what is the ultimate fate of the universe? nick kaiser
Post on 19-Dec-2015
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What is the Ultimate Fate of the Universe?
Nick Kaiser
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The Universe is full of galaxies
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The Universe is Expanding!
Expansion discovered in the ‘30sExtrapolating back, the “Big Bang” occurred about 13 billion years ago
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Big-bang cosmology
• Future evolution depends on:– How fast is the expansion?
– How much stuff is there to pull it back?
• The key question: Does the universe have “escape velocity”?
• Or: Does the density of stuff exceed the “critical value”?
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How much matter is there….
• Ordinary matter (atoms, ions, electrons)– Galaxies (1% of critical density)
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The Coma clusterOptical image X-ray image
Roughly 4 times as much mass in hot gas as in all the galaxies
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How much matter is there….
• Ordinary matter (atoms, ions, electrons)– Galaxies (approx1% of critical density)– Hot gas (approx 3%)
• Much too small to make the universe recollapse
• 4% total value also confirmed independently from physics of the first 3 minutes
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CL0024
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A2218
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calvin
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How much matter is there….
• Ordinary matter (atoms, ions, electrons)– Galaxies (1% of critical density)– Hot gas (approx 3%)
• Dark Matter– Approx 23% of critical density– Still too little to halt the expansion
• Is that all?
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Accelerating expansion
• Observers were using supernovae to measure the expansion history
• They expected to see the expansion slowing down because of gravity
• They found the opposite - the expansion is speeding up!
• The future expansion will be dominated by “Dark Energy”
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“Concordance” cosmology
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How will the Universe end?
• Currently favored model says the universe will expand forever– Most of all the galaxies we see will disappear– The future is cold, dark and rather lonely
• However– Observations are difficult and uncertain– The theory is incomplete– So expect future surprises
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Dark Energy• The new ingredient
– Rebirth of an old idea• Invoked by Einstein as the “cosmological constant”
– His self-confessed “biggest blunder”
• And by Fred Hoyle in the “steady state cosmology”
– Gained credibility in the ‘80s when applied to the early universe in the “inflationary theory”
• Solved many problems
– Similar to a magnetic field• Allows creation of matter from nothing
• Causes a repulsive gravitational field
• Leads to accelerating expansion
– Now seen in the recent expansion history