Gravitational-wave research as an emerging field in the Max Planck Society. The long roots of GEO600 and of the Albert Einstein Institute.

This chapter will explore the interplay between the renaissance of general relativity and the advent of relativistic astrophysics following German involvement in gravitational-wave research through the window of the Max Planck Society, from the very first interests of its scientists, to the point when gravitational-wave detection became established by the appearance of full-scale detectors and international collaborations. On the background of the spectacular astrophysical discoveries of the 1960s and the growing role of relativistic astrophysics, Ludwig Biermann and his collaborators at the Max Planck Institute for Astrophysics in Munich became deeply involved in research related to such widening horizons, already unveiled by radio astronomy during the 1950s. At the end of the 1960s, Joseph Weber's announcements claiming detection of gravitational waves sparked the decisive entry of this group into the field, in parallel with the appointment of the renowned relativist Juergen Ehlers. The Munich area group of Max Planck institutes provided the fertile ground for acquiring a leading position in the 1970s, facilitating the transition from resonant bars towards laser interferometry and its innovation at increasingly large scales, eventually finding a dedicated site in Hannover in the early 1990s. An early pan-European initiative broke up into two major projects: the British-German GEO600, and the French-Italian Virgo. The German approach emphasized perfecting experimental systems at pilot scales, and never developed into a fully-scaled interferometer, rather joining the LIGO collaboration at the end of the century. In parallel, Ehlers founded an institute for gravitational physics in Potsdam, and soon both branches were unified as the Albert Einstein Institute of the Max Planck Society, one of the central contributors to the detection of gravitational waves in 2015.