Our universe - · PDF file• The origin of the matter-antimatter asymmetry •...
Transcript of Our universe - · PDF file• The origin of the matter-antimatter asymmetry •...
Our universe:
facts
speculations &
Levon Pogosian
Simon Fraser University and
DAMTP, University of Cambridge
• Inflation • Dark Matter • Dark Energy
with a few key components:
and some remaining unknowns:
• Inflation • Dark Matter • Dark Energy
A working cosmological model
Fact: The universe is expanding
Expanding universe
a(t)�k=0�
Redshift z
a(t)�
Einstein’s static universe
aE�kE>0�
A. Friedmann, “Über die Krümmung des Raumes”, Zeitschrift für Physik (1922)
Meine größte Eselei!
Implication of the expansion:
the universe was dense and hot in the past
We can see the evidence:
looking deep into space = looking back in time
Us in the center
• 1940: Andrew McKellar observed excited rotational states of CN molecules in interstellar absorption lines, “temperature of space” of 2.4 K • 1941: Walter Adams made similar observations • 1948-1956: Gamow, Alpher and Herman published predictions of CMB • 1955 Emile Le Roux: λ=33 cm radio astronomy, isotropic emission with T=3±2 K • 1955 Tigran A. Shmaonov: λ=3 cm isotropic emission with T=4±3 K
Cosmic Microwave Background (CMB)
1965: A. Penzias and R. W. Wilson of Bell Labs 1978 Nobel Prize in Physics
Discovery of CMB
The CMB temperature map
http://map.gsfc.nasa.gov/ By NASA
Evolution of the map
By NASA
The spectrum
The spectrum of CMB anisotropies
Plateau: scale-invariant initial spectrum
Position of the peak: adiabatic perturbations
Δ ΔΔ
Oscillations: passive perturbations Inter-peak distance: flat geometry
Dark Matter
Facts from CMB Generic prediction of simplest inflationary models
Almost isotropic
Almost flat
Almost Gaussian statistics
Adiabatic initial conditions
Almost scale-invariant spectrum
r = Tensor/Scalar < 0.1
Homogeneity*
Flatness
Gaussianity
Adiabatic initial conditions
Almost scale-invariant spectrum
Gravitational wave background
Basics of Inflation
• A period of rapid expansion in the early universe:
• Driven by the potential energy of a scalar field, inflaton
• Quantum fluctuations of the inflaton “freeze” on super-horizon scales, become classical curvature fluctuations
• Inflation ends when the kinetic energy of the inflaton becomes large
• During “reheating”, the kinetic energy of the inflaton is converted into thermal energy of radiation
• Reheating, i.e. the transition from (cold) inflationary phase to the hot radiation dominated phase, should be considered to be the time of the Hot Big Bang
Status of Inflation
• Accepted as a working paradigm, fits existing data
• Quantum origin of fluctuations – a beautiful theoretical idea
• Not a theory – many proposals, predictions not unique
• Unresolved theoretical problems
o what was before inflation – singularity? o what are the conditions for inflation to start? o what is the inflaton? o is it related to the known particle physics?
• Alternative proposals:
o Cyclic/Ekpyrotic models o Bouncing universe o String Gas Cosmology o Varying Speed of Light
Small fluctuations grow to form galaxies
Need dark matter
Fritz Zwicky (1898 –1974)
Galactic rotation curves
Gravitational Lensing
By Hubble
Evidence for Dark Matter
Chandra, VLT, Hubble, Magellan, 2006
The “Bullet” cluster
Credit: NASA/CXC/M.Weiss
Evidence for dark matter
• Cosmology
o CMB spectrum o Supernovae Ia o Baryon Acoustic Oscillations o Power spectrum of visible matter o Big Bang Nucleosynthesis
• Astrophysics
o Motion of visible matter o X-ray surveys o Gravitational lensing
• Particle physics
o axions? o SUSY?
LHC, CDMS
CDMS
LHC
Zepplin-II
Status of Dark Matter
• Required properties
o not made of baryons (e.g. burned out stars etc) o very weak interactions o m > 2 keV if thermalized o only a small fraction in massive SM neutrinos allowed
• Candidate particles
o WIMPS – e.g. supersymmetric partners, Kaluza-Klein modes o Axions – very light and very slow o gravitino o Sterile neutrino o Hidden sector dark matter
• Alternatives
o Modified Newtonian Dynamics (MOND) o TeVeS o Moffat Gravity (MOG) o Manyfold universe
Cosmic Acceleration - beyond a reasonable doubt
A. Riess et al, Astron.J.116:1009-1038 (1998) S. Perlmutter, Astrophys.J.517:565-586 (1999)
1998: the evidence
S. Perlmutter, Astrophys.J.517:565-586 (1999) A. Riess et al, Astron.J.116:1009-1038 (1998)
Since 1998
• WMAP: spectacular CMB • 2dF, SDSS: galaxy distribution • Baryon Acoustic Oscillations • Gravitational Lensing • 500+ supernovae (42+17 in 1998) • Integrated Sachs Wolfe effect positive correlation between CMB
and number of galaxies caused by accelerating expansion
The ISW efffect
Evidence for Dark Energy
t stars > t universe
CMB and BAO The ISW efffect
http://www-supernova.lbl.gov
Supernovae
What is causing Cosmic Acceleration?
Time-varying Dark Energy
Constant Dark Energy (Lambda)
Candidate theories
• Domain walls: w=-2/3, ruled out
• Quintessense: scalar field(s), any w(a), ad hoc same as Lambda in the w=-1 limit
• Extra dimensions: effective w=-1, ad hoc new forces, modified equations of motion
• Modified Gravity: effective w=-1, ad hoc new forces, modified equations of motion
• Inhomogeneous models: don’t fit all of the data
A popular viewpoint
• Acceleration is beyond reasonable doubt (Nobel Prize)
• Cosmological Constant (Lambda) works
• Lambda already well measured
• No compelling alternatives to Lambda
- either create more problems than they solve - or are indistinguishable from Lambda
IT IS LAMBDA, THE SUBJECT IS CLOSED.
A different viewpoint
• Observers only mapped a small fraction of the available volume
• The Old Cosmological Constant problem is not solved
• Gravity is not tested on cosmological scales
• Dark Matter is not detected
Euclid, ESA, 2019 launch
• L2 Orbit • 5-6 year mission • galaxy shapes, photo-z’s, redshifts
Dark Energy Survey (DES) begins in Sept, 2012
• Blanco 4-meter telescope • 5 years • galaxy shapes, photo-z’s,
redshifts, SNe
• 8.4 meter mirror • half of the sky to redshift z=3 • galaxy shapes, photo-z’s, SNe
Today Matter Spectrum (SDSS)
CMB
SDSS
Tomorrow
CMB Temperature
& Polarization
Weak Gravitational Lensing (L) of galaxies, 3D lensing potential
Galaxy Counts (G): trace evolution of structures through several epochs
Cosmic Tomography
• The nature of Dark Matter • The cause of Cosmic Acceleration • A proper theory of Inflation • Neutrino masses • Validity range of General Relativity • Gravitational waves • The origin of the matter-antimatter asymmetry • Magnetic monopoles and other topological defects • Thermal history and phase transitions • The origin of cosmic magnetic fields • …
Topics of fundamental interest