Invited papers from the international meeting on 'New Frontiers in Numerical Relativity' (Albert Einstein Institute, Potsdam, Germany, 17–21 July 2006)

Abstract

Traditionally, frontiers represent a treacherous terrain to ventureinto, where hidden obstacles are present and uncharted territories lieahead. At the same time, frontiers are also a place where newperspectives can be appreciated and have often been the cradle of newand thriving developments. With this in mind and inspired by thisspirit, the Numerical Relativity Group at the Albert EinsteinInstitute (AEI) organized a `New Frontiers in Numerical Relativity' meeting on 17–21 July 2006 at the AEI campus in Potsdam, Germany.It is an interesting historical remark that the suggestion of themeeting was first made in the late summer of 2005 and thus at a timethat for many reasons has been a turning point in the recent historyof numerical relativity. A few months earlier (April 2005) in fact,F Pretorius had announced the first multi-orbit simulations ofbinary black holes and computed the waveforms from the inspiral,merger and ring-down (`Numerical Relativity', Banff InternationalResearch Station, Banff, Canada, 16–21 April 2005). At that time, the work of Pretoriusserved as an important boost to the research in this field andalthough no other group has yet adopted the techniques he employed, his results provided the numerical relativity community with clear evidence that the binary black hole problem could besolved. A few months later (November 2005), equally striking resultswere presented by the NASA Goddard and Texas/Brownsvillegroups, who also reported, independently, multi-orbitevolutions of binary black holes using numerical techniques andformulations of the Einstein equations which were markedly distinctfrom those suggested by Pretorius (`Numerical Relativity 2005',Goddard Space Flight Centre, Greenbelt, MD, USA, 2–4 November 2005).A few months later other groups were able to repeat the samesimulations and obtain equivalent results, testifying that thecommunity as a whole had reached comparable levels of maturity inboth the numerical techniques and the mathematical methods neededfor successful solution of the Einstein equations for binary blackholes. Clearly, an important frontier, and actually a long-awaitedone, was finally open and the `gold rush' was just about to begin bythe time the `New Frontiers in Numerical Relativity' meeting started its sessions in July2006.And so, almost 20 years since the almost homonymous meeting held atUrbana–Champaign (`Frontiers in Numerical Relativity', University of Illinois, IL, USA, 1988), the`New Frontiers in Numerical Relativity' meeting at the AEI saw the enthusiasticparticipation of a great part of the community, with 127 participantspresent (in 1988 they were 55) and with a large majority beingrepresented by students and postdocs, a reassuring sign of good healthfor the community. Faithful to the title of the conference, theprogramme was dedicated to the many and diversified `frontiers' innumerical relativity and organized so as to have few talks with ampletime dedicated to discussions.Overall, the talks presented at the meeting covered all of the mostsalient aspects of numerical relativity: from the formulation of theEinstein equations, over to the initial-value problem in generalrelativity, from the evolution of vacuum and non-vacuum spacetimes, tomultiblock adaptive mesh-refinement techniques, from boundaryconditions and perturbative methods, to relativistic fluids andplasmas. The contributions in this special issue represent a selectionof that research, but also include invited papers from authors whowere not present at the meeting but were pursuing research at theforefronts of numerical relativity.In addition to the more traditional sessions, the `New Frontiers in Numerical Relativity'meeting also hosted a less traditional session, dedicated to an`unconstrained' discussion which covered some of the mostcontroversial issues that emerged during the conference. During thissession, chaired by E Seidel, a lively discussion took place in thenon-trivial attempt of marking the new frontiers on the map ofnumerical relativity. The transcript of this discussion is an integral part of this issue and it is available, along with the audio recording, in the online version only. We believe they embody an important part of the development of this fieldand, like a good bottle of wine, it will be interesting to read themagain once sufficiently aged.As a concluding remark we note that it is almost one year sincethe `New Frontiers in Numerical Relativity' meeting and dozens of excellent papers have beenpublished or posted on the preprint archive. Some of the scientificresults obtained over these months, especially those revolving aroundbinary black holes, were simply unimaginable a few years ago andrepresent an indisputable evidence that the research in numericalrelativity has never been as exciting as it is now.These results have already had an impact in astrophysics and thecommunity interested in the analysis of gravitational-wave data, thusopening new and different frontiers in numerical relativity. Interestingly, all of this is happening while ground-based gravitationalwave detectors in the US and Europe are operating at a sensitivity suchthat gravitational radiation may soon be directly detected.While much still needs to be understood and improved, the gold rushtowards the new frontiers of numerical relativity does not yet show anysign of being close to a rapid end.