Ημερομηνία: 23/6/2021
Ομιλητής: Prof. Sir John Pendry
Imperial College London, UK
Τίτλος: A New Mechanism for Gain in Time Dependent Media
Περίληψη : Time dependent systems do not in general conserve energy invalidating much of the theory developed for static systems and turning our intuition on its head. This is particularly acute in luminal space time crystals where the structure moves at or close to the velocity of light. Conventional Bloch wave theory no longer applies, energy grows exponentially with time, and a new perspective is required to understand the phenomenology. In this letter we identify a new mechanism for amplification: the compression of lines of force that are nevertheless conserved in number.
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Ημερομηνία: 14/5/2021
Ομιλητής: Prof. Marc Mezard
Ecole Normale Supérieure Paris, France
Τίτλος: Statistical Physics and Statistical Inference
Περίληψη: A major challenge of contemporary statistical inference is the large-scale limit, where one wants to discover the values of many hidden parameters, using large amount of data. In recent years, ideas from statistical physics of disordered systems, notably the cavity method, have helped to develop new algorithms for important inference problems, ranging from community detection to compressed sensing, machine learning (notably neural networks) and generalized linear regression. The talk will review these developments and explain how they can be used, together with the replica method, to identify phase transitions in benchmark statistical ensembles of inference problems.
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Ημερομηνία: 7/4/2021
Ομιλητής: Prof. Costas Bachas
Ecole Normale Supérieure Paris, France
Τίτλος: Quantum + Gravity: the Unfinished Revolution
Περίληψη: A century after the discovery of General Relativity and Quantum Mechanics, their combination continues to challenge our understanding of both. I will discuss the current status of quantum gravity, a theory still under construction that is guided by two main themes: String Theory, and the paradoxes raised by the Hawking evaporation of black holes.
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Ημερομηνία: 5/3/2021
Ομιλητής: Prof. Reinhard Genzel (Nobel Prize Laureate 2020)
Max Plack Institute for Extraterrestrial Physics, Garching, Germany
Τίτλος: A 40-Year Journey
Περίληψη: More than one hundred years ago, Albert Einstein published his Theory of General Relativity (GR). One year later, Karl Schwarzschild solved the GR equations for a non-rotating, spherical mass distribution; if this mass is sufficiently compact, even light cannot escape from within the so-called event horizon, and there is a mass singularity at the center. The theoretical concept of a 'black hole' was born, and was refined in the next decades by work of Penrose, Wheeler, Kerr, Hawking and many others. First indirect evidence for the existence of such black holes in our Universe came from observations of compact X-ray binaries and distant luminous quasars. I will discuss the forty year journey, which my colleagues and I have been undertaking to study the mass distribution in the Center of our Milky Way from ever more precise, long term studies of the motions of gas and stars as test particles of the space time. These studies show the existence of a four million solar mass object, which must be a single massive black hole, beyond any reasonable doubt.
