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Posted by n/a on September 21, 1998 05:58:39 UTC

This is my report for World History. It should help.

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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