Download Exploring the Early Universe - Solar Physics and Space Weather

ASTR 113 – 003
Lecture 13 April 26, 2006
Spring 2006
Introduction To Modern Astronomy II
Review (Ch4-5): the Foundation
1.
2.
3.
4.
5.
6.
7.
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)
1.
2.
3.
Our Galaxy (Ch25)
Galaxies (Ch26)
Active Galaxies (Ch27)
Galaxy (Ch 25-27)
1. Evolution of Universe (Ch28)
Cosmology (Ch28-29)
Extraterrestrial Life (Ch30)
2. Early
Universe (Ch29)
1. Extraterrestrial Life (Ch 30)
A Short Movie
Universe
Note: this movie can only run in-class
ASTR 113 – 003
Lecture 13 April 26, 2006
Exploring the Early
Universe
Chapter Twenty-Nine
Spring 2006
Guiding Questions
1. Has the universe always expanded as it does today, or
might it have suddenly “inflated”?
2. How did the fundamental forces of nature and the
properties of empty space change during the first
second after the Big Bang?
3. What is antimatter? How can it be created, and how is it
destroyed?
4. Why is antimatter so rare today?
5. What materials in today’s universe are remnants of
nuclear reactions in the hot early universe?
6. How did the first galaxies form?
7. Are scientists close to developing an all-encompassing
“theory of everything”?
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?
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”
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
Inflation Theory
• Inflationary epoch: a short period of 10-32 second,
during which the universe expanded by a factor of
about 1050
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)
Inflation explain flatness
• The observable universe was a tiny fraction of the
entire inflated universe that any overall curvature in
it is virtually undetectable
Trigger of Inflation
Four basic forces in nature
1. Gravity, e.g., holding the Earth to the Sun
2. Electromagnetic force, e.g., holding electrons to nuclei
3. Strong force, e.g., holding protons, neutrons together to form
nuclei
4. Weak force, e.g., cause neutron decay into proton
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”
Trigger of Inflation
•
Inflation occurs at 10-35 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
ASTR 113 – 003
Lecture 14 May 3, 2006
Spring 2006
Introduction To Modern Astronomy II
Review (Ch4-5): the Foundation
1.
2.
3.
4.
5.
6.
7.
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)
1.
2.
3.
Our Galaxy (Ch25)
Galaxies (Ch26)
Active Galaxies (Ch27)
Galaxy (Ch 25-27)
1. Evolution of Universe (Ch28)
Cosmology (Ch28-29)
Extraterrestrial Life (Ch30)
2. Early
Universe (Ch29)
1. Extraterrestrial
Life (Ch 30)
Trigger of Inflation
•
Inflation occurs at 10-35 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
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
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
Create Matter from “Empty” Space
• For instance, the pair of electron and anti-electron (called
position) can last for 6.4 X 10-22 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
Create Matter from “Empty” Space
• Annihilation: when a real particle collides with a real antiparticle, 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)
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
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
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
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 10-18 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.
“Bottom-up” galaxy formation
• Galaxies were formed from smaller “galaxy building
blocks”, which were later coalesced along filaments
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