E 4.8 - E 4.10

Graph showing the 3 possible fates of the Universe:

Taken from Chris Hamper's Physics texbook for the IB

Definitions of the three possible fates:

• Open universe
• The density of the Universe is lower than the critical density therefore the universe continues to expand
• Flat universe
• The density of the Universe is exactly at the critical density therefore the universe ceases to expand or contract.
• Closed universe
• The density of the Universe is greater than the critical density, therefore the universe would contract and may in turn lead to a "Big-crunch".

Definition of Critical Density:

• The Critical Density is the exact density of the universe required for the fate of the universe to neither expand or contract (flat fate).

How does the density of the Universe relate to its fate in terms of the critical density?:

• The density of the Universe is the deciding factor when you consider its fate in the long run. We deduce the fate of the universe by comparing its density to the critical density. If the density of the Universe is over the critical density the the universe will contract and collapse into singularity. If the density of the universe is lower than the critical density then the universe will continue to expand. If the critical density and density of the universe are identical the universe will stop expanding and turn static. Although this is highly unlikely as the density of the universe has to match the critical density EXACTLY.