Mar_6 - Complete History of the Universe (Abridged)...

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Complete History of the Universe (Abridged) Thursday, March 6
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The moment in time when the universe started expanding from its initial extremely dense state. t = 0 The Big Bang
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t=0: The Big Bang How do we know that this happened? Universe was denser in the past; if we daringly extrapolate backward to infinite density , that was a finite time ago.
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t=0: The Big Bang Why do we care that this happened? If the universe had remained dense, it wouldn’t have cooled enough for nuclei, atoms, galaxies, and us us to form. (Speaking to an audience of humans, I make no apologies for my human chauvinism.)
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t = 10-35 seconds Inflation A brief period when the expansion of the universe was greatly accelerated.
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t=10-35 sec: Inflation How do we know? The universe is nearly flat now; it was insanely close to flat earlier. Inflation flattens the universe.
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t=10-35 sec: Inflation Why do we care? If the universe hadn’t been flattened, it would have long since collapsed in a Big Crunch or fizzled out in a Big Chill . No inflation, no galaxies.
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t = 7 minutes Primordial Nucleosynthesis A period when protons and neutrons fused to form helium.
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Primordial Nucleosynthesis How do we know? The earliest stars contain 75% hydrogen, 25% helium, as predicted from primordial nucleosynthesis. (Later stars contain more
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Mar_6 - Complete History of the Universe (Abridged)...

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