Factbox: What Is the Big Bang?

(Reuters) - Scientists at the CERN physics research centre said on Tuesday they had found signs of the Higgs boson, an elementary particle believed to have played a vital role in the creation of the universe after the Big Bang.

Leaders of two experiments, ALTAS and CMS, revealed their answer in which finding the Higgs was a key goal for the $10 billion Large Hadron Collider (LHC), designed to re-create the conditions just after the Big Bang in an attempt to answer fundamental questions of science and the universe itself.

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

* RECREATING THE BIG BANG:

- Tests have 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 travel around the speed of light, are monitored on computers at CERN and laboratories around the world by scientists looking for, among other things, a particle that made life possible.

* HIGGS BOSON:

- The elusive particle, which has been called the "Higgs boson" after British physicist Peter Higgs, 82, a particle-physics theorist who first showed in 1964 that it must exist, is thought to be the mysterious factor that gives everything mass.

* WHAT IS THE BIG BANG?

- Recreating a "Big Bang," which most scientists believe is the only explanation of an expanding universe, ought to show how stars and planets came together out of the primeval chaos that followed, the CERN team believes.

- Its essential feature is the emergence of the universe from a tiny speck about the size of a coin but in a state of extremely high temperature and density.

- The name "Big Bang" was coined in 1949 by British scientist Fred Hoyle to disparage a then emerging theory about origins that countered his own "steady state" view: that the universe had always existed and was evolving but not expanding.

- According to the Big Bang model, the universe expanded rapidly from a highly compressed primordial state, which resulted in a significant decrease in density and temperature. Soon afterward, the dominance of matter over antimatter (as observed today) may have been established by processes that also predict proton decay. During this stage many types of elementary particles may have been present. After a few seconds, the universe cooled enough to allow the formation of certain nuclei.

- The theory predicts that definite amounts of hydrogen, helium and lithium were produced. Their abundances agree with what is observed today. About a million years later the universe was sufficiently cool for atoms to form.

* WHAT IS CERN:

- CERN, the European Organisation for Nuclear Research, is one of the world's largest centers for scientific research. Its business is fundamental physics, finding out what the universe is made of and how it works.

- Founded in 1954, the CERN Laboratory sits astride the Franco-Swiss border near Geneva. It was one of Europe's first joint ventures and now has 20 member states, plus six actively participant observers including the United States and Russia.

Sources: Reuters/Britannica.com/CERN/www2.ph.ed.ac.uk/peter-higgs/