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Cosmology I

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Cosmology I & II Fall 2010 – PowerPoint PPT presentation

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Title: Cosmology I


1
Cosmology I II
  • Fall 2010

2
Cosmology I II
  • Cosmology I 7.9.-22.10.
  • Cosmology II 1.11.-17.12.
  • http//theory.physics.helsinki.fi/cosmology
  • Lectures in A315, Mon Tue 14.15-16.00
  • Syksy Räsänen, C326, syksy.rasanen_at_iki.fi
  • Exercises in D112, Fri 14.15-16.00 (starting
    17.9.)
  • Stanislav Rusak, A314 , stanislav.rusak_at_helsinki.f
    i
  • Exercises form 20 of the score, the exam 80
  • Exercises are handed out on Monday, and returned
    by following Monday.
  • Exception next week they are due on Wednesday.

3
Cosmology I
  • Introduction
  • Basics of general relativity
  • Friedmann-Robertson-Walker (FRW) models
  • Thermal history of the universe
  • Big Bang nucleosynthesis (BBN)
  • Dark matter

4
Cosmology II
  • Quantum field theory (QFT) for children
  • Inflation
  • Structure formation
  • Brief introduction to perturbation theory
  • Cosmic microwave background (CMB) anisotropy

5
Observations basics
  • Electromagnetic radiation
  • Radio waves
  • Microwaves
  • IR
  • Visible light
  • UV
  • X-Rays
  • Gamma rays
  • Massive particles
  • Cosmic rays (protons, antiprotons, heavy ions,
    electrons, antielectrons)
  • Neutrinos
  • Gravity waves?
  • Composition of the solar system

6
Observations in practice
  • Motion of galaxies
  • Distribution of galaxies (large scale structure)
  • Abundances of light elements
  • Cosmic microwave background
  • Luminosities of distant supernovae
  • Number counts of galaxy clusters
  • Deformation of galaxy images (cosmic shear)
  • ...

7
Laws of physics
  • General relativity
  • Quantum quantum field theory
  • Atomic physics, nuclear physics, the Standard
    Model of particle physics
  • Statistical physics and thermodynamics

8
Homogeneity and isotropy observations
http//map.gsfc.nasa.gov/media/101080/index.html
9
Homogeneity and isotropy observations
http//sci.esa.int/science-e/www/object/index.cfm?
fobjectid47333
10
Homogeneity and isotropy observations
  • arXivastro-ph/0604561, Nature 4401137.2006

11
Homogeneity and isotropy observations
12
Homogeneity and isotropytheory
  • The observed statistical homogeneity and isotropy
    motivates theory with exact HI
  • The Friedmann-Robertson-Walker models
  • The expansion of the universe is described by the
    scale factor a(t)
  • Extrapolating the known laws of physics we find
    that 14 billion years ago
  • a ? 0, ? ? 8, T ? 8

13
The Big Bang
  • The early universe was
  • Hot
  • Dense
  • Rapidly expanding
  • HI and thermal equilibrium
  • ? easy to calculate
  • High T ? high energy ? quantum field theory

14
Timeline of the universe
10-12 s
TeV
Baryogenesis?
Electroweak (EW) transition Fermions, W,W-,Z0
become massive g massless
10-6 s
GeV
QCD phase transition quarks g p, n

? decoupling ee- annihilation n/p 1/6
1 s
MeV
Big bang nucleosynthesis (BBN) 2H, 3He, 4He, 7Li
1 h
15
Short history of the universe
1 yr
keV
eV
Decoupling of light and baryons gt atoms The
universe becomes transparent Cosmic Microwave
background (CMB)
106 yr
Dark ages
Structure formation Formation of galaxies, first
stars
meV
1010 yr
Now
16
Short history of the universe
10-42 s
1019 GeV Planck time
1018
Inflation?
Baryogenesis? Topological defects formed?
(monopoles, cosmic strings, domain walls)
10-36 s
GUT era?
1015
10-30 s
1012
10-24 s
109
10-18 s
106
Supersymmetry breaks?
10-12 s
103 GeV
SU(3) Ä SU(2) Ä U(1)
17
Structure formation
  • CMB shows the initial conditions
  • The early universe is exactly homogeneous up to
    small perturbations of 10-5 to 10-3
  • Seeds of structure
  • Gravity is attractive
  • ? fluctuations grow into galaxies, clusters of
    galaxies, filaments, walls and voids, which form
    the large-scale structure of the universe

18
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21
Structure formation
  • Origin of fluctuations inflation
  • A period of acceleration in the early universe
  • Quantum fluctuations are stretched by the fast
    expansion and frozen in place
  • Growth of fluctuations
  • Due to ordinary gravity
  • Depends on the initial state plus the matter
    composition
  • Baryonic matter is too smoothly distributed at
    last scattering

22
Dark matter
  • Luminous matter stars, gas (plasma), dust
  • Large-scale structure, CMB anisotropies, motions
    of stars in galaxies, galaxies and gas in
    clusters, gravitational lensing, BBN, ...
  • ? there is invisible matter
  • Baryonic matter cold and hot gas, brown dwarfs
  • However, the majority of matter (about 80) is
    non-baryonic, either cold dark matter (CDM) or
    warm dark matter (WDM, m gt 10 keV)
  • Neutralinos, technicolor dark matter,
    right-handed neutrinos, ...

23
Dark energy
  • Exactly homogeneous and isotropic models with
    baryonic and dark matter dont quite agree with
    the observations
  • Measured distances are longer by a factor of
    1.4-1.7 and the expansion is faster than
    predicted by a factor of 1.5-2
  • Three possibilities
  • 1) There is matter with negative pressure which
    makes the universe expand faster (dark energy)
  • 2) General relativity does not hold (modified
    gravity)
  • 3) The homogeneous and isotropic approximation is
    not good enough

24
Dark energy
  • Dark energy is the preferred option
  • Dark energy
  • has large negative pressure
  • is smoothly distributed
  • has an energy density about three times that of
    baryonic plus dark matter
  • The most natural candidate is vacuum energy
  • The greatest mystery in physics.
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