Module 8: Modelling the universe

Question 1

Olber’s paradox

Answer 1

For an infinite, uniform and static universe, the night sky should be bright because of light received in all directions from stars.

Question 2

Hubble’s law

Answer 2

Speed of recession of galaxy is proportional to distance of galaxy.

Question 3

The cosmological principle

Answer 3

The universe is:
Isotropic: on a large scale the universe looks the same in all directions.
Homogeneous: on a large scale, the matter is spread out evenly in the universe.
Universal: all physical laws that apply on the Earth are equally valid in the rest of the universe.

Question 4

Critical density

Answer 4

The density of the universe that will give rise to a flat universe.

Question 5

Astronomical unit

Answer 5

The mean distance between the Earth and the Sun. 1.49x1011 m

Question 6

Parsec

Answer 6

The distance that gives a parallax angle of 1 arc second. 3.1x1016 m

Question 7

Light year

Answer 7

Distance travelled by light (in a vacuum) in a time of 1 year. 3.0x108 m