This picture is about the question of the cosmological density parameter of our universe.
The density parameter is a parameter that measures the average density of our universe. There are three different kinds.
Ωtot> 1; The density parameter is bigger than 1; then the universe expands and later contracts. This is because the density is high enough for gravity to letting the universe contract. This would end in a Big Crunch, a kind of “Reverse Big Bang”. Thus our universe would have a positive geometry, like a sphere. (In the background there is a sphere in this picture.)
Ωtot= 1; The density parameter is equal to 1; then the universe expands until forever. The density would be too low to letting gravity allow to letting the universe contract. This end is called Big Chill. Thus our universe would have a flat geometry.
Ωtot< 1; The density parameter is smaller than 1; then the universe expands and later expands so fast that galaxies and matter get ripped apart. Then gravity is far weaker than expansion. This end is called Big Rip. Thus our universe would have a negative geometry, like a hyperbolic paraboloid or saddle.
Here are the geometries:
Here is a short summary of the three possible models:
The thing on the left is an accelerating universe, the right thing is a coasting universe and the spehere in the background is a decelerating universe.
Then, did you nothice the colours? The spehere is blue – But why? It has something to do with redshift.
Red light has a longer wavelength, whilst blue has a shorter wavelength. If something moves very fast towards you it will appear more blueish, if something moves very far away from you it will appear reddish. This picture describes it pretty well:
This is because of the Doppler effect:
Thus the sphere is blue, because all the galaxies are moving towards each other. In the right object there the galaxies are pink, a kind of mixture between drifting away and coming closer. In the left object there the galaxies are utterly red as symbol for redshift and drifting away.
Then the ghost symbolizes a special figure-background relationship.
© Dywiann Xyara 2018