For scientists, today is D-day: the long-awaited moment when they fire the first sub-atomic particles round the world's largest particle accelerator in search of the keys to the cosmos.  

Built under the fields of Switzerland by a pan-European team of physicists at a cost of £5bn, the Large Hadron Collider (LHC) will recreate conditions not seen since just after the Big Bang 14 billion years ago.  

Doing that requires a machine of truly awe-inspiring dimensions. The sub-atomic particles race round a huge vacuum-filled racetrack 17 miles in circumference, and then smash together at almost the speed of light inside detectors the size of five-storey office blocks.  

It is mind-boggling stuff - and has prompted understandable concern that scientists don't really know what they're doing, with the energies unleashed in the LHC capable of triggering the end of the world. Such fears have got short shrift from the LHC's designers, who point out that the earth is regularly hit with particles from space with energies far higher than anything attainable by the LHC.