25 Years of the AEI

Today is the 25th anniversary of the opening of the Albert Einstein Institute (AEI) in 1995. It was a day that changed my life — for the better! — and that has affected the science of Einstein’s general relativity in lots of ways, also I believe for the better! So I hope it will be interesting to some readers if I ramble and reminisce today about the foundation of the AEI 25 years ago. Since today much of the world is shut down because of the SARS-CoV-2 pandemic, what could be a better time for a virtual history dig into this important institution? Our real silver anniversary celebration is planned for October this year, COVID-19 willing!

The AEI belongs to the Max Planck Society (MPS), and its formal name is the Max Planck Institute for Gravitational Physics, or even better das Max-Planck-Institut für Gravitationsphysik. I will talk about how it got two names in a minute, but the first thing is how the AEI got started. 

Jürgen Ehlers’ one political idea

The AEI exists because of a political event — the fall of the Berlin Wall in 1989 followed by the reunification of Germany in 1990 — and a political idea — the proposal by Jürgen Ehlers to the MPS that it should set up a new research institute for general relativity.

(The early history is much more complicated than this brief statement might suggest, since there were different suggestions by a number of others as to how to re-establish relativity research in Germany in this period, where reunification seemed to open up many possibilities. See the essay by Hubert Gönner for a very different perspective.)

Jürgen by 1989 had become one of the world’s leading experts in general relativity theory, a gentle mathematician who ran a small but world-class research group in the Max Planck Institute for Astrophysics in Garching, near Munich. He was at home with the most difficult mathematical challenges of Einstein’s theory, and to address them he liked working alone or with a small group of collaborators. His work had sometimes led him into controversy, such as with the eminent Nobel Prize winning astrophysicist Chandrasekhar, but he was not a mover and shaker, not someone who wanted to organise the world of science. But he could recognise an opportunity when he saw it, and he saw it in 1991. 

The Max Planck Society had decided, with the support of its funder, the German government, that it needed to expand into the states of the former East Germany by setting up new institutes. So it was looking for suggestions. Jürgen decided to pursue what he later called the one political idea of his life: one of them should be dedicated to general relativity. This wasn’t just a scientific proposal, it was also a political one, because after all Einstein had developed general relativity in Berlin, and then in the Nazi times his work had been vilified in Germany. So the MPS ought to do this not only for the science, but also as a public affirmation of the importance of this science and an acknowledgement of its German roots. The force of this argument was strong, and Jürgen soon found himself the nominal leader of the project to shape a formal proposal and get it approved by MPS. He recruited his two closest collaborators and group members, Bernd Schmidt and Helmut Friedrich, to help him.

From idea to actuality

Bernd Schmidt took me aside as early as December 1991, when were were both attending the ICGC-91 conference in Ahmedabad, to ask if I would be interested to be one of the founding directors if the proposal succeeded. This is how setting up an institute works — in MPS, an institute’s management is focused on a small number of directors, and MPS likes to stand back once it is started and let the directors run the show. So a proposal for a new institute is partly to do with the scientific need and partly to do with who will run it. 

The scientific case was going to include the growing impact of general relativity in astrophysics as seen in the early 1990s: ultra-relativistic neutron stars were being monitored as pulsars by radio astronomers, black holes almost certainly existed in many of the systems being studied by X-ray astronomers, the famous Hulse-Taylor binary pulsar had already proved that Einstein was right about gravitational waves, and it was looking like large-scale gravitational wave detectors were going to be built to look for such waves directly. I was involved in the theory behind a lot of these issues, so Bernd said that I might be a possible candidate for a director. 

Was I interested? You bet!

Between the Wall coming down in 1989 and the opening of our doors in 1995 is only six years, so in retrospect things moved quite fast! The proposal took shape rapidly, for an institute with three directors for its three divisions: mathematical relativity plus the two burgeoning research applications of Einstein’s theory, astrophysical relativity and quantum gravity. To start up quickly it might go with two directors (Jürgen and possibly me), expanding soon afterwards into string theory and quantum gravity. A small symposium was held in 1993 where I and a number of other people working at the interface between relativity and astrophysics were invited to speak, and where the most important part of the audience was a committee of senior scientists whose job it was to oversee the scientific decisions involved in founding the institute. After this committee ratified the idea that I should be the second founding director, it was time to inform myself more about the MPS, which works in a very different way from that of the universities I was accustomed to.

I began visiting the headquarters in Munich. In meetings with various MPS people, I was being informed but also recruited. One meeting stands out vividly in my memory, with the then MPS Vice President Herbert Walther. At one point in our amiable conversation he smiled and said that, if I became a director, that would mean that MPS would have such faith in my scientific judgement that if I were to decide to switch my division’s work from relativity to, say, chemistry, they would not do anything to stop me, as long as the work I did continued to be world-class! I understand that this is still said to new prospective directors today. It reflects the immense independence that directors have, which in my view is one of the reasons that research in the MPS is so strong.

I also began visiting Potsdam and Berlin: the association with Einstein made it a no-brainer that this was where the institute was going to be. Some of those visits included Jürgen and Bernd. We were scouting for start-up locations for the institute, discussing research priorities, and reaching understandings about how to run such an institute. Jürgen and I saw eye-to-eye on that one; we both wanted our scientists to work in a supportive and relaxed atmosphere. In early 1995, when we interviewed for our support positions, we explicitly looked for (and found) people who would help our scientists focus their time on science. On one of the visits, sitting with Bernd near the circular fountain beneath Sans Sousci palace, I remember first talking about the idea that later became the online open-access journal Living Reviews in Relativity: using a part of the financial resources we would control to develop a scholarly resource for our graduate students and for the whole community. It was a creative period, one I feel privileged to have been lucky enough to experience.

How we got our name

The whole process of founding an institute in MPS culminates with the final meeting with the President, which is called a negotiation because your terms of employment will be settled, as well as the budget for your institute. In 1994, Jürgen and I did the institute part together, meeting with then President Hans Zacher in Munich. Zacher wanted to discuss an important question that was on our minds: besides the long name Max-Planck-Institute für Gravitationsphysik, should the institute have a secondary name, the Albert Einstein Institute? 

This would be unusual: few Max Planck institutes have a secondary name, and few are named after individual scientists. On the positive side, putting Einstein’s name on an institute in Potsdam would be a way for MPS, representing the German academic community, to repudiate the way Einstein had been treated by Germany, to affirm Germany’s recognition of his huge importance to science. On the other hand, Zacher, who was a scholar of law, was concerned that we did not have the moral right to do that, that Einstein had said he didn’t want anything more to do with Germany, and that using his name might be misconstrued as wilful ignorance of the history of Germany’s dealings with Einstein. 

In the end, the three of us agreed that this affirmation was past due, that the positives were important enough to take a risk with the negatives, and so the AEI officially got its name. We were good to go!

The doors opened on 1 April 1995 to our rented accommodation in the new office block called Haus der Wirtschaft (Commerce House). We had only a handful of staff, all of whom could sit around a single table to drink tea in the afternoon. I wasn’t even officially on board: my contract with Cardiff University wouldn’t release me until after exams, on 1 June. But I was nevertheless present for the first day, taking these photos. A small and slightly bewildering but also exciting beginning, all of us wondering how we would learn to work together, where we would go!

A worldwide home for general relativity

Younger scientists today may not be aware that general relativity research always had a political side, at least starting from the mid-1950s, one that explicitly aimed to protect research in the field from the global divisions of that era. Ehlers had grown up with this, and was very keen that part of the mission of the AEI would be to maintain this global view, to be a place that scientists around the world could visit and feel welcome, and that would assist relativists around the world if possible. Most research institutes, like most university science departments, are keenly aware of the competition with other places around the world. But Jürgen took the view that, because the AEI would be the only institute in the world dedicated to research across all of general relativity, it had a responsibility to keep its doors open to all.

A bit of an aside might be in order on what I called the political nature of this research field. This had its roots in three circumstances: (a) the field in the 1950s was very small; (b) there were very good relativists on both sides of the Iron Curtain; and (c) the subject desperately needed reviving. The field had almost died of neglect from the 1930s onwards, partly because quantum theory and then quantum field theory were the hot topics that attracted top theorists, and partly because the war had put the focus on nuclear physics. Einstein, who died in 1955, hadn’t helped by frequently asserting that gravitational waves were not real, nor were black holes. 

But in the 1950s and ‘60s, people like Wheeler in the US, Bondi and Pirani in the UK, Trautman in Poland, and Zel’dovich in the USSR were turning toward relativity, and there were big problems to solve: was gravitational radiation real, were black holes real, how could one separate coordinate effects from real ones, could general statements be made about solutions even when exact solutions were lacking? This was not the time to splinter apart because of international rivalries. 

So in the mid-‘50s, relativists organised the International Committee on General Relativity and Gravitation (now the International Society of General Relativity and Gravitation). This was in itself unusual. Normally, subject-specific scientific societies exist within single countries: the American Physical Society, the Royal Astronomical Society, and so on. Physics societies then acquire international links by adhering to the International Union of Pure and Applied Physics (IUPAP) through subject-oriented commissions. But in 1957 the ICGRG exceptionally became itself a commission of the IUPAP, recognising its inherently international scope. The ICGRG began publishing a newsletter to keep its members informed of research around the world; this later evolved into the General Relativity and Gravitation (GRG) Journal. And the ICGRG encouraged exchanges across the Iron Curtain. When the political winds blew cold and national scientific societies felt that they had to represent their own national interests, the ICGRG steadfastly remained apart, working to make sure that lines of communication remained open, that scientists could still visit one another and exchange ideas across the Iron Curtain. (It helped, of course, that even the most rabidly nationalistic politicians couldn’t find anything about research in general relativity that might have any strategic importance to their countries!) 

This was all very recent history when the AEI opened. The Iron Curtain had lifted only 6 years earlier. Jürgen wanted the AEI to actively help to continue this spirit, which he felt was going to be needed because the growing importance of general relativity for astrophysics and in quantum gravity was inevitably going to change the nature of the field into one with more competition, more rivalry. The AEI should be a place where good scientists did their own work, but where visitors could come and bring in different points of view, where rivals would want to come to put their own views.

To this end, Jürgen had two big priorities in our negotiation with President Zacher: a well-funded library (especially attractive to visiting relativists from small universities or underdeveloped countries), and a big dedicated fund to support visits. He got what he wanted. The new building in Golm included huge space for the library. And for many years the visitor money supported something like 60 visitors a year, and it was well used by all three divisions (Hermann Nicolai had joined the AEI to direct the quantum gravity division very soon after we started up). A big help was the Max Planck guest house on the Golm campus, which the AEI initially managed on behalf of the MPS, because so many of our visitors used it. I think that Jürgen supported the unusual enterprise of publishing the Living Reviews journal because he saw it serving this function of making the AEI into a focus for world research.

Growth and impact

This is the end of my reminiscences about the founding of the AEI, but I can’t close without reflecting on the enormous changes we have seen. By the time we moved from our office block to the Golm campus in 1998, we were three active divisions. By the time the Golm building was officially dedicated in 1999, we were already overflowing it. We also were developing our plans for the new branch in Hannover, taking into the MPS the existing university group of Karsten Danzmann and expanding further. In 1999 we also hosted the annuals international Strings conference, attended by Stephen Hawking, and got on the cover of the important German news weekly, Der Spiegel. We had arrived! 

By now we have over 300 staff on two sites, big hardware projects for ground-based and space-based gravitational wave detection in Hannover, big supercomputing projects in both Hannover and Golm, and enormous presence in the worlds of string theory and of the theoretical support of gravitational wave detection. The gravitational wave enterprise has moved from expectations to enormous success, and the AEI has contributed massively to that. Jürgen, who saw part of this development but who passed away in 2008, would I think have been astonished by how far the AEI has come, and I certainly hope he would have loved it. The AEI still owes a huge debt to his one political idea ever!