Lecture 28

Front 1

What is Hubble's expansion law?

Back 1

V_exp = H * D

Front 2

The more distant the galaxy, the larger the _________.

Back 2

Redshift.

Front 3

Where does quasars seem to pile up in terms of redshift?

Back 3

z = 2.5~2.6

Front 4

The black hole in the center of our milky way is calm. (T/F)

Back 4

Yes

Front 5

What are the big questions about the universe? (6 questions)

Back 5

1) How big is the universe? Is it infinite? 2) What will happen in the future? Will the universe just keep expanding forever? 3) How did expansion start? 4) Where did all this matter itself come from? 5) How old is the universe? 6) What is it expanding into?

Front 6

What is "omega"?

Back 6

Critical density. visual matter (5%?) + dark matter (75%) + dark energy (7%?)

Front 7

What critical density do we seem to be at?

Back 7

omega = 1

Front 8

What do we have if omega is less than 1?

Back 8

We have an open universe.

Front 9

What do we have if omega is greater than 1?

Back 9

We have a closed universe.

Front 10

What is Olber's Paradox?

Back 10

Olber's Paradox: Why is the sky dark? "If an infinite number of stars fill the Universe, should not the night sky be infinitely bright?" Universe cannot be infinitely old and infinitely big. Universe has a finite age -- universe had a start -- a time where there were no stars.

Front 11

What was the model that was proposed from a distaste for a universe that was expanding?

Back 11

Steady state model.

Front 12

What is the steady state model?

Back 12

Universe always looks the same and is of infinite age. As the universe thins out due to Hubble flow of expansion, matter is created out of nothing. This requires continuous creation of matter, but surprisingly very little to make the theory work with observations. Particles come at a very slow rate.

Front 13

How can you explain the redshift of galaxies without having the galaxy move (having a constant universe)? (Explained by Zwicky.)

Back 13

Light is losing energy after having traveled a great distance, meaning that the wavelength gets longer (redshift).

Front 14

What is the Tired Light idea?

Back 14

Using the idea of a redshift caused by Einstein's General Relativity theory, Zwicky suggested the idea of "Tired Light." He argued that when General Relativity is applied to a gravity field, gravity will drain some of light's energy and hence change its wavelength moving it to become redder. A galaxy's gravity or the collection of all the galaxies between us and a galaxy would effect the wavelength of the light observed. This, not a Doppler shift due to velocity, could be a simpler explanation of Hubble's redshift observations. The Tired Light idea is incorrect.

Front 15

Zwicky was the first to propose that:

Back 15

1) stars blow up (i.e. supernovae); 2) neutron stars are the remains of the core of a high mass star; 3) origin of cosmic rays; 4) there is some sort of "dark" matter around galaxies BUT he was wrong on the expansion of the universe.

Front 16

How did one prove the Big Bang Theory?

Back 16

The proof came out of theorizing what would happen if the universe was compacted into a very small space. If we go back in time, we have all the matter in one spot. All the matter would have been extremely hot, and everything would have been radiation.

Front 17

Early on, the universe was ________-dominated, and all matter was in the form of ____________ particles.

Back 17

Early on, the universe was radiation-dominated, and all matter was in the form of elementary particles. The radiation density exceeded the particle density in the early universe.

Front 18

After about _______ years after the Big Bang, the density of the radiation field decreased sufficiently enough to allow protons and electrons to combine to form atoms of hydrogen, known as the era of ____________.

Back 18

380,000; recombination.

Front 19

After about __________ years from the Big Bang, the particle density exceeded the radiation density. At this time, radiation and matter "_______," equivalent to a redshift z= ~2000.

Back 19

10,000; decouple

Front 20

At the time of recombination, what would the radiation field look like?

Back 20

The radiation field would look like a simple blackbody with a surface temperature around 3000 K.

Front 21

After the time of recombination, what happens to the electrons?

Back 21

The electrons become bound to the protons, creating the first atoms and the universe becomes transparent.

Front 22

What happens to the 3000 K blackbody radiation field after the time of recombination?

Back 22

The 3000 K blackbody radiation field goes everywhere and expands with the rest of the universe.

Front 23

Does Hydrogen scatter light well? How about electrons?

Back 23

Hydrogen does not scatter light well. Electrons scatter light well. That is why the universe became transparent at the era of recombination.

Front 24

At what temperature do you get neutral hydrogen?

Back 24

3000 K (this temperature is at which the universe became transparent because the electrons bound to the protons)

Front 25

The universe started out so hot that photons (_________ _________) could be transformed into _________.

Back 25

pure energy; matter

Front 26

Two gamma rays produce

Back 26

electron (-) and antielectron (+), called pair production. They can annihilate. They combine again and produce gamma rays again.

Front 27

Somehow, in the end, more _______ was created than _________. There was an asymmetry in the production (that we do not understand) of matter.

Back 27

matter; antimatter

Front 28

Pair production with asymmetry produces __________.

Back 28

real matter.

Front 29

Radiation-dominated universe eventually turned into a _________-dominated universe.

Back 29

matter

Front 30

____________ ____________ from Big Bang has been freely streaming across the universe since atoms formed at temperature ~3000 K: ______/___

Back 30

Background radiation; visible/IR

Front 31

What are the two key predictions of the Big Bang?

Back 31

1) The Cosmic Microwave Background (CMB) is thermal blackbody radiation 2) The CMB is highly uniform (1 part in 10**5) difference from one spot to another.

Front 32

3000 K redshifted to what degrees K?

Back 32

3 degrees K.

Front 33

When does a blackbody spectrum occur? Which part of the key predictions of the Big Bang is this?

Back 33

When radiation is constantly scattered by matter, which are exactly the conditions during the "Era of Nuclei." It is part of the prediction of the Big Bang that the Cosmic Microwave Background (CMB) is thermal blackbody radiation.

Front 34

Who predicted that the cosmic microwave background (CMB) is thermal blackbody radiation?

Back 34

George Gamow in the 1940s.

Front 35

Where does the prediction that the cosmic microwave background is highly uniform?

Back 35

It comes from running gravitational instability backwards; by the time of the CMB, the matter fluctuations (and hence temperature fluctuations) should be very small.

Front 36

How uniform is Cosmic Microwave Background (CMB)?

Back 36

1 part in 10**5 difference from one spot to another

Front 37

One of the strongest pieces of evidence in support of the Standard Hot Big Bang Model is

Back 37

the 2.7 degree Kelvin radiation seen in all directions.

Front 38

Who discovered one of the strongest pieces of evidence in support of the Standard Hot Big Bang Model, the 2.7 degree Kelvin radiation seen in all directions, and how?

Back 38

Arno Penzias and Robert Wilson in 1965 by sheer accident trying to do transoceanic communications. Using a special "horn" radio antenna, Penzias and Wilson found an unidentified source of radio emission that seemed to be the same in all directions. When they measured its spectrum, they discovered that it perfectly fit the Planck curve from a thermal blackbody source with a temperature of 2.7 degrees Kelvin.

Front 39

What is the CMB (cosmic microwave background)?

Back 39

It is the echo of the Big Bang. The flash of radiation coming off the era of recombination. The 3 degree radiation that is seen in the microwaves coming off the 3000 degrees in the early hot big bang.

Front 40

What is the COBE?

Back 40

COsmic Background Explorer in the early 1990s. It found a nearly perfect black body radiation spectrum with at temperatre of 2.728 +/- 0.004 K. The CMB was very smooth and uniform across the sky as predicted. It did find very slight temperature variations from place to place on the level of a few parts in 100,000.

Front 41

What role did the slight temperature variation in the CMB play?

Back 41

There would be no cosmic web, no granularity in the expanding universe to make galactic clusters. You need some subatomic variations for this to happen.

Front 42

Expansion of universe has redshifted thermal radiation from that time to ~1000 times longer wavelength: ________.

Back 42

microwaves. Redshifted by z=1000.

Front 43

What is the most perfect blackbody spectrum shown?

Back 43

CMB