The skeptics theorize that a byproduct of the collisions could be micro black holes, subatomic versions of collapsed stars whose gravity is so strong they can suck in planets and other stars.

"It's nonsense," said James Gillies, chief spokesman for CERN, before Wednesday's start.

CERN is backed by leading scientists like Britain's Stephen Hawking in dismissing the fears and declaring the experiments to be absolutely safe.

Gillies told the AP that 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 accelerator itself and burrow into the rock around the tunnel.

And full power is probably a year away.

"On Wednesday we start small," said Gillies. "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."

He said a good result for Wednesday would be to have one beam going all the way around the tunnel in a counterclockwise direction. If that works, the scientists will then try to send a beam in the other direction.

"A really good result would be to have the other beam going around, too, because once you've got a beam around once in both directions you know that there is no show stopper," Gillies said. "It's going to work."