Journées Relativistes Weimar 1999

Volker Perlick, TU Berlin and Albert Einstein Institute, Max Planck Society
The ``Journées Relativistes'' started as a regular meeting of French relativists several decades ago. Over the years, they have grown into a series of international conferences held in various Western-European cities. The most recent meeting in this series took place in Weimar, Germany, from September 12 to September 17, 1999. The main organizers were G. Neugebauer (Chairman), R. Collier (Secretary) and R Wagner (Conference office) from the relativity group in Jena. The conference was sponsored by the Max Planck Society, by the Deutsche Forschungsgemeinschaft, by the Ministry for Science, Research, and Culture of the state of Thuringia, Germany, and by the Friedrich Schiller University at Jena.

Weimar is a city of approximately 60,000 inhabitants, situated some 20 kilometers west of Jena in the state of Thuringia. The meeting took place in a hotel at the outskirts of Weimar so that most participants stayed together not only during the day but also during the evening. As a consequence, there was ample time for vivid discussions in a pleasant atmosphere. On Thursday afternoon there was no scientific program; instead, everyone had the opportunity to visit the city, either with an organized tour or on his or her own. Weimar is best known for its cultural tradition, given the fact that, among others, J. S. Bach, J. W. Goethe, F. Schiller, and F. Liszt spent at least some years in this city and left their traces in various places. For this reason, Weimar is visited by a large number of tourists every year. In the year of the conference this number was even higher than usual because Weimar was nominated ``European City of Culture 1999'' by the European Union. Incidentally, the same fact had a somewhat unwanted impact on the beer prices.

This meeting in Weimar clearly demonstrated the international character of the ``Journées Relativistes''. It was attended by participants not only from Western Europe but also from Eastern-European countries, from various parts of the former Soviet Union, and from both Americas. The total number of participants came up to almost 100 which was even slightly beyond the seating capacity of the lecture room.

Following the tradition of earlier meetings in this series, the conference covered all aspects of general relativity. The scientific program was divided into morning sessions with invited plenary lectures of 60 minutes or of 30 minutes, two parallel afternoon sessions with contributed talks of 30 minutes, and poster sessions. In the following I give a brief overview on the morning sessions.

The conference started with a welcome address by G. Neugebauer (Jena) and a speech by R. Kerner (Paris) honoring the late André Lichnerowicz. The first scientific talk was by Y. Choquet-Bruhat (Paris) on the so called ``null condition'' and its relevance in view of the Christodoulou-Klainerman result on the global existence of solutions to Einstein's vacuum field equation which are close to Minkowski space. Classes of solutions to Einstein's field equation were investigated also in the following talks. H. Friedrich (Golm) considered asymptotically flat solutions and showed how to calculate some asymptotic quantities near spacelike infinity. J. Bicák (Prague) reviewed some recent developments in the investigation of radiative spacetimes. D. Kramer (Jena), stepping in as a plenary speaker for Lee Lindblom who could not attend the meeting, presented an axially-symmetric gravitational wave solution. Z. Perjés (Budapest) talked about general properties of rotating perfect fluid solutions and on strategies of finding such solutions that may serve as models of rotating stars. For the idealized case of a rigidly rotating disk of dust, this problem was solved by Neugebauer and Meinel a few years ago. G. Neugebauer (Jena) in his talk demonstrated that the disk of dust and several black-hole configurations (Kerr, double Kerr) are boundary value problems for the exterior vacuum region which can be solved by the inverse scattering method. R. Meinel (Jena) in his talk discussed the properties of this disk-of-dust solution in a common setting with the Kerr solution. (There was also a video presentation in one of the afternoon sessions by M. Ansorg (Jena) and D. Weiskopf (Tübingen) visualizing the optical appearance of the Neugebauer-Meinel disk to an outside observer.)

Various aspects of black holes were at the center of a second group of talks. Th.Damour (Paris) spoke on a correspondence between self-gravitating string states and Schwarzschild black holes. D. Brill (Maryland) presented solutions to the (2+1)-dimensional source-free Einstein equation that are constructed by gluing together several black-hole configurations. W. Israel (Victoria) discussed some aspects of the thermodynamics of spinning black holes. G. Schäfer (Jena) reported on his results with P. Jaranowski, presenting the dynamics of binary black-hole systems to within 3rd post-Newtonian approximation. B. Brügmann (Golm) gave a status report on results of the so-called Grand Challenge Alliance, aiming at numerically investigating dynamical processes such as binary black-hole mergers.

Quantum field theory on a classical spacetime background was the topic of the talk by V. Belinski (Moscow) who critically discussed various derivations of the Unruh effect. In addition, there were two talks aiming at quantizing the gravitational field itself. S. Deser (Brandeis) talked about ultraviolet divergences in quantum (super-)gravity, indicating the necessity of stringlike, nonlocal, extensions. A. Ashtekar (Penn State) considered spacetimes with ``isolated horizons'', a notion which generalizes the event horizons known from the theory of static black holes, and the non-perturbative quantization of such objects.

Another group of talks can be summarized under the heading ``cosmology''. This includes a review on the microwave background radiation and its anisotropies by N. Deruelle (Paris) and a talk on how to find limits for the cosmological parameters with the help of gravitational lens statistics by N. Straumann (Zürich). The foundations of gravitational lens theory from a spacetime perspective, concentrating on the geometry of light cones, were discussed by J. Ehlers (Golm). There were two more talks with a relation to cosmology. B. Carter (Paris) discussed various aspects of cosmic strings, and M. Demianski (Warsaw) reviewed the history of the gravitational constant.

The program was rounded out by one plenary talk on experimental aspects of gravity. H.-P. Nollert (Tübingen) gave an overview on the prospects of gravitational wave astronomy.

Further information can be found on the conference homepage
Written versions of all presentations (invited talks, contributed talks, and posters) that survive a refereeing process will be published in a double issue of Annalen der Physik (Leipzig).

Jorge Pullin