Scientists will today aim to make particles collide at close to the speed of light to create mini-versions of the 'Big Bang'.
"We are opening the door to new physics, to a new period of discovery in the history of humankind," says Professor Rolf-Dieter Heuer, director-general of CERN, the European Organisation for Nuclear Research on the Franco-Swiss border near Geneva.
Particle beams will start circulating in opposite directions around the 27-kilometre oval tunnel of the Large Hadron Collider, the LHC, at an energy of 3.5 Tera (billion billion) electron volts, or TeV.
When particles smash into each other, each collision will create an explosion that will enable scientists linked to the project to track and analyse what happened a fraction of a second after the real Big Bang, 13.7 billion years ago.
The scientists hope their experiment will throw light on key mysteries of the cosmos like the origin of the stars and planets and what is dark matter.
Over the next few years, the beam energy will be raised to 7 TeV and the LHC is set to see many billions of collisions providing vast amounts of data about the primordial blast and what came after.
Lining up needles
But it may well be hours or even days before the first collisions happen in the world's biggest scientific experiment.
"Just lining the beams up is a challenge in itself; it's a bit like firing needles across the Atlantic and getting them to hit head-on half way," says Dr Steve Myers, CERN's director for accelerators and technology.
The vast amount of information the collisions will produce will have to be processed, with findings checked and rechecked, which means it could be months or even years before CERN can firmly announce discoveries.
Physicists are focusing on identifying the Higgs boson. The particle, named after Scottish professor Peter Higgs who was one of the first to postulate its existence, is thought to make possible the conversion of matter created by the Big Bang into mass.
Earlier bids have failed to find the boson, whose presence would have turned the blast's gaseous debris into galaxies and their stars and planets, and made possible the eventual emergence of life on Earth and perhaps elsewhere in the cosmos.
CERN scientists also hope to find concrete evidence of the dark, or invisible, matter that is believed to make up some 25% of the universe.
They also hope that, further down the road in the 20 years of the projected life of the LHC, real proof of the existence of dark energy, which accounts for 70% of the cosmos, will emerge.
But it could also tap into science fiction, and the predictions of many cosmologists, about the existence of other, parallel, universes, of further dimensions beyond the five known to exist, and about what was before the Big Bang.