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What does modern science tell us about the history of

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Unformatted text preview: What does modern science tell us about the history of the universe? • The entire universe is expanding • The fact that distances between galaxies are increasing implies that these distances must have been smaller in the past. If we go back far enough, there must have been a time when galaxies, or the materials from which they were made, were all on top of one another, marking the beginning of the universal expansion • Big Bang – happened 14 billion years ago and universe is 13.7 billion years old • If Big Bang occurred, universe should have begun with its matter compressed to extremely high temperature and density • Cosmic microwave background • Evidence for Big Bang: detected radiation left over from Big Bang and chemical composition • Only H and He • While the universe as a whole has continued to expand, individual galaxies and their contents do not expand • Nuclear fusion: the process in which lightweight atomic nuclei smash together and stick (or fuse) to make heavier nuclei • During most of a star’s life, nuclear fusion combines H nuclei to make He nuclei • Massive stars die in titanic explosions called supernovae • Galaxies reuse material expelled from dying stars to make new generations of stars and planets • All elements were manufactured by stars • Most of the material from which we and our planet are made was created inside stars that died before the birth of our Sun • Many star systems have the necessary raw materials to build Earth-like planets and life • Conclusion: On a cosmic calendar that compresses the history of the universe into 1 year, human civilization is just a few seconds old, and a human lifetime lasts only a fraction of a second. How big is the universe? • Our observable universe , the portion of the entire universe that we can potentially observe, consists only of objects that lie within 14 billion light-years of Earths • We lie at the center of our own observable universe • Expansion rate had to be “just right” for galaxies to form, a fact that looks even more remarkable when you take into account the recently discovered acceleration of expansion, which also has to be of just the right value so that it would have accelerated neither too much not too little by now • Conclusion: The total number of stars in all galaxies of the observable universe is comparable to the number of grains of dry sand on all Earth’s beaches combined. How do other worlds in our solar system compare to Earth? • Four inner planets (Mercury, Venus, Earth, and Mars) are made almost entirely of metal and rock. They have solid surfaces and their atmospheres are quite thin compared to the planets themselves. Higher densities. (Terrestrial planets – Earth-like) • Four outer planets (Jupiter, Saturn, Uranus, and Neptune) are made from hydrogen, helium, and hydrogen compounds. Lower densities....
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