The workshop will take place at Headquarters of Dublin Institute for Advanced Studies (DIAS)
10 Burlington Road, D04 C932,
Dublin, Ireland
Lectures will be held the main lecture room on the first floor. The most convenient way to get there from UCD accommodations is by bus 39A from stop 767 to Burlington Road (Ongar direction). Bus lines S2, 38, 38A, 38B, 38D, 39, 39A, 39X, 51D, 70 and 77X also all stop nearby DIAS Headquarters.
Physicists often make progress by testing their theories to the breaking point. When a theory fails, it may need to be modified, or even replaced by a new paradigm. In theoretical physics, one way to do this is to explore the most extreme situations a theory allows. In this talk, I will examine the limits of our current theories of gravity by asking a question that has fascinated scientists and science-fiction fans alike: could the laws of physics allow us to build a time machine?
Semi-classical dilaton gravity in (1+1)-dimensions remains one of the only arenas where quantum black holes can be exactly constructed, fully accounting for backreaction due to quantum matter. In this talk I will present an analysis of the mass and thermodynamic properties of static asymptotically flat quantum black holes, both analytically and numerically. Analytically, for the eternal quantum black hole solutions to a one-parameter family of models interpolating between Russo-Susskind-Thorlacius and Bose, Parker, and Peleg gravities. In particular, I will discuss the appearance of naked singularities and the computation of the entropy. Finally, I will present the numerically constructed eternal black hole solutions to semi-classical Callan-Giddings-Harvey-Strominger gravity and show that their thermal behavior is qualitatively different from their analytic counterparts. Based on: https://arxiv.org/abs/2512.19812
In this talk, I will present how techniques from quantum information theory and quantum thermodynamics can be used to derive the second law of thermodynamics for quantum fields. I will begin with the case of a finite quantum system undergoing a Markovian evolution driven by an infinite bath, whose dynamics are governed by the Lindblad equation and whose thermodynamic properties are well understood. Building on this framework, I will show how a natural generalization allows us to extend these methods to the thermodynamics of quantum fields defined on causal horizons. Unlike finite quantum systems, quantum field theory admits many unitarily inequivalent Hilbert spaces, each constructed from a distinct choice of vacuum state. I will argue that these different vacua can be interpreted as corresponding to different reservoirs driving the dynamics. In particular, I will demonstrate how Wall’s proof of the generalized second law fits naturally within this framework, and how analogous thermodynamic laws describing black hole thermodynamics emerge for asymptotic observers. These laws correspond to different thermodynamic potentials associated with distinct vacuum states, such as the Boulware, Hartle–Hawking, and Unruh vacua.
…
Recent advances in semiclassical gravity is suggesting that, in spherical black holes with outer and inner horizons, the Hawking process drives the complete evaporation of the trapped region in timescales shorter than the ones predicted for Schwarzschild black holes. However, this does not mark the end of the story, as said process is accompanied by the formation of an anti-trapped region, or white hole. In this talk, I will present a novel analytic treatment of black hole evaporation. Within simplified two-dimensional models describing the formation of charged and regular black holes, we show that the emergence of the anti-trapped region is unavoidable and is caused by the amplification of quantum negative energy fluxes created along the outgoing direction inside the black hole. Analogously, the energy fluxes originated by the white hole along the ingoing direction can trigger the subsequent formation of a black hole, producing a cascade of black-to-white hole transitions which might terminate in a spacetime free of horizons.
We advocate for a holographic definition of thermodynamic pressure and volume for black holes based on quasi-local gravitational thermodynamics. When a black hole is enclosed by a finite timelike boundary, York’s quasi-local first law includes a surface pressure conjugate to the boundary area. Assuming the existence of a holographically dual theory living on this boundary, these geometric quantities correspond to the pressure and volume of the dual thermal system. In this work we focus on static, spherically symmetric black holes, for which these quantities reduce to global thermodynamic variables. The holographic volume provides a notion of system size, allowing extensivity to be defined in standard thermodynamic terms, and it yields a definition of the large-system limit. For the asymptotically flat case, we show that, in the canonical thermodynamic representation, small Schwarzschild black holes are non-extensive, whereas large black holes become extensive in the large-system limit. A similar conclusion applies to Anti-de-Sitter Schwarzschild black holes, with the difference that the quasi-local energy of the large black hole also becomes extensive in the large-system limit. Before this limit, the energy decomposes into subextensive and extensive contributions, and we derive an explicit expression for the extensive part as a function of the finite volume and entropy.
Gravitational wave solutions to the Einstein field equation of general relativity are commonly regarded as examples proving how gravity in general relativity transmits energy from a source body to a distant body. The famous 1957 Feynman sticky bead thought experiment illustrates the reality of this phenomenon by imagining two beads generating heat in a rod on which they slide with friction, due to their changing proper distance in the presence of the waves. I argue that gravitational waves, rather than transmitting energy in the sense that appears as a source in the Einstein field equation, facilitate the transformation between different types or stores of energy locally. The same holds for other mechanisms for geodesic deviation more generally, with the implication that isolated thermodynamics systems may not stay in the same thermodynamic state unless acted upon by some outside driving force or through the exchange of heat.
I discuss the representation theory of the universal corner symmetry group, which lies at the basis of the corner proposal for quantum gravity. In two dimensions, one can completely classify the irreducible unitary projective representations of the corner symmetry group. I then explain how this classification admits a geometric interpretation through the study of coadjoint orbits and their quantization. In addition to describe the classical phase space, coadjoint orbits parametrize the manifold of coherent states, which can be used to construct semiclassical states.
I conclude with more recent and speculative considerations about the use of these states to glue together patches of spacetime at the quantum level.
Regular black holes provide a framework for describing black holes without curvature singularities. Although such objects have been studied phenomenologically for decades, only recently have they emerged as generic exact solutions of gravitational theories with infinite towers of higher-curvature corrections. Understanding the thermodynamics of regular black holes has historically presented challenges. This is because quantities such as the black hole entropy depend crucially on the underlying Lagrangian and therefore probe information beyond the spacetime geometry alone. In this talk, I will give a brief overview of the construction of regular black holes as exact solutions of higher-curvature gravity and discuss their thermodynamic properties. I will emphasize, in particular, the role of the regularization scale, which enters the thermodynamic description in a manner analogous to a finite molecular volume.
The use of statistical methods to model gravitational systems is crucial to physics practice, but the extent to which thermodynamics and statistical mechanics genuinely apply to these systems is a contentious issue. This paper provides new conceptual foundations for gravitational thermodynamics by reconsidering the nature of key concepts like equilibrium and advancing a novel way of understanding thermodynamics. The challenges arise from the peculiar characteristics of the gravitational potential, leading to non-extensive energy and entropy, negative heat capacity, and a lack of standard equilibrium. Hence it has been claimed that only non-equilibrium statistical mechanics is warranted in this domain, whereas thermodynamics is inapplicable. We argue instead that equilibrium statistical mechanics applies to self-gravitating systems at the relevant scale, as they display equilibrium in the form of metastable quasi-equilibrium states. We then develop a minimal framework for thermodynamics that can be applied to these systems and beyond. Thermodynamics applies in the sense that we can devise macroscopic descriptions and explanations of the behaviour of these systems in terms of coarse-grained quantities like energy and temperature within equilibrium statistical mechanics.
Quantum gravity to a large extent is the implied answer for many of general relativity’s edge cases. Most famously, this applies to the very early universe and what happens at the end of a black hole’s evaporation. Both in reply to this and as a study of the kinematics of general relativity (i.e., the physics of any potential metric), various “reverse engineered solutions” have been advanced. This ranges from regular black holes as heuristic models of black holes without singularities, to various concepts of science-fiction: Time travel, warp drives, wormholes, and tractor beams. In cases with closed time-like curves, this runs into immediate thermodynamic conundra. In other cases, thermodynamics in general relativity is already so thorny that the relevant questions become difficult to tackle. In this talk, I will first introduce various reverse-engineered metrics, what problems they relate to, and what thermodynamic problems they are connected to. Then I will wrap up with ongoing efforts to build toy models of time travel in “canonical” quantum gravity, explain the just-used quotation marks, and how to connect these with thermodynamics in the absence of space and time.
We show that spacetime symmetries on any background give rise to stealth vector fields obeying Proca-type equations supplemented by curvature terms. This observation, which is true for solutions of any theory of gravity and with arbitrary matter content, effectively promotes spacetime symmetries to `physical fields’ whose characteristic property is that their backreaction on the geometry vanishes. In particular, this allows one to construct exact Proca hair charged and magnetized rotating black holes in all dimensions. In fact, such a construction is not limited to Killing vector fields, and equally works for conformal Killing vectors and hidden symmetries encoded in Killing-Yano tensors.
In this talk I present an analysis of Bianchi I and Bianchi II universes as solutions to an effective quantum-gravity dynamics. We have found modified Bianchi solutions with different matter fields and studied their dynamics. I focus my discussion on the connection of this analysis with the classical BKL conjecture and the study of information flow in strong-gravity regimes.
The covariant phase space (CPS) formalism provides a geometric framework to derive equations of motion and endow the space of solutions with a symplectic structure. This variational approach additionally provides Noether charges and plays a central role in modern gravitational physics and gauge theories. Despite its conceptual elegance, explicit computations in physically relevant models (particularly in gravitational theories with higher-derivative or non-minimal couplings) can become technically demanding and error-prone.
In this talk, after a brief introduction to the CPS formalism, I will present xCPS, a Mathematica package designed to automate the covariant phase space formalism for general Lagrangian field theories. The package computes equations of motion, presymplectic potentials, symplectic currents, Noether currents and charges, and related geometric structures in a fully covariant manner. I will conclude with some interesting examples.
In quantum theory, different observers can assign different descriptions to the same physical system. The framework of quantum reference frames makes this idea precise by treating reference frames themselves as quantum systems, and has shown that properties such as superposition, entanglement, and even subsystem structure can depend on the chosen perspective. These observations raise a natural question: if entropy is assigned relative to an observer or reference frame, how much can different observers disagree? In this talk, I will discuss recent work on information-theoretic aspects of quantum reference frames. I will present a coherence-entanglement trade-off between observers, as well as new results extending this structure to networks of many quantum reference frames, including non-ideal ones. These results identify structural constraints on how information can be redistributed under changes of perspective and lead to quantitative bounds on the extent to which the entropy assigned to a common system can depend on the observer and on the quality of their reference frame. Taken together, these results place fundamental limits on observer-dependent entropy and provide a quantum-information-theoretic perspective on recent discussions of entropy in gravitational contexts.
Gauss-Bonnet term in 4D becomes topological and its presence in the gravitational action does not affect the equations of motion. Nevertheless, it has been argued that it shifts black hole entropy by a term proportional to the Euler characteristic of the horizon. In my talk, I discuss how the choice of boundary conditions affects the physical and thermodynamic relevance of Gauss-Bonnet term. I also draw a parallel with Aharonov-Bohm effect, suggesting that while the physical role of Gauss-Bonnet term is suggested by classical physics, its observation may require quantum gravitational phenomena.
…
It is often argued that inflation generates quantum correlations between cosmological perturbations with opposite wavenumbers, yet no clear observational signatures of this primordial quantum behavior have been identified.
In this talk, I show that this apparent tension can be clarified by examining how entanglement is distributed among local observables. In particular, I analyze the entanglement structure of the Bunch–Davies vacuum of a light scalar field in de Sitter spacetime.
I find that while correlations between localized, spacelike-separated modes grow as their separation exceeds the Hubble scale, the entanglement between them sharply decreases. In other words, the growth of correlations does not imply stronger quantum entanglement.
These results suggest that inflation amplifies correlations while simultaneously suppressing the entanglement accessible to local observables, providing a mechanism for the emergence of classical behavior on observable scales.
…