Events

Why Black Holes Are Hot

When is a system ‘really’ thermal? Such philosophical questions are increasingly difficult to answer given the many varieties of black hole radiation, acoustic horizon radiation, and other curiosities of modern physics. In this talk, I defend one precise definition of what it means to be ‘thermal’ in the sense of admitting a precise geometrical definition of heat, together with a clear philosophical interpretation. This framework clarifies one sense in which black holes really are hot, and which applies equally to analogical black holes like acoustic horizons, although their thermodynamic properties are radically different from familiar models of thermodynamics like a box of gas.

Zoom

Monday, October 20, 2025 11:00 AM

Inperson
G10

Minimal Coupling, the Strong Equivalence Principle, and the Adaptation of Matter to Spacetime Geometry

I provide precise explications of two principles which are often taken to capture senses in which special relativity is “locally valid” in general relativity: minimal coupling, and the strong equivalence principle. I then discuss the relationship between these principles and other principles of general relativity, and show that minimally coupled, quasilinear, symmetric hyperbolic matter theories necessarily satisfy (versions of) local causality and the geodesic principle. This goes some way towards providing a precise answer to the question what would happen if a matter theory failed to be locally special relativistic. (Joint work with James Owen Weatherall.)

Zoom

Monday, October 20, 2025 9:30 AM

Inperson
BHI Conference Room

Standing Out From The Crowd: Finding Supermassive Black-hole Binaries in Gravity & Light

Despite huge efforts, there remains a paucity of tight-separation supermassive black-hole binaries, and no unambiguous systems known below a parsec. I will discuss ongoing efforts to resolve these systems out of the confusion gravitational-wave signal seen by pulsar-timing
arrays, how we can maximize the information and prospects from these searches, how we can link these signals to their host galaxies, and also discuss the potential for associated electromagnetic signatures. The latter raises the possibility of performing simultaneous
multi-messenger analyses for supermassive black-hole binaries, piloting the kind of searches that the next-decade LISA mission will need to do on an accelerated timescale at different wavelengths. I will also discuss the ways in which we can learn about the
demographics and dynamics of supermassive black holes using the PTA gravitational-wave background as a census of the entire population, and using sophisticated population synthesis simulations with deep-learning emulators.

Zoom

Monday, October 27, 2025 11:00 AM

Inperson
G10

How I Learned to Stop Worrying and Love General Relativistic Black Holes

Specific properties of general relativistic black holes render the latter objects of preoccupation within quantum gravity research, despite suspicions regarding the literal attribution of those properties to astrophysical black holes. A fetish is an object of inappropriate attribution of value. Fetishists have an excessive — which is to say irrational — commitment to that object, given their overall interests. On this definition, the claim that someone is a fetishist is a criticism, an accusation against them. Are quantum gravity researchers fetishists concerning general relativistic black holes? In this talk, I sketch a preliminary refutation of the criticism. I defend the reasonableness of quantum gravity researchers’ preoccupation with general relativistic black holes by providing a basic rationale for attending to the very same features as are usually met with suspicion. The strategy of the defense is, chiefly, to motivate definitions of verified and observable spacetime properties, which cross-cut a traditional distinction between local and global spacetime properties and are better suited for singling out mathematical results in general relativity of phenomenological significance.

Zoom

Monday, October 27, 2025 9:30 AM

Inperson
BHI Conference Room

The Spectre of Underdetermination in Modern Cosmology

The scientific status of physical cosmology has been the subject of philosophical debate ever since detailed mathematical models of the universe emerged from Einstein’s general theory of relativity. Such debates have revolved around whether and to what extent cosmology meets established demarcation criteria for a discipline to be scientific, as well as determining how to best characterize cosmology as a science, given the unique challenges and limitations faced by a discipline that aims to study the origin, composition, and fate of the universe itself. The present article revisits, in light of the dramatic progress in cosmology in recent decades, an earlier debate held in the 1950s between Herman Bondi and Gerald Whitrow regarding the scientific status of cosmology. We analyze cosmology’s transition from an emerging science to a cornerstone of modern physics, highlighting its empirical successes in establishing the Λ-Cold Dark Matter (ΛCDM) model and in its delivery of various successful novel predictions. Despite this remarkable scientific success and progress, we argue that modern cosmology faces a further profound challenge: the permanent underdetermination of the microphysical nature of its exotic energy components: inflation, dark matter, and dark energy. Drawing historical parallels with the role of spectroscopy in revealing the microphysical nature of atomic physics, we argue that the epistemic barriers obstructing us from ascertaining the microphysical nature of these exotic energy components are significant, in turn casting doubt upon whether cosmology can ever transcend these particular challenges. We conclude by reflecting on the prospects for future breakthroughs and/or non-empirical arguments, which could decide this issue conclusively. (Joint work with Pedro G. Ferreira and William J. Wolf.)

Zoom

Monday, November 3, 2025 9:30 AM

Inperson
BHI Conference Room

The Local Validity of Special Relativity from a Scale-Relative Perspective

Most contemporary physicists hold that the local validity of special relativity within general relativity is expressed by means of an interdependent cluster of mathematical concepts, one of which is the existence of normal coordinate systems. Nonetheless, there remains conceptual work to be done with regard to this ‘standard story’ on the local validity of special relativity in, first, clarifying how a network of mathematical concepts is recruited in a particular modelling context in order to account for the local validity of special relativity within general relativity and, second, highlighting the richness and subtlety of this mode of modelling, as well as how it interacts with the concept of approximate Killing symmetry. With this article, we carry out this work, thereby also defending the standard story from concerns recently voiced in the philosophy of physics literature.

Zoom

Monday, November 10, 2025 9:30 AM

Inperson
BHI Conference Room