GENEVA – The world's largest atom smasher made another leap forward Monday by circulating beams of protons in opposite directions at the same time and causing the first particle collisions in the $10 billion machine after more than a year of repairs, organizers said.

The true test of the Large Hadron Collider will come in the first two months of 2010, when scientists plan to start deliberately crashing protons into each other to see what they can discover about the makeup of the universe and its tiniest particles.

The collisions — seen by massive detectors — were a side effect of the quick advances being made by the LHC during its startup phase, which began Friday night, said Rolf Heuer, director-general of the European Organization for Nuclear Research, known as CERN.

"It's a great achievement to have come this far in so short a time," said Heuer. "But we need to keep a sense of perspective — there's still much to do before we can start the LHC physics program."

Collisions were recorded in all four of the main detectors at "experiments" in rooms the size of cathedrals about 100 meters (300 feet) underground around the collider.

"This is great news, the start of a fantastic era of physics and hopefully discoveries after 20 years' work by the international community to build a machine and detectors of unprecedented complexity and performance," said Fabiola Gianotti, who represents the Atlas partical physics experiment for about 2,000 other scientists.

"It was standing room only in the ALICE control room and cheers erupted with the first collisions," said Juergen Schukraft, spokesman for that experiment, which involves heavy ion physics. "This is simply tremendous."

A CERN statement said the simultaneous beams and collisions demonstrate the excellent performance of the control system.

While the initial collisions were a side effect, intentional hits could begin within the next 10 days, mainly to check how the machine is working, said CERN spokesman James Gillies.

Ultimately, the collider aims to create conditions like they were 1 trillionth to 2 trillionths of a second after the Big Bang — which scientists think marked the creation of the universe billions of years ago. Physicists also hope the collider will help them see and understand other suspected phenomena, such as dark matter, antimatter and supersymmetry.

The collider was started with great fanfare Sept. 10, 2008, only to be heavily damaged by an electrical fault nine days later. It took 14 months to repair and add protection systems to the machine before it was restarted.

The protons were traveling Monday at almost the speed of light — 11,000 times a second in each direction around the 27-kilometer (17-mile) tunnel under the Swiss-French border at Geneva.

Initial signs are very good, physicists told a news conference. The beam is of superb quality, with the protons tightly packed into hairlike lines and guided by some 1,600 superconducting magnets — 15 meters (50 feet) long — operating at temperatures colder than outer space for maximum electrical efficiency.

So far the machine is operating at 450 billion electron volts of energy, which is relatively low compared with its design capability of more than 14 times that. It soon will overtake the world's current most powerful accelerator, the Tevatron at Fermilab outside Chicago, which operates at 1 trillion electron volts, or TeV.

Myers said the CERN collider should be ramped up to 1.2 TeV by Christmas. CERN might decide to make the first collisions at the current low energy or at 1.2 TeV, but that will be more for calibration purposes than for making scientific discoveries, he said.

Physicists said the discoveries could begin in the first half of next year when the collider reaches 3.5 TeV. CERN is hoping to have the first collisions at that energy in January or early February, said Gillies.

"That would really mark the start of the research program," he said.

Myers said the collider may even go up to 5 TeV before the end of 2010.

Tejinder S. Virdee, a physicist from London's Imperial College who represents more than 2,000 scientists on CMS, another of the experiments with its own detectors at CERN, said it could take several years before the collider discovers the elusive Higgs boson, a particle that theoretically gives mass to other subatomic particles, and thus everything in the universe.

That is because the Higgs boson is believed to be hard to see and needs powerful energy to be revealed, Virdee said.

"This is going to take a few years," he said.

Director-General Heuer said CERN was being as cautious as a driver would be with the first production model of a new car.

"We'll never accelerate this the first time with a kick-start to its maximum velocity," he said.

Once it is tested out, he added, "we can open windows into new physics and that could happen already next year. It depends on how kind nature is to us."