•General Relativity allows a repulsive term
–Einstein proposed it to allow “steady
state” universe
–He decided it wasn’t needed after Hubble Law
discovered
–
•Is
the acceleration right?
–Could
it be observational effect – dust dims distant supernova?
–Could
it be evolution effect – supernova were fainter in the past?
–So
far the results seem to stand up
•
•Still
being determined: 1) density, 2) cosmological constant
–With
cosmological constant included, can have a “flat universe” even with acceleration.
–Given
“repulsion” need to use relativistic “geometrical”
definition of flatness,
not the escape argument one given earlier.
–Energy
(and equivalent mass) from cosmological constant may provide density needed to produce flat universe.