Events

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. Speaker will be in person this week.

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

From AI to the Moon: The Next Frontiers in Gravitational-Wave Astrophysics

Ten years of LIGO observations have reshaped our view of black hole populations while tempering the early promise of multi-messenger astrophysics. I will begin by discussing what LIGO has revealed about an emerging class of “lite” intermediate-mass black holes, providing new clues to the cosmic assembly of massive black holes. Building on these discoveries, I will introduce new approaches that use foundational AI models to enhance the interpretive power of gravitational-wave signals for astrophysics and for testing General Relativity. As gravitational-wave astronomy enters its second decade, it finds new discovery potential in the United States’ return to the Moon. I will present the Laser Interferometer Lunar Antenna (LILA), a proposed U.S. flagship observatory operating in the mid-band between LIGO and LISA. LILA would provide weeks of advance warning for the broadest class of multi-messenger sources, with sky localization comparable to the angular size of a galaxy. Access to the mid-band makes LILA the most promising facility for observing intermediate-mass black holes and offers the first opportunity to directly measure the primordial gravitational-wave background.

Zoom

Monday, November 3, 2025 11:00 AM

Inperson
G10

Algebraic Structures in QFT in the Presence of a Quantum Reference Frame

I will start with introducing the framework of algebraic quantum field theory (also on curved spacetimes) and explain how to understand measurement in this framework using the approach of Fewster and Verch. In particular, I will demonstrate that in the presence of symmetries one needs to use a quantum reference frame to be able distinguish between measurements related by symmetry transformations. This leads to interesting consequences regarding the type of relevant observable algebras, as observed by Chandrasekaran, Longo, Penington and Witten in the context of QFT on de Sitter. This talk will be mostly based on my joint paper with Fewster, Janssen, Loveridge and Waldron, “Quantum reference frames, measurement schemes and the type of local algebras in quantum field theory.”

Zoom

Monday, November 17, 2025 11:00 AM

Inperson
BHI Conference Room