Monthly Archives: June 2015

Designing curved blocks of quantum space-time…Or how to build quantum geometry from curved tetrahedra in loop quantum gravity

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Etera Livine

Etera Livine is a CNRS researcher and focuses especially on mathematical aspects of loop quantum gravity and spinfoam path integral models. Etera and Christoph both work on quantum gravity at the Laboratoire de Physique de l’Ecole Normale Supérieure de Lyon (LPENSL) in France.

Among the various approaches to the quantum gravity challenge, loop quantum gravity proposes a framework for a canonical quantization of general relativity, describing how the 3d geometry evolves in time. It does not require a priori extra dimensions or supersymmetry. It defines spin network states for the quantum geometry directly at the Planck scale, with a discrete spectra of areas and volumes, and computes their transition amplitudes by path integrals inspired from topological field theory, called spinfoam models. This framework is mathematically rigorous but Continue reading →

New realizations of quantum geometry

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Bianca Dittrich is faculty researcher at Perimeter Institute, previously she has been at the Max Planck Institute for Gravitational Physics and at Utrecht University.

Bianca Dittrich is faculty researcher at Perimeter Institute, previously she has been at the Max Planck Institute for Gravitational Physics and at Utrecht University.

The main lesson taught by Einstein’s theory of gravity is that the gravitational field has a geometrical nature, while that of quantum theory is that fields are quantized and come with fundamental excitations. This suggest a realization of quantum gravity in terms of quantum geometry.

In loop quantum gravity, this idea is realized explicitly, and observables encoding the intrinsic and extrinsic data of a spatial geometry are represented as quantum operators on a Hilbert space. This allows to discuss rigorously the quantum properties of geometrical operators measuring the area or Continue reading →

Black-hole superradiance and the hunt for dark matter

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Paulo Pani

Paolo Pani is a Marie Curie Fellow at Sapienza University of Rome and FCT Researcher at Instituto Superior Tecnico in Lisbon. His research interests include black holes, foundations of General Relativity and relativistic astrophysics. He is co-author of the book “Superradiance” (Springer-Verlag), now in press.

Little is known about dark matter, despite the numerous searches for its constituents. Fortunately, everything falls in the same way, so possible imprints of dark matter can be found in gravitational fields. In particular, if ultralight bosons exist in nature, they would make spinning black holes unstable. How does such instability evolve in realistic scenarios? And what can it teach us about the existence of dark matter?

In our recent CQG paper, we take the first step to address these questions by studying how a light scalar field grows near Continue reading →

Interview with Patricia Schmidt, winner of the 2015 GPG thesis prize

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Patricia Schmidt

Patricia Schmidt is a Postdoctoral Scholar in TAPIR at Caltech

What was the most interesting thing that happened during your PhD?

The most interesting thing was that literally every day, you would do something new. Even looking at the same set of equations again and again you would get new ideas and new insights.

Were there any big surprises?

The biggest surprise was that it actually worked out! We didn’t have a path set out to reach this result when we started, so who would have thought when Mark and I set out that we would actually have exactly Continue reading →

Book Review: On the topology and future stability of the universe, by Hans Ringström

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Mihalis Dafermos

Mihalis Dafermos is Professor of Mathematics at Princeton University

This impressive new book is first and foremost an original and thought-provoking contribution to the study of cosmology in research monograph form, in the best tradition of the kind of deep mathematical work which has played a crucial role in the development of the subject. At the same time, the book doubles as a dependable introduction and  reference for several foundational results in the analysis of the Einstein equations and relativistic kinetic theory which are hard to find elsewhere but which form the basis of so much current (and hopefully, future!) work.

Both these roles are most welcome.

Let me first discuss what this Continue reading →