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The World's Largest Particle Accelerator

The cows grazing by the roads outside Geneva, Switzerland, have witnessed some pretty strange things these past few years: Trucks roll by carrying big, superconducting magnets that look like missiles, and other brightly colored pieces of scientific equipment. The pieces are all taken to warehouse-sized buildings, where they disappear down shafts that reach 300 feet into the earth.

The work is all part of an $8 billion project at the international physics laboratory called CERN. At its heart will be an enormously powerful particle accelerator capable of smashing subatomic particles together, reproducing the energies that existed a fraction of a second after the big bang. What comes out may solve some fundamental mysteries about how the universe is put together.

But that's if everything works. Physicists hope to begin operation this fall of what is arguably the largest and most complex science experiment ever constructed.

The Weight of Five Jumbo Jets

To visit CERN these days, is to feel very small in all sorts of ways.

On this early morning in February, technicians are lowering what they say is the world's largest electromagnet into one of the 300-foot shafts. The magnet is the size of a house, and can store enough energy to melt 18 tons of gold. It is incredibly heavy and dangles over the mouth of the shaft on four little bundles of black cables.

Christoph Schaefer, one of CERN's safety personnel, says the electromagnet is almost 2,000 tons. That's the weight of five jumbo jets, or one-third of the weight of the Eiffel tower.

With only seven inches of clearance, the electromagnet is lowered into the hole. The shaft is round, white-walled, and well lit. The magnet is a gray, metal cylinder — it looks like it might be part of a space station. It sits inside a huge, red octagon, and layers of scientific equipment.

The whole thing will be part of an even larger contraption which, oddly enough, is designed to detect ultra-tiny subatomic particles. The detector is called CMS for Compact Muon Solenoid. It will sit far below our feet in a huge cavern.

When it is all hooked up, the detector will have a special pipe running through it. If you leave the chamber you can follow the pipe on foot into a tunnel that makes a 16-mile loop. In five or six hours, you'll end up back where you started. Everyone calls it the LHC — short for Large Hadron Collider — the most powerful accelerator ever built.

When the machine is running, particles taken from hydrogen atoms will zip both ways around the loop at close to the speed of light. They will collide in the center of the detector with enormous energy, giving birth to a spray of new particles, perhaps some that no one has seen before.

"We hope to complete a journey started with Newton's description of gravity," says Jim Virdee, physicist and spokesman for the CMS team.

"The source of gravity is mass," says Virdee. "It's a very poorly understood concept. Certain particles have certain masses. We don't know why."

That may sound like a peculiar question to ask, and all this equipment may seem like an elaborate way to go about finding an answer. But it turns out if you smash things together, very strange particles emerge that are not part of the everyday world: Z bosons, pi mesons, strange quarks. Some only live a very short time, but they are clues to the fabric of the universe.

The Descent

Behind Jim Virdee, the 2,000 ton magnet begins — imperceptibly — to disappear down the shaft. And even though it is 6:30 in the morning, dark and rainy, other physicists have dragged themselves out of bed to watch. One of them is Dan Green, the project manager for the U.S. contribution to this detector.

"It's awe-inspiring actually," Green says. "This is the most excited I've been about physics for about 20 years. We expect to see things which will change the way we view the universe. That only happens once or twice in a lifetime."

No one really knows what the machine will give birth to. But the equations suggest that some weird stuff could be just around the corner — maybe "dark matter," the invisible stuff that seems to hang around galaxies.

"It's kind of an embarrassment that we don't know what 95 percent of the universe is made of by weight," Green says. "We hope — it's possible — we may be making dark matter."

Some theories say it is possible the collider will cause miniature black holes to momentarily appear.

But for now, what has appeared is a table of croissants, an urn of coffee, and more people. Everyone stands around in blue hard hats. They don't talk about black holes or dark matter. A few say things like "I hope the magnet doesn't fall."

A Test of Faith

Some people at the lab think that these projects are pushing the boundaries of what can be achieved by humans: financially, politically, and organizationally. There are more than 2,000 physicists from all over the world working on just this detector. The list of names alone takes up more space than some scientific journals allow for an entire research paper.

The physical scale is also unprecedented. Milan Nikolic, a graduate student from the University of California Santa Barbara, describes the cavern where the detector will sit as larger than one of the New York subway's stations — the 168th Street IRT (Interborough Rapid Transit).

"The size is amazing," Nikolic says. "It's actually in an underground river. We had to sink liquid nitrogen probes and freeze the river around it to lay the concrete structure down. [It was a] massive civil engineering project. And the detector itself dwarfs anything I've seen. It's like a five-story building. It's ridiculous."

Nikolic is hoping they discover evidence of extra tiny dimensions to space-time.

"Because then I would have a job and stuff," he says.

Nikolic is not entirely joking. People don't like to talk about it, but it is possible these experiments may not find much at all. The answers may simply be out of reach, so hard to probe that it would take an accelerator the size of the solar system to sort things out.

At the end of the day, the magnet nears the bottom of the shaft, hanging like a giant yo-yo. For no good reason, everyone whispers.

It's a classic test of faith. On the one hand, everyone trusts the math that this huge thing won't fall. On the other hand, no one wants to stick their head under it, though we do for a second.

The experiment is supposed to start running this fall. But a lot of people, a lot of languages, a lot of pieces, means a lot could go wrong. And this gargantuan detector is actually the "little one." It has a much larger brother named ATLAS, which is seven stories high.

When we go to see it, people are crawling over it like insects.

There's an unintentional beauty to it all, with so many pieces all fitting perfectly. Because the particles go every which way, the equipment is symmetric, cylinders within cylinders, with giant pale green wheels. The equipment will precisely track and identify the spray of particles.

It will take years to fully analyze the data. When the accelerator is running, collisions will occur 30 million times a second.

I ask one physicist how much time she was putting in. "Infinite," she says.

'It Rivals the Pyramids'

We leave the cavern, and walk into what looks like a gently curving subway tunnel. This is what people call "the ring," the particle accelerator itself. Thousands of magnets are arranged like boxcars on a long, 16-mile racetrack – so long, the tunnel seems almost straight.

"It's actually very relaxing to go walking down this way," says Peter Limon, a physicist from Fermilab, outside Chicago.

CERN staffers use bicycles to get around down here. If a magnet breaks it could take a while to get to it, much less fix it.

"This is just the most amazing thing I've ever seen built," Limon says. "I think it rivals the pyramids."

The pyramids long outlasted its builders. And one physicist here wonders whether thousands of years from now, a future civilization would find these strange tunnels and equipment buried in the ground.

Copyright 2023 NPR. To see more, visit https://www.npr.org.

David Kestenbaum
David Kestenbaum is a correspondent for NPR, covering science, energy issues and, most recently, the global economy for NPR's multimedia project Planet Money. David has been a science correspondent for NPR since 1999. He came to journalism the usual way — by getting a Ph.D. in physics first.
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