1. Cosmological Background

Question 1

What happens to the Hubble constant at very large distances/early times?

Answer 1

It is no longer constant

Question 2

What happens to light as it travels through an expanding universe?

Answer 2

It is stretched to longer wavelengths
- The further it travels, the more it is redshifted

Question 3

What is the value of redshift now, and at the BB?

Answer 3

Now: z=0
BB: z=infinity

Question 4

What happens to the Universe as we look at higher redshifts

Answer 4

It is smaller and younger

Question 5

State what the Universe contains

Answer 5

Matter (baryonic and dark), radiation, and dark energy

Question 6

What does matter interact with?

Answer 6

All matter interacts with gravity
- Baryonic matter interacts with electromagnetism
- DM: 23%, BM: 0.4%

Question 7

Describe dark energy and the percentage of the universe

Answer 7

It acts as a pressure which resists gravity
- 73%

Question 8

Describe radiation and the percentage of the universe

Answer 8

Very small component of the Universe but most relevant after BB
- 0.0005%

Question 9

Describe the relationship between the energy density and mass, radiation and dark E with relationship to the scale factor

Answer 9

Mass: a^-3
Rad: a^-4
Dark E: a^0

Question 10

Describe how the different Universe components changed over time

Answer 10

Radiation dominated for a short period after BB
Then Matter dominated for 8Gyr
Then Dark E dominated for 5Gyr

Question 11

State the equation of state and its values for matter, radiation and cosmological constant

Answer 11

P = wε
- w = eqn of state parameter
Matter: w=0
Radiation: w=1/3
Λ: w=-1

Question 12

Describe the properties which define the critical energy density

Answer 12

Flat (k=0)
Static (ä =0)
Matter dominated (Λ=0)

Question 13

How is the density parameter defined?

Answer 13

Ω =ε / ε_crit
- Can also equal the same with the energy density substituted for density