Ústavu teoretické fyziky

Seminář se koná v úterý ve 13:10 v posluchárně ÚTF MFF UK

v 10. patře katedrové budovy v Tróji, V Holešovičkách 2, Praha 8

- 13. června 2017
- Horizon thermodynamics from Einstein's equation of state

(See also seminar at 10:40) *Dr. David Kubizňák*- Perimeter Institute for Theoretical Physics, Waterloo, Ontario
- (seminář v angličtině)
Padmanabhan's horizon thermodynamics is an alternative proposal for seeking connections between black hole physics and thermodynamics. I will overview the original Padmanabhan's argument and point towards its weaknesses and how to amend them. Namely, I will show that by regarding the Einstein equations as equations of state, a full cohomogeneity horizon thermodynamics first law can be derived. In this approach both the entropy and the free energy are derived concepts, while the original (degenerate) horizon first law is recovered by a Legendre projection. These results readily generalize to higher curvature gravities and establish a way of how to formulate consistent black hole thermodynamics without conserved charges.

- 16. června 2017
- !!! MIMOŘÁDNĚ V PÁTEK (ve 13:10) !!!
- Gravitational-wave echoes from macroscopic quantum gravity effects
*Prof. Luis J. Garay*- Department of Theoretical Physics, Faculty of Physics, Complutense University of Madrid
- (seminář v angličtině)
- 27. června 2017
- Dark energy without dark energy: Observational tests and theoretical challenges
*Prof. David L. Wiltshire*- Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand
- (seminář v angličtině)
I will give an overview of the timescape cosmology. It is assumed that inhomogeneities - voids, walls and filaments - modify the average background geometry of the universe, which is no longer a simple solution of Einstein's equations with homogeneous dust. To obtain a viable phenomenology without dark energy, I provide a framework for interpreting Buchert's backreaction formalism, by revisiting fundamental issues relating to the definition of gravitational energy in a complex geometry. Cosmic acceleration is realized as an apparent effect due both to backreaction and the relative calibration of the asymptotic clocks of observers in gravitationally bound structures relative to the time parameter that best describes the average statistical evolution. The cosmic coincidence problem is solved directly in relation to the growth of the void fraction.

Predictions of the timescape phenomenology are very close to the standard cosmology, but with differences which can be tested. I will outline current observational constraints, future tests (e.g., with the Euclid satellite), and also theoretical challenges that need to be overcome for backreaction models to fully compete with the Lambda Cold Dark Matter cosmology.

*Jiří Bičák*
*Oldřich Semerák*