Τμήμα Φυσικής

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.

 Title: Quantum + Gravity: the Unfinished Revolution

Abstract: 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. 

Marc Mezard 
Ecole Normale Supérieure, Paris, France

Οι διαφάνειες της ομιλίας του κ. M. Mezard , που ευγενικά παραχώρησε, βρίσκονται εδώ.

Title: A new mechanism for gain in  time dependent media

 Abstract: 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.