space where the long-sought Higgs particle might exist. Some competition came from a machine at Fermilab, called the Tevatron, which had been running since 1976 and in 1984 came online as the world’s most energetic proton-antiproton machine. By 1986, the collision energy of protons and antiprotons circulating around the 6.5 kilometer ring of superconducting magnets at Fermilab was almost two thousand times the equivalent rest mass energy of the proton.
As significant as this was, it was not sufficient to probe most of the available parameter space for the Higgs, and a discovery at the Tevatron would have required nature to have been kind. The Tevatron did garner one great success, the long-anticipated discovery, in 1995, of the mammoth top quark, 175 times the mass of the proton, and the most massive particle yet discovered in nature.
With no clear competition therefore, within fourteen months of the demise of the SSC the CERN council approved the construction of a new machine, the Large Hadron Collider, in the LEP tunnel. Design and development of the machine and detectors would take some time to complete, so the LEP machine would continue to operate in the tunnel for almost another six years before having to close down for reconstruction. It would then take almost another decade to complete construction of the machine and the particle detectors to be used in the search for the Higgs and/or other new physics.
That is, if a working machine and viable detectors could be constructed. This would be the most complicated engineering task humans had ever undertaken. The design specifications for superconducting magnets, computing facilities, and many other aspects of the machine and detectors called for technology far exceeding anything then available.
Conceptual design of the machine took a full year, and another year later two of the main experimental detector collaboration proposals were approved. The United States, with no horses in this race, was admitted as an “observer” state to CERN, allowing US physicists to become key players in detector development and design. In 1998 construction of the cavern to hold one of the two major detectors, the CMS detector, was delayed for six months as workers discovered fourth-century Gallo-Roman ruins, including a villa and surrounding fields, on the site.
Four and a half years later, the huge caverns that would house both main detectors underground were completed. Over the next two years, 1,232 huge magnets, each fifteen meters long and weighing thirty-five tons, were lowered fifty meters below the surface in a special shaft and delivered to their final destinations using a specially designed vehicle that could travel in the tunnel. A year after that, the final pieces of each of the two large detectors were lowered into place, and at 10:28 a.m., September 10, 2008, the machine officially turned on for the first time.
Two weeks later, disaster struck. A short occurred in one of the magnet connectors, causing the associated superconducting magnet to go normal, releasing a huge amount of energy and resulting in mechanical damage and release of some of the liquid helium cooling the machine. The damage was extensive enough that a redesign and examination of every weld and connection in the LHC was required, taking more than a year to complete. In November of 2009 the LHC was finally turned back on, but because of design concerns, it was set to run at seven thousand times the center-of-mass energy of the proton, instead of fourteen thousand. On March 19, 2010, the machine finally began running with colliding beams at the lower energy, and both sets of detectors began to record collisions with this total energy within two weeks.
These simple timelines belie the incredible challenges of the technical feats achieved at CERN during the fifteen years since the machine was first proposed. If you land at Geneva airport and look outside, you will see gentle farmland, with mountains in the distance. Without being told, no one would guess that underneath that farmland lies the most complicated machine humans have ever constructed. Consider some of the characteristics of the machine, which lies at some points 175 meters below this calm and pastoral scene:
1. In the 3.8-meter-wide tunnel, traversing twenty-seven kilometers, are two parallel beamline circles, intersecting at four points around the ring. Distributed around the ring are more than sixteen hundred superconducting magnets, most weighing more than twenty-seven tons. The tunnel is so long that, looking down it, one almost cannot se
e its curvature:
2. Ninety-six tons of superfluid 4He are used to keep the magnets operating at a temperature of less than two degrees above absolute zero, colder than the temperature of the radiation background in the depths of interstellar space. In total, 120 tons of liquid helium are utilized, cooled first by using about ten thousand tons of liquid nitrogen. Some forty thousand leak-tight pipe connections had to be made. The volume of He used makes the LHC the largest cryogenic facility in the world.
3. The vacuum in the beamlines is required to be sparser than the vacuum in outer space experienced by the astronauts performing space walks outside the ISS, and ten times lower than the atmospheric pressure on the Moon. The largest volume at the LHC pumped down to this vacuum level is nine thousand cubic meters, comparable to the volume of a large cathedral.
4. The protons accelerated around the tunnel in either direction move at a speed of 0.999999991 times the speed of light, or only about three meters per second less than light speed. The energy possessed by each proton in the collision is equivalent to the energy of a flying mosquito, but compressed into a radial dimension one million million times smaller than a mosquito’s length.
5. Each beam of protons is bunched into 2,808 separate bunches, squeezed at collision points to about one-quarter the width of a human hair, around the ring, with 115 billion protons in each bunch, yielding bunch collisions every twenty-five-billionths of a second, with more than 600 million particle collisions per second.
6. The computer grid designed to handle data from the LHC is the largest in the world. Every second the raw data generated by the LHC are enough to fill more than a thousand one-terabyte hard drives. This must be reduced considerably to be analyzed. From the 6 million billion proton-proton collisions analyzed in 2012 alone, more than twenty-five thousand terabytes of data were processed—more than the amount of information in all the books ever written and corresponding to a stack of CDs about twenty kilometers tall. To do this, a worldwide computer grid was created with 170 computer centers in thirty-six countries. When the machine is running, about seven hundred megabytes per second of data are produced.
7. The requirements for the sixteen hundred magnets to produce beams intense enough to collide is equivalent to firing two needles from a distance of ten kilometers with such precision that they collide exactly halfway between the two firing positions.
8. The alignment of the beams is so precise that account must be taken for the tidal variations on the ring from the gravity of the Moon as its position over Geneva changes, causing a variation of one millimeter in the circumference of the LHC each day.
9. To produce the incredibly intense magnetic fields needed to steer the proton beams, a current of almost twelve thousand amps flows through each of the superconducting magnets, about 120 times the current flowing through an average family house.
10. The strands of cable needed to make up the magnetic coils in the LHC span about 270,000 kilometers, or about six times the circumference of the Earth. If all the filaments in the strands were unraveled, they would stretch to the Sun and back more than five times.
11. The total energy in each beam is about the same as that of a four-hundred-ton train traveling at 150 km/hr. This is enough energy to melt five hundred kilograms of copper. The energy stored in the superconducting magnets is thirty times higher than this.
12. Even with the superconducting magnets—which make power consumption in the machine manageable—when the machine is running, it uses about the same power as the total consumption of all of the households in Geneva.
So much for the machine itself. To analyze the collisions at the LHC, a variety of large detectors have been built. Each of the four currently operating detectors has the size of a significant office building and the complexity of a major laboratory. To have the opportunity to go underground and see the detectors is to feel like Gulliver in Brobdingnag. The scale of absolutely every component is immense. Here is a photo of the CMS detector, the smaller of the two largest detectors at the LHC:
If you are actually at the detector, it is hard to even grasp the full picture, as can be seen in the more up-close-and-personal view:
The complexity of the machines is almost unfathomable. For a theorist such as me, it is hard to imagine how any single group of physicists can keep track of the device, much less design and build it to the exacting specifications required.
Each of the two largest detectors, ATLAS and CMS, was built by a collaboration of over two thousand scientists. More than ten thousand scientists and engineers from over a hundred countries participated in building the machine and detectors. Consider the smaller of the two detectors, CMS. It is more than twenty meters long, fifteen meters high, and fifteen meters wide. Some 12,500 tons of iron are in the detector, more than in the Eiffel Tower. The two halves of the detector are separated by a few meters when it is being worked on. Even though they are not on wheels, if the two halves were apart when the large magnetic field of the detector was turned on, they would be dragged together.
Each detector is separated into millions of components, with trackers that can measure particle trajectories to an accuracy of ten-millionths of a meter, with calorimeters, which detect to a high accuracy energy deposited in the detectors, and with devices for measuring the speed of particles by measuring the radiation they emit as they traverse the detector. In each collision hundreds or thousands of individual particles may be produced, and the detector must keep track of almost all of them to reconstruct each event.
Physicist Victor Weisskopf was the fourth director general of CERN, between 1961 and 1966, and he likened the great accelerators of that time to the Gothic cathedrals of medieval Europe. In thinking of CERN and the LHC, the comparison is particularly interesting.
The Gothic cathedrals stretched the technology of the time, requiring new building techniques and new tools to be created. Hundreds or thousands of master craftsmen from dozens of countries built them over many decades. Their scale dwarfed that of any buildings that had previously been created. And they were built for no more practical reason than to celebrate the glory of God.
The LHC is the most complicated machine ever built, requiring new building techniques and new tools to be created. Thousands of PhD scientists and engineers from hundreds of countries speaking dozens of languages, and hailing from a background of at least an equal number of religions, were required to build the accelerator and the detectors that monitor it—taking almost two decades to complete the task. Its scale dwarfs that of all machines constructed before it. And it was built for no more practical reason than to celebrate and explore the beauty of nature.
Seen in this perspective, the cathedrals and the collider are both monuments to what may be best about human civilization—the ability and the will to imagine and construct objects of a scale and complexity that requires the cooperation of countless individuals, from around the globe if necessary, for the purpose of turning our awe and wonder at the workings of the cosmos into something concrete that may improve the human condition. Colliders and cathedrals are both works of incomparable grandeur that celebrate the human experience in different realms. Nevertheless, I think the LHC wins, and its successful construction over two decades demonstrates that the twenty-first century is not yet devoid of culture and imagination.
Which brings me finally to the road to July 4, 2012.
By 2011 the LHC was cruising along, as one of the CERN officials put it. The amount of data taken by October of that year was already 4 million times higher than during the first run in 2010, and thirty times higher than had been obtained by the beginning of 2011.
At this point in the collection of data that physicists had been waiting forty years for, rumors began to fly in the community. Many of these came from the experimenters themselves. I have a part-time position at Australian National University in Canberra, and the International Conference on High Energy Physics was going to be in held in Melbourne in July of 2012. Melbourne has a big LHC contingent
, and when visiting, I kept hearing how a greater and greater possible mass range for the Higgs particle had been ruled out by the experiments already.
Many experimentalists relish being able to prove theorists wrong. So it was in this case. One experimentalist had excitedly told me less than six months before the meeting that the entire Higgs mass region had been ruled out except for a narrow range between 120 and 130 times the mass of the proton. She expected that by July they would be able to rule out that region too. As one who was skeptical of the Higgs, I wasn’t unhappy to hear this. In fact, I was getting a paper ready to explain why the Higgs might not exist.
On April 5, the situation got more interesting as the LHC center-of-mass beam energy was increased slightly, to eight thousand times the rest energy of the proton. This translated into an increased potential for new particle discovery. By mid-June it was announced that the leaders of the two main experiments, along with the director general of CERN, would not be traveling to Melbourne for the meeting, but would be presenting results remotely from a televised conference on the morning of July 4 in the main colloquium room at CERN—the same room where Rubbia had announced the discovery of the W particles.
On July 4 I was at a physics meeting in Aspen, Colorado. Because of the significance of the impending announcement, the physics community there had set up a live remote presentation screen—so that at 1:00 a.m. we could all sit and watch history unfold. About fifteen of us showed up in the dark at the Aspen Center for Physics, mostly physicists, but also a few journalists, including Dennis Overbye from the New York Times, who knew he was going to have a late night writing. As it turned out, so would I. The Times had asked me for an essay for the following week’s Science Times section if things worked out as expected.
The Greatest Story Ever Told—So Far Page 25