E.4 Cosmology

E.4.8 Distinguish between the terms open, flat and closed when used to describe the development of the universe.

A Closed Universe is one that will eventually collapse back on itself

An Open Universe is one that continues to expand. Gravity slows the rate of expansion but is not strong enough to stop it

A Flat Universe is somewhere between the 2 possibilities the force of gravity slows the expansion, but theoretically will take an infinite amount of time to come to rest.

E.4.9 Define the term "Critical density" by reference to a flat model of the development of the universe.

Critical Density - is defined as the theoretical value of the density that would create a flat universe. It is approximately 5 x 10^-26 kg m^-3 (Extremely Small)

E.4.10 Discuss how the density of the universe determines the development of the universe

The Outcome of the universe depends on the Mass Density, the amount of matter available per unit volume available to provide gravitational attraction.

Critical density = Flat Universe

More than Critical Density = Closed Universe

Less than Critical Density = Open Universe

Ω = Density of the Universe / Critical Density

Closed Universe: Ω > 1

Open Universe: Ω < 1

Flat Universe: Ω = 1

E.4.11 Discuss problems associated with determining the density of the universe


The main problem with determining the density of the universe is the fact that we can only 'see' approximately 10% of the universe. This is because the majority of the universe is made up of 'Dark Matter'

Dark Matter - Mass that is too cool for radiation to be detected

Macho's and Wimp's serve as hypothetical particles which serve as an alternate solution to the problem of Dark Matter.

MACHO's - Massive Astronomical Compact Halo Objects

WIMP's - Weak Interacting Massive Particles