After 14 years of preparation, a new scientific wonder of the world opened for business Wednesday with the official startup of Europe's Large Hadron Collider.
The $10 billion particle accelerator is the biggest, most expensive science machine on earth, designed to probe mysteries ranging from dark matter and missing antimatter to the existence of extra, unseen dimensions in space.
Scientists, journalists and dignitaries watched from the control room at Europe's CERN particle-physics center on the French-Swiss border, near Geneva, as beams of protons were sent all the way around the collider's 17-mile (27-kilometer) underground ring of supercooled pipes for the first time.
"Today is a great day for CERN," the organization's director general, Robert Aymar, told the crowd in the control room as the startup process began.
Controllers checked the alignment of the beam as barriers were removed at each stage of the route. Applause and shouts greeted every report of progress along the 330-foot-deep (100-meter-deep) tunnel — climaxing when the beam made its first full clockwise circuit, less than an hour after it was turned on.
"It’s a fantastic moment," Lyn Evans, the project leader for the Large Hadron Collider, said afterward. "We can now look forward to a new era of understanding about the origins and evolution of the universe.”
As champagne flowed in the control room, former CERN chief Luciano Maiani noted that the money spent on the project over 14 years was a mere fraction of the $40 billion that China spent for this summer's Olympic Games in Beijing. "These are the Olympics of science," CERN spokeswoman Paola Catapano replied during a Webcast interview.
Hours later, the LHC's counterclockwise proton beam made its first-ever circuit. The next steps in the process will be to fine-tune the beams and bring them together for their first collisions. It will take weeks for the collider to go through its commissioning process, and the LHC isn't expected to reach full power until next year.
‘First Beam,’ first celebration
Even though the first scientific results are months away, CERN used Wednesday's "First Beam" events as a high-profile occasion for celebration. For the more than 10,000 scientists, engineers and other workers involved in the project, the Large Hadron Collider represents a revolutionary new research opportunity as well as an unprecedented engineering achievement.
"The combination of the size, scale, complexity and technology — well, the comparison I always use is the pyramids," Peter Limon, a U.S. physicist from Fermilab who played a part in building the device, said during a pre-startup walkthrough. "This is what we do today comparable to the pyramids of 4,000 years ago."
The LHC is designed to do things the pyramid's builders never imagined.
Once the machine is in full operation, two streams of invisible protons will be whipped up in opposite directions around an underground racetrack to 99.999999 percent of the speed of light. When the two waves of protons slam into each other, scientists expect particles to melt into bits of energy up to 100,000 times hotter than the sun's core — a state that should replicate what the entire universe was like just an instant after it came into being.
How can the Large Hadron Collider possibly perform such feats? That's where the wonder begins.
Going down ...
No one was allowed in the underground tunnel for Wednesday's maiden run, but a visit during the final phases of the LHC's construction provided an inside look at the wonder at work.
During the seven-year construction phase, components of the collider and its detectors had to be lowered down piecemeal from CERN's assembly halls, then put together in underground caverns as big as cathedrals.
Although the scale of the project is impressive, these cathedrals are no gleaming shrines to science: Our trip felt more like going into the bowels of a well-worn power plant or subway system. That's because most of the facility was actually carved out in the 1980s for an earlier particle-smasher called the Large Electron Positron collider, or LEP. CERN has spent the past seven years remodeling the space for the Large Hadron Collider.
Steven Nahn, a physicist at the Massachusetts Institute of Technology, conducted research at CERN during the LEP era. "They stole our tunnel, that's the way I see it," Nahn joked as Limon showed us around.
For years, Nahn, Limon and thousands of other researchers have pitched in on the design and assembly of the LHC's instruments, forsaking quiet laboratories for the din of the construction site — as well as the occasional industrial mishap.
The LHC tunnel: Misbehaving magnets
Limon is a veteran of Fermilab's Tevatron, which had been the world's most powerful collider but is being dethroned by the LHC. At full power, the proton beams at the LHC will run into each other with the force of two 400-ton bullet trains going 100 mph. That amounts to 14 trillion electron volts, or about seven times the Tevatron's maximum power.
To bend those subatomic bullet trains into a circular path requires a chain of more than 1,800 superconducting magnets that have been chilled so close to absolute zero that they're colder than the average temperature of outer space (1.9 Kelvin, or 456.3 degrees below zero Fahrenheit).
Some of those magnets have to be collimated to focus the beams precisely at the ring's four collision points, like a telescope focusing light onto its mirrors. Drawing on its experience from Tevatron, Fermilab was put in charge of providing many of those magnets. But back in March 2007, a design flaw led to a violent breakdown during a cooldown test. The supports that held the magnet in place came loose with a loud bang and a cloud of dust.
"Everybody ducked about two seconds after it happened," Limon recalled.
The LHC's scheduled startup had to be delayed 10 months to install and test a fix for the faulty magnets. Even with the fix, there's no guarantee that the magnetic field will always hold. A runaway proton beam could blast right through its helium-cooled pipeline and kill anyone who got in its way. That's why the tunnel is sealed off for each run. If anything goes wrong, a computer-controlled system will shut down the collider and send the errant beam down a blind alley within milliseconds.
However, if everything goes right, each pulse of protons will whip around the ring 11,000 times a second, traveling the equivalent of a trip to Neptune and back before they slam into the protons going the other way at four points around the ring. Four main detectors will watch what happens next.
ATLAS and CMS: What the detectors do
For millennia, people have studied how things work by breaking them apart and watching what happens to the pieces. Physicists started doing that with atoms about 90 years ago, confirming that atoms were composed of electrons, protons and neutrons — plus a menagerie of other particles they never expected to find. (After the discovery of the muon, physicist Isidor Rabi famously exclaimed, "Who ordered that?")
Physicists determined that protons, neutrons and many of the other particles were built up from even more fundamental constituents known as quarks. The particles built up from quarks are classified as hadrons, and that's where the LHC's name comes from: It's a large collider that smashes hadrons together.
So what will come out of those tiny, trillion-degree smash-ups? The LHC will look for exotic high-energy particles that supposedly came into existence just after the big bang — for example, the Higgs boson (which is thought to give other particles their mass) or supersymmetric particles (which may account for much of the universe's dark matter).
These particles can't be detected directly, because they interact so weakly with ordinary matter. Instead, the LHC's detectors will track how those particles decay into more easily detectable particles as they fly out from the collision point.
It's like reconstructing the scene of a crime from forensic evidence: Scientists will try to track down the usual suspects (or, they hope, the extremely unusual suspects) by analyzing the subatomic evidence that the culprits leave behind.
To solve their mysteries, the LHC's scientific sleuths will use the latest and greatest tools of the trade, built at a cost of billions of dollars. The two main detectors — ATLAS (A Toroidal LHC ApparatuS) and CMS (Compact Muon Solenoid) — are structured like the layers of an onion to spot different kinds of particles:
- Trackers: Both detectors have tracking devices at the center to follow the paths of short-lived particles.
- Calorimeters: The next layers are two different types of calorimeters that measure the energies of the particles given off. One captures electromagnetic energy, while the other captures the energy from particles such as protons, neutrons and pions.
- Magnets: Huge magnets are built into each detector to bend the paths of the particles so they can be identified by their charge.
- Muon detectors: The outer layers of the detector track the paths of muons, particles that can't be stopped by any of the inner layers.
Probing the smallest scales of matter requires some of the biggest machines ever devised. ATLAS is the largest of all detectors, measuring 151 feet long and 82 feet high — bigger than your typical apartment building.
"It has an awful lot of free space inside," CERN theoretical physicist John Ellis explained. "The reason for that is, they want to be able to measure particles which come out of the collision ... even if the interior of the detector is so clogged with collision products they can't measure them properly there."
Over on the other side of the LHC's ring, CMS takes up less than half as much space as ATLAS but weighs almost twice as much. It contains more iron than the Eiffel Tower, built into alternating magnetized layers with particle detectors like a metallic jelly roll. CMS' built-in magnets and its expensive fine-resolution silicon tracker are part of a different strategy to do the same things that ATLAS does.
"You get big arguments between the ATLAS guys and the CMS guys as to which is the best way to measure these particles," Ellis said. "ATLAS is going to bend them that way, CMS is going to bend them this way, and we'll see in a few years' time which is the better idea."
ALICE: The big bang in the machine
ATLAS and CMS get most of the attention, but the contraption that best merits the title of "Big Bang Machine" is about a mile (1.5 kilometers) down the road from ATLAS. The ALICE detector (A Large Ion Collider Experiment) is designed exclusively to study the stuff that the universe was made of less than a millionth of a second after the big bang.
ALICE will run for only about a month out of every year, conducting experiments that will require the collider to switch over from smashing protons to smashing lead ions, which are 100 times heavier than protons. The high-energy collisions should blast those ions so thoroughly that, for just an instant, they turn into a plasma of free-flying quarks plus gluons, the particles that usually bind quarks together.
Past experiments indicated that the quark-gluon plasma behaved like a liquid. When ALICE gets up and running, "then maybe we reach the gas phase," said Jurgen Schukraft, CERN's spokesperson for the ALICE experiment. That would be something never before seen in the cosmic scheme of things.
LHCb: The mystery of antimatter
The fourth detector is also designed to answer a specific cosmic question. LHCb will study particles containing particular "flavors" of quarks and antiquarks, known as B mesons and anti-B mesons, with the aim of figuring out why matter has a huge edge over antimatter in our universe.
Earlier studies revealed that the particles and antiparticles decayed differently, which runs counter to the idea that matter and antimatter should be in symmetry. LHCb will follow up on those studies, using a battery of high-tech detectors that are lined up on one side of the collision point. Among those instruments are a tracker that can locate particles with a precision of 10 microns, or a tenth the width of a human hair.
Two smaller experiments round out the ring: LHCf, which studies cosmic-ray-like events near ATLAS; and TOTEM, which measures the effective size of protons using a detector near CMS.
The Grid: Getting out the data
The LHC is designed to produce as many as 600 proton collisions per second, and that creates a flood of digital data that gushes out from the detectors' wiring. If you were to put all the data from one of the main detectors onto CDs, the stack of disks would pile up to the orbit of the moon in six months. The challenge is to pick out only the most promising readings.
Each of the detectors uses "triggers" to pick out the good stuff. Only about 100 events per second are sent to thousands of computers and tape drives at CERN for storage. It's like narrowing down that moon-high stack of CDs to a stack that's only 6 miles high — which is still high enough for a transcontinental jet to run into.
To get the data out to researchers around the world, CERN has set up a multi-tier computer network called the Grid. Digital information goes out to the "Tier 1" data centers on a fiber-optic network at a rate of up to 10 gigabits per second — or roughly 1,000 times the speed of a typical cable Internet connection.
If the system works, it could set the model for future computing — not only for physics but also for other high-end applications such as climate simulation, genetic analysis and petroleum prospecting. Just as the World Wide Web was the best-known spin-off from CERN's LEP experiment back in the 1990s, the Grid could well become the LHC's most visible legacy.
Magnet for innovation
Who will benefit the most from that legacy? The Grid may distribute the data across the world — but it's hard to argue with the idea that Europe's 21st-century wonder of the world will serve as a magnet for innovation over the next decade.
That has sparked more than a few cases of "collider envy" among American researchers, and some worry about the prospects of a reverse brain drain. Michio Kaku, a theoretical physicist at the City College of New York, is already noticing a trend in his colleagues' travel plans.
"They're going where the action is, and that is Europe," Kaku said.