1. Introduction To Modern Astronomy II
ASTR 113 – Spring 2006
Lecture April 26, 2006
Introduction To Modern Astronomy II
Review (Ch4-5): the Foundation
Sun, Our star (Ch18)
Nature of Stars (Ch19)
Birth of Stars (Ch20)
After Main Sequence (Ch21)
Death of Stars (Ch22)
Neutron Stars (Ch23)
Black Holes (Ch24)
Star (Ch18-24)
Our Galaxy (Ch25)
Galaxies (Ch26)
Active Galaxies (Ch27)
Galaxy (Ch 25-27)
1. Evolution of Universe (Ch28)
2. Early Universe (Ch29)
Cosmology (Ch28-29)
1. Extraterrestrial Life (Ch 30)
Extraterrestrial Life (Ch30)

2. A Short Movie Universe Note: this movie can only run in-class

3. Exploring the Early Universe
ASTR 113 – Spring 2006
Lecture April 26, 2006
Exploring the Early Universe
Chapter Twenty-Nine

4. Guiding Questions
Has the universe always expanded as it does today, or might it have suddenly “inflated”?
How did the fundamental forces of nature and the properties of empty space change during the first second after the Big Bang?
What is antimatter? How can it be created, and how is it destroyed?
Why is antimatter so rare today?
What materials in today’s universe are remnants of nuclear reactions in the hot early universe?
How did the first galaxies form?
Are scientists close to developing an all-encompassing “theory of everything”?

5. Inflation Theory: the Isotropy Problem
The temperature of microwave background radiation from all parts of the sky is incredibly uniform, the same to an accuracy of 1 part in 10000
Point A and B, in the opposite parts of the cosmic light horizon, can not communicate with each other.
Isotropy problem: how is it possible that the unrelated parts of the universe have almost the same temperature?

6. Inflation Theory: the flatness problem
In order for space to be flat as it is today, the mass density must have been exactly equal to critical density right after the Big Bang
If mass density were slightly smaller than the critical density, the universe would have expanded so rapidly that matter could have never clumped together to form galaxies.
If mass density were slightly larger than the critical density, the gravitational attraction would long ago have collapsed the entire universe in a reversed Big Bang or “Big Crunch”

7. Inflation Theory
Because of the isotropy problem and flatness problem, the universe may not expand at the same rate as we see today
Inflation theory: the universe experienced an extremely rapid expansion shortly after the Big Bang
An initially small universe (comparatively, much smaller than the size of the cosmic light horizon) becomes much larger after the inflation

8. Inflation Theory
Inflationary epoch: a short period of second, during which the universe expanded by a factor of about 1050

9. Inflation explains the isotropy
During the inflationary epoch, the parts of the universe, which were originally in intimate contact and thus had the same temperature, were moved out to tremendous distance (larger than the cosmic light horizon)

10. Inflation explain flatness
The observable universe was a tiny fraction of the entire inflated universe that any overall curvature in it is virtually undetectable

11. Trigger of Inflation Four basic forces in nature
Gravity, e.g., holding the Earth to the Sun
Electromagnetic force, e.g., holding electrons to nuclei
Strong force, e.g., holding protons, neutrons together to form nuclei
Weak force, e.g., cause neutron decay into proton

12. Trigger of Inflation
Studies of particle physics show that the forces may be identical if the energy of particles involved in the interaction is high enough
E.g., electromagnetic force and weak force is identical if particle energy is greater than 100 Gev, or equivalently, temperature greater than 1015 K
If the temperature of universe became lower as it expanses, the forces will separate, which is called “Spontaneous Symmetry Breaking”

13. Trigger of Inflation
Inflation occurs at second after the Big Bang when temperature of universe dropped to 1027 K; at this temperature, strong force became distinct from the electromagnetic-weak force

14. Introduction To Modern Astronomy II
ASTR 113 – Spring 2006
Lecture May 3, 2006
Introduction To Modern Astronomy II
Review (Ch4-5): the Foundation
Sun, Our star (Ch18)
Nature of Stars (Ch19)
Birth of Stars (Ch20)
After Main Sequence (Ch21)
Death of Stars (Ch22)
Neutron Stars (Ch23)
Black Holes (Ch24)
Star (Ch18-24)
Our Galaxy (Ch25)
Galaxies (Ch26)
Active Galaxies (Ch27)
Galaxy (Ch 25-27)
1. Evolution of Universe (Ch28)
2. Early Universe (Ch29)
Cosmology (Ch28-29)
1. Extraterrestrial Life (Ch 30)
Extraterrestrial Life (Ch30)

15. Trigger of Inflation
Inflation occurs at second after the Big Bang when temperature of universe dropped to 1027 K; at this temperature, strong force became distinct from the electromagnetic-weak force

16. Create Matter from “Empty” Space
Matter and energy of the universe is created during the inflation
Before the inflation, the space is “empty”, filled with only virtual particles dictated by quantum mechanics

17. Create Matter from “Empty” Space
In quantum mechanics, Heisenberg’s uncertainty principle states that there is a reciprocal uncertainty between position and momentum
Heisenberg uncertainty principle for energy and time: the shorter the time interval, the greater the energy uncertainty, or the greater the mass uncertainty
In “empty space”, pairs of particles and antiparticles can spontaneously appear and then disappear anywhere in space provided that each exists only for a very short time interval
Antiparticle, or antimatter, is the same as the normal particle, but with opposite electric change
The spontaneously created pair of particles from empty space is called virtual pair, since they can not be directly observed

18. Create Matter from “Empty” Space
For instance, the pair of electron and anti-electron (called position) can last for 6.4 X s
During the inflation, the universe expanded so fast that particles were rapidly separated and were deprived the opportunity of spontaneous recombination. As a result, virtual particles became real particles in the real world
After the inflation, the universe was flooded with particles and antiparticles

19. Create Matter from “Empty” Space
Annihilation: when a real particle collides with a real anti-particle, they are converted into high energy gamma ray ---- the creation of energy
Pair production: inversely, when two gamma-ray photons collide, a pair of particle-antiparticle is created. But the photon energy must be equal or larger than particle energy (E=MC2)

20. Create radiation or photons
Just after the inflationary epoch, the universe was filled with particles, antiparticles and energetic gamma-ray photons
At t=10-6 second, the temperature in the universe dropped to the threshold temperature of 1013 K, at which the photons can not produce proton and anti-proton pairs (and neutron and anti-neutron pairs)
As a result, matter and anti-matter content decreased, and radiation content increased
At about t = 1 second, temperature fell below 6 X 109 K, electrons and positions annihilated to form low energy gamma-ray photons that can not reverse the process, which further raising the radiation content in the universe
From 1 second to 380,000 years, the universe is dominated by the radiation (so called primordial fireball) derived from the annihilation of particles and antiparticles created early by the inflation

21. Create ordinary matter: asymmetry
If there had been perfect symmetry between particles and antiparticles, every particles would have been annihilated, leaving no matter at all in the universe
The stars, galaxies in the Universe are made of matter, not antimatter
There are 109 photons in the microwave background for each proton/neutron in the universe
Therefore, there is a slight but important asymmetry between matter and antimatter
Right after the inflation, for every 109 antiprotons, there must have been 109 plus one ordinary protons, leaving one surviving after annihilation

22. Hydrogen and Helium: relics of primordial fireball
When the universe was 3 minutes older, the temperature was low enough to pass the deuterium (2H, one proton + one neutron) bottleneck to further produce helium
At 15 minutes, the temperature of the universe is too low for any further nucleosynthesis
Therefore, the relics of primordial fireball are hydrogen, helium (1 helium out of every 10 protons), and photons (1 billion photons for every proton)
Heavier elements are formed later in the stars, not in the early universe

23. Density fluctuations in the Early universe
Jeans length: the scale size of density distribution determined by temperature and density
At the era of recombination, temperature was 3000 K, density was km/m3, then the Jean length was 100 light years
An object can grow if it exceeds the Jean’s length. Otherwise, it will be dispersed.

24. “Bottom-up” galaxy formation
Galaxies were formed from smaller “galaxy building blocks”, which were later coalesced along filaments

25. Universe may have 11 dimensions
The physical forces are equivalently to the curvature of space, e.g, gravity from mass resembles the curvature of 3 dimension space
The search for a theory that unifies gravity with the other physical forces suggests that the universe actually has 11 dimensions (ten of space and one of time), seven of which are folded on themselves so that we cannot see them