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DTSTART;TZID=America/New_York:20210910T093000
DTEND;TZID=America/New_York:20210910T103000
DTSTAMP:20240304T105748Z
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UID:10002468-1631266200-1631269800@cmsa.fas.harvard.edu
SUMMARY:9/10/2021 General Relativity Seminar
DESCRIPTION:Title: Asymptotic localization\, massive fields\, and gravitational singularities \nAbstract: I will review three recent developments on Einstein’s field equations under low decay or low regularity conditions. First\, the Seed-to-Solution Method for Einstein’s constraint equations\, introduced in collaboration with T.-C. Nguyen generates asymptotically Euclidean manifolds with the weakest or strongest possible decay (infinite ADM mass\, Schwarzschild decay\, etc.). The ‘asymptotic localization problem’ is also proposed an alternative to the ‘optimal localization problem’ by Carlotto and Schoen. We solve this new problem at the harmonic level of decay. Second\, the Euclidian-Hyperboloidal Foliation Method\, introduced in collaboration with Yue Ma\, applies to nonlinear wave systems which need not be asymptotically invariant under Minkowski’s scaling field and to solutions with low decay in space. We established the global nonlinear stability of self-gravitating massive matter field in the regime near Minkowski spacetime. Third\, in collaboration with Bruno Le Floch and Gabriele Veneziano\, I studied spacetimes in the vicinity of singularity hypersurfaces and constructed bouncing cosmological spacetimes of big bang-big crunch type. The notion of singularity scattering map provides a flexible tool for formulating junction conditions and\, by analyzing Einstein’s constraint equations\, we established a surprising classification of all gravitational bouncing laws. Blog: philippelefloch.org
URL:https://cmsa.fas.harvard.edu/event/9-10-2021-general-relativity-seminar/
LOCATION:MA
CATEGORIES:General Relativity Seminar
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DTSTART;TZID=America/New_York:20210917T093000
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DTSTAMP:20240304T105845Z
CREATED:20240213T105100Z
LAST-MODIFIED:20240304T105845Z
UID:10002462-1631871000-1631874600@cmsa.fas.harvard.edu
SUMMARY:9/17/2021 General Relativity Seminar
DESCRIPTION:Title: Stable Big Bang formation for the Einstein equations \nAbstract: I will discuss recent work concerning stability of cosmological singularities described by the generalized Kasner solutions. There are heuristics in the mathematical physics literature\, going back more than 50 years\, suggesting that the Big Bang formation should be stable under perturbations of the Kasner initial data\, as long as the Kasner exponents are “sub-critical”. We prove that the Kasner singularity is dynamically stable for all sub-critical Kasner exponents\, thereby justifying the heuristics in the full regime where stable monotonic-type curvature blowup is expected. We treat the 3+1-dimensional Einstein-scalar field system and the D+1-dimensional Einstein-vacuum equations for D≥10. This is joint work with Speck and Fournodavlos.
URL:https://cmsa.fas.harvard.edu/event/9-17-2021-general-relativity-seminar/
LOCATION:MA
CATEGORIES:General Relativity Seminar
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DTSTART;TZID=America/New_York:20210924T093000
DTEND;TZID=America/New_York:20210924T103000
DTSTAMP:20240304T100711Z
CREATED:20240213T113915Z
LAST-MODIFIED:20240304T100711Z
UID:10002510-1632475800-1632479400@cmsa.fas.harvard.edu
SUMMARY:9/24/2021 General Relativity Seminar
DESCRIPTION:Title: On the Observable Shape of Black Hole Photon Rings \nAbstract: The photon ring is a narrow ring-shaped feature\, predicted by General Relativity but not yet observed\, that appears on images of sources near a black hole. It is caused by extreme bending of light within a few Schwarzschild radii of the event horizon and provides a direct probe of the unstable bound photon orbits of the Kerr geometry. I will argue that the precise shape of the observable photon ring is remarkably insensitive to the astronomical source profile and can therefore be used as a stringent test of strong-field General Relativity. In practice\, near-term interferometric observations may be limited to the visibility amplitude alone\, which contains incomplete shape information: for convex curves\, the amplitude only encodes the set of projected diameters (or “widths”) of the shape. I will describe the freedom in reconstructing a convex curve from its widths\, giving insight into the photon ring shape information probed by technically plausible future astronomical measurements.
URL:https://cmsa.fas.harvard.edu/event/9-24-2021-general-relativity-seminar/
LOCATION:MA
CATEGORIES:General Relativity Seminar
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