The Big Bang Model

Question 1

What is the cosmological principle?

Answer 1

On a large scale the universe is homogeneous and isotropic - so it doesn’t have a centre

Question 2

What does homogeneous mean?

Answer 2

Every part is the same as every other part

Question 3

What does isotropic mean?

Answer 3

Everything looks the same in each direction - so it doesn’t have a centre

Question 4

Why do astronomers disagree on the value of Hubble’s constant?

Answer 4

Distance is difficult to measure

Question 5

Why did Hubble suggest the universe was expanding?

Answer 5

He observed red shift and blue shift.

He used type 1a supernovae as standard candles

Question 6

Which galaxies show redshift?

Answer 6

all (apart from very close ones)

Question 7

What does redshift determine?

Answer 7

Recessional velocity

Question 8

What is recessional velocity?

Answer 8

How fast the galaxy is moving away

Question 9

What is proportional to recessional velocity?

Answer 9

Distance:

Further away = faster it’s travelling

Question 10

What is Hubble’s law?

Answer 10

Question 11

Why must the universe have been smaller and hotter in the past?

Answer 11

Because it is expanding and cooling down (because it’s a closed system) today.

So further back it must have been denser and hotter

Question 12

What is the Hot Big Bang theory?

Answer 12

The universe was in a hot dense state.

14 million years ago expansion started.

Question 13

What does the rate of expansion of the universe all around us show?

Answer 13

Uniform expansion away from us.

We appear to be at the centre.

Question 14

What equation can estimate the age of the universe if it has been expanding at the same rate its whole life?

Answer 14

t = distance/velocity
v = Hd
1/H = d/v
Therefore,

t = 1/H

Question 15

How do scientists describe the limit of the size of the OBSERVABLE universe?
+How old do they think it is, with and without taking into account expansion of the universe?

Answer 15

A sphere - earth in the centre.
Radius = maximum distance light can travel during the age of universe (taking into account the expansion of space).

If H = 75kms^-1 Mpc^-1,
then this sphere would have a radius of about 13 billion light years.
Taking into account the expansion of the universe, it is though to be more like 46-47 billion light years

Question 16

Why do cosmologists use dark energy to explain the expansion of the universe

Answer 16

causing expansion to accelerate.

Question 17

How are cosmic microwaves formed

Answer 17

Big Bang model predicts that:

Loads of EM radiation was produced in the early universe.

Because the universe has expanded, the wavelengths of the cosmic radiation has stretched and are now in the microwave region.

This is cosmic microwaves background radiation.

Question 18

cosmic microwave radiation is evidence for what?

Answer 18

Hot big bang

Question 19

What observations were made about Cosmic background microwave radiation?

Answer 19

Perfect black body.

Largely isotropic and homogenous.

Question 20

What does background radiation showing the Doppler effect show about the milky way?

Answer 20

It’s rushing towards an unknown mass (Great attractor) at over a million miles an hour.

Question 21

What does the amount of helium in the universe show evidence for?

Answer 21

Large abundance of Helium = Hot big bang theory