Chapter 5: Cosmic foundations for origins of life

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Chapter 5 Cosmic foundations for
origins of life
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Is life a natural consequence of cosmology?

• - Evidence for origin of evolution by Big Bang
  becoming very secure
• - expansion of the universe,
• - cosmic microwave background radiation,
• - synthesis of simple elements - hydrogen,
  helium, lithium.
• - Galaxies are a consequence of small
  fluctuations produced during the Big Bang
• - Stars form in galaxies first stars created
  first carbon in universe life not possible
  before this?
• - Stars produce all the heavier elements (dubbed
  metals) produced by fusion in stellar interiors
  (eg. O, C, N, .)
• - Synthesis of carbon finely tuned a slight
  change in strength of forces could result in
  universe with no
• heavy elements, so no life.

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Our Milky Way Galaxy is a spiral galaxy much
like Andromeda our most massive partner in the
Local Group of Galaxies.
Note this spiral galaxy has a galactic bulge,
halo, and disk. There are also 2 dwarf galaxies
visible that orbit Andromeda.
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THE EXPANDING UNIVESE

• Edwin Hubble
• 1889 - 1953

At the 48 inch on Mt. Palomar
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Cepheid variable stars in M100 galaxy in the
Virgo cluster used by Hubble to measure the
distance to galaxies. P vs. L relation
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Hubble Diagram (1929) all galaxies receed from
us. Speed of separation (v) is measured from the
red shift of some typical well-observed line. -
Hubble founds that v is proportional to the
distance to the galaxy HUBBLES LAW
Hubbles original data and graph.
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Red-shift distance relation for galaxies
enormously more distant than in Hubbles original
study. Galaxies studied here are members of
galactic clusters (eg. Virgo, Hydra, etc)
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Galaxies move away from us - the same for
observers in any other galaxy at some past time,
all the matter must have been at one point a
Big Bang must have occurred!
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• Best measured value for Hubbles constant
• Good distance measurements from 1. HST
  observations of Cepheids in other galaxies and
• 2. Tully-Fischer relations
• Hubble constant has units of 1/time so a good
  estimate of age of the universe is
• 1/Ho 15 billion years!

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CFA survey of galaxies out to 200 MPC covering
6 deg. thick slice of sky. 1057 galaxies shown.
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Cosmological Model a homogenous and isotropic
universe

• Probe structure in the universe on ever larger
  scales there is a largest scale seen Great
  Wall of about 200 Mpc in scale.
• On scales gt 300 Mpc universe appears to be
  homogenous (same everywhere).
• Universe is same in every direction on these
  largest scales isotropic.

23,697 galaxies within 1000 Mpc (Las Campanas
survey). Voids and walls no larger than 100
200 Mpc.
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• Picturing the Expansion of the Universe
• It is spacetime that expands the distance
  between galaxies grows!
• The Big-Bang is not like a bomb going off
  inside some space it is spacetime itself that
  explodes about 15 billion yrs ago.
• Picture dots on a balloon (galaxies). As
  balloon expands (ie spacetime), galaxies carried
  away from one another. Every observer on every
  dot sees all the other dots recede ie, Hubbles
  law is measured by all observers in the universe

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General relativity and cosmology

• Cosmological model assume homogenous and
  isotropic distribution of matter on largest
  scales
• General relativity shows space-time is dynamic!
  Evolution of universe depends on its density.
• Critical density for universe at greater than
  the critical density, the expansion of the
  universe will ultimately cease and it will
  re-collapse. At densities lower that critical
  value, the universe will continue to expand
  forever.
• Critical density in general relativity can be
  accurately calculated using Hubbles law, and
  Newtonian gravity to find

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General relativity The fate of the universe
depends on how dense it is.
A low density universe (open) will continue to
expand forever. A critical density universe will
coast to a stop after an infinite time. A high
density universe (closed) will expand to a
maximum size in a finite time and collapse into
a singularity again the Big Crunch
Distance between galaxies as a function of time
model with critical density labelled marginally
bound
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Geometry of the universe in four dimensions
Closed Universe Critical
Open Universe (sphere)
(flat)
(saddle)
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• Predicted in 1948 (Alpher, Bethe, and Gamow)
• Discovered in 1964 by Penzias and Wilson Nobel
  prize

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Cosmic Microwave Background Radiation (CMBR)

• Major prediction of the Big Bang is that the
  universe started very dense and hot, and then
  cooled with time.
• CMBR pervades all space, and should be
  black-body.
• Explanation Wiens law for black body
  radiation increasing wavelength implies that
  temperature decreases

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• Expansion of universe stretches out the
  wavelength of a photon like wave drawn on a
  balloon that is stretched with time
• This is why galaxies appear to be redshifted!
  NOT that galaxies move relative to one another
  but that universe expands during the time it
  takes light to travel from another galaxy to us.
• Temperature varies inversely as scale factor of
  universe

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COBE measurement of CMBR spectrum T2.735 K

• Experimental errors are smaller than size of
  dots in figure. Blue line is best fit black-body
  spectrum

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COBE map (1989) fluctuations in
temperature one part in a hundred thousand
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WMAP (2003) 45 times more sensitive, and 33
times the spatial resolution of COBE
Data from WMAP gives age of universe of 13.7
billion yrs to accuracy of 1! Fluctuations
are the seeds of galaxy formation
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Inflation and CMBR(Alan Guth, 1981)

• At a time when the age of the universe was
• Universe underwent a brief(!) epoch during which
  exponentially fast expansion occurred -
  increasing its size by 50 orders of magnitude!
• (before and after this episode, the size of the
  universe grows as a power-law function of time
  much slower!).
• - Universe grew out of a single fluctuation of
  this new phase solving problems

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Big Bang Nucleosynthesis

• During first 3 minutes in time that universe
  cools from 10 billion to 1 billion deg. K
  nucleosynthesis is possible.
• Elements fabricated are Helium-3, Helium-4,
  Deuterium, and a trace of Lithium.
• Deuterium and Helium isotopes produced using
  neutrons unlike proton-proton chain.

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Producing simplest elements in the Big Bang

• Observations of Helium 3 4, deuterium, -gt
• specific density and temperature conditions
• -gt strongly constrain the cosmological model
  fraction of matter in baryons.
• Deuterium is not produced significantly in stars
  so are seeing primordial abundance.
• Best fit baryon density that is a few of
  critical.

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Supernovae Type Ias mapping the cosmos to
furthest distances discovery of dark energy
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Composition of universe

• Measure density in units of the critical density
  define density parameter
• Contribution of baryonic (ordinary) matter
• Contribution of all matter (baryonic dark)
• Contribution of dark energy (cosmological
  constant) from CMBR and supernova measurements
• Key result

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Text
History of our universe
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Origin of Galaxies

• Density fluctuations arise at earliest moments
  when universe is still a quantum-mechanical
  object. This is the Planck scale
• Quantum fluctuations in Planck era are ultimate
  density fluctuations that grow to be galaxies!
• This spectrum of fluctuations is preserved in the
  CMBR fluctuations - predicts many aspects of
  galaxies such as their size distribution,
  evolution with time (hierarchical), etc.

Computer simulation courtesy Hugh Couchman
(McMaster University)
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Formation of the first star

• Physics is much simpler no magnetic fields, no
  dust or complex molecules, primordial gas
  contains hydrogen and helium.
• Start with a small, cold, dark matter halo
  about a million times mass of the Sun.
• Gas within it cools down to 200 K, (molecular
  hydrogen is the coolant)
• A 100 solar mass core forms inside a filamentary
  molecular cloud

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The very first star 100 times the mass of our
Sun - a single star forms
Abel et al (2002), Science
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First stars turned on perhaps 200 million years
after the Big Bang they started to make the
elements out of which planets, and living things,
are made.
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Stellar evolution forming the elements for
biolmolecules and planets.