The Life of the Universe From Beginning to End.
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Transcript of The Life of the Universe From Beginning to End.
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The Life of the Universe
From Beginning to End
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• Early Universe is extremely hot and dense
• All 4 forces were merged• As Universe cooled,
forces became unique• Energy of photons high
enough to create matter and vice versa
• GUT – strong and electroweak forces united
• SuSy – GUT and Gravity united
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The Big Bang Theory
• The early Universe was exceedingly hot and dense
• Big Bang theory explains how the early Universe cooled and evolved into the Universe we observe today
• Relies on Theoretical and Observational data
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Planck Era
• t < 10-43 s
• T > 1032 K
• Current physics is unable to understand times before the Planck era– Need to unite physics of large
scales (general relativity) with physics of small scales (quantum mechanics)
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GUT Era
• 10-43 s < t < 10-38 s
• 1029 K < T < 1032 K
• Supersymmetry force splits into GUT force and gravity
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Electroweak Era• 10-38 s < t < 10-10 s
• 1015 K < T < 1029 K
• GUT force splits into strong and electroweak forces– Huge release of energy
Inflation
• Inflation expands Universe at exponential rate
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Particle Era• 10-10 s < t < 10-3 s• 1012 K < T < 1015 K• Electroweak splits into weak
force and electromagnetism– All four forces distinct
• T too low for spontaneous conversion of photons to particles
• Photons became quarks, which merge into protons and neutrons
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Era of Nucleosynthesis• 0.001 s < t < 5 min
• 109 K < T < 1012 K
• Fusion begins– T still so high that most He
nuclei will break apart again
• Expansion reduces density so fusion ceases despite T being so high
• 75% H, 25% He, trace others
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Era of Nuclei• 5 min < t < 380,000 years
• 3000 K < T < 109 K
• Photons still hot enough to ionize, so electrons and nuclei stay separated
• Photons cannot travel far because they are scattered by electrons
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Era of Atoms• 380,000 yrs < t < ~109 yrs
• T < 3,000 K
• T drops low enough for atoms to form
• With electrons bound to nuclei, photons can travel long distances– Cosmic Microwave
Background
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Era of Galaxies• t > 109 years
• Universe filled with nearly homogeneous distribution of matter and dark matter after era of atoms
• Slightly overdense regions collapse to form first stars and galaxies
• Gravity dominates on large scales
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A Few Questions
• Where did the large scale structure come from?
• Why is the Universe so uniform?
• Why is the density of the Universe so close to the critical density?
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Inflation
• Separation of strong force from GUT force would release enormous amount of energy
• Energy would cause the Universe to expand by factor of 1030 in 10-36 sec
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Inflation and Structure
• Huge expansion would make tiny quantum fluctuations in density large ripples
• A ripple the size of a nucleus would become the size of our solar system
• Creates density enhancements that give rise to the structure we observe today
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Inflation and Uniformity
• No reason why things so far away should be similar
• Things close by should be
• Inflation takes things that were very close together and spreads them out a lot– Universe was all close together, so everything
was uniform, then inflation spread it out
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Inflation and Density
• Density implies curvature of spacetime– Think general relativity– Critical density has flat
geometry
• If Universe started somewhat curved, inflation would make it seem much flatter
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Evidence for the Big Bang
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The Cosmic Microwave Background
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The CMB
• Line – a theoretically calculated thermal radiation spectrum based on the Big Bang Theory
• Dots – Observed data
• They match!
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The Fate of the Universe
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Two Things to Consider
• Expansion of the Universe
• Gravity – makes things collapse
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• Critical density – the density required to balance gravitational attraction and expansion
• Dark energy – a repulsive force opposite of gravity
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An Accelerating Universe
• SN Ia data show that we most likely live in an accelerating universe
• Acceleration is driven by some force that is not well-understood– Dark energy
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The Big Rip
The End