What is the Ultimate Fate of the Universe? Nick Kaiser

The Universe is full of galaxies

The Universe is Expanding! Expansion discovered in the ‘30s Extrapolating back, the “Big Bang” occurred about 13 billion years ago

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”?

How much matter is there…. Ordinary matter (atoms, ions, electrons) –Galaxies (1% of critical density)

The Coma cluster Optical imageX-ray image Roughly 4 times as much mass in hot gas as in all the galaxies

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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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?

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”

“Concordance” cosmology

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

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