SCIENTISTS began the world's largest science experiment today hoping to unlock some of the secrets of the universe.
The £5 billion Large Hadron Collider (LHC) will smash protons – one of the building blocks of matter – into each other at velocities only a fraction less than the speed of light.
In the flashes from the collisions, scientists expect to reproduce c
onditions that existed during the first billionth of a second after the Big Bang at the birth of the universe.
No one knows precisely what will come tumbling out of the primordial soup of disintegrating protons.
But the scientists have dismissed suggestions that the experiment could somehow cause the end of the world.
The LHC could help scientists explain mass, gravity, mysterious "dark matter" and why the universe looks the way it does.
It could also produce the first evidence of extra spatial dimensions and even create mini-black holes that blink in and out of existence in a fraction of a second.
The LHC, a colossal machine housed in a 27 kilometre (17 mile) tunnel under 100 metres of rock, straddles the borders of Switzerland and France between Lake Geneva and the Jura mountains.
Beams of protons will be accelerated in opposite directions through the ring-shaped tunnel, which is supercooled to just 1.9 degrees above absolute zero (minus 271C), the lowest temperature allowed by nature.
Reaching velocities of 99.99% of the speed of light, each beam will pack as much energy as a Eurostar train travelling at 150 kilometres per hour.
The particles will be brought together in four huge "detectors" placed along the ring. Each detector is like a giant microscope, designed to probe deeper into the heart of matter than has ever been possible before.
Concerns have been voiced – in particular by German chemist Professor Otto Rossler – that black holes created by the LHC will grow uncontrollably and "eat the planet from the inside".
But those involved in the project insist they have reviewed all the evidence and concluded that it poses no risk to the universe.
Particle physicist Dr James Gillies, a spokesman for the LHC, said: "We have received a lot of worried calls from people about it.
"There's nothing to worry about, the LHC is absolutely safe because we have observed nature doing the same things the LHC will do.
"Protons regularly collide in the earth's upper atmosphere without creating black holes.
"What we are looking at is a global community representing 10,000 people working in 500 universities in 80 countries, none of whom has the slightest worry about risks of this kind.
"Then we have a retired German chemist who has never published a paper in this field in his life, who has come up with this theory.
"We are very excited about the project. We hope to learn more about this wonderful universe of ours."
Turning on the LHC was nothing like as simple as flipping a switch.
A chain of smaller accelerators, built for earlier projects, were first used to speed up the proton beams to the point where they could be injected into the machine.
The start of the process involved a bottle of hydrogen gas no bigger than a fire extinguisher.
Hydrogen atoms were stripped of their electrons to produce streams of protons that are fed into accelerators of increasing size.
The last link in the chain before the LHC, the Super Proton Synchrotron (SPS), is buried underground and covers a distance of seven kilometres.
Timing between the SPS and the LHC has to be accurate to within a fraction of a nanosecond.
Today's "switch on" involved transferring a beam from the SPS to the LHC so that it is circulating around the machine in a stable fashion.
The first particle collisions are likely to take place within a few weeks.
In some cases teams of more than 2,000 collaborating scientists will be sifting and analysing data from the machine.
Most will not be at the LHC's operating base at CERN, the European nuclear research organisation, in Geneva.
A revolutionary computer network called the "Grid" – the next step beyond the World Wide Web – will make it possible for scientists all over the world to share huge amounts of processing power and carry out
much of the work on their PCs.
The cost of the LHC is mainly shared by CERN's 20 European member states, which include Britain. Six "observer" nations, including the US, Russia and Japan, make significant contributions.
CERN estimates the total cost of the project to be 10 billion Swiss francs, or £5 billion. The material cost alone is put at £2.6 billion.
Britain's direct contribution to the LHC each year is £34 million.
* Kate McAlpine, a Michigan State University graduate at the European Organisation for Nuclear Research, has produced the Large Hadron Rap, a video clip which explains the CERN experiment.
Click here to watch the video