Cosmology the study of the structure and evolution of the entire universe'

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Cosmology the study of the structure and
evolution of the entire universe.
Observation based on what we see, we believe
that the universe is --homogeneous --isotropic
This assumption is called the Cosmological
Principle. This then implies --there is
no edge to the universe --there is no
center to the universe
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Olberss Paradox Because the universe is
infinite then no matter where you look you
should see the surface of a star and the sky
should be bright. But that is not
what we see! The sky is dark at night. So, if
the universe is homogeneous and isotropic then
EITHER, the universe is NOT
infinite, OR, the universe evolves with
time.
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From Hubbles Law Recession Velocity ? (Ho) x
(Distance) and, time
(distance)/(velocity) Combining these two
expressions gives time 1/Ho age of
universe if Ho 65 km/s/Mpc then,
the age of the universe 15 billion years.
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At a time 1/Ho the universe began in an event we
call the Big Bang. All matter and radiation was
concentrated at a single point, called a
singularity.
But like living on the surface of a balloon, we
can see no beginning.
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Also, as the balloon expands we see all parts
receeding from all others. This explains why we
see all the other galaxies speeding away from us.
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The expanding universe also caused the
wavelengths of radiation from the Big Bang to be
red shifted. The photon expands with the
universe. We see this today as the microwave
background radiation.
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The ultimate fate of the Universe
Once we believed that the universe was
unchanging, and would always remain the same.
But now we know that the universe is expanding.
Depending on how much matter there is in the
universe we have three possible outcomes.
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• too little mass means we expand forever (death by
  ice)
• 2) too much mass and we get the big crunch
  (death by fire)
• 3) just the right amount and we eventually stop
  expanding

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O0 is a number that represents the Cosmic Density
Parameter O0 actual density of the universe
critical density
Currently astronomers cannot find enough mass to
close the Universe. They estimate O0 to be less
than 1
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But, not only is the Universe expanding, it
appears to be accelerating outward! We see the
farthest galaxies moving away from us more slowly
than we would expect. What can cause us to be
expanding faster and faster? Gravity attracts,
but what repels? Vacuum pressure? (The
Cosmolgical Constant) Dark energy?
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The Geometry of Space
The greater the total density of the cosmos
(rmatter, radiation, dark energy), the greater
the curvature of space.
There are only 3 possibilities (1) Density
gt ?0 closed universe No boundary, but finite
(2D analogy is surface of balloon) Positive
curvature Consequence light emitted returns
from other direction (2) Density lt ?0 open
universe Saddle shaped, curves up in 1
direction, down in the other Infinite and
unbounded (3) Density ?0 flat
universe No curvature, flat, Euclidean
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Cosmic Microwave Background
Cosmic Background Explorer
Wilkinson Microwave Anisotropy Probe
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As the Big Bang occurred we went from a radiation
dominated universe to a matter dominated universe
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Hydrogen (75) and Helium (25) are the only two
atoms made during the Big Bang. All other
elements were manufactured in by the stars and
supernovae explosions. The ratio of Helium to
Hydrogen is an important constraint to current
theories. It is difficult to tell if spacetime
is curved because the distances we can measure
are so small compared to the universe
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Cosmic Inflation
In the course of trying to unify all forces into
one grand unified force that existed at the
beginning of the universe, theory predicts that
the universe went through a brief, odd, period in
an unstable high-energy state. At the end of
this brief period the universe expanded at an
accelerated rate, a great rush, termed
Inflation. So now the universe is nearly flat
and the total density must be near critical.
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Large Scale Structure
The large scale structure of the universe grew
out of the small inhomogeneities that existed
early on. COBE is mapping the small temperature
differences in the microwave background even now.
It shows ripples similar to the voids, walls and
filaments of matter we observe today. The
importance of these observations is that they
support inflation theory that asserts that the
universe is of exactly critical density, and is
flat. However.