Relativity Seminar
of the Institute of Theoretical Physics

spring 2017

Given seminars:

March 7, 2017
Dissipative effects in cosmology
Dr. Giovanni Acquaviva

I review some models that take into account dissipative effects of fluids in an expanding Universe, in the context of General Relativity. The effect of dissipation on the cosmic evolution is assessed by means of different methods, such as perturbation theory and dynamical systems analysis.

March 14, 2017
Generalising the coupling between spacetime and matter
Dr. Sante Carloni
Multidisciplinary Centre for Astrophysics (CENTRA), Instituto Superior Técnico (IST), University of Lisbon
March 21, 2017
Exact solutions with a scalar field in general relativity
Prof. Hideki Maeda
Hokkai-Gakuen University, Sapporo, Japan
March 28, 2017
Canonical quantization of homogeneous cosmological models
MSc. Manto Zampeli
National and Kapodistrian University of Athens
April 4, 2017
Hypervelocity stars and S-stars
Dr. Jaroslav Haas
Astronomical Institute, Charles University
April 11, 2017
Celestial Cinematography with Large Synoptic Survey Telescope
Dr. Andrei Nomerotski
Brookhaven National Laboratory (Cosmology and Astrophysics Group), New York

April 25, 2017
A short introduction to xAct - efficient tensor computer algebra for Mathematica
Dr. Tomáš Málek
Institute of Mathematics of the Czech Academy of Sciences (Department of algebra, geometry a mathematical physics)

The package is availabe on the website There you can find synopsis:
xAct is a suite of free packages for tensor computer algebra in Mathematica. xAct implements state-of-the-art algorithms for fast manipulations of indices and has been modelled on the current geometric approach to General Relativity. It is highly programmable and configurable. Since its first public release in March 2004, xAct has been intensively tested and has solved a number of hard problems in GR.

Below you can find notebooks prepared for the seminar:

May 2, 2017
Kerr-Newman black hole in the formalism of isolated horizons
Mgr. Aleš Flandera
May 9, 2017
Pictures at an exhibition (of GW collapse)
Mgr. Anton Khirnov
May 23, 2017
Analytical study of spinning objects in general relativity
Dr. Satish Kumar Saravanan
National Institute for Subatomic Physics (Nikhef), Amsterdam
June 13, 2017
Horizon thermodynamics from Einstein's equation of state
Dr. David Kubizňák
Perimeter Institute for Theoretical Physics, Waterloo, Ontario

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.

June 16, 2017
!! ON FRIDAY !!!
Gravitational-wave echoes from macroscopic quantum gravity effects
Prof. Luis J. Garay
Department of Theoretical Physics, Faculty of Physics, Complutense University of Madrid
June 23, 2017
!!! Beware the change in date, time is still 13:10 !!!
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

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.

June 29, 2017
Primordial power spectra in loop quantum cosmology
Dr. Daniel Martin de Blas
Instituto de Física, Pontificia Universidad Catolica de Chile

July 20, 2017
!!! MIMOŘÁDNÝ SEMINÁŘ, ve ČTVRTEK od 13:10 !!!
Lorentz invariance and the zero-point stress-energy
Prof. Matt Visser
School of Mathematics, Statistics, and Computer Science, Victoria University of Wellington, New Zealand

Some 65 years ago (1951) Wolfgang Pauli noted that the zero-point energy density could be set to zero by a carefully fine-tuned cancellation between bosons and fermions. In this seminar I will argue in a slightly different direction: The zero-point energy density is only one component of the zero-point stress energy tensor, and it is this tensor quantity that is in many ways the more fundamental object of interest. I shall demonstrate that Lorentz invariance of the zero-point stress energy tensor implies finiteness of the zero-point stress energy tensor, and vice versa.

Other semesters:

© October 6, 2017; Oldřich Semerák <>
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