: The earliest record of anything, anything at all, was the "Big Bang." : The "Big Bang" was a cataclysmic explosion. This occurred approximately: 16 billion years ago.: For an incomprehensibly small fraction of a second (10^-35 seconds),: the universe is an infinitely dense, hot fireball. One millionth second after the: "Big Bang" the universe continued to expand, just not as quickly. As it: expanded, it became less dense and cooled (10^-6 seconds). With the: expansion, came the basic forces of nature. They were gravity,: electromagnetic forces, and the strong forces that held nuclei together. After: the first second passed, the universe developed basic particles, like quarks,: electrons, photons, neutrinos and less familiar types. Three seconds after the: explosion, protons and neutrons came together to form the nuclei of simple: elements: hydrogen, helium and lithium. It would take another 300,000 years: for electrons to be captured into orbits around these nuclei to form stable: atoms. The first major era in the history of the universe happened 10,000: years after the explosion, in which most of the known energy was radiation. : A few different types of light waves created were X rays, radio waves and: ultraviolet rays. As the universe expanded, and the light waves were: stretched and diluted until today. As the waves continued to stretch: microwaves were formed. At 300,000 years, the energy in matter and the: energy in radiation were equal, but as the universe continued to expand, the: energy became less. At about this time, neutral Atoms formed as electrons: linked up with hydrogen and helium nuclei. The microwave background: radiation hailed from this moment and thus gives us a direct picture of how: matter was distributed at this early time. The creation of galaxies occurred: 300 million years after the "Big Bang". Gravity made small irregularities in: the density of the primordial gas. Even as the universe continued to expand: rapidly, pockets of gas became more and more dense. Stars ignited within: these pockets, and groups of stars become the earliest galaxies. This point is: between 12 and 15 billion years before today. : Five billion years ago our sun was created. The sun was formed within: a cloud of gas in the spiral arm of the Milky Way Galaxy. (A huge circular: formation of gas and debris that swirled around this new star gave birth to the: planets, moons, and asteroids. Approximately 3.8 billion years ago the earth: cooled and an atmosphere developed. Microscopic living cells, neither plants: nor animals, begin to evolve and flourish in earth's many volcanic: environments. : In 1917 Einstein and others applied General Relativity to the structure: and evolution of the universe. The theory called the "Big Bang" was: formulated in 1922 by the Russian mathematician and meteorologist: Alexander Friedmann. Friedmann started with Einstein's equations of: Realitivity. He found a solution to them, in which the universe began in a: state of extremely density and temperature. It expanded in time, thinning and: cooling. One of the most stunning successes of the Big Bang theory is the: prediction that the universe is approximately ten billion years old. This: approximation was obtained by the rate at which distant gallaxies are flying: away from each other. : According to the "Big Bang" theory the universe may keep expanding: forever. Its inward gravity is not strong enough to counteract the outward: expantion, or maybe the universe will reach a maximum point of expansion: and start collapsing, growing denser and denser, eventually disrupting: galaxies, stars, planets, people, and eventually even individual atoms. The: fate of our universe can be determined by measuring the density of matter: versus the rate of expansion. Much of modern cosmology has been an: attempt to measure these two numbers with much better accuracy. The: numbers say that our universe will never stop expanding. It will continue to: grow thinner and cooler.

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