Cosmology

Question 1

Obler’s paradox

Answer 1

If universe is infinitely large, old, homogenous and isentropic then entire sky should be as bright as the sun
Sky is dark at night
Universe isn’t infinitely old or large

Question 2

Critical density

Answer 2

(3H0^2)/(8Pi*G)
Density/critical density <1 open universe
=1 critical
<1 closed

Question 3

Hubble flow

Answer 3

1/H0

Doesn’t affect gravitationally bound systems eg galaxies

Question 4

Evidence of the Big Bang (3)

Answer 4

Abundance of light elements
Cosmic microwave background
Expanding universe