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ORIGIN AND EVOLUTION OF THE UNIVERSE
I.
Solar System – Sun with 9 (or10?) planets and 34 moons
mass = 2 x 1033 grams
age = 5 x 109 years
diameter = 2 x 1015 cm
temperature = 5700 K
73% H, 25% He, 1% carbon and oxygen
Galaxy – consists of 2 x 1011 stars
Local Group – a cluster of 30 galaxies
Super Cluster – several clusters so that the density is
at most 10-31 g/cm3
Quasars – interstellar objects at much greater distance
*Homogeneity and isotropy of the universe
* Based on cosmological principle – on a large enough scale the
universe looks very much the same no matter where the
observer is located. The universe has no unique center and
therefore no unique boundary.
galaxies
are distributed evenly across the sky
stars – size ~ 1 light year
1 light year = 9.461 x 1015 m
galaxies – size ~ 106 light years
clusters – size ~ 3 x 107 light years
evidence:
1)
2)
3)
distribution of galaxies in the sky and in the
distribution of their apparent magnitudes and
red-shifts
isotropy of the distribution of radio sources
in the sky
isotropy of the cosmic microwave radiation
(discovery in 1965)
Standard Hot Big Bang Model
Evolution governed by laws of thermodynamics, hydrodynamics,
atomic physics, nuclear physics, high-energy physics and
gravitation dominates the over-all expansion.
Assumption of the model: The universe “began” in a state of rapid
expansion from a very nearly homogeneous, isotropic condition of
infinite (or near infinite) density and temperature ( a singularity –
incomplete physical understanding).
Time after beginning
initial state, decoupling, free propagation of gravitons & neutrinos
1 s , temperature of the universe was so high that there was
complete thermodynamic equilibrium between photons,
neutrinos, electrons, positrons, neutrons, protons, various
hyperons, and mesons, and perhaps even gravitons
(gravitational waves).
thermal equilibrium, decay of particles, recombination
few s,
temperature dropped to about 1010 K and its density
was down to ~105 g/cm3; so all nucleon-antinucleon
pairs had recombined, all hyperons and mesons had
decayed, and all neutrinos and gravitons had decoupled
from matter. Universe consisted of freely propagating
neutrinos, perhaps gravitons, with black-body spectra
at temperature T ~ 1010 K, plus electron-positron pairs
in the process of recombining, plus electrons, neutrons,
protons and photons all in thermal equilibrium at T ~ 1010
The gravitons (if present) and neutrinos have continued to
propagate freely, maintaining black-body spectra, but
their temperature have been red-shifted by the expansion
of the universe in accordance with the law
T  a-1 ,
a = radius of universe
Their temperatures today should be roughly 3K and should
fill the universe. “Sea” of neutrinos and gravitons still
undetected with today’s technology.
Primordial element formation
2s  t  103 s, temperature is ~1010 to ~109 K,  ~ 10+5
10-1g/cm3, during which primordial element formation occurred
Calculations reveal that about 25% of the baryons in the
universe should have been converted into He4 during this
period, and about 75% should have been left as protons (H1)
Traces of deuterium, He3, and Li should have been also
created, but essentially no heavy elements. Heavy elements
observed today must have been made later, in stars.
Current astronomical studies of the abundances of the
elements give some support for these predictions, but the
observational data are not yet very conclusive.
thermal interaction of matter and radiation
103s  t  105 years
Matter and radiation continue to interact thermally through
frequent ionization and recombination of atoms keeping
each other at same temperature, if not, radiation will cool
more slowly than matter.
For adiabatic expansion, Tr  a-1, but Tm a-2 ,Tr is the radi
temperature. Thus thermal equilibrium was maintained
only by a constant transfer of energy from radiation to
matter. Energy transfer held up the temperature of matter
(Tm = Tr) without significantly lowering the temperature
of the radiation. The total mass-energy of matter was and
is dominated by rest mass. So energy transfer had
negligible influence on m (density of matter).
plasma recombination and transition to matter dominance
T ~ 105 years. The falling temperature reached a few
thousand degrees (a/a0 ~ 10-3; a = radius at time of
emission; a0 – initial radius;  ~ 10-20 g/cm3), two things
of interest happened: universe ceased to be radiation –
dominated and became matter dominated;
photons ceased to be energetic enough to keep hydrogen
atoms ionized; so electrons and protons quickly recombined.
That these two events were roughly coincident is a result of
the specific, nearly conserved value that the entropy per baryon
has in our universe.
S  entropy per baryons
~ (number of photons in universe)/
(number of baryons in universe)
~ 108
Recombination of the plasma at t ~ 105 years was crucial,
because it brought an end to the interaction and thermal
equilibrium between radiation and matter. With very few
electrons off which to scatter, and with Rayleigh scattering
of atoms and molecules unimportant, the photons
propagated almost freely through space.
The expansion of the universe has red-shifted the
temperature of the freely propagating photons in
accordance with T  a-1. As a consequence, today they have
a blackbody spectrum with a temperature of 2.7 K. They
identified with the cosmic microwave radiation
are discovered in 1965 and they give one direct information
about the nature of the universe at the time they last
interacted with matter (a/ao ~ 10-3 , t ~ 105 years if reionization
did not occur; a/ao ~ 0.1 , t ~ 108 years if reionization did occur).
condensation of stars, galaxies and clusters
103y  t  109 years
Before plasma recombination, the photon pressure prevented
uniform matter (25% He4, 75% H1) from condensing into
stars, galaxies, or clusters of galaxies. After recombination, the
photon pressure was gone, and condensation could begin.
Small perturbations in the matter density, perhaps dating
back to the beginning of expansion, then began to grow
larger and larger.
Somewhere between a/a0 ~ 1/30 and a/a0 ~ 1/10, these
perturbations began developing into stars, galaxies and clusters
of galaxies. Slightly later, at a/a0 ~ 1/4 , quasars probably “turne
on”, emitting light which astronomers now receive on Earth.
Other cosmological theories
1.
Steady-state theory (Hoyle, Bondi and Gold, 1948) –
has not succeeded in accounting for the cosmic microwave
radiation or in explaining observed evolutionary effects in
radio sources and quasars.
2.
Hierarchic cosmology of matter in an asymptotically
flat space time (Alfven-Klein, Moritz, de Vaucauleurs) –
disagrees with cosmic ray and gamma-ray observation.
The standard big-bang model of the universe predicted
by general relativity accords remarkably well with observation.
Fate of the Universe: Parameters
Central problem of cosmology – will the universe continue
to expand forever; or will it slow to a halt, reverse into
contraction, and implode back to a state of infinite
(or near infinite) density, pressure, temperature and curvature?
*universe after big bang expands to maximum dimension,
then recontracts and collapses
Reprocessing the universe reprocesses also the physical
constants.
parameters
hc/2e2 = 137.036 = fine structure constant
~ 1080 particles in the universe
~ 1040 = e2/GmM = electric force/gravitational force
~ 1020 = [e2/mc2]/[hG/2c3] = ‘size’ of elementary
particle/Planck length
Planck length = 1.616 x 10-33 cm
~ 1010 = number of photons in universe/number of
baryons in universe
These are part of the initial value data. Such #s are freshly given for each
fresh cycle of expansion of the universe.
A % change one way will cause all stars to be red stars; and a
comparable change the other way will make all stars blue stars. In neither
case will any star like the Sun be possible. So life as we know it may not exis
Could life have developed if the determinants of the physical constants
had differed substantially from those that characterize this cycle of the
universe?
1.
2.
3.
4.
5.
6.
What good is that universe without awareness of that universe?
But awareness demands life.
Life demands the presence of elements, heavier than hydrogen.
The production of heavy elements demands thermonuclear combustion.
Thermonuclear combustion normally requires several 109 years of cookin
time in a star.
Several 109 years of time will not and cannot be available in a closed
universe, according to general relativity, unless the radius-at-maximum
expansion of that universe is several 109 light years or more.
Hubble’s Work
1.
2.
isotropic universe
all galaxies except our nearest neighbors show a
red shift in their spectral features (an expanding
universe)
Hubble’s law v = Hr, H = 17 x 10-3 m/(s ly)
velocity of recession indicated by the red shift is  distance
of galaxy from us.
1 ly =3.0856 x 10exp18 cm
Arno Pensias and Robert Wilson
-
Discovered the cosmic microwave background – the echo
of the Big Bang itself
 = 7 cm
equivalent to the radiation from a blackbody with a
temperature between 2.5 K (actually 2.7 K) and 4.5 K,
left-over radiation from the hot phase still permeating today.
The basic parameter that governs the physical processes is
the temperature of the gas of interacting quantum particles
that fills the whole space of the universe. Temperature
because it is proportional to the average energy of the
colliding particles, establishes which new quantum particles
can be created from the energy of the collisions.
Birth, Life & Death of Stars
What is the source of stellar energy? 1926
subatomic nuclear processes according to Arthur
Eddington were responsible for the star’s energy.
center is about 40 million K (today ~ 14 million K)
1928 Quantum Theory of Gamow, Gurney and Condon
(tunnel effect) particles did not have to surmount the
repulsive energy barrier but could tunnel under it
1929 Robert d’Atkinson and Fritz Houtermans
energy production of stars by nuclear fusion
explained through the “tunneling effect”
1938 Hans Bethe and Carl Friedrich von Weizsacker
suggested the “carbon cycle” – where hydrogen
nuclei and carbon nucleus as a catalytic agent,
burned hydrogen
Some scientific advances.
A. Observational facilities in understanding features of stars
1.
2.
3.
4.
5.
B.
C.
sensitive electronic detector
artificial satellites
X-ray astronomy
new optical, infrared and radio telescopes
sophisticated electronic system.
Emergence of quantum theory of atoms, the theoretica
and experimental understanding of nuclear physics and
plasma physics (charged particles) .
Advent of powerful computers.

A star is a sphere of a hot gas, (H2 & He) held together by gravity.
Gravitational force increases with mass, so the larger the star, the greater
The force tending to collapse the star. But there is an opposing pressure
to prevent this collapse. The rapidly moving gas particles collide with
each other. The frequent collisions means greater pressure, thus,
making the gas expands more thereby preventing the collapse. At the
core of the star, the nuclei are squeezed closely together. The
enormous weight due to the entire mass - equivalent to about 2 million
tons resting on a peso coin. The extreme pressure high burning
temperature at the core ignites the thermonuclear burning process of
hydrogen fusing into helium, generating heat energy. If temperature
is small in the core, nucleus fusion will not last and the star lives for
about 20 million years. When a star contracts, ½ of gravitational
energy released becomes heat energy, which in turn supports the star.

The stability of a star is due to the dynamic balance
of gravity and the heat that this collapse generates.

Stars continue to shrink as fuel is burned and due to
relentless crush of gravity – so they are not really
that stable. Some sources of energy to prevent
utter collapse are:
1. chemical sources to last 20 million years.
2. nuclear burning of Hydrogen to keep a solar-mass star
going for billions of years.
3. burning of He extends this period.
The Interior of Stars.
Core inner connective layer
– connective currents of hot matter
cooking pot for heavy elements essential for building
planets and life
layer of gas – transfers radiant energy from core to stars
outer connective layer
Jupiter has 0.1% of sun’s mass – about 1/20 the mass of
the lowest-mass star.
Planets form out of flattened disk of gas and cosmic debris
surrounding a newly born star.
Stars are opaque – light cannot get out right away from the core.
This radiation heats up the gas in the star’s outer layers stirring
them up the way the sun heats the air on a hot day. This
interior movement creates sound waves, which bounce
around inside the star.
This acoustic energy is dumped in the solar corona – upper
very hot atmosphere of the sun. These groans, screams,
drum-rolls can be detected. The sun also vibrates like a
shaking bowl of gelatin, which gives clues on the internal
motion of the core relative to its outer layer.
A picture of the universe can be gleaned from distant
sources of electromagnetic radiation: visible, radiowave,
infrared and microwave, X-rays and -rays.
A star has color and luminosity – its total energy output.

red to blue  cold to hot surface

related to These are plotted as luminosity vs. temperatur
surface temperatur called Hetzspring – Russell diagram
Spectra stars from modern spectroscopy developed by
Fraunhoffer, Kirchoff and Bunsen – stars differ in chemical
composition.
A. Population I – 1 to 2% of chemical elements heavier
than H or He.
B. Population II – those relatively lacking in heavy elements.
How is a star made?
formation of stars in giant molecular – cloud complexes –
clouds consisting mostly of hydrogen and whose mass >>
individual star.
cloud fragments into smaller clump and results in mutual
gravitational attraction of gas particles and dust.
Sun was probably formed by a disk of leftover matter
swishing around it like the white (scalar nebula) of a
fried egg surrounding the yolk and from it the solar
system of planets subsequently formed.
Stars lead uneventful, middle-class lives, lasting for
billions of years.
Stars lead uneventful, middle-class lives, lasting for billions of years.
A.
B.
T - Tauri stars – about 100 K to 106 years; they exhibit unconventional
behavior – rich, complex, often anomalous emission spectra.
Surrounded by hot gas and luminous sets of matter.
Cepheid variables – brightness oscillates with period ranging from 3
days to weeks. Blinking beacons in the sky, e.g. polaris, the Ninth star.
They release energy by pulsating their intrinsic brightness. Discovered
by Henrietta Leavitt in 1912, period – luminosity relation.
Death of Stars: when burning stops, star resumes collapsing.
Three possible fates
white dwarfs – tiny stars made of solid carbon matter thousands
of times denser than ordinary matter. Stars with mass < 1.4 times the
sun’s mass.
2. Neutron – star – recurrent of a supernova explosion when more
cursive stars collapse. The recurrence is a gigantic atomic nucleus the
size of a city. (discovered in 1967) pulsars – spring neutron star.
3. Black hole – stars with masses > 2 solar masses collapse to objects
in which space itself gets turned “inside out”
Puzzles from particle physics
Standard model says
 There are four fundamental forces
 There are three families of matter
-- 1st: electron and its neutrino; up and
down quarks
-- 2nd: muon and its neutrino; charm and
strange quarks
-- 3rd: tau and its neutrino; top and bottom quarks
st
 1 family makes up all of ordinary matter (elements,
molecules, compounds, proteins, DNA, cells, etc.)
Puzzles from particle physics
Unification of fundamental forces is an
attractive idea
 So far unification of weak and e.m. forces
verified
 Models of grand unified theories unify weak,
e.m. and strong forces
These models are characterized by:
-- unstable proton with lifetime 1032 years
-- observed particles with integral charges
-- existence of magnetic monopoles not verified

Puzzles from particle physics
Unification idea anchored on notion of
spontaneous breaking symmetry (Higgs mechanism)
to differentiate forces at low energies
 3 major puzzles
-- “rareness” of magnetic monopoles
-- smallness of contribution of symmetry breaking to
cosmological constant
-- masses of particles affect the value of ῼ of the
universe
 Theories of elementary particles describe the
universe at very early stages
 Study of elementary particles, the subatomic domain
or inner space is linked to study of the universe

Puzzles from cosmology
The Big Bang Theory is the most
popular cosmological theory. It accounts
for:
-- the relative abundance of elements in
the universe
-- the background microwave radiation
with characteristic temperature of 2.7K

Puzzles from cosmology

The smoothness problem – the
background radiation is fairly uniform.
Opposite regions in the universe, which
are not casually connected (the time it
takes for light to traverse the distance is
more than the age of the universe)
have the same background radiation
Puzzles from cosmology

The age problem – present estimates from
Hubble expansion suggest that the universe is
between 15 to 20 billion years old. This
means that the universe started with a value
of ῼ = 1 because otherwise it would have
reached its final state of the Big Chill (infinite,
very cold universe) or the Big Crunch
(recollapsed universe). Present value of ῼ ~ 1
but the matter distribution to support this
value is still not found yet (the missing mass
problem)
Puzzles from cosmology


The lumpiness problem – the universe
contains lumps of matter: clusters of galaxies,
stars, etc. What is the origin of these lumps?
The 1990 experiment COBE (Cosmic
Background Explorer) took a picture of the
universe at 300,000 years old showing “hot”
and “cold” spots representing the evolution of
the “wrinkles” in space-time at 10-43 s after
creation. Large galactic clusters formed at the
“cold” spots.
The rotation problem – why is it that the
universe has zero rotation? This follows from
the fact that the Hubble expansion has no
center.
The Inflationary Universe

In 1980, Alan Guth, was applying the
physics of unification to the problem of
the evolution the universe. In particular,
he was trying to solve the monopole
problem. His solution is revolutionary
and he gave it a catchy name, the
Inflationary Universe Model (IUM)

The IUM did not only solve the monopole
problem, it also solved the other 4 problems
that the BBT failed to solve. The BBT was
amended that the universe expanded very
fast (inflated) during the brief period 10-35 to
10-32 s after creation. This period saw the
separation of strong force from others. After
this period, the usual expansion of the
universe under the BBT resumed.
How does the inflationary phase during the brief
period after creation solved the problems of Big
Bang Cosmology?


First, IU assumes that the universe came
from a single bubble of space-time out of the
zillions that came to be after the Big Bang.
Each bubble contained only a single
monopole, explaining why monopoles are
hard to come by
Coming from a single point, all points are
causally connected, explaining the
smoothness problem



As the universe expanded fast, its rotation
will be quickly damped to zero, solving the
rotation problem
The large structures come from the small
fluctuations in energy density inside the
bubble, a way out of the lumpiness problem
Inflation will make any curved region in
space-time flat making ῼ = 1 explaining the
age problem

The Higgs mechanism of particle
physics sustained the inflationary
universe.