COBE

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Cosmology
Steve King
Physics CSG Day at Southampton University 5/6/7
13.7Gyr ABB
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Revolutionaries
These men taught us that the Earth is not the
centre of the Universe
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Newfangled Cosmology
Hubble Space Telescope
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The Universe Age 700 million years
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• Cosmological Principle
• Our position in the Universe is not special
• -all points in the Universe are equivalent just
  as all points on the surface of the Earth are
  equivalent
• the Universe looks the same wherever you are
  
• - cosmological principle is an approximate
  property of the global Universe, which only
  applies on the largest distance scales
  
  
  

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The Milky Way Spiral Galaxy
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The Milky Way Local Group satellites
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The Milky Way Local Group including Andromeda
galaxy
N.B. Large galaxies separated by about 1,000,000
pc 1 Mpc
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The Virgo Supercluster containing Virgo Cluster
and our Local Group
Each dot is a bright galaxy. Milky Way is dot in
the exact centre.
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Our Neighbouring Superclusters Virgo
Supercluster at the centre
Note the presence of filaments and voids in an
irregular cellular pattern.
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On the largest distance scales the Universe
appears smooth, with no further structures
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Homogeneity and Isotropy


The fact that the Universe is smooth on the
largest distance scales (bigger than a billion
light years) supports the cosmological
principle. In fact the Universe appears to have
two separate features Homogeneous the same at
each point (c.f. homogenised
milk) Isotropic the same in all directions Very
small departures from homogeneity are clearly
present due to the irregular cellular large scale
structure of the Universe.
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The Expansion of the Universe
Hubbles Law all galaxies are moving away from
us with a speed of recession v proportional to
the distance of the galaxy d
Hubbles constant
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How is the galactic speed v measured? from
redshift z of absorption and emission lines
(Doppler effect) How is galactic distance d
measured? from the apparent luminosity of
standard candles in the galaxy (e.g. Cepheid
variables, type Ia supernovae,) What is the
interpretation of Hubbles law? the Universe
is expanding at a constant rate
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If the Universe is expanding at a constant rate
then every galaxy will be moving away from every
other galaxy in accordance with Hubbles law
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This implies that in the distant past the
Universe would have been much smaller than now.
We infer that the Universe started from a small,
dense, hot region from some initial explosion
called the Big Bang.
Modern Cosmology
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History of the Universe\_PC START.exe
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The Universe Age 380,000 years just after the
atoms were formed and the Universe becomes
transparent -- henceforth these Big Bang photons
travel unhindered through the Universe
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As the Universe expands, the Big Bang photons in
the visible spectrum get redshifted into
microwave photons
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Cosmic microwave background
The Big Bang photons from the time of atom
formation (380,000 yrs) are observed as microwave
background radiation, with a Black Body spectrum
corresponding to a temperature of about 3 K
-270o C
(redshifted from a temperature of about 3,000 K )
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Penzias Wilson
In 1965 Penzias and Wilson discovered the CMB as
an irremovable background hiss in their antenna

Nobel Prize 1978
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About 1 of TV White Noise is due to CMB
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These days more sophisticated equipment is used
to make temperature maps of the sky
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John Mather, NASA GSFC Overall PI of COBE and PI
of FIRAS
George Smoot, Berkley PI of DMR
The first people to make a temperature map of the
sky
COBE Nobel Prize 2006
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Temperature Maps
Earth
Universe
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COBE 1992
WMAP 2006
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We can learn a lot from these temperature maps
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The Standard Cosmological Model

• Requirements
• Flat Universe
• Dark Energy
• Dark Matter
• WOW!!

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means the Universe is flat
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Why did nature choose this one?
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This could be due to an exponential inflation
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Atoms only make up 4 of the mass of the
Universe The rest is unknown Dark Energy (fluid
like) and Dark Matter
(particle like)
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A Final Word on Dark Energy
Could the Dark Energy be Einsteins Cosmological
Constant?
My biggest blunder
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Dark Matter has been seen
Do you believe in Dark Matter?
Seeing is believing!
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The Bullet Cluster of Galaxies
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How Dark Matter Evolves
This computer simulation takes the CMB
temperature fluctuations as seeds of density
fluctuations which evolve in time to give long
filaments of dark matter
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By the time the Universe is 100 million years
old it is dominated by filaments of dark matter
around which the galaxy clusters and
superclusters will form
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Who is the dark matter particle?
An excellent candidate for dark matter is the
spin ½ partner to the photon called the photino
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The photino could be discovered at the CERN Large
Hadron Collider which starts later this year
Atlas
particle_event_full_ns.mov
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How Did it All Begin? Some believe it was a
vacuum quantum fluctuation quickly followed by
inflation
.
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Conclusion

• Cosmology has now entered a precision era
• Landaus adage that cosmologists are often in
  error never in doubt is undoubtedly no longer
  true!
• There is now a Standard Model of the Universe
  consisting of 74 Dark Energy which looks like
  Einsteins Cosmological Constant
• But only 4 is atoms
• The remaining 22 is Dark Matter consisting of
  particles which could be discovered soon at CERN
  (with the help of Southampton students!)

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Appendices

• Parsecs
• Spherical Harmonics
• Angular Power Spectrum
• Fluids in the Early Universe
• Sound Waves
• First Peak Geometry
• Second Peak Baryons
• Third Peak Dark Matter

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Stars main source of visible light from nuclear
fusion in stars Sun is typical
1 Parsec 3.26 light years 3 1016 meters
Sun
Earth
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We want to understand this
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Position of First Peak Measures the Geometry of
the Universe
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The Relative Height of Second Peak Measures the
Density of Baryons
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The Relative Height of Third Peak Measures the
Density of Dark Matter
Dark Matter Domination (later times lower
peaks)
Photon Domination (earlier times higher
peaks)