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Theories of how the Universe Began BEGINNING WITH A BANG Big Bang Theory Scientists believe Universe started with a big explosion 15 billion years ago Matter, gravity, and electromagnetism were created by the blast Universe expanded Edwin Hubble First to discover Universe expanding Distant galaxies moving away from Earth faster than close ones Discovery of cosmic background radiation supported Hubble’s theory Four basic forces control the Universe: gravity, electromagnetism, strong nuclear forces, weak nuclear forces Hubble Cont. As Universe expanded, it began to cool One billionth years old, started condensing into galaxies, stars and planets Oscillating (Big Squeeze Theory) Expansion of the Universe (Big Bang) will be followed by a contraction or a squeezing of the Universe This is caused by gravity Farther planets will slow down and stop, then fall toward the center Planets will collide A new Big Bang will occur Steady State Theory Challenged Big Bang Theory in 1940 Scientists believe that Universe did not begin with an explosion Believe Universe will exist forever (steady state) Theory discarded after discovery of cosmic background radiation Today Scientist believe a fraction of a second after Big Bang explosion, gravity emerged At birth, Universe was 180 billion degrees Fahrenheit 60 seconds later it cooled to 18 billion degrees Fahrenheit Today average temperature of Universe is 454 degrees Fahrenheit Measuring Vast Universe Basic unit of distance: light year Light year – the distance light travels in one year or about 6 trillion miles.