Recent developments in Cosmology

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Recent developments in Cosmology

• Ana Achúcarro
• Kaleidoscoop, 23 Nov 2004

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Before we start
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The First Fundamental Equation of
Cosmology very far very old (because light
takes a long time to reach us!)
Hubbles law (1929)
v H d vvelocity (from Doppler shifts)
ddistance HHubbles constant (about 71
Km/s/Mpc)
1 Mpc (Megaparsec) 1 million parsecs, 1 parsec
3.3 light-years
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Second fundamental equation (ca. 1980)

• In astronomy (and cosmology)
• 1 2
• so distances, ages,
• speeds, etc. are (very) approximate...

p
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Second fundamental equation (ca. 2004)

• In astronomy (and cosmology)
• 1 1.1
• so distances, ages,
• speeds, etc. are (somewhat) approximate...

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COSMOLOGY IN 2004

• The Universe we observe seems to be
• Isotropic and homogeneous (on scales gtgt 10
  Mpc)
• (31)-dimensional
• Spatially flat
• and is expanding at an increasing rate
• (the
  cosmological constant is positive).
• About 90 of the matter in the Universe is dark
  (not luminous)

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The evolution of a homogeneous, isotropic
Universe according to Einsteins equations is
governed by Matter content
Cosmological constant
(dark energy) Spatial curvature
measured directly by
Cosmic dynamics / gravitational lensing
Supernovae Cosmic microwave background
radiation
baryonic fraction light element
abundances in stars
and those independent measurements seem to agree
in a model of the Universe, the Concordance
Model .
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Surveys
The nearby Universe is not homogeneous or
isotropic Planets/Stars ?
Galaxies ? Galaxy clusters ? Superclusters
( Earth / Solar system ? Milky way ? Local
group ? ... ) We have to go
to much larger scales...
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Las Campanas Redshift Survey
North 11263 galaxies
2dFGRS 250.000 galaxy redshifts (finished, final
data June 2003) SLOAN 1 million galaxy
redshifts (ongoing)
South 12434 galaxies
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The strongest evidence for the homogeneity and
isotropy of the Universe comes from the Cosmic
Microwave Background Radiation
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The Cosmic Microwave Background Radiation (CMB)
The cosmic background radiation was
discovered by A. Penzias and R.W.Wilson in
1965 at Bell Labs. Radio waves, mm-cm
Perfect black body at T 2.7 K Redshifted
photons from the time of recombination, z 1000
R.W.Wilson
A. Penzias
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A map of the CMB
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COBE (COsmic Background Explorer, 1992)
Temperature variations less than 0.001
Angular size of spots 7º.
Between 1999-2001 many other experiments
(BOOMERanG, MAXIMA, DASI) improved sensitivity.
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WMAP (Wilkinson Microwave Anisotropy Probe)
First year of data released in March 2003
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WMAP power spectrum of temperature fluctuations
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A detailed analysis of the temperature anisotropie
s seems to indicate that the Universe is
spatially flat.
This supports inflation
It is a direct measurement
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How do you measure the curvature of the
Universe without leaving it?
Gauss (1777-1855)
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The curvature of the Universe
M.Berry, Principles of Cosmology and Gravitation
k 0 k
1 k -1
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Supernovae
Evidence for the cosmological constant comes from

• Supernova 1987a

before
after
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Expansion is accelerated
S. Perlmutter et al B.P. Schmidt et al
(1997/98)
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Weighing the Universe
There are two ways to measure (directly) the
amount of matter in the Universe. Cosmic
dynamics - a study of the trajectories of
celestial bodies Gravitational
lensing Strong Microlensing Weak
COMA CLUSTER
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Gravitational lensing
Source
Lens
Observer
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COSMOLOGY IN 2003(THE CONCORDANCE
MODEL)OFFICIAL WMAP RESULTShttp//map.gsfc.nasa.
gov/ last updated 9 January 2003

• The Universe is 13.7 billion years old (with a
  margin of error of about 1)
• First stars ignited 200 million years after the
  Big Bang.
• Light in WMAP picture from 379,000 years after
  the Big Bang.
• Content of the Universe
• 4 Atoms, 23 Cold Dark Matter, 73 Dark energy.
• The data places new constraints on the dark
  energy. It seems more like a "cosmological
  constant" than a negative-pressure energy field
  called "quintessence". But quintessence is not
  ruled out.
• Fast moving neutrinos do not play any major role
  in the evolution of structure in the universe.
  They would have prevented the early clumping of
  gas in the universe, delaying the emergence of
  the first stars, in conflict with the new WMAP
  data.
• Expansion rate (Hubble constant) value Ho 71
  km/sec/Mpc (with a margin of error of 5)
• New evidence for Inflation (in polarized signal)
• For the theory that fits our data, the Universe
  will expand forever. (The nature of the dark
  energy is still a mystery. If it changes with
  time, or if other unknown and unexpected things
  happen in the universe, this conclusion could
  change.)

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A possible history of the Cosmos
t 13.5 billion years
Today
Life on earth Solar system
Quasars
Galaxy Formation Gravitational
collapse
Recombination relic radiation
decouples
Matter domination onset of grav.
instability
The standard model of cosmology
Nucleosynthesis light elements D, He, Li
Quark-hadron transition
protons, neutrons form
Electroweak phase transition
Supersymmetry
(There may be alternative models braneworlds)
Grand Unification transition
Inflation,
defects, baryogenesis
The Planck epoch
quantum gravity
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In the concordance model, the nature of 96 of
the contents of the Universe is unknown (23
dark matter, 73 dark energy!)
Inflation is powered by a scalar field, the
inflaton.
Its microscopic origin is unclear
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Understanding the microscopic degrees of
freedom of the Universe is a major challenge
for theoretical physicists in the 21st
century.
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Fossils of the early Universe?
When a substance undergoes a phase transition
there is a qualitative change in its properties
water ? ice
In other substances, very quick cooling may
lead to defects, bags of the hot phase
getting trapped inside the cold phase. The
expansion of the Universe caused it to cool very
fast, and it is possible that defects formed,
small regions or bags of the Universe as it
was before the phase transition.
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These were cosmic strings Another example could
be isolated magnetic poles (very heavy) Inside
the defects, the Universe is still as it was
before the phase transition. If we could detect
defects and study them we would know what the
early Universe was made of
But they have not been seen ...
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At atmospheric pressure, helium never freezes.
At ultra-low temperatures it undergoes a phase
transition and becomes a superfluíd liquid,
with no viscosity. If the transition is very
quick, it leads to defects that can be studied
in the laboratory. The properties of defects
in superfluim helium are very similar to those
in the early Universe.
COSMOLOGY IN THE LABORATORY
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The great paradox
In order to understand the Universe at a
temperature of
trillions of degrees we study liquid helium at
milikelvin
- 273.15 C
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And, finally, this years development
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The Universe starts hot and dense. The expansion
cools it down. Symmetry -
breaking phase transitions Topological
defects
Points monopoles Lines
cosmic strings Surfaces domain walls .
. . branes
textures
ALSO superstrings
Topological defects are ruled out as the main
agent in structure formation but they are a
powerful tool to constrain the microscopic
degrees of freedom of the early Universe.