Scientists at the world's largest atom smasher suffered an initial setback on Tuesday in their quest to unravel the secrets of the universe, when two high-enegry proton beams failed to collide.
The European Organisation for Nuclear Research (CERN) in Geneva made two aborted attempts to collide the beams in its 27-kilometre (16.8-mile) long Large Hadron Collider (LHC) at close to the speed of light.
"They lost the beam," CERN scientist Karsten Eggert said after attempts that began at about 6.00 am (0400 GMT), then two hours later.
"We've had a few minor problems," said Paul Collier, head of CERN's beams department.
"These are the kind of things that happen when you have such a complicated machine. In one to one-and-a-half hours from now we'll inject again."
CERN has warned that it might take hours or days to line up the high energy collisions as they cautiously tread uncharted scientific territory.
The experiment is aimed at unleashing powerful but microscopic bursts of energy that would mimic conditions after the Big Bang that created the universe.
A senior scientist on the project, Steve Myers, has likened the attempt to firing needles across the Atlantic and getting them to collide half way, while the particles speed around the ring more than 5,000 times a second.
The stage beginning Tuesday, dubbed "First Physics", would mark only the beginning of an initial 18- to 24-month series of billions of such collisions.
Two separate beams of protons have been thrust at a combined speed of 7.0 teraelectronvolts (TeV) -- within a fraction of the speed of light -- in recent weeks, but without being steered into each other at that speed.
"It has been a long way to get here but it has been a very successful one and we are now ready for the collisions," said CERN Director General Rolf Heuer.
The 3.9 billion euro (5.6 billion dollars) LHC, which is located in a tunnel under the Franco-Swiss border near Geneva, ground to halt with a major breakdown within days of its launch in 2008.
The huge scientific experiment has passed several milestones since it was restarted from repairs last November, allowing physicists to start to collecting data.