A Singular Big Bang
15 billion BC
-1015000 -1015000

NAT

	Most scientists believe the universe began from a "singularity," an impossible-to-imagine point so small that it had no size at all. Then that point, which they think contained everything that there is in the universe -- matter, energy, and even time and space -- exploded with an enormous rush.
	Scientists don't know what caused this point to explode in a "Big Bang" about 15 billion years ago, and they don't know what -- if anything -- existed before the bang occurred, or even if there was a "before" before it happened.
	So-called "black holes" are believed to be similar to this singularity except that they contain far less of the universe. Black holes are believed to be collapsed stars of such density and gravitational strength that once caught, nothing -- not even light -- can escape their pull.
	Scientists believe that as the Big Bang, which started the universe, exploded outward in a blaze of energy, the universe was blown up like a child blows up a balloon.
	But as it expanded -- and continues to expand -- the universe rapidly cooled and some of the energy condensed into tiny particles.  Then an unexplained phenomenon called electromagnetic force began pulling these tiny particles together into hydrogen atoms.
	Gravity, another mysterious force, caused more and more atoms to gather together.  The larger these clouds of atoms, the stronger the gravitational force became, until the gravity squeezed the atoms so hard that it sparked a nuclear reaction and the clouds became huge balls of fire -- the first stars.
	These stars burned at tremendously high temperatures as their hydrogen atoms joined to form helium atoms in a process called fusion.  Small stars can burn like this for billions of years, until they run out of hydrogen.  Then they cool down and collapse, becoming white dwarfs.  But the largest stars burn up much more quickly, then collapse inward, fusing their atoms together into heavier elements.  Finally they explode into supernovas, scattering new atoms of copper, gold, uranium and many other elements into the surrounding galaxy.