Time Wed 12/12 Thu 13/12 Fri 14/12
09:00-10:00   Robert B. Mann (Cotton 350) Jorma Louko (Cotton 350)
10:00-11:00   Robert B. Mann (Cotton 350) Netta Engelhardt (Cotton 350)
11:00-11:30 Welcome with Tea and Coffee (Cotton 119) Morning Tea/Coffee
11:30-12:30 Matt Visser (Cotton 119) Jessica Santiago (Cotton 350) Netta Engelhardt (Cotton 350)
12:30-14:00 Lunch
14:00-15:00 Matt Visser (Cotton 119) Luis C. Barbado (Cotton 350) Valentina Baccetti (Cotton 119)
15:00-16:00 Matt Visser (Cotton 119) Luis C. Barbado (Cotton 350) Valentina Baccetti (Cotton 119)
16:00-16:30   Afternoon Tea/Coffee
16:30-17:30   Jorma Louko (Cotton 350) Discussion & End (Cotton 119)

More details will be published as they become available. Two hour slots are planned to have a short break at half-time.


  • Matt Visser
    • Introductory remarks
    • Coarse grained entropy
  • Robert B. Mann
    • Observer Dependent Entropy in Accelerating Black Holes
  • Jessica Santiago
    • Observer-Dependent Tolman-temperatures
    In this talk we will explore the physics behind temperature gradients in thermal equilibrium states (Tolman temperature), specifically discussing the role played by the universality of free fall. We will analyse two possible different ways of measuring temperatures and explain how different observers may disagree about the temperature of a system in thermal equilibrium.
  • Luis C. Barbado
    • Observer dependent temperature of perceived radiation in black hole physics
    An observer in the exterior region of a black hole should perceive the Hawking radiation emitted by the black hole of a given quantum field. Moreover, depending on the motion of the observer, it may also perceive some Unruh effect of this same field, due to its own acceleration. But, how do these two effects combine to give the observer's net particle perception? In this talk we will address this question, within a restricted but conceptually clear framework, by using the so-called effective-temperature (or peeling) function. Far from just getting a set of concrete quantitative results for different trajectories of the observer, we will obtain general results which are clearly interpretable in terms of well-known physical phenomena. Furthermore, these results will let us address some interesting questions: Which part of the radiation perceived can be assigned to Hawking radiation and which to the Unruh effect? Can these two effects interfere destructively? Does always the Unruh temperature scale with the proper acceleration of the observer? Is it strictly necessary to form a horizon in order to have Hawking radiation emitted? Can Hawking radiation make a test particle to float nearby a black hole due to radiation pressure?
    • A tensorial description of particle perception in black hole physics
    In quantum field theory in curved backgrounds, one typically distinguishes between objective, tensorial quantities such as the renormalized stress-energy tensor (RSET) and subjective, nontensorial quantities such as Bogoliubov coefficients which encode perception effects associated with the specific trajectory of an observer. In this work, we propose a way to treat both objective and subjective notions on an equal tensorial footing. For that purpose, we define a new tensor which we will call the perception renormalized stress-energy tensor (PeRSET). The PeRSET is defined as the subtraction of the RSET corresponding to two different vacuum states. Based on this tensor, we can define perceived energy densities and fluxes. We will find that the PeRSET is strongly related to the effective-temperature function, and it helps us to have a more organized and systematic understanding of various results in the literature regarding quantum field theory in black hole spacetimes. With the notions of observer-dependent temperature, energy and flux at hand, we will discuss possible constructions of a notion of observer-dependent entropy.
  • Jorma Louko
    • Second law non-violation theorem for Lorentz-noninvariant black holes
    Black holes in Lorentz-violating theories of gravity have been claimed to violate the second law of thermodynamics by perpetual motion energy extraction. We analyse the possibility of such classical energy extraction in Penrose splitting processes in which the energy budget of incoming and escaping particles is unambiguously defined with respect to time translations at an asymptotically flat infinity. We show, in a spherically symmetric setting with two species of particles, that energy extraction cannot happen in any Lorentz-violating theory in which gravity remains attractive, in the sense of a geometric inequality that we describe. This inequality is satisfied by all known black hole solutions to Einstein-aether and Horava theories of gravity.
    Based on arXiv:1803.01624 (published in Physical Review D) with Robert Benkel, Jishnu Bhattacharyya, David Mattingly and Thomas Sotiriou.
    • Does the chicken survive the firewall?
    Creation of an an isolating wall for a quantum field will disturb the field, the more the quicker the creation. We analyse this phenomenon as a model for the firewall that has been proposed to replace the horizon of an evaporating black hole, with a view to the firewall's efficacy to break correlations between spacetime regions. We consider a set of scenarios in the rapid creation limit, comparing the energy emitted into the field and the experiences of a localised matter system that traverses the burst of radiation. We find that both tend to be singular, but the degree of singularity depends on the specific situation, and is not necessarily strong enough to annihilate an infalling chicken, or to obliviate its memories of the universe outside.
  • Netta Engelhardt
    • (Tentative) Coarse-grained entropy and apparent horizons
  • Valentina Baccetti
    • Black Hole Entropy: Its history, its meaning, and what we can learn from it
    In the first part of this talk I will review the classical definition of black holes, and the path that brought us from a purely geometrical interpretation of the laws of black hole mechanics to the definition of a theory of thermodynamics for black holes.
    I will also present how the concepts of entropy and temperature of a classical black hole were introduced, in order to recover the second law of thermodynamics, and how these were considered as purely mathematical concepts without any possible physical meaning.
    I will show how the discovery that black holes emit a black body radiation by Hawking, (Hawking radiation), led to a reconciliation between the mathematical concept of black hole entropy and its physical meaning, and how at the same time it brought about deeper issues such as the information loss paradox.
    In the second part of the talk I will briefly introduce some proposed solutions to the information loss paradox, what they may be suggesting about black holes, their entropy, and the microscopic nature of space and time.


  • Arbab Mohamed
    • Black hole massive thermodynamics
    A photon inside a gravitational field defined by the accelerates $g$ is found to have a gravitational mass given by $m_g=(\hbar/2c^3)g$, where $\hbar$ is the reduced Planck's constant, and $c$ is the speed of light in vacuum. This force is equivalent to the curvature force introduced by Einstein's general relativity. These photons behave like the radiation emitted by a black hole. A black hole emitting such a radiation develops an entropy that is found to increase linearly with black hole mass, and inversely with the photon mass. Based on this, the entropy of a solar black hole emitting photons of mass $\sim 10^{-33}eV$ amounts to $\sim 10^{77}\,k_B$. The created photons could be seen as resulting from quantum fluctuation during an uncertainty time given by $\Delta t=c/g$. The gravitational force on the photon is that of an entropic nature, and varies inversely with the square of the entropy. The power of the massive photon radiation is found to be analogous to Larmor power of an accelerating charge.