Geometry of the Universe

							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 image                       X-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
CL0024
A2218
calvin
   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