Unit 12: Cosmology

Question 1

What is the distance ladder?

Answer 1

Step 1: Parallax distances to measure luminosity of cepheids
Step 2: Cepheid distances to measure luminosity of SNe
Step 3: SNe to measure distances to far-away galaxies

Question 2

What is Hubble time?

Answer 2

The estimate as to how old the Universe is; If the universe were to expand at a constant rate, then inverse of the expansion rate is the age

Question 2

What is the difference between dark matter and dark energy?

Answer 2

-Dark matter: Yet to be found particles that make up most of the matter in the Universe
-Dark energy: Property of spacetime that makes space want to expand

Question 3

Dark energy accounts for the majority of what?

Answer 3

Density

Question 4

Since dark energy is a property of space and space expands, what happens to the relative fraction of dark energy?

Answer 4

It increases

Question 5

What is the Cosmic Microwave Background?

Answer 5

The temperature of the Universe’s blackbody radiation decreases (from 3000K to 3000K/1100 since photons are redshifted by a factor of 1100). This puts the peak wavelength of the radiation at ~2mm, in the microwave range.

Question 6

How do physicists predict the Universe will expand?

Answer 6

They predict that the Universe will expand forever at an increasing rate

Question 7

What percent of matter IN TOTAL is dark matter?

Answer 7

25%

Question 8

Of the 30% matter in the Universe, what percent is dark matter?

Answer 8

85%

Question 9

Of the 5% of ordinary matter, what percent is in luminous galaxies?

Answer 9

1%

Question 10

What two things combined tell us the distance of galaxies?

Answer 10

Their Hubble expansion rate and the redshift of galaxies