Big Bang, Dark Matter & Dark Energy

Question 1

What is Dark Matter?

Answer 1

The stars at the edge of galaxy are moving at 220km/s i.e. so quickly that they should just fly off into space - theory is that ‘dark matter’ holds it together to stop it from happening.

Question 2

How do we estimate Dark Matter?

Answer 2

The observed rotation curve and applying Newton’s laws you can calculate the mass of the galaxy which gives us the calculated value for ‘dark matter’.

Question 3

What is Hubble’s Law?

Answer 3

In 1920s Hubble discovered that everything is moving apart at ‘velocity’ proportional to their separation - the Hubble Law.

Question 4

What is Steady State Theory?

Answer 4

Steady State theory i.e. competing theory to expanding theory idea. Steady state suggests that the universe has already been here.

The Steady State theory was closed down about 50 years ago.

Question 5

Who is Fred Hoyle?

Answer 5

Proposed the Steady State Theory as an alternative to the Expanding Theory idea.

Hoyle is also the one who gave the ‘big bang’ theory its name in 1949 (BBC radio) - oh the irony!

Question 6

What are cosmological redshifts?

Answer 6

The galaxies are carried along with this expansion and the redshift results from stretching of the light wave. We infer that the Universe had zero size about 13.7bn years ago - the Big Bang.

Question 7

Who are Ralph Alpher and Robert Herman?

Answer 7

In 1948, Ralph Alpher and Robert Herman postulated Cosmic Microwave Background at 5K (later revised to 28K) and Penzias and Wilson discovered that Cosmic Background Radiation (CBR) purely by accident when they discovered a radio hiss/noise caused by the left over glow from the formation of the Universe. They won the 1979 Nobel Prize. The temperature of that signal was 3K.

Question 8

Who is Robert Dicke?

Answer 8

Independently did the same calculation and came to the same theory of CMB Radiation. When he heard of Penzias and Wilson he understood what had been discovered.

Question 9

What is COBE?

Answer 9

COBE (COsmic Background Explorer) was put into space in 1989 and measured that the CBR spectrum corresponds perfectly to a Planck spectrum with a corresponding temperature of 2.728K. Small fluctuations in temp result in galaxy clusters that we know today.

Question 10

How is the Big Bang Model supported?

Answer 10

1. Expansion
2. Temperature
3. Abundances of light elements (how much H & He you should see)

Question 11

What is ‘inflation’?

Answer 11

In a minute fraction of time the universe suddenly inflated. Inflation would explain why:

• opposite sides of the universe are so similar.
• the universe didn’t collapse after initially forming.

It is supported by quantum theory. The universe expanded at an exponential rate.

Question 12

What is the earliest we can see in terms of history of the universe?

Answer 12

We can’t see anything futher back than 700m years after big bang as the light is too compressed for us to see anything.

Question 13

What proportion of the universe is matter we can actually see?

Answer 13

Approximately 5%.

Question 14

What proportion of the universe is Dark Matter?

Answer 14

Approximately 27%.

Question 15

What proportion of the universe is Dark Energy?

Answer 15

Approximately 68%.

Question 16

What is the history of the ‘cosmological constant’?

Answer 16

Einstein believed in the Steady State theory. Therefore he made his equations fit this theory and introduced the ‘cosmological constant’. This balanced his equations so that the universe didn’t need to expand.

15 years later Hubble found the universe was actually expanding and disproved Einstein’s theory - the irony being that had he not introduced this parameter of the ‘cosmological constant’ his equations would actually support the universe is expanding!

Question 17

What is the cosmological constant today?

Answer 17

The cosmological constant is now known as ‘dark energy’.

We are trying to work out what dark energy is. We launched Planck space telescope recently and we were able to determine that the universe is 4.9% matter, 26.8% dark matter, 68.3% dark energy.