Relativistický seminář
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


Příští semináře:

5. března 2024
TBP (to be persuaded)
(seminář v angličtině)
12. března 2024
Singularity regularization: Possibilities and implications
Dr. Francesco Di Filippo
ÚTF
(seminář v angličtině)

Black holes contain, deep in their interior, theoretical evidence of the failure of general relativity. A series of fundamental results, starting from the 1965 Penrose singularity theorem, proved that physically realistic initial conditions will inevitably produce a singular black hole spacetime. It is generally expected that a full theory of quantum gravity should remove the singularities that appear in general relativity. However, the lack of proper understanding of the dynamical laws dictating the evolution of spacetime and matter in these extreme situations hinders the extraction of predictions in specific models. I will discuss, in a model-independent manner, the different possibilities that singularity regularization may open, focus on fundamental open issues that need to be addressed to obtain viable nonsingular black hole candidates, and finally discuss observational signatures.

19. března 2024
Quantum superpositions of black holes
Prof. Robert Mann
Department of Physics, University of Waterloo, Ontario
(seminář v angličtině)

If relativistic gravitation has a quantum description, it must be meaningful to consider a spacetime metric in a genuine quantum superposition. But how might such a superposition be described, and how could observers detect it? I will present a new operational framework for studying "superpositions of spacetimes" via model particle detectors. After presenting the general approach, I show how it can be applied to describe a spacetime generated that is a superposition of two expanding spacetimes. I will then move on to show how black holes in two spatial dimensions can be placed in a superposition of masses and how such detectors would respond. The response exhibits signatures of quantum-gravitational effects reminiscent of Bekenstein’s seminal conjecture concerning the quantized mass spectrum of black holes in quantum gravity. I will provide further remarks concerning the meaning of the spacetime metric, and on distinguishing spacetime superpositions that are genuinely quantum-gravitational, notably with reference to recent proposals to test gravitationally-induced entanglement.


Minulé semináře:

20. února 2024
Polarizations in phase space: Boundary conditions and gravitational charges
Dr. Gloria Odak
Département de Physique, Aix-Marseille Université / ÚTF
(seminář v angličtině)

We study the relationship between symmetries, boundary conditions, and conservation or flux-balance laws in General Relativity with the covariant phase space formalism. Non-trivial symmetries occur in arbitrary spacetimes if they admit a boundary, and the nature of the symmetries and of the charges one can construct depends on the chosen boundary conditions. These charges offer a refined solution to the issue of quasi-local observables in general relativity, although one must resolve potential ambiguities in their definitions. We consider both asymptotic and charges at finite distances, supported on both time-like and null boundaries. For time-like ones, we examined the dependency of the expression for the energy on boundary conditions, and proposed new Brown-York-type charges for Neumann and York’s boundary conditions. A comparison with canonical treatments confirmed a perfect agreement. For null boundaries, it is possible to consider leaky boundary conditions in a non-ambiguous way. We study the most general phase space permitting arbitrary metric variations, identify a one-parameter family of covariant symplectic potentials, and explain how restricting some of the variations is necessary for the symplectic potential to satisfy physical requirements of stationarity. This allows us to not only recover previous charge expressions, but introduce a new set of charges that extends the stationarity property to flat light-cones, with promising implications for dynamical entropies.

27. února 2024
Towards rotating disks around Kerr black holes (in linearized regime)
Dr. David Kofroň
ÚTF
(seminář v angličtině)

Analytical solution of a rotating black hole surrounded by accretion disc in full GR is, so far, unknown. The Ernst equation is nonlinear. In this talk we will provide a framework in which the solutions of linearised Ernst equations can be obtained from the linear perturbations of Kerr black hole treated in the formalism of the Debye potentials. In this way we recover all the metric perturbations in term of a single complex scalar function (which solves the Laplace equation).


Předchozí ročníky:


Jiří Bičák                                                                                                  Oldřich Semerák


© 22. února 2024; Oldřich Semerák <semerak@mbox.troja.mff.cuni.cz>
© 28. února 2024; vygenerováno pomocí aplikace seminar, verze 2.04 (2003-09-02); správce <Pavel.Krtous@utf.mff.cuni.cz>