Events

Finding Merging SMBHs with Time-Domain Surveys

Inspiraling supermassive black hole binaries (SMBHBs), expected products of galaxy mergers and strong low-frequency gravitational-wave sources, are difficult to resolve at sub-parsec scales. Their orbits may instead be traced through periodic or chirping AGN variability, including relativistic Doppler boosting. I will present optical-survey methods combining accretion-flow models and Bayesian chirp detection. My results suggest that mixtures of mini-disk and circumbinary-disk emission are present in observations by Rubin’s LSST. In PTF, a Bayesian chirp-plus-noise search finds 33 apparent multi-cycle fits among 35,383 quasars, but none remains phase-coherent with extended ASAS-SN and ZTF data. Ten-year LSST simulations recover chirps across broad merger-time and amplitude ranges under the assumed binary and noise models. However, mini-disks may be more visible in UV/X-rays for many systems considered, motivating broad, deep surveys to probe more binary parameter space.

Monday, November 9, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

Spacetime from Entanglement: What Emerges and Why Does It Matter?

Over the last fifteen years, an increasing number of findings have variously been framed as showing that spacetime emerges from entanglement in AdS/CFT. In this presentation, I investigate how unified these findings actually are, whether they qualify as instances of emergence, and why we should care. I show that otherwise very similar-sounding claims concern the distinct spatiotemporal aspects of metric, gravitational dynamics, and topological connectivity. In each case, emergence requires more than entanglement. For metric and topological connectivity, those additional ingredients include a metric and topological connectivity, respectively. What spacetime emerges from is entanglement and spacetime, albeit a different one. To my knowledge, these distinct claims have never been confused in the physics literature, so why care? One part of the answer is that this clarifies the scope of what we have learned from AdS/CFT. The other is that many seek to use these lessons as general heuristics for quantum gravity. Getting them right matters both for how to use them and for what to expect from them.

Monday, November 9, 2026 9:30 AM

Inperson
BHI Conference Room

Virtual
Zoom

Singular Regions of Spacetime

In this talk, I revisit the problem of defining spacetime singularities in classical general relativity. In particular, I will argue that spacetime singularities are not objects, but properties of spacetime regions. I will also argue that there is no unique, best definition of a singular region of spacetime; there is, however, a schema that any adequate definition instantiates. Moreover, the question of what particular instantiation of the schema is adequate is intimately connected to the question of what kind of curves represent trajectories of possible observers in “physically reasonable” motion. Then, I will argue that for any instance of the definition schema, “being singular” is best conceptualized as an extrinsic, non-local, but nevertheless localizable (and hence non-global) property of spacetime regions. As a part of that argument, I will discuss various senses in which spacetime regions can be “small”, and show that according to two well-motivated ways of measuring “smallness” of spacetime regions, every singular spacetime has a small singular region.

Monday, November 16, 2026 9:30 AM

Inperson
Speaker will be in person – BHI Conference Room

Virtual
Zoom

Monday, November 23, 2026 – Monday, November 30, 2026

Simplicity and Equipoise: The Origins of Criteria for Astronomical Models in Ancient Greece

Why do astronomers value theories and models that are as simple as possible? Historically, this criterion emerged as a solution to a dilemma ancient Greek mathematicians faced. The aim of ancient Greek astronomy was to construct models that corresponded to the true configurations of bodies in the heavens— that is, the realm from the Moon outward to the spherical circumference of the cosmos—but two models equally accounted for the Sun’s apparent motion: the eccentric model and the epicyclic model. In this talk, I will examine two criteria that mathematicians used to choose between these models: simplicity and equipoise. In the Almagest, Ptolemy appeals to simplicity as grounds for preferring the eccentric model for the Sun’s motion, whereas Theon of Smyrna, a second-century Platonist, ascribed to Hipparchus the use of equipoise as a criterion for preferring the epicyclic model. I will analyze what Ptolemy and Theon meant by ‘simplicity’ and ‘equipoise’, how they used these criteria to adjudicate between competing astronomical models, and why, philosophically, they were concerned with simplicity and equipoise, respectively.

Monday, December 7, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

Monday, December 7, 2026 9:30 AM

Inperson
Speaker will be in person – BHI Conference Room

Virtual
Zoom

Monday, December 14, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

Monday, December 21, 2026 – Monday, January 18, 2027