Never before has such attention been focused on the click of a mouse. Yesterday, the click in question started up the biggest, most complicated machine in the world, the $10bn Large Hadron Collider, which was put through its paces for the first time at Cern, the European nuclear research organisation in Geneva.

The man with his finger on the button was Lyn Evans, a Welsh engineer who has devoted 14 years of his life to the machine. The moment came at 8.32am UK time and was broadcast around the world, and via videolink to more than 300 journalists who had descended on the laboratory to witness the event.

The LHC lies 100 metres beneath fields and farmland, where it occupies a 17-mile (27km) circular tunnel carved through rock and sandstone.

When it is working at full speed, it will be the most powerful particle collider on the planet. Inside, it will crash subatomic particles together with enough energy to re-create the intense conditions that existed one trillionth of a second after the big bang.

Yesterday, the scientists' ambitions were more modest. Before the machine can be put to work, its makers had to take it for a test drive.

The goal was to send beams of protons around the collider's hollow ring in both directions, to make sure there were no obstructions and to check that powerful superconducting magnets surrounding the ring can steer the beams with exquisite precision. When Cern attempted this on an older, less powerful collider in 1996, it found two beer bottles stuck inside the ring.

Yesterday, the tests went more smoothly than many scientists dared hope for. At 9.28am UK time, two spots flickered on to a screen in the control room, one spot caused by the beam on the way in, the other as it completed its first lap. Cheering, relieved scientists clapped and slapped each other on the back. The test had taken less than one hour. "My first thought was one of relief. I'm too preoccupied at the moment to have emotions," said Evans, who later confessed to laying a bet with fellow physicist Steve Meyers, head of Cern's accelerator and beam operations, that he could get the beam to circulate within an hour.

Moments after the test was declared successful, scientists in the control room cracked open bottles of champagne.

Verena Kain, a physicist on the machine, said: "I didn't believe it, I had to see it a second time. Everybody is just floating right now. It's a first step, but it's fantastic it works so well."

By 2pm UK time, the scientists had sent a beam of protons around the machine in the opposite, anticlockwise direction to the first beam.

David Evans, a physicist from the University of Birmingham, who works on one of the machine's giant detectors, said: "It's gone so well I'm optimistic we can probably do low-energy collisions within days. We could be looking at high-energy collisions within weeks." Now the real work begins. Scientists will spend the coming days and weeks fine-tuning the machine and testing the four huge detectors, which will sift through the subatomic debris of the collisions for evidence of new physics.

Tejinder Virdee, a physicist at Imperial College London and head of one of the LHC's detector groups, said: "With the LHC, we will be able to look deeper into matter, and look further back in time than ever before.

"Particle physics is a modern name for the centuries-old effort to understand the laws of nature."

Within weeks, the machine could produce particles of dark matter, a mysterious substance that stretches through the universe and clings around galaxies. The discovery would be profound.

Astronomers know that normal matter, the stuff of stars and planets, makes up only 5% of the observable universe. Dark matter accounts for a further 25%, with the remaining 70% being the even more exotic dark energy, which drives the expansion of the cosmos.

By creating a microcosm of the big bang, scientists hope the machine will explain how the forces of nature became what they are today.

The machine will also hunt the famed Higgs boson, or "God particle". Named after Peter Higgs, an Edinburgh University physicist, the Higgs boson is crucial to understanding the origin of mass.

Cern thought it had caught a glimpse of the Higgs particle before with its previous particle collider in 2000.

It will now race against scientists at the American Fermilab, near Chicago, which is working around the clock to discover the particle first. "This is a unique machine and it will certainly advance the knowledge of mankind. But we also know that pushing technology to the limit always has spinoffs. We don't know what the LHC will bring apart from wonderful science, but we're already working on a far more powerful system than the internet. Where we lead, others will follow," said Evans.