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