FACTBOX - What is the Big Bang?

(Reuters) - The European Organisation for Nuclear Research, known as CERN, on Wednesday began an experiment to recreate conditions surrounding the Big Bang, which scientists believe gave birth to the universe.

Its Large Hadron Collider (LHC) will seek to collide two beams of particles at nearly the speed of light. Scientists will circulate a beam in one direction around the accelerator, then the other, later sending beams both ways to cause collisions.

Following are some facts about the Big Bang and CERN's particle-smashing experiment:

* RECREATING THE BIG BANG:

-- The final tests involved pumping a single bunch of energy particles from the project's accelerator into the 27-km (17-mile) beam pipe of the collider and steering them counter- clockwise around it for about 3 km (2 miles).

-- The collider aims to simulate conditions milliseconds after the "Big Bang" which created the universe around 13.7 billion years ago.

-- The collisions, in which both particle clusters will be travelling at the speed of light, will be monitored on computers at CERN and laboratories around the world by scientists looking for, among other things, a particle that made life possible.

-- The elusive particle, which has been dubbed the "Higgs Boson" after Scottish physicist Peter Higgs who first postulated nearly 50 years ago that it must exist, is thought to be the mysterious factor that holds matter together.

* WHAT IS THE BIG BANG?