Aichelburg Fest


A meeting in honor of Peter Aichelburg

Please note that the number of participants is limited to 50, and registration by sending an email to Ruth Fröler is required. Confirmation of registration will be sent on a first come first served basis.

Vienna University Covid-19 rules require that we maintain a list of participants, with emails and telephone numbers, and check the 2.5G certificates upon entrance. In particular we need a confirmation of your participation, and we will not be able to admit further participants after the limit of 50 participants has been reached.

  • 14.00 Opening
  • 14.10-14.40 Herbert Balasin (TU Wien): The scientific life of Peter Aichelburg
  • 14.40-15.20 Birgit Schoerkhuber (Innsbruck): Self-similar blowup in supercritical wave equations

Abstract: One of the most distinct features of nonlinear time-dependent partial differential equations is the possible onset of singularities. This means that either the solution itself blows up in finite time or that it looses regularity in the sense that derivatives diverge. Understanding these mechanisms for physical models is challenging and one is naturally led to the investigation of suitable toy problems. In this talk, I will review recent developments and results concerning self-similar blowup for energy supercritical wave equations including stable blowup and threshold phenomena. This line of research was initiated by Peter and his group almost two decades ago and has attracted many young researchers since.

  • 15.30-16.10 Piotr Bizon (Cracow): What are quasinormal modes?

Abstract: Quasinormal modes (QNMs) for open systems are what normal modes are for closed systems. They have characteristic frequencies of oscillations (as normal modes) and decay rates. In black hole physics QNMs play the key role in relaxation to an equilibrium state (so called ringdown) and Peter and his collaborators were the first to study QNMs in critical gravitational collapse. Despite their physical relevance,  the mathematical status of QNMs has not been quite satisfactory. I will discuss  recent advances in understanding of QNMs, focusing on their new definition proposed by Gajic and Warnick. It touches upon subtle regularity properties that I hope Peter will find interesting.

  • 16.15-16.55 Abhay Ashtekar (Penn State), by zoom: Probing the Big Bang with Quantum Fields

Abstract: Singularity theorems of Penrose and Hawking are based on geodesic incompleteness.Physically, this criterion refers to the fate of classical test particles. What if one uses quantum fields instead? Quantum fields are operator valued distributions even in Minkowski space and, surprisingly, they continue to be well-defined across the big bang. The renormalized products of fields  such as the expectation value of the energy-momentum tensor also remain well-defined as distributions. Thus, when probed with observables associated with quantum fields, the big bang (and the big crunch) singularities are quite harmless. In semi-classical gravity, then, solutions to the quantum corrected Einstein’s equations would continue yield distributional metrics. I hope that the key role distributions play in this analysis would delight Peter who has shed much light on the physics in distributional space-time geometries. (pdf)

  • 17.00-18.00 Drinks