The Cosmic Perspective

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The Cosmic Perspective of Cosmology
NOTES Cosmological Terminology Cosmology
the study of the large scale structure and
evolution of the universe. Homogeneity the
claim the universe has the same density in
all locations at the largest scale. Isotropy
the claim the universe looks the same in all
directions.
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Cosmology is NOT cosmetology
though a cosmologist makes up the face of the
universe.
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Cosmology is the study of the large scale
structure and evolution of the universe in
space time.
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Homogeneity the claim the universe has the same
density in all locations at the largest scale.
(Center for Cosmological Physics at the
University of Chicago)
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Cosmological redshift
z redshift) ??/? v/c (for small v
expansion speed)
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Isotropy the claim the universe looks the same
in all directions.
Counts of distant galaxies and radio-sources
appear to provide evidence that the universe is
isotropic.
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Pre 1998 Cosmology --ignoring dark energy in
space In 1998, using Supernova Ias, universe
was found to be ruled by dark energy, making it
accelerate. We ignore this at first.
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O (Omega) density of
universe/critical density
critical density 10-29 grams per cubic
centimeter
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Alexander Friedmann (Russian) 1920 (utilizing
Einsteins General Theory) gave us three
possible expanding universes.
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With no dark energy Flat Universe Curvature
0 Omega 1 Destiny barely stop expanding, it
reaches a maximum speed but with no
collapse Closed Universe Curvature gt 0 Omega
gt 1 Destiny collapse Open Universe Curvature
lt 0 Omega lt 1 Destiny endless decelerating
expansion
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Graph of Friedmanns three expansions
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Galaxies are not flying apart through space,
they are being carried away by the expansion of
space itself (like small marks in the surface
on an inflating balloon). The Big Bang was not
like an explosion in a pre-existing space, but
rather an explosion of space itself.
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However, there were problems with Friedmanns
universe which resulted in the Inflationary
Universe of Andre Linde (Russia1979) and Alan
Guth (US 1980).
Guth got the Nobel Prize for a theory that didnt
work. Later, Linde adapted his own theory to one
that worked.
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Three problems led to a theory of early
rapid inflation
1. Horizon Problem  The isotropy of the microwave
background indicates that regions A and B in the
universe were very similar to each other when
the radiation we observe left them, but there
has not been enough time since the Big Bang for
them ever to have interacted physically with one
another. Why then should they look the same?
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2. Flatness Problem If the universe deviates even
slightly from critical density, that deviation
grows rapidly in time. For the universe to be as
close to critical as it is today, it must have
differed from the critical density in the past
by only a tiny amount.
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3. Magnetic monopole problem Universe is
believed to produces North magnetic poles
without a South, but we dont observe
any. Friedmanns universe didnt expand enough
to make them far apart.
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Inflation Scale vs time (sec)
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Just as ice takes up more volume than
water, space was believed to have undergone a
expanded phase change related to the Grand
Unified Theory (GUT) of elementary particles.
(Guths Theory). However, this meant that
protons should decay and they dont.
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Chaotic Inflation Among many parallel
universes, one expands like ours with a bubble
that bursts and explains the lumpy structure of
the universe necessary to produce clusters,
galaxies, and stars. This is called Scale-free
lumpiness. Andrei Linde (now at Stanford)
showed this.