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This core of the world's largest superconducting solenoid magnet is a key component of the Large Hadron Collider. ((AP Photo/Keystone, Martial Trezzini))

Scientists will launch an experiment in a tunnel deep beneath the French-Swiss border Wednesday, hoping to find evidence of extra dimensions, invisible "dark matter," and an elusive particle called the "Higgs boson."

And although leading physicists such as Stephen Hawking say the atom-smashing experiment will be absolutely safe, some skeptics fear the proton collisions could unleash microscopic black holes that would eventually doom the Earth.

The most powerful atom-smasher ever built will produce collisions of protons travelling at nearly the speed of light in the circular tunnel, giving off showers of particles that will provide more clues about how everything in the universe is made.

In the $10 billion US project — the most extensive physics experiment in history — the Large Hadron Collider will come closer to re-enacting the "big bang," which, the theory states, was a colossal explosion that created the cosmos.

The project, organized by the 20 member nations of the European Organization for Nuclear Research — known by its French initials CERN — has attracted researchers of 80 nationalities. Some 1,200 are from the United States, an observer country that contributed $531 million US.

The collider is designed to push proton beams close to the speed of light, moving around the 27-kilometer tunnel at 11,000 times a second when at full power.

Smaller colliders have been used for decades to study the atom. Scientists once thought protons and neutrons were the smallest components of an atom's nucleus, but experiments have shown they are made of still smaller quarks and gluons, and that there are other forces and particles.

The CERN experiments could reveal more about dark matter, antimatter and possibly hidden dimensions of space and time. It could also find evidence of the hypothetical particle called the Higgs boson, which is sometimes called the "God particle." It is believed to give mass to all other particles, and thus to matter that makes up the universe.

Two beams of protons will travel in two tubes about the width of fire hoses, speeding through a vacuum that is colder and emptier than outer space. Their trajectory will be curved by supercooled magnets to guide the beams. The paths of these beams will cross, and a few protons will collide. The two largest detectors, essentially huge digital cameras weighing thousands of tons, are capable of taking millions of snapshots a second.

Naysayers' theory called nonsense

Some skeptics have said the collisions could result in tiny black holes — subatomic versions of collapsed stars with gravity so strong they can suck in planets and other stars.

"It's nonsense," said CERN chief spokesman James Gillies. Leading scientists like Hawking agree.

Gillies said the most dangerous thing that could happen would be if a beam at full power were to go out of control, and that would only damage the collider itself and burrow into the rock around the tunnel. Full power is probably a year away.

"On Wednesday, we start small," Gillies said. "What we're putting in to start with is one single low intensity bunch at low energy and we thread that around. We get experience with low energy things and then we ramp up as we get to know the machine better."

Huge amounts of data will pour in — so much that the lab's computers can't sift through it all. Scientists, who will monitor the experiment at above-ground control centres, have devised a way to share the load among dozens of leading computing centres worldwide.

The result is the "LHC Grid," a network of 60,000 computers that will analyze what happens when protons are hurled at each other. That computing power is needed if scientists are to find what they are looking for among the mountains of data.