Download Cosmology Notes

Cosmology- the Study of
the Universe
Newton opens the door to the
universe
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The same laws of force that apply to
the earth also apply to the entire
universe.
Problem with Gravity
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If the universe was not infinite, then gravity
would pull it back together.
If the universe was infinite, then gravity
would cause clumping.
Newton’s solution was to postulate that the
universe was infinite, and also perfectly
uniform.
The flaw in this solution was that a comet or
any other change would break the perfect
symmetry and start to clump matter.
Problem with infinitely large
universe
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An infinite number of stars results in an
infinite amount of light and heat, yet
our night sky is dark and cold.
Dust can not explain the dark sky, as
infinite age and infinite heating would
cause it to glow.
Current solution
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The universe is very large, although
finite in size.
The universe has not been here forever.
The universe is expanding.
The sky is dark because some light has
not had time to reach us, and some
light never will.
The Einsteinium View – the
Growing Universe
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Before the 1920s, it was believed that
the universe consisted of only the Milky
Way galaxy.
Hubble proved that the “spiral nebulae”
were beyond the Milky Way galaxy
using the brightness of a Cepheid star
to determine distance.
The Expanding Universe
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In 1912, Vestro Slipher used the redshift of light to conclude that all of the
objects in the universe were moving
away from us.
Later in 1929, Hubble demonstrated
that at one time, all matter was in one
location. This is the start of the big
bang theory.
Age of universe
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Speed/distance = Hubble’s constant
1/Hubble’s constant = Age of universe
The first calculated age was 1.8 billion
years, but we know now that this was
way off- 13.7 billion years is the
accepted value.
Relativity Equation and
Universe Expansion
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During the 1920s, Alexander Friedmann and
Georges Lemaitre independently concluded
that the universe had to be either expanding
or contracting.
Einstein built in a fudge factor to prevent
expansion called the cosmological constant,
though he would later call this his biggest
blunder.
It is space itself that is expanding.
The balloon analogy for
expansion
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The galaxies separate from each other just as
dots on a balloon separate as the balloon is
inflated.
Gravity keeps the galaxies from expanding as
they separate.
The furthest galaxies are speeding away from
us faster than the speed of light.
Space expanding does not violate the speed
of light speed limit.
Evidence of Big Bang
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Velocity and distance calculations of any
galaxy results in the fact that each one
started off at the same location.
Microwave (heat) radiation left over
from the big bang (2.7 K)– as space
expanded, radiation was stretched out
from short wavelengths to longer
waves.
Big Bang Theory fate of
universe
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If there is enough mass in the universe,
gravity will stop expansion and pull the
universe back into another big bang.
If there is not enough mass, gravity
cannot stop the expansion.
The Modern View
(quantum mechanical)
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There had to be some asymmetry at
the big bang, or the universe would
have canceled out, and we would not
be here.
This asymmetry shows up in the WMAP
satellite map of the 2.7 K heat radiation
left over from the big bang.
What we know
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Looking back in time, we know how the
universe has shaped and evolved up to
the very instant of the big bang.
Read Phases of the Universe, pages 104
to 107, of Parallel Worlds.
What we don’t know
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The source of the big bang.
What the mysterious “dark matter” that
actually makes up the majority of the
matter of the universe is.
What “dark energy” is.
Dark Matter
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In the 1930s, Fritz Zwicky noticed that the
Coma cluster of galaxies were rotating so fast
that they should fly apart.
In 1962, astronomer Vera Rubin studied the
rotation of the Milky Way galaxy and found
the same problem.
In 1978, Rubin and her colleagues had
examined eleven spiral galaxies, all of which
were spinning too fast to stay together.
Dark Matter
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It bends light, like anything with mass.
About 25% of the universe is dark
matter, whereas only 5% is our known
matter.
There is no agreement as to what dark
matter is.
Dark Energy
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Dark energy is a theoretical construct to
help explain the observed expansion of
the universe, so it may or may not be
real.
To understand dark energy, you need to
understand Friedmann’s simplification of
Einstein’s equation.
Friedmann’s Simplification of
Einstein’s equation
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Friedmann assumed that the universe
was isotropic, or the same from all
directions.
He also assumed that the universe was
homogeneous, or totally uniform.
Three input numbers for
description and fate of universe
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H- the expansion number, Hubble’s
constant.
Omega- the average density of matter
in the universe .
Lambda - the amount of dark energy in
the universe.
Omega and Critical Density at
zero Lambda
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The critical density is 10 H atoms/m3.
If the omega value is greater than the critical
density, the universe will be positively curved,
like a sphere, and come back together.
If omega is less than the critical density, the
universe will be negatively curved, like a
saddle, and expand forever.
If omega is equal to the critical density, the
universe will be flat and expand forever.
Surprising Result
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Scientists found the universe to be flat, and yet
omega, the mass density, was only found to be 30%
of the value it needed to be for a flat universe.
The mass used in the calculation included dark
matter.
Conclusion: there must be even much more “stuff” in
the universe than the known matter (5% of universe)
and dark matter (25% of the universe).
This mysterious “other stuff” must make up 70% of
the universe.
More Surprises
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Close examination of red-shift data from
distant galaxies showed that the rate of
universe expansion was actually increasing.
This was an impossible result- gravity should
be slowing the expansion down, not speeding
it up.
It was now impossible to fit the data with any
value of Omega.
The solution
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Scientists had to reintroduce Lambda as a
repulsive, antigravity type of energy (dark
energy).
When Lambda was adjusted to fit the known
expansion acceleration it accounted for about
70% of the “stuff” in the universe.
This was also the value required for the
known flatness of the universe 
What could dark matter be?
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Hydrogen, helium, lithium, and other atoms
are unlikely, because observed matter
matches calculated matter.
Neutrinos are all around us, and yet
undetectable, like dark matter- however, this
is unlikely because their mass is too low.
Supersymmetry particles (sparticles),
although undetected, are candidates.
Dark Energy
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Homogeneous.
The mass equivalent of its energy
density is 10-29 g/cm3.
It is very difficult to detect directly.
When the volume of the universe
doubles, the density of matter is cut in
half, but the dark energy density is
nearly unchanged.
The Universe as a Free Lunch
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0 = 1 + (-1). Mathematically, something
from nothing seems possible with opposites.
This seems to violate the first law of
thermodynamics (which states that energy
cannot be created or destroyed).
Can we find an example of nothing to
something or something to nothing in nature?
Cancellation of light
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Light is its own opposite, and will cancel
if it is exactly out of phase. Let’s
explore, and see what happens to the
energy upon cancellation.
Examples of light cancellation
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Thin film interference – The light does not
exist where waves “cancel”; however, energy
is not lost, because light transmits 100%
instead.
Using out of phase, superimposed radio
transmitters, waves cancel; however, energy
is not lost, because transmitters stop drawing
energy at all.
These examples are not something from
nothing.
Negative – Positive energy
concept seems to work
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Negative energy comes from the
Heisenberg uncertainty principle.
Quantum jitters fluctuate above and
below the zero energy line of a vacuum.
Virtual particle pairs of positive and
negative energy pop in and out of
existence.
The Casimir Effect is evidence of this.
Evidence of a something-fromnothing universe
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“Nothing” has zero spin– the spin of
everything in the universe adds up to
zero.
Similarly, “nothing” has zero charge– all
the charge in the universe adds up to
zero.
The Big Bang Process
A broader understanding of
“Condensation”
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Use the term to apply to almost any
change that happens as a result of
cooling temperatures
Condensation example – First
look at reverse process
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As heat is added ice melts to water
As heat is added water vaporizes to gas
Water vapor breaks into O2 and H2
O2 and H2 separate into O and H atoms
The electrons are driven off of O and H
(plasma)
The O and H nuclei start to break down
The reverse (cooling) process
results in condensations
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Plasma of electrons and H and O nuclei
“condense” into H and O atoms
H and O atoms “condense” into H2O gas
H2O gas condenses into liquid water
Liquid water “condenses” into solid
water
Before 10-43 seconds
(Planck Era)
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Almost nothing is known
considered a “singularity” (the math
breaks down such as infinities at a
point)
four forces were all unified into one
“superforce
Planck Length of 10-33 centimeters
10-43 to 10-35 seconds,
(Inflation era)
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gravity split off of the superforce
10-35 sec, Strong force splits off – starts
inflation
supper cooled Higgs field results in inflation
Tremendous amounts of potential energy
liberated
potential energy into heat and particles
almost identical number of particles and
antiparticles
Inflation continued
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extremely high energy gamma rays
Matter and energy interchangeable and
in equilibrium
quarks, gluons, leptons, antiparticles
super heated plasma “soup”
Inflation provided “bang” for expansion
Inflation insured that universe will be
“flat”
10-34 seconds to 1 second
(end of inflation)
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Start - universe size of our solar system
Antimatter combines with matter = light
Friedmann expansion – gravity slows
expansion
Dark energy not yet a factor
quarks “condensed” into groups of 3
(baryons)
Proton, neutron, neutrino, electron plasma
1 second to 4 minutes
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protons and neutrons were almost
equal at the start
With cooling temps neutrons broke
down to form protons and electrons
86% proton, 14% neutron
Universe cools and protons and
neutrons form helium nuclei
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After a few minutes mostly hydrogen
nuclei, helium nuclei, and electrons
universe is still a high temperature
plasma
The only element nuclei that existed at
that time was hydrogen and helium in a
3:1 ratio and trace lithium
No larger elements at this time
4 minutes to 380,000 years
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Universe continues to cool as it expands
Friedmann expansion – gravity slowing
it down a bit
Radiation wavelength expands with
space (gamma > x-ray > UV)
Radiation interacted with electrons
Universe was opaque to “light”
380,000 years - 3,000 K
(The dawn of light)
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Light weakens to less than the
ionization energies of hydrogen and
helium (the UV range)
electrons and nuclei condense to form
hydrogen and helium atoms
The universe becomes transparent to
light
Wavelengths increase to visible range
Back Into darkness
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As the universe continues to cool the
wavelength continues to lengthen until
it completely enters the IR range.
The universe went from white to red to
darkness
The hydrogen and helium gasses
continue to be bathed in heat radiation
One billion years, 18 K
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universe is now extremely cold (18 K)
as a result on a very slight asymmetry
at the very start of the universe giant H
and He clouds form
The first stars ignite - there are now
points of light in the universe
Universe about 1/5 of its current size
6.5 billion years (de Sitter
expansion)
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The space between galaxies continues
to expand
dark energy becomes a significant
factor
As dark energy increases the expansion
of the universe accelerates
de Sitter expansion
Stars evolve, galaxies and planets form
Life and death of star creates
more elements
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Protons and electrons are compressed and
heated to create neutrons
Hydrogen combines to make helium
Hydrogen is used up and star shrinks, heats
up more and burns helium to form element
up to the size of iron
Once helium is used up star collapses and
forms larger elements in a super nova
13.7 billion years (now)
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Dark energy continues to speed up
expansion of the universe
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In view of the fact that we still know
little about 96% of the universe, we will
end this course with Newton’s quote.
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“I do not know what I may appear to
the world; but to myself I seem to have
been only like a boy, playing on the sea
shore, and diverting myself, in now and
then finding a smoother pebble or a
prettier shell than ordinary, whilst the
great ocean of truth lay all
undiscovered before me.”