Unit 4 Cosmology

Question 1

What is cosmology?

Answer 1

The understanding of our universe on a large scale.

Question 2

What did Hubble discover the universe was doing?

Answer 2

Expanding.

Question 3

How did Hubble work out that the universe was expanding?

Answer 3

He saw that the wavelengths of 50 known galaxies was longer than they should have been. They had red shifted. This is a good example of the Doppler Effect.

Question 4

What is the Doppler Effect?

Answer 4

Shifts in frequency that make higher frequencies as the object moves closer (relatively) and lower frequencies as the object moves away (relatively).

Question 5

Are there galaxies moving closer to ours?

Answer 5

Yes. Some galaxies in our Local Group show small blue shifts such as Andromeda.

Question 6

Is the universe expanding?

Answer 6

Yes. The red shift of galaxies confirms this and if we trace it backwards there must’ve been a point where there was an infinitely dense singularity from which everything must’ve expanded from. This is the Big Bang.

Question 7

What is Hubble’s Law?

Answer 7

That the velocity that a galaxy is moving away is proportional to its distance from us.

Question 8

What is the equation for Hubble’s Law?

Answer 8

v = Hd
When:
v = recession velocity (km/s)
d = distance (Mpc)
H = Hubble's constant

Question 9

What is the value of Hubble’s constant?

Answer 9

It has been difficult to determine exactly but most would agree its 77 km/s/Mpc with 15% uncertainty.

Question 10

How old is the universe?

Answer 10

4.35 x 10^17 seconds, or 13.8 billion years.

Question 11

What is CMBR?

Answer 11

Cosmic Microwave Background Radiation. Wherever we look in the universe there is microwaves and a constant temperature of 2.7 K.

Question 12

What is COBE?

Answer 12

COsmic Background Explorer. A space probe launched by NASA with very sensitive detectors that study the CMBR. It has given data to confirm the uniform nature of the CMBR on a large scale but has also detected ripples.

Question 13

What is WMAP?

Answer 13

COBE’s successor, the Wilkinson Microwave Anisotropy Probe. It is a space probe launched by NASA to study the CMBR and estimate the contribution of dark matter, but also confirm dark energy.

Question 14

What is dark matter and dark energy?

Answer 14

Matter and energy that is invisible. Its nature is unknown but could include black holes and WIMPs (Weakly Interacting Massive Particles).

Question 15

Why was dark matter proposed?

Answer 15

Because there was not enough mass to explain why certain stars were so far away from the nucleus of a spiral galaxy.

Question 16

True or false, dark matter cannot help explain gravitational lensing.

Answer 16

False, the added mass of dark matter can “bend” the light of some galaxies in an image.

Question 17

How much of the universe do cosmologists agree is dark energy?

Answer 17

About 90%.

Question 18

What is the “Big Crunch”?

Answer 18

When the universe reaches a critical density it will stop expanding and will contract under the force of its own gravitational pull.

Question 19

What is dark energy?

Answer 19

When the universe was discovered to in fact be accelerating not slowing down an explanation was needed as to why this was happening. Michael Turner coined the term dark energy to explain the repulsive force.