Astrophysics

The spectrum of the cosmic microwave background (CMB) is known to be extremely close to a perfect blackbody. However, even within standard cosmology several processes occurring in the early Universe lead to distortions of the CMB at a level that might become observable in the future. This could open an exciting new window to early Universe physics. In my talk I will then explain in more detail why the cooling of matter in the early Universe causes a negative mu- and y-type distortion and how the damping of primordial small-scale perturbations before recombination could allow placing interesting constraints on different inflationary models.

For the first time in human thought it is now
possible to observationally determine how much matter is in the Universe as a
whole. These observations strongly support the “Concordance Model” of Hot Big
Bang Cosmology, and reinforce earlier indications that ordinary matter (atoms,
nuclei and electrons) make up at present at most 4% of the total of the
Universal energy density. The big surprise was that the rest consists of *two*
kinds of unknown forms of matter: the so-called Dark Matter and Dark Energy.
This talk summarizes for non-specialists the various lines of evidence for
their existence, and some of the theoretical ideas which have been proposed to
account for their properties

There is strong theoretical evidence that black holes have a finite thermodynamic entropy equal to one quarter the area A of the horizon. Providing a microscopic derivation of the entropy of the horizon is a major task for a candidate theory of quantum gravity. Loop quantum gravity has been shown to provide a geometric explanation of the finiteness of the entropy and of the proportionality to the area of the horizon. The microstates are quantum geometries of the horizon. What has been missing until recently is the identification of the near-horizon quantum dynamics and a derivation of the universal form of the Bekenstein-Hawking entropy with its 1/4 prefactor. I report recent progress in this direction. In particular, I discuss the covariant spin foam dynamics and and show that the entropy of the quantum horizon reproduces the Bekenstein-Hawking entropy S=A/4 with the proper one-fourth coefficient for all values of the Immirzi parameter.