The Dark Side of the Universe L. Van Waerbeke APSNW may 15 th 2009

PLANCK & HERSCHEL launched may 14 th 2009

The Big-Bang model Power spectrum: A n k n S A T k n T  8 /A n, d n s / d lnk End of dark age: flash Re-ionisation: , z   m ,w     b  k  =n b/ n  Age and expansion rate: t + h Last scattering surface: z dec, t dec,  z dec Primordial fluctuations: origin? Nature? Dark matter halos and baryon coupling: mass and light biasing properties b,r

SDSS Galaxy distribution Large Scale Structures

Understanding the content of the Universe is a bit like trying to understand what exists at the surface of the Earth only from what you can “see” outer space

EVIDENCE for DARK MATTER Cornelia Parker Cold Dark Matter: An Exploded View, 1991

NGC3198 Spiral galaxies rotation curves

Dynamics of cluster of galaxies Abel 1689

Dark matter in clusters was “discovered” in 1933 (Zwicky) based On dynamical arguments and always systematically confirmed with newer observations.

Gravitational lensing as a probe of dark matter

Strong gravitational lensing

Weak gravitational lensing

Gavazzi et a Mass versus stellar profile of early-type galaxies (from strong and weak lensing)

Mass to light ratio as function of scale

Dark Matter has been detected by several independent probes: -dynamical -gravitational lensing -Xray (dynamical-clusters of galaxies) -Cosmic microwave background Wilkinson Microwave Anisotropy Probe Map of the photon temperature fluctuations “released” when the Universe was only years old.

EVIDENCE for DARK ENERGY …none yet, but cosmological constant, yes! “fluids” present in the Universe: Matter (baryons and dark matter) Radiation (photons, e.g. cosmic microwave background) Unknown fluid? (with specific equation of state) Ideal gas equation of state: PV=nk B T Unknown fluid equation of state: P=w  The cosmological constant “  ” has w=-1 A cosmological constant is allowed by G.R. Dark energy is a cosmological constant with w not -1

Effect of a cosmological constant on the Universe Matter dominated With cosmological constant

Matter Cosmological constant Combination of the cosmic microwave background and large scale structure distribution

Supernovae of type Ia are “standard candles”

Supernovae dimming with Redshift consistent with a cosmological constant. Friedman 2009

Combined constraints from all cosmological data

From WMAP The cosmological pie w~-1

Physical origin of Dark Matter… The bullet cluster: Bradac et al. 2006, Clowe et al …not known, but… Dark Matter is Dissipationless/ pressureless Blue: dark matter Pink: hot gas (Xray)

Dark matter cannot be made of dark compact objects (e.g. brown dwarfs) constraints from MACHO Dark matter cannot be baryonic anyway (constraints from nucleosynthesis) Dark matter cannot be neutrinos only (strong mass constraint from CMB and LSS) Dark matter could be weakly interacting particles (WIMPS). Direct and indirect detection experiments under way. Dark matter could be no matter at all, just modified gravity, but severe observational constraints are coming… What could dark matter be and not be… How can we probe dark matter?

Physical origin of Dark Energy… …so far no evidence of deviation from cosmological constant …and the amplitude of DE/cosmological constant remains one of the major issues in physics (fine tuning).   QFT ~     cosmo

Uzan 2007 Standard matter gg  Standard matter gg  Standard Matter A  gg Standard matter GiGi Ex: Quintessence, Chaplyin gas, K-essence,…. Ex: photon-Axion mixing Ex: scalar-tensor theories, f(R), Chameleon,… Ex: Brane-induced gravity, multiD Obs: CMB T(z) Obs: test of Poisson eq., variation Of constants Obs: strong field effects (BH, GW), Local tests of gravity

-DE equation of state: high precision observation of intermediate redshift universe (galaxy photometric and spectroscopic surveys) -> access to space and upcoming ground based facilities Copernician revolution made possible from accurate observations (Tycho+Kepler) -More theoretical investigations are absolutely necessary: None of the proposed explanations resolve the cosmological constant fine tuning problem A worry is: is there enough observational constraints available to fully characterize one or more of the dark energy models? Fortunately we don’t have to explain something which has not been observed yet How to probe dark energy if w is different from -1?

What should you take away from this talk? Over the past 100 years, cosmology has become a solid science, based on observations and falsifiable assumptions. This lead to the astounding conclusion that 95% of the Universe is unknown dark stuff. There is undisputed evidence that something is fundamentally incomplete in t he Big Bang model. Cosmology has also turned in a big science with the need for expensive, international projects, which is exciting but could also be frustrating.