Events

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Meeting ID: 930 4120 7032 Password: HarvardBHI

Monday, March 10, 2025 9:30 AM

Why null infinity is not smooth, and how to measure it

Abstract: Be it numerical, formal, or mathematical, the typical setup for the evolution of spacetimes describing, for instance, the merger of two black holes is to make an ad hoc assumption on the initial data to have compactly supported gravitational radiation content.
This ensures that the spacetime has a smooth null infinity (it “peels”), but essentially pretends the spacetime has been stationary at some time “before” the initial data.

My talk will be about what happens when one does not ignore the past dynamics of the system: I will present mathematical results that convert scattering data assumptions in the infinite past into precise predictions on the asymptotics towards spacelike and future null infinity, showing in particular that null infinity is not smooth.
Furthermore, I will explain how this failure of null infinity to be smooth affects the asymptotics of gravitational radiation at late times (“tails”), predicting decay up to three powers slower than the usual “Price’s law” decay.

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Monday, March 10, 2025 11:00 AM

Spring Break

There will be no Foundations Seminar today.

Monday, March 17, 2025

Multi-messenger astronomy with high-energy neutrinos

Abstract: The recent discoveries of high-energy astrophysical neutrinos and gravitational waves have opened new windows of exploration to the Universe. Neutrinos can escape dense environments from where photons can not reach us and travel undeflected through the Universe. In combination with measurements of electromagnetic radiation, neutrinos can help to solve long-standing problems in astrophysics and probe physics that plays a role at extreme conditions that otherwise are hardly accessible to laboratory experiments. For example, TeV-PeV neutrinos have the potential to reveal the origin of cosmic rays. Possible source candidates include the core of active galaxies or the tidal disruption of a star by a supermassive black hole. I will give an overview of recent discoveries in the field of high-energy neutrino astronomy.

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Bio: I did my PhD in 2011 at University of Bonn, followed by a postdoc at SLAC. Then I came back to Germany to lead a Helmholtz Young Investigator group at DESY Zeuthen and since 2021 I’m a professor at Ruhr-University Bochum.

Monday, March 24, 2025 11:00 AM

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Meeting ID: 930 4120 7032 Password: HarvardBHI

Monday, March 24, 2025 9:30 AM

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Monday, March 31, 2025 11:00 AM

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Meeting ID: 930 4120 7032 Password: HarvardBHI

Monday, March 31, 2025 9:30 AM

Model-Based Explication and Quantum Singularity Resolution

Abstract: There are, at present, no singularity theorems (or resolution theorems) valid for the full domain of quantum gravity. Moreover, lack of empirical data means that a limited range of constraints in model building are available. Finally, limited analytically tractability means most existent treatments are focused on the quantization of finite dimensional truncations of classical cosmological or black hole models — and, even then, often require numerical approaches for exploration of the solutions. These worries notwithstanding, one can certainly ask, and in some cases answer,  physically interesting questions regarding the resolution or not of singularities within this restricted context. The approach is a form of model-based reasoning in which idealized models mediate our understanding of the properties of full, physically representational, theory. In this talk I will consider the idea of model-based explication in the context of refining the concept of singularity resolution, drawing upon my own past work on big bang singularity resolution in quantum cosmology and my current work on black hole singularity resolution.

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Bio: I am an Associate Professor in the Department of Philosophy at the University of Bristol. My current research is principally within physics and the philosophy of physics. My main research focus is the problem of time in classical and quantum theories of gravity. Further topics of current interest include dynamical approaches to symmetry, black hole physics, analogue gravity, quantum cosmology, the arrow of time in quantum theory, the foundations of general relativity, and quantum chemistry. I have written two books: Analogue Quantum Simulation (Springer, 2022) is a monograph on the epistemology of analogue quantum simulation written with Dominik Hangleiter and Jacques Carolan; and Time Regained Volume 1: Symmetry and Evolution in Classical Mechanics (OUP 2023) is the first volume of project on the problem of time with Sean Gryb.

Monday, April 7, 2025 11:00 AM

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Meeting ID: 930 4120 7032 Password: HarvardBHI

Monday, April 7, 2025 9:30 AM

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Monday, April 14, 2025 11:00 AM

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Meeting ID: 930 4120 7032 Password: HarvardBHI

Monday, April 14, 2025 9:30 AM

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Monday, April 21, 2025 11:00 AM

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Meeting ID: 930 4120 7032 Password: HarvardBHI

Monday, April 21, 2025 9:30 AM

Event Horizon and Environs (ETHER)

Abstract: To date, the Event Horizon Telescope (EHT) has imaged only two supermassive black holes at resolutions finer than 50 gravitational radii: M87 and SgrA*.
Ongoing and planned upgrades to the EHT enable demographic studies
of black holes at these scales – the focus of this talk.

We will present the Event Horizon and Environs (ETHER) sample of single and
binary black holes, a curated database for selection of (current and future) EHT targets. We will also present the progress in imaging  single black holes in ETHER with the EHT, and the expectations of imaging and monitoring binary black holes into the future. Finally, we will discuss a newly identified population of the most massive black holes (thus the largest black hole shadows) in the nearby universe, and its implications for the EHT.

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Bio: Neil Nagar is a professor at the University of Concepcion, Chile, and a member of the Event Horizon Telescope Collaboration. He is is the Director of the ‘TITANs Millennium Nucleus’, a group of forty researchers and students across four universities in Chile. Nagar graduated as an engineer and mathematician at BITS, Pilani, India, before completing his Doctorate in Astronomy at the University of Maryland, College Park in 2000.

Nagar’s interests include supermassive black holes, galaxy evolution, and the origin of ultra high energy cosmic rays.

Monday, April 28, 2025 11:00 AM

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Meeting ID: 930 4120 7032 Password: HarvardBHI

Monday, April 28, 2025 9:30 AM