1. HW3 was difficult. (in-class discussion)
You should have finished reading Ch. 4
HW4 due Monday, HW5 coming soon
Finish chapter 5 by Wednesday
Course grades (let’s be clear!)
50% Homeworks
HWs replace exams.
Late HW’s now penalized.
30% Term paper: “what’s really new”
5-10 pages. Due Feb 22 or so (stay tuned)
20% Term paper: “what’s wrong with BB?”
5-10 pages. Due March 3

2. Start planning first term paper:
“What’s really New in the Big Bang Story of Creation?”
Identify some of the fundamental elements of the Big Bang story, select any 3 cultural stories and compare their most closely corresponding elements
5-10 pages. Preliminary due date Feb 22.
30% of course grade

3. Zwicky and Oort proposed dark matter
EXIT THE 1930s
Hubble continues work on the Diagram, but his distance measurement method is flawed, even with Baade’s help
e.g., TUniverse = 1/Ho is way too small: 4 Gy
Zwicky and Oort proposed dark matter
Their ideas seem whacky. No one listens
Studies of distant galaxies and their spectra continue
Zwicky recognizes clusters of galaxies
But no big breakthroughs or insights
Quantum physics explores atomic nuclei
No evidence to guide theoretical studies of the early Universe

4. Optical spectra of stars and nebulae
EXIT WORLD WAR II
Optical spectra of stars and nebulae
Details of the spectra enable comparison of the chemical abundances
Theoretical nuclear physics leaps forward
A “crop” of aspiring young nuclear physicists enters the story
By 1948 the cosmic abundance of He/H leads to a secure prediction of a very hot early Universe
Healthy confusion and divergence of viewpoints about how to apply the new tools and nuclear physics to cosmology

5. The formation of the heavier elements
Lecture Road Map
He/H universally 10%
Suggests that the early Universe was as hot as the centers of stars like the Sun: 14 million K
The formation of the heavier elements
Interpreting the new optical spectra
Radar/radio astronomy becomes ready for cosmic studies
Cosmic abundance of He/H leads to a prediction of a very hot early Universe
Healthy confusion and divergence of viewpoints about the influence of nuclear physics on cosmology

6. Late 1940s: Cosmic Helium Infuences Cosmology
H:He:all other = 100:10:1

7. 1940s: Cosmic Helium Motivates the Big Bang
10% of all nuclei in the Universe today (incl the Sun and Jupiter)
The ratio is the same in the oldest stars (>10 billion years old)
The He/H ratio had this value when the first stars formed
What’s up with that?

8. 1940s: Cosmic Helium Motivates the Big Bang
10% of all nuclei in the Universe today (incl the Sun and Jupiter)
The ratio is the same in the oldest stars (>10 billion years old)
The He/H ratio had this value when the first stars formed
What’s up with that?

9. Making Cosmic Helium
Helium is forged by nuclear fusion of protons and neutrons
Need high temperatures and densities
Gamov
1942
1031 K
@ s
109 K

10. Making Cosmic Helium requires high temperatures
Once upon a time, as the Universe was cooling, plentiful protons and neutrons forged into heavier nuclei that could survive.
• This episode was brief (≈10 minutes).
• Before this nuclei were quickly destroyed by very energetic collisions.
• After this era it was too cool for charged particles to overcome their repulsive electric forces and to partake in nuclear reactions. Moreover, neutrons vanished after 10 min as they decayed into protons and electrons.

11. Making Cosmic Helium H:He:all other ≈ 100:10:0.001
Elements beyond He produced later in stars
(BBFH 1956)

12. Review

13. You are here: 10 min ABB Now
Gamov, Alpher (1948) realized that relic heat might be observable now if the Universe had once been opaque
1031 K
@ s
Now
2.735 K
@ 4 X 1017 s
You are here:
10 min ABB
109 K

14. Cosmic Background Radiation (CMB): Hot “Embers” of the Big Bang
Studying embers probes the fire that formed them

15. Gamov, Alpher (1948) realized that relic heat might be observable now if the Universe had once been opaque. The spectrum of relic radiation would have been highly redshifted to about 10 above zero (<10 K??) by the stretching of light waves in an expanding space.
Waves are elongated (i.e., redshifted) as the space through which they propagate stretches over time

16. Gamov, Alpher (1948) realized that relic heat might be observable now if the Universe had once been opaque. The spectrum of relic radiation would have been highly redshifted to about 10 above zero (<10 K??) by the stretching of light waves in an expanding space.
CMB emitted at ≈4 x 105 y when Tcosmos ≈ 3000K
We observe the CMB at a Doppler shift of ≈1000
So the expected radiation temperature of the CMB is 3K

17. CMB Temperature
You

18. First all-sky “map” of the CMB
Discovery of the CMB (1964)
What’s this??
First all-sky “map” of the CMB

19. Infrared Radiation (aka “heat radiation”) from opaque objects

20. Footnote: Projecting a Spherical Surface onto Paper

21. Discovery of the CMB (1964) First all-sky “map” of the CMB
The emission appeared uniform

22. Review Looking forward
Why does the Universe today have any structure whatsoever?