It is now generally agreed among both astronomers and physicists alike that the Universe was created some 10 to 20 billion years ago in a leviathan explosion dubbed the "Big Bang". The exact nature of the initial event is still cause for much speculation, and it's fair to say that we know little if anything about the first instant of creation. Nevertheless we do know that the Universe used to be incredibly hotter and more dense than it is today. Expansion and cooling after this cataclysm of the Big Bang, resulted in the production of all of the physical contents of the Universe which we see today. Namely: light in the form of "photons"; matter in the form of "leptons" (electrons, positrons, muons) and "baryons" (protons, antiprotons, neutrons, antineutrons); more esoteric particles like "neutrinos" and perhaps some exotic "dark matter" particles; and the subsequent formulation of the Universe's first chemical elements.