MEYRIN, Switzerland — It is the biggest machine ever built. Everyone says it looks like a movie set for a corny James Bond villain. They are correct. The machine is attended by brainiacs wearing hard hats and running around on catwalks. They are looking for the answer to the question: Where does everything in the universe come from? Price tag: $8 billion plus.

The world's largest particle accelerator is buried deep in the earth beneath herds of placid dairy cows grazing on the Swiss-French border. The thing has been under construction for years, like the pyramids. Its centerpiece is a circular 17-mile tunnel that contains a pipe swaddled in supermagnets refrigerated to crazy-low temperatures, colder than deep space.

The idea is to set two beams of protons traveling in opposite directions around the tunnel, red-lining at the speed of light, generating wicked energy that will mimic the cataclysmic conditions at the beginning of time, then smashing into each other in a furious re-creation of the Big Bang — this time recorded by giant digital cameras.

On Wednesday, they fired this sucker up.

It will be months before the proton beams reach full power and produce the kinds of exotic collisions that may herald an age of "new physics." But if the machine works — this most ambitious, expensive, technologically advanced civilian scientific experiment in history — it would be a happening for humanity.

"I think we may have to rewrite our textbooks," said Fabiola Gianotti, a project leader for ATLAS, one of the four huge detectors that will record and analyze the collisions. "There must be something more than we have seen. There is something missing from the puzzle."

The Large Hadron Collider, as it is called by the 8,000 scientists, engineers and technicians from 85 countries who dote on it, will probe the most fundamental mysteries. From the fireballs, there might spring forth black holes and the elusive thing that gives matter its mass. Or not! There might be particles called "strangelets" and evidence of "dark matter" and signs of "supersymmetry" and maybe a little antimatter.

Oh, and they might find some extra dimensions. But this is the delicious part. They. Don't. Exactly. Know.

That accounts for the last-minute legal challenges by opponents who worry that the Large Hadron Collider — hadrons, by the way, are collections of quarks, which are the particles inside protons and neutrons, which form the nucleus of the atom — might spark a chain reaction of runaway events that could destroy the planet.

Their greatest concern is that the black holes, the stuff of a hundred Star Trek subplots, could grow and suck, grow and suck, which is what black holes do. A retired radiation safety expert in Hawaii sought a restraining order in a U.S. court but was denied. Another group filed its doomsday appeal with the European Court of Human Rights, which also declined to act.

To calm public anxiety, the proton smashers investigated safety concerns and said any black holes "would be entirely benign" and would decay almost instantly. They would be "mini black holes," just like the ones that occur (the theorists say) whenever a couple of cosmic rays collide in space. Nature has already conducted experiments just like this, the report concludes, "and the planet still exists."

So make your plans accordingly.

The Large Hadron Collider was built by the European Organization for Nuclear Research, known as CERN, which on the surface looks like a slightly down-at-the-heels state college in the middle of a cow pasture in the dull suburbs of Geneva. CERN, however, is now the mecca for international physics, where the streets are named for Einstein, Newton and Curie.

To see what the excitement is about, you have to put on a hard hat and get into one of the elevator shafts and travel 300 feet below the Earth's surface to the tunnel, which was possible earlier this summer, before they closed the doors.

You drop into towering caverns lined with thick slabs of concrete that hold the detectors. The detectors look like building-size barrels, honeycombed with wafers of silicon and doughnut-shaped magnets. They are crawling, Medusa-like, with blue, red, green cables, like arteries and veins.

The tunnel itself is like a subterranean racetrack. Protons stripped from hydrogen atoms will be accelerated to high energies and whizzed around and around the tunnel, through an ordinary-looking blue pipe, which is not ordinary at all but quite extraordinary — because it is coiled with thousands of superconducting magnets, which bend the proton beam so it can travel in circles. The magnets are superconducting because they are supercooled by superfluid helium, which is superstrange.

"A completely novel engineering material," is how Lyn Evans, the project manager of the collider, describes supercold helium. "For example, if you were to put it into a beaker? It could crawl out."

These protons whizzing through the pipe and around the track? They travel in bunches. These bunches are inches long and half the width of a human hair. Each bunch contains 100 billion protons, give or take a few. Each beam carries about 3,000 bunches. They travel at 99.9999991 percent the speed of light. So they are able to complete 11,245 laps a second. In 10 hours of operation, the beam could travel to Neptune and back.

At four major intersections along the way, the parallel beams will cross one another and collide. The crash sites are the business end of the machine. That is where they put the detectors.

"Think of oranges," Evans said. "You collide two oranges together, you get a lot of pulp. We're not so interested in the pulp. What we want to do is see what happens when the pips — the seeds — hit each other."

And how many times will these pips collide? That would be 600 million collisions a second. The good head-on-smashup will erupt into a cloud of scattering particles, and the detectors (and their computers) will attempt to record the trajectories, energies, speeds, decays.

In one of the very useful cartoon books produced by the CERN public relations staff, an illustration shows a stack of 3 million CDs that is equal to the data flow from a year's worth of collider experiments. It is 12 miles tall.

But the general idea is this. "Humans have always asked, 'Where do we come from?' " Cousins said. "And this is the way that physicists ask that question."

The Large Hadron Collider will not operate at full intensity for a year, and so many variables could hold up its work. But the physicists at CERN have reached a milestone. Now that the machine has been turned on, Cousins said, "the trick for us is to be as full of wonder as we can be — and simultaneously as skeptical as you can get."