Chapter 14

Question 1

Who were the people who inadvertently discovered CMB?

Answer 1

Penzias and Wilson

Question 2

When they first heard the consistent noise that eventually was proven to be CMB, what did they think it actually was?

Answer 2

The pigeons that had nested in the horn. However, when it was removed, the noise persisted

Question 3

What can a radio signal such as CMB be characterised as?

Answer 3

A temperature

Question 4

What was the temperature of the radiation that Penzias and Wilson detected?

Answer 4

3.5k

Question 5

What does CMB tell us about the conditions in the early universe?

Answer 5

That it was very hot, consistent with the Big Bang model

Question 6

At what stage is CMB created?

Answer 6

recombination

Question 7

Why has CMB been redshifted?

Answer 7

Because the universe is expanding

Question 8

What spectrum does the CMB have?

Answer 8

The same as that of a blackbody

Question 9

Why is the CMB photon density redshifted?

Answer 9

Because of the cosmic expansion

Question 10

What is the relationship of the CMB’s energy and time?

Answer 10

CMB loses energy over time

Question 11

What did recombination of electrons with nuclei allow photons to do?

Answer 11

move freely throughout the universe

Question 12

What principle does the existence of CMB back up?

Answer 12

The cosmological principle

Question 13

What is the issue with observing CMB from Earth?

Answer 13

The atmosphere of Earth makes it very difficult to detect anything. It is opaque to many forms of radiation

Question 14

What did COBE determine the CMB temperature to be?

Answer 14

2.725K (uncertainty of +/- 0.002K)

Question 15

How well did COBE see CMB obeying the blackbody spectrum?

Answer 15

To a precision of 0.03%

Question 16

What does the coherence with a blackbody spectrum mean about the source of CMB?

Answer 16

It comes from the universe and not other objects like gas

Question 17

What did COBE find about the temperature of CMB across the whole sky?

Answer 17

That it was evenly distributed, showing isotropy of the universe

Question 18

Are there fluctuations in the temperature of CMB?

Answer 18

Yes, some very small ones

COBE was too blurry to see this variation very well

Question 19

What kind of thing affects the radiation fluctuations in the CMB?

Answer 19

The dust from places like the Milky Way can be seen to be emitting more radiation

Question 20

What can COBE detect with regards to the motion of the solar system?

Answer 20

It can detect redshifts and blueshifts with respect to the cosmic background to show things like the motion of the Milky Way

Question 21

Why does CMB and redshirting only tell us part of the story with regards to the speed of the universe?

Answer 21

It tells us if the universe is moving towards us or away from us, but does not give us a 3 dimensional sense of the movement

Question 22

How are sound waves created in the universe?

Answer 22

Gravitational perturbations in the universe

Question 23

What do CMB fluctuations reveal about the early universe?

Answer 23

They reveal perturbations in the early universe

Question 24

What do the temperature fluctuations in the CMB appear to be?

Answer 24

Noise

Question 25

What was WMAP

Answer 25

It measured temperature differences in the CMB more precisely than COBE

Question 26

What can WMAP tell us about the shape of the universe?

Answer 26

The universe is flat to within 2%

Question 27

What is reionisation

Answer 27

The hydrogen in the universe (which is mostly ionised) is recognising to help to form new stars

Question 28

What was the superior satellite to WMAP and COBE?

Answer 28

Planck Satellite