View source for Jürgen Ehlers

{{short description|German physicist}}
{{Use dmy dates|date=December 2024}}
{{featured article}}
{{Infobox scientist 
|name        = Jürgen Ehlers
|caption     = At the award ceremony for the Charles University Medal in Potsdam, September 2007
|image       = Juergen Ehlers.jpg
|birth_date  = {{birth date|1929|12|29|df=y}}
|birth_place = [[Hamburg]], [[Weimar Republic]]
|nationality = German
|death_date  = {{death date and age|2008|5|20|1929|11|29|df=y}}
|death_place = [[Potsdam]], [[Brandenburg]], Germany
|field       = [[Physics]]
|work_institutions = [[University of Hamburg]]<br/>[[Max Planck Institute for Astrophysics]]<br/>[[Max Planck Institute for Gravitational Physics]]
|alma_mater  = [[University of Hamburg]]
|doctoral_advisor  = [[Pascual Jordan]]
|doctoral_students = 
|known_for   = [[General relativity]]<br/>[[Mathematical physics]]
|prizes      = [[Max Planck Medal]] (2002)
|religion    = 
|signature   = 
|footnotes   = 
}}
{{Cosmology|scientists}}
'''Jürgen Ehlers''' ({{IPA|de|ˈjʏʁɡn̩ ˈʔeːlɐs|lang}}; 29 December 1929 – 20 May 2008) was a German [[physicist]] who contributed to the understanding of [[Albert Einstein]]'s theory of [[general relativity]]. From graduate and postgraduate work in [[Pascual Jordan]]'s relativity research group at [[Hamburg University]], he held various posts as a lecturer and, later, as a professor before joining the [[Max Planck Institute for Astrophysics]] in [[Munich]] as a director. In 1995, he became the founding director of the newly created [[Max Planck Institute for Gravitational Physics]] in [[Potsdam]], Germany.

Ehlers' research focused on the foundations of general relativity as well as on the theory's applications to [[astrophysics]]. He formulated a suitable classification of [[Exact solutions in general relativity|exact solutions]] to [[Einstein's field equations]] and proved the [[Ehlers–Geren–Sachs theorem]] that justifies the application of simple, general-relativistic model universes to modern [[Physical cosmology|cosmology]]. He created a [[spacetime]]-oriented description of [[gravitational lens]]ing and clarified the relationship between models formulated within the framework of general relativity and those of [[Newtonian gravity]]. In addition, Ehlers had a keen interest in both the history and [[philosophy of physics]] and was an ardent populariser of science.

==Biography==

===Early life===
Jürgen Ehlers was born in Hamburg on 29 December 1929.<ref name="Arimondo Ertmer Schleich Rasel 2009 p. 9">{{cite book | last1=Arimondo | first1=E. | last2=Ertmer | first2=W. | last3=Schleich | first3=W. | last4=Rasel | first4=E.M. | title=Atom Optics and Space Physics: Proceedings of the International School of Physics "Enrico Fermi", Course CLXVIII, Varenna on Lake Como, Villa Monastero, 3-13 July 2007 | publisher=IOS Press | series=International School of Physics Enrico Fermi | year=2009 | isbn=978-1-58603-990-5 | url=https://books.google.com/books?id=91s7GiBaAE0C&pg=PR9 | access-date=28 December 2022 | page=9}}</ref> He attended public schools from 1936 to 1949, and then went on to study physics, mathematics and philosophy at [[Hamburg University]] from 1949 to 1955. In the winter term of 1955–56, he passed the high school teacher's examination (''[[Staatsexamen]]''), but instead of becoming a teacher undertook graduate research with [[Pascual Jordan]], who acted as his thesis advisor. Ehlers' doctoral work was on the construction and characterization of solutions of the [[Einstein field equations]]. He earned his doctorate in physics from Hamburg University in 1958.<ref>The dissertation is {{Harvnb|Ehlers|1957}}; cf. {{Harvnb|Ellis|2009}}.</ref>

Prior to Ehlers' arrival, the main research of Jordan's group had been dedicated to a [[Scalar-tensor theory|scalar-tensor]] modification of general relativity that later became known as [[Jordan–Brans–Dicke theory]]. This theory differs from general relativity in that the [[gravitational constant]] is replaced by a variable [[Field (physics)|field]]. Ehlers was instrumental in changing the group's focus to the structure and interpretation of Einstein's original theory.<ref>{{Citation|last=Schücking|first=Engelbert|contribution=Jürgen Ehlers|editor-last=Schmidt|editor-first=Bernd G.|title=Einstein's Field Equations and Their Physical Implications|year=2006|publisher=Springer|pages=V–VI|isbn=3-540-67073-4}}</ref> Other members of the group included Wolfgang Kundt, [[Rainer K. Sachs]] and Manfred Trümper.<ref>As described in {{Harvnb|Ellis|Krasiński|2007}} and {{Harvnb|Sachs|2009}}.
</ref>
The group had a close working relationship with [[Otto Heckmann]] and his student [[Engelbert Schücking]] at [[Hamburger Sternwarte]], the city's observatory. Guests at the group's colloquium included [[Wolfgang Pauli]], Joshua Goldberg and [[Peter Bergmann]].<ref>{{Harvnb|Ellis|2009}}</ref>

In 1961, as Jordan's assistant, Ehlers earned his [[habilitation]], qualifying him for a German professorship. He then held teaching and research positions in Germany and in the US, namely at the [[University of Kiel]], [[Syracuse University]] and Hamburg University. From 1964 to 1965, he was at the [[Graduate Research Center of the Southwest]] in [[Dallas]]. From 1965 to 1971, he held various positions in [[Alfred Schild]]'s group at the [[University of Texas at Austin]], starting as an [[associate professor]] and, in 1967, obtaining a position as full professor. During that time, he held visiting professorships at the universities of [[University of Würzburg|Würzburg]] and [[University of Bonn|Bonn]].<ref>{{Harvnb|Huisken|Nicolai|Schutz|2009}}, cf. the English version online as {{Harvnb|Huisken|Nicolai|Schutz|2008}}, and the associated CV, {{Citation|title=Lebenslauf von Prof. Dr. Jürgen Ehlers|publisher=Max Planck Institute for Gravitational Physics|date=27 May 2008|url=http://www.aei.mpg.de/pdf/pm_news/2008/Ehlers_Lebenslauf.pdf|access-date=27 May 2008|url-status=dead|archive-url=https://web.archive.org/web/20090519055819/http://www.aei.mpg.de/pdf/pm_news/2008/Ehlers_Lebenslauf.pdf|archive-date=19 May 2009}} (in German, English translation of title: "CV for Prof. Dr. Jürgen Ehlers"). Dates and positions also summarized in {{Harvnb|Weber|Borissoff|1998}}.</ref>

===Munich===
In 1970, Ehlers received an offer to join the [[Max Planck Institute for Physics and Astrophysics]] in [[Munich]] as the director of its gravitational theory department.<ref>{{Harvnb|Henning|Kazemi|2011}}, p. 472</ref> Ehlers had been suggested by [[Ludwig Biermann]], the institute's director at the time. When Ehlers joined the institute in 1971, he also became an adjunct professor at Munich's [[Ludwig Maximilian University]]. In March 1991, the institute split into the [[Max Planck Institute for Physics]] and the [[Max Planck Institute for Astrophysics]], where Ehlers' department found a home.<ref>{{Harvnb|Henning|Kazemi|2011}}, p. 634</ref>  Over the 24 years of his tenure, his research group was home to, among others, [[Gary Gibbons]], John Stewart and Bernd Schmidt, as well as visiting scientists including [[Abhay Ashtekar]], [[Demetrios Christodoulou]] and [[Brandon Carter]].<ref>As described in {{Harvnb|Breuer|2008}}</ref>

One of Ehlers' [[postdoctoral student]]s in Munich was Reinhard Breuer, who later became editor-in-chief of ''Spektrum der Wissenschaft'', the German edition of the popular-science journal ''[[Scientific American]]''.<ref>{{Harvnb|Breuer|2008}}</ref>

===Potsdam===
When German science institutions reorganized after [[German reunification]] in 1990, Ehlers lobbied for the establishment of an institute of the Max Planck Society dedicated to research on gravitational theory. On 9 June 1994, the Society decided to open the [[Max Planck Institute for Gravitational Physics]] in [[Potsdam]]. The institute started operations on 1 April 1995, with Ehlers as its founding director and as the leader of its department for the foundations and mathematics of general relativity.<ref>{{Harvnb|Henning|Kazemi|2011}}, p. 676</ref> Ehlers then oversaw the founding of a second institute department devoted to [[gravitational wave]] research and headed by [[Bernard F. Schutz]]. On 31 December 1998, Ehlers retired to become founding director [[emeritus]].<ref>{{Harvnb|Henning|Kazemi|2011}}, p. 737</ref>

Ehlers continued to work at the institute until his death on 20 May 2008.<ref>See p. 520 in the Max Planck Society's annual report for 2000, {{Citation|title=Jahrbuch 2000|publisher=Max-Planck-Gesellschaft|year=2000|url=http://www.mpg.de/english/illustrationsDocumentation/documentation/jahrbuch/2000/index.html}}. Time as emeritus and death cf. {{Harvnb|Braun|2008}}.</ref> He left behind his wife Anita Ehlers, his four children, Martin, Kathrin, David, and Max, as well as five grandchildren.<ref>{{Harvnb|Huisken|Nicolai|Schutz|2009}}; English version online as {{Harvnb|Huisken|Nicolai|Schutz|2008}}</ref>

==Research==
Ehlers' research was in the field of general relativity. In particular, he made contributions to [[cosmology]], the theory of [[gravitational lenses]] and [[gravitational waves]]. His principal concern was to clarify general relativity's mathematical structure and its consequences, separating rigorous proofs from [[heuristic]] conjectures.<ref>{{Harvnb|Schücking|2000}}</ref>

===Exact solutions===
For his doctoral thesis, Ehlers turned to a question that was to shape his lifetime research. He sought exact solutions of [[Einstein's equations]]: [[Universe Models|model universes]] consistent with the laws of general relativity that are simple enough to allow for an explicit description in terms of basic mathematical expressions. These exact solutions play a key role when it comes to building general-relativistic models of physical situations. However, general relativity is a fully [[general covariance|covariant]] theory – its laws are the same, independent of which [[coordinate]]s are chosen to describe a given situation. One direct consequence is that two apparently different exact solutions could correspond to the same model universe, and differ only in their coordinates. Ehlers began to look for serviceable ways of characterizing exact solutions ''[[Invariant (physics)|invariantly]]'', that is, in ways that do not depend on coordinate choice. In order to do so, he examined ways of describing the intrinsic geometric properties of the known exact solutions.<ref>B. Schmidt, Preface to {{Harvnb|Schmidt|2000}}</ref>

During the 1960s, following up on his doctoral thesis, Ehlers published a series of papers, all but one in collaboration with colleagues from the Hamburg group, which later became known as the "Hamburg Bible".<ref>{{Harvnb|Ellis|2009}}, p. 2180</ref>
The first paper, written with Jordan and Kundt, is a treatise on how to characterize exact solutions to Einstein's field equations in a systematic way. The analysis presented there uses tools from [[differential geometry]] such as the [[Petrov classification]] of [[Weyl tensor]]s (that is, those parts of the [[Riemann tensor]] describing the [[curvature]] of [[space-time]] that are not constrained by Einstein's equations), [[isometry group]]s and [[Conformal map|conformal]] transformations. This work also includes the first definition and classification of [[pp-waves]], a class of simple gravitational waves.<ref>A later version of this paper is {{Harvnb|Ehlers|Kundt|1962}}.
For an assessment, see J. Bicak, p. 14f. in {{Harvnb|Schmidt|2000}}</ref>

The following papers in the series were treatises on [[gravitational radiation]] (one with Sachs, one with Trümper). The work with Sachs studies, among other things, [[vacuum solutions]] with special [[algebra]]ic properties, using the 2-component [[spinor]] formalism. It also gives a systematic exposition of the geometric properties of bundles (in mathematical terms: congruences) of light beams. Spacetime geometry can influence the propagation of light, making them converge on or diverge from each other, or deforming the bundle's cross section without changing its area. The paper formalizes these possible changes in the bundle in terms of the bundle's expansion (convergence/divergence), and twist and shear (cross-section area-conserving deformation), linking those properties to spacetime geometry. One result is the ''Ehlers-Sachs theorem'' describing the properties of the shadow produced by a narrow beam of light encountering an opaque object. The tools developed in that work would prove essential for the discovery by [[Roy Kerr]] of his [[Kerr solution]], describing a rotating [[black hole]] – one of the most important exact solutions.<ref>Ehlers-Sachs theorem see sec. 5.3 in {{Harvnb|Frolov|Novikov|1998}}. An assessment of the work and its connection with Kerr solution is given by J. Bicak on p. 14f. of {{Harvnb|Schmidt|2000}}. The original work with Sachs is {{Harvnb|Jordan|Ehlers|Sachs|1961}}.</ref>

The last of these seminal papers addressed the general-relativistic treatment of the mechanics of continuous media. However useful the notion of a point mass may be in classical physics; in general relativity, such an idealized mass concentration into a single point of space is not even well-defined. That is why relativistic [[hydrodynamics]], that is, the study of continuous media, is an essential part of model-building in general relativity. The paper systematically describes the basic concepts and models in what the editor of the journal ''[[General Relativity and Gravitation]]'', on the occasion of publishing an English translation 32 years after the original publication date, called "one of the best reviews in this area".<ref>The English translation, by [[George F. R. Ellis|G. F. R. Ellis]], is {{Harvnb|Ehlers|1993}}. The quotation can be found on p. 1225 in the editor's comments section.</ref>

Another part of Ehlers' exploration of exact solutions in his thesis led to a result that proved important later. At the time he started his research on his doctoral thesis, the [[Golden age of general relativity]] had not yet begun and the basic properties and concepts of black holes were not yet understood. In the work that led to his doctoral thesis, Ehlers proved important properties of the surface around a black hole that would later be identified as its [[horizon]], in particular that the [[gravitational field]] inside cannot be static, but must change over time. The simplest example of this is the "Einstein-Rosen bridge", or [[Wormhole#Schwarzschild wormholes|Schwarzschild wormhole]] that is part of the Schwarzschild solution describing an idealized, spherically symmetric black hole: the interior of the horizon houses a bridge-like connection that changes over time, collapsing sufficiently quickly to keep any space-traveler from traveling through the wormhole.<ref>The changing views of what eventually be regarded as black holes can be found in {{Harvnb|Israel|1987}}. Ehlers' thesis is {{Harvnb|Ehlers|1957}}.
</ref>

===Ehlers group===
{{main|Ehlers group}}
In physics, [[Duality (mathematics)|duality]] means that two equivalent descriptions of a particular physical situation exist, using different physical concepts. This is a special case of a physical [[Symmetry (physics)|symmetry]], that is, a change that preserves key features of a physical system. A simple example for a duality is that between the [[electric field]] '''E''' and the [[magnetic field]] '''B''' [[electrodynamics]]: In the complete absence of electrical charges, the replacement '''E''' <math>\to</math> –'''B''', '''B''' <math>\to</math> '''E''' leaves [[Maxwell's equations]] invariant. Whenever a particular pair of expressions for '''B''' and '''E''' conform to the laws of electrodynamics, switching the two expressions around and adding a minus sign to the new '''B''' is also valid.<ref>{{Harvnb|Olive|1996}}</ref>

In his doctoral thesis, Ehlers pointed out a duality symmetry between different components of the [[Metric (general relativity)|metric]] of a stationary [[vacuum]] [[spacetime]], which maps solutions of Einstein's field equations to other solutions. This symmetry between the tt-component of the metric, which describes time as measured by clocks whose spatial coordinates do not change, and a term known as the ''twist potential'' is analogous to the aforementioned duality between '''E''' and '''B'''.<ref>Cf. Dieter Maison's contribution "Duality and Hidden Symmetries in Gravitational Theories", pp. 273–323 in {{Harvnb|Schmidt|2000}}.</ref>

The duality discovered by Ehlers was later expanded to a larger symmetry corresponding to the [[special linear group]] <math>SL(2)</math>. This larger [[symmetry group]] has since become known as the ''Ehlers group''. Its discovery led to further generalizations, notably the infinite-dimensional [[Geroch group]] (the Geroch group is generated by two [[commutativity|non-commuting]] [[subgroup]]s, one of which is the Ehlers group). These so-called ''hidden symmetries'' play an important role in the [[Kaluza–Klein reduction]] of both general relativity and its generalizations, such as [[eleven-dimensional supergravity]]. Other applications include their use as a tool in the discovery of previously unknown solutions and their role in a proof that solutions in the stationary [[axi-symmetric]] case form an [[integrable system]].<ref>
Maison op. cit., {{Harvnb|Geroch|1971}}, and, for various applications, {{Harvnb|Mars|2001}}.</ref>

===Cosmology: Ehlers–Geren–Sachs theorem===
{{main|Ehlers–Geren–Sachs theorem}}
[[File:WMAP 2010.png|thumb|right|250px|The inhomogeneities in the temperature of the cosmic background radiation recorded in this image from the satellite probe [[WMAP]] amount to no more than 10<sup>−4</sup> [[kelvin]]s.]]

The Ehlers–Geren–Sachs theorem, published in 1968, shows that in a given universe, if all freely falling observers measure the [[cosmic background radiation]] to have exactly the same properties in all directions (that is, they measure the background radiation to be [[isotropic]]), then that universe is an isotropic and homogeneous [[Friedmann–Lemaître–Robertson–Walker metric|Friedmann–Lemaître]] spacetime.<ref>{{Harvnb|Hawking|Ellis|1973}}, p. 351ff. The original work is {{Harvnb|Ehlers|Geren|Sachs|1968}}.</ref> Cosmic isotropy and homogeneity are important as they are the basis of the modern standard model of cosmology.<ref>E.g. {{Harvnb|Liddle|2003}}, p.2</ref>

===Fundamental concepts in general relativity===
In the 1960s, Ehlers collaborated with [[Felix Pirani]] and [[Alfred Schild]] on a constructive-axiomatic approach to general relativity: a way of deriving the theory from a minimal set of elementary objects and a set of axioms specifying these objects' properties. The basic ingredients of their approach are primitive concepts such as [[Event (relativity)|event]], [[light]] ray, [[Subatomic particle|particle]] and [[free fall|freely falling particle]]. At the outset, spacetime is a mere set of events, without any further structure. They postulated the basic properties of light and freely falling particles as axioms, and with their help constructed the [[differential topology]], [[conformal structure]] and, finally, the [[Metric (mathematics)|metric]] structure of spacetime, that is: the notion of when two events are close to each other, the role of light rays in linking up events, and a notion of distance between events. Key steps of the construction correspond to idealized measurements, such the standard range finding used in [[radar]]. The final step derived Einstein's equations from the weakest possible set of additional axioms. The result is a formulation that clearly identifies the assumptions underlying general relativity.<ref>See {{Harvnb|Ehlers|Pirani|Schild|1972}}; a summary can be found in {{Harvnb|Ehlers|1973}}.</ref>

In the 1970s, in collaboration with Ekkart Rudolph, Ehlers addressed the problem of rigid bodies in general relativity. Rigid bodies are a fundamental concept in classical physics. However, the fact that by definition their different parts move simultaneously is incompatible with the relativistic concept of the [[speed of light]] as a limiting speed for the propagation of signals and other influences. While, as early as 1909, [[Max Born]] had given a definition of rigidity that was compatible with relativistic physics, his definition depends on assumptions that are not satisfied in a general space-time, and are thus overly restrictive. Ehlers and Rudolph generalized Born's definition to a more readily applicable definition they called "pseudo-rigidity", which represents a more satisfactory approximation to the rigidity of classical physics.<ref>See {{Harvnb|Köhler|Schattner|1979}}. The original publication is {{Harvnb|Ehlers|Rudolph|1977}}.</ref>

=== Gravitational lensing ===
[[File:Gravitational lens-full.jpg|thumb|right|Most astrophysical modeling of gravitational lens systems makes use of the quasi-Newtonian approximation]]

With Peter Schneider, Ehlers embarked on an in-depth study of the foundations of [[gravitational lensing]]. One result of this work was a 1992 monograph co-authored with Schneider and Emilio Falco. It was the first systematic exposition of the topic that included both the theoretical foundations and the observational results. From the viewpoint of astronomy, gravitational lensing is often described using a quasi-Newtonian approximation—assuming the [[gravitational field]] to be small and the deflection angles to be minute—which is perfectly sufficient for most situations of astrophysical relevance. In contrast, the monograph developed a thorough and complete description of gravitational lensing from a fully relativistic space-time perspective. This feature of the book played a major part in its long-term positive reception.<ref>A review of the book itself is {{Harvnb|Bleyer|1993}}. The long-term impact can be judged by the way it is held up as a reference in the reviews of later books on the same topic, e.g. {{Harvnb|Perlick|2005}} and {{Harvnb|Bozza|2005}}; see also the assessment of {{Harvnb|Trümper|2009}}, p. 154.</ref> In the following years, Ehlers continued his research on the propagation of bundles of light in arbitrary spacetimes.<ref>{{Harvnb|Seitz|Schneider|Ehlers|1994}}, cf. section 3.5 of {{Citation|title=Annual Report 1994|publisher=Max Planck Institute for Astrophysics|year=1995|url=http://www.mpa-garching.mpg.de/mpa/institute/annual_rep/Jahresbericht_94.ps.gz|url-status=dead|archive-url=https://web.archive.org/web/20090519202655/http://www.mpa-garching.mpg.de/mpa/institute/annual_rep/Jahresbericht_94.ps.gz|archive-date=19 May 2009}}
</ref>

===Frame theory and Newtonian gravity===
A basic derivation of the Newtonian limit of general relativity is as old as the theory itself. Einstein used it to derive predictions such as the [[anomalous perihelion precession]] of the planet [[Mercury (planet)|Mercury]]. Later work by [[Élie Cartan]], [[Kurt Friedrichs]] and others showed more concretely how a geometrical generalization of [[Newtonian gravity|Newton's theory of gravity]] known as [[Newton–Cartan theory]] could be understood as a (degenerate) limit of [[general relativity]]. This required letting a specific parameter <math>\lambda</math> go to zero. Ehlers extended this work by developing a ''frame theory'' that allowed for constructing the Newton–Cartan limit, and in a mathematically precise way, not only for the physical laws, but for any spacetime obeying those laws (that is, solutions of Einstein's equations). This allowed physicists to explore what the Newtonian limit meant in specific physical situations. For example, the frame theory can be used to show that the Newtonian limit of a [[Schwarzschild solution|Schwarzschild black hole]] is a simple [[point particle]]. Also, it allows Newtonian versions of exact solutions such as the [[Friedmann–Lemaître–Robertson–Walker metric|Friedmann–Lemaître models]] or the [[Gödel metric|Gödel universe]] to be constructed.<ref>{{Harvnb|Ehlers|1997}}; a description can be found on p. 216f. in Luc Blanchet's contribution "Post-Newtonian Gravitational Radiation", pp. 225–271 in {{Harvnb|Schmidt|2000}}.</ref> Since its inception, ideas Ehlers introduced in the context of his frame theory have found important applications in the study of both the Newtonian limit of general relativity and of the [[Post-Newtonian expansion]], where Newtonian gravity is complemented by terms of ever higher order in <math>1/c^2</math> in order to accommodate relativistic effects.<ref>
{{Harvnb|Oliynyk|Schmidt|2009}}
</ref>

General relativity is [[nonlinear system|non-linear]]: the gravitational influence of two masses is not simply the sum of those masses' individual gravitational influences, as had been the case in Newtonian gravity. Ehlers participated in the discussion of how the [[back-reaction]] from gravitational radiation onto a radiating system could be systematically described in a non-linear theory such as general relativity, pointing out that the standard [[quadrupole]] formula for the energy flux for systems like the [[binary pulsar]] had not (yet) been rigorously derived: a priori, a derivation demanded the inclusion of higher-order terms than was commonly assumed, higher than were computed until then.<ref>A description that includes the historical context can be found in {{Harvnb|Schutz|1996}}. The original work is {{Harvnb|Ehlers|Rosenblum|Goldberg|Havas|1976}}.</ref>

His work on the Newtonian limit, particularly in relation to [[physical cosmology|cosmological]] solutions, led Ehlers, together with his former doctoral student Thomas Buchert, to a systematic study of [[Perturbation theory|perturbations]] and inhomogeneities in a Newtonian cosmos. This laid the groundwork for Buchert's later generalization of this treatment of inhomogeneities. This generalization was the basis of his attempt to explain what is currently seen as the cosmic effects of a [[cosmological constant]] or, in modern parlance, [[dark energy]], as a non-linear consequence of inhomogeneities in general-relativistic cosmology.<ref>See {{Harvnb|Buchert|Ehlers|1993}}, {{Harvnb|Buchert|Ehlers|1997a}} and {{Harvnb|Buchert|Ehlers|1997b}}. The current status of Buchert's further work is summarized in {{Harvnb|Buchert|2008}}.</ref>

===History and philosophy of physics===
Complementing his interest in the foundations of general relativity and, more generally, of physics, Ehlers researched the history of physics. Up until his death, he collaborated in a project on the history of quantum theory at the [[Max Planck Institute for the History of Science]] in Berlin.<ref>Cf. {{Harvnb|Braun|2008}}. Details about the project can be found on its [http://quantum-history.mpiwg-berlin.mpg.de/ website].</ref> In particular, he explored Pascual Jordan's seminal contributions to the development of [[quantum field theory]] between 1925 and 1928.<ref>
{{Harvnb|Ehlers|2007}}
</ref> Throughout his career, Ehlers had an interest in the philosophical foundations and implications of physics and contributed to research on this topic by addressing questions such as the basic status of scientific knowledge in physics.<ref>See {{Harvnb|Ehlers|2006a}} and {{Harvnb|Breuer|Springer|2001}} as well as its later English translation {{Harvnb|Breuer|Springer|2009}}, as well as {{Harvnb|Ehlers|2005}}.
</ref>

===Science popularization===
Ehlers showed a keen interest in reaching a general audience. He was a frequent public lecturer, at universities as well as at venues such as the [[Urania (Berlin)|Urania]] in [[Berlin]]. He authored popular-science articles, including contributions to general-audience journals such as ''Bild der Wissenschaft''. He edited a compilation of articles on gravity for the German edition of ''Scientific American''.<ref>Public lectures: {{Citation|title=Biennial Report 2004/2005|publisher=Max Planck Institute for Gravitational Physics|year=2006|url=http://www.aei.mpg.de/pdf/illustrationsDocs/biennial2004_05.pdf|url-status=dead|archive-url=https://web.archive.org/web/20070611081634/http://www.aei.mpg.de/pdf/illustrationsDocs/biennial2004_05.pdf|archive-date=11 June 2007}}, lists 25 popular talks (p. 158f.) for that time-frame alone. The compilation of articles is Börner & Ehlers 1996, listed under [[Jürgen Ehlers#Selected publications|Selected Publications]]. An example for a popular article is {{Harvnb|Ehlers|Fahr|1994}}.</ref>
Ehlers directly addressed physics teachers, in talks and journal articles on the teaching of relativity and related basic ideas, such as [[mathematics]] as the language of physics.<ref>{{Citation|title=Biennial Report 2004/2005|publisher=Max Planck Institute for Gravitational Physics|year=2006|url=http://www.aei.mpg.de/pdf/illustrationsDocs/biennial2004_05.pdf|url-status=dead|archive-url=https://web.archive.org/web/20070611081634/http://www.aei.mpg.de/pdf/illustrationsDocs/biennial2004_05.pdf|archive-date=11 June 2007}} lists 11 talks to teachers or in an interdisciplinary setting (p. 147f., p. 154f.). Mathematics and physics {{Harvnb|Ehlers|2006b}}</ref>

==Honours and awards==
Ehlers became a member of the [[Berlin-Brandenburg Academy of Sciences and Humanities]] (1993), the [[Akademie der Wissenschaften und der Literatur]], [[Mainz]] (1972), the [[German Academy of Sciences Leopoldina|Leopoldina]] in [[Halle (Saale)|Halle]] (1975) and the [[Bavarian Academy of Sciences and Humanities]] in Munich (1979).<ref>Berlin: {{Harvnb|Huisken|Nicolai|Schutz|2009}}; initial membership date in brief note on p.35 of the same publication. Mainz: p. 13 of {{Harvnb|Lütjen-Drecoll|2008}}. Leopoldina: listed as member on {{Citation|title=Mitgliederverzeichnis|url=http://www.leopoldina.org/de/mitglieder/mitgliederverzeichnis/member/3228/|publisher=Deutsche Akademie der Naturforscher Leopoldina|access-date=28 May 2012}} (in German, English translation of title: ''Members list''). Bavarian Academy: {{Harvnb|Trümper|2009}}.
</ref> From 1995 to 1998, he served as president of the [[International Society on General Relativity and Gravitation]].<ref>{{Citation|url=http://www.isgrg.org/history.php|title=GRG Society History|publisher=International Society on General Relativity and Gravitation|access-date=28 May 2013}}.</ref> He also received the 2002 [[Max Planck Medal]] of the [[Deutsche Physikalische Gesellschaft|German Physical Society]], the [[Alessandro Volta|Volta]] Gold Medal of [[Pavia University]] (2005) and the medal of the Faculty of Natural Sciences of [[Charles University]], [[Prague]] (2007).<ref>Max Planck Medal: Press release about the 2002 awards, {{Citation|url=http://www.dpg-physik.de/presse/pressemit/2001/dpg-pm-2001-024.html|title=Physikalische Spitzenleistung|publisher=Deutsche Physikalische Gesellschaft|date=17 December 2001|access-date=27 May 2008|archive-url=https://web.archive.org/web/20070213222143/http://www.dpg-physik.de/presse/pressemit/2001/dpg-pm-2001-024.html|archive-date=13 February 2007|url-status=dead}} (in German, English translation of title: ''Top achievement in physics''), and {{Harvnb|Rogalla|2001}}. Volta Medal: {{Citation|title=Namen: Prof. Dr. Jürgen Ehlers|url=http://www.berliner-zeitung.de/archiv/namen,10810590,10285232.html|newspaper=Berliner Zeitung|date=18 May 2005|access-date=27 May 2008}} (in German) and {{Citation|title=Medaille für Golmer Forscher|newspaper=Märkische Allgemeine Zeitung|date=19 May 2005|url=http://www.maerkischeallgemeine.de/mazarchiv/detail.php?article_id=843958}} (in German, English translation of title: ''Medal for researcher from Golm''). Charles University Medal: {{Harvnb|Trümper|2009}}, p. 154.</ref>

In 2008, the International Society on General Relativity and Gravitation instituted the "Jürgen Ehlers Thesis Prize" in commemoration of Ehlers. It is sponsored by the scientific publishing house [[Springer Science+Business Media|Springer]] and is awarded triennially, at the society's international conference, to the best doctoral thesis in the areas of mathematical and numerical general relativity.<ref>{{Citation|url=http://www.isgrg.org/ehlersprize.php|title=The Jürgen Ehlers Thesis Prize|publisher=Website of the International Society on General Relativity and Gravitation|access-date=28 May 2013}}</ref> Issue 9 of volume 41 of the journal ''[[General Relativity and Gravitation]]'' was dedicated to Ehlers, in memoriam.<ref>{{Harvnb|Nicolai|Ellis|Schmidt|2009}}</ref>

==Selected publications==
*{{Citation|editor-last=Börner|editor-first=G.|editor2-last=Ehlers|editor2-first=J.|title=Gravitation|publisher=Spektrum Akademischer Verlag|year=1996|isbn=3-86025-362-X}}
*{{Citation | last=Ehlers | first = Jürgen | contribution=Survey of general relativity theory | editor-last=Israel | editor-first=Werner | title=Relativity, Astrophysics and Cosmology | year=1973 | publisher=D. Reidel | pages=1–125 | isbn=90-277-0369-8 }}
*{{Citation|first1=P.|last1=Schneider|first2=J.|last2=Ehlers|first3=E. E.|last3=Falco|title=Gravitational lenses|publisher=Springer|year=1992|isbn=3-540-66506-4}}

==Notes==
{{reflist|30em|group=note}}
{{Reflist|30em}}

==References==
{{Refbegin|30em}}
*{{Citation|title=Book-Review - Gravitational Lenses|last=Bleyer|first=U.|journal=Astronomische Nachrichten|volume=314|issue=4|pages=314–315|year=1993|bibcode=1993AN....314..314S|doi=10.1002/asna.2113140412}}
*{{Citation|first=Valerio|last=Bozza|title=Book review: Silvia Mollerach, Esteban Roulet: Gravitational Lensing and Microlensing|journal=General Relativity and Gravitation|volume=37|issue=7|pages=1335–1336|year=2005|doi=10.1007/s10714-005-0117-9|bibcode = 2005GReGr..37.1335B |s2cid=120764050}}
*{{Citation|last=Braun|first=Rüdiger|title=Wo Zeit und Raum aufhören. Der Mitbegründer des Golmer Max-Planck-Instituts für Gravitationsphysik, Jürgen Ehlers, ist unerwartet verstorben|newspaper=Märkische Allgemeine Zeitung|date=27 May 2008|url=http://www.maerkischeallgemeine.de/mazarchiv/detail.php?article_id=1578607|access-date=28 May 2013}} (in German, English translation of title: ''Where time and space end. The co-founder of the Max Planck Institute for Gravitational Physics, Jürgen Ehlers, has died unexpectedly'')
*{{Citation|last1=Breuer|first1=Reinhard|last2=Springer|first2=Michael|title=Die Wahrheit in der Wissenschaft|journal=Spektrum der Wissenschaft|volume=7|year=2001|page=70|url=http://www.spektrum.de/artikel/827796}} (in German)
*{{Citation|last1=Breuer|first1=Reinhard|last2=Springer|first2=Michael|title=The truth in science|journal=General Relativity and Gravitation|volume=41|issue=9|year=2009|pages=2159–2167 |doi=10.1007/s10714-009-0844-4|bibcode = 2009GReGr..41.2159B |s2cid=123226152}}
*{{Citation|first=Reinhard|last=Breuer|title=Jürgen Ehlers und die Relativitätstheorie|date=26 May 2008|publisher=Spektrum der Wissenschaft Verlagsgesellschaft mbH|url=http://www.wissenslogs.de/wblogs/blog/forschern-auf-der-spur/physik/2008-05-26/j-rgen-ehlers-und-die-relativit-tstheorie|url-status=dead|archive-url=https://web.archive.org/web/20080928070016/http://www.wissenslogs.de/wblogs/blog/forschern-auf-der-spur/physik/2008-05-26/j-rgen-ehlers-und-die-relativit-tstheorie|archive-date=28 September 2008}} (in German, English translation of title ''Jürgen Ehlers and the Theory of Relativity'')
*{{Citation | last=Buchert | first=Thomas | year=2008 | title=Dark Energy from Structure—A Status Report | journal=General Relativity and Gravitation | volume=40 | issue=2–3 | pages=467–527 | doi=10.1007/s10714-007-0554-8 | arxiv=0707.2153 |bibcode = 2008GReGr..40..467B | s2cid=17281664 }}
*{{Citation | last1=Buchert | first1=Thomas | last2=Ehlers | first2=Jürgen | year=1993 | title=Lagrangian theory of gravitational instability of Friedmann-Lemaître cosmologies – second-order approach: an improved model for nonlinear clustering | journal=Mon. Not. R. Astron. Soc. | volume=264 | issue=2 | pages=375–387 | bibcode=1993MNRAS.264..375B | doi=10.1093/mnras/264.2.375 | doi-access=free | hdl=11858/00-001M-0000-0013-5C2D-A | hdl-access=free}}
*{{Citation | last1=Buchert | first1=Thomas | last2=Ehlers | first2=Jürgen | year=1997a | title=Averaging inhomogeneous Newtonian cosmologies | journal=Astron. Astrophys.
 | volume=320 | pages=1–7|arxiv = astro-ph/9510056 |bibcode = 1997A&A...320....1B }}
*{{Citation | last1=Buchert | first1=Thomas | last2=Ehlers | first2=Jürgen | year=1997b | title=Newtonian cosmology in Lagrangian formulation: foundations and perturbation theory    | journal=General Relativity and Gravitation | volume=29 | issue=6 | pages=733–764 | doi=10.1023/A:1018885922682 |arxiv = astro-ph/9609036 |bibcode = 1997GReGr..29..733E | s2cid=15670330 }}
*{{Citation | last=Ehlers | first=Jürgen | title=Konstruktionen und Charakterisierungen von Lösungen der Einsteinschen Gravitationsfeldgleichungen | publisher=University of Hamburg | year=1957 }} (dissertation, in German; title in English translation: ''Constructions and characterizations of solutions to Einstein's gravitational field equations'')
*{{Citation|last=Ehlers|first=J.|title=Contributions to the relativistic mechanics of continuous media|journal=Gen. Rel. Grav.|volume=25|issue=12|pages=1225–1266|year=1993|doi=10.1007/BF00759031|bibcode=1993GReGr..25.1225E|hdl=11858/00-001M-0000-0013-5C1E-C|s2cid=122689869|hdl-access=free}} 
*{{Citation |last=Ehlers |first=Jürgen |date=January 1997 |title=Examples of Newtonian limits of relativistic spacetimes |journal=[[Classical and Quantum Gravity]] |volume=14 |issue=1A |pages=A119–A126 |bibcode=1997CQGra..14A.119E |doi=10.1088/0264-9381/14/1A/010 |url=http://pubman.mpdl.mpg.de/pubman/item/escidoc:153004:1/component/escidoc:153003/328699.pdf |hdl=11858/00-001M-0000-0013-5AC5-F |s2cid=250804865 |hdl-access=free }}
*{{Citation| last=Ehlers| first=Jürgen| contribution=Modelle in der Physik| title=Modelle des Denkens| publisher=Berlin-Brandenburgische Akademie der Wissenschaften | year=2005| pages=35–40}} (in German, English translation of contribution title: ''Models in physics''; English translation of title: ''Models of thinking'')
*{{Citation| last=Ehlers| first=Jürgen| contribution=Physikalische Erkenntnis, dargestellt am Beispiel des Übergangs von Newtons Raumzeit zu Einsteins spezieller Relativitätstheorie| title=Die Kultur moderner Wissenschaft am Beispiel Albert Einstein| editor-last=Balsinger| editor-first=Philipp W.| editor2-first=Rudolf| editor2-last=Kötter| publisher=Elsevier/Spektrum Akademie Verlag| year=2006a| pages=1–16| url=http://edoc.mpg.de/345888| access-date=8 July 2008| archive-url=https://web.archive.org/web/20180324223918/http://edoc.mpg.de/345888| archive-date=24 March 2018| url-status=dead}} (in German, English translation of title: ''Gaining knowledge in physics, shown for the example of the transition from Newton's spacetime to Einstein's special theory of relativity'')
*{{Citation|last=Ehlers|first=Jürgen|title=Mathematik als "Sprache" der Physik|journal=Praxis der Naturwissenschaften – Physik in der Schule|volume=55|year=2006b|url=http://edoc.mpg.de/345898|access-date=8 July 2008|archive-url=https://web.archive.org/web/20170420143228/http://edoc.mpg.de/345898|archive-date=20 April 2017|url-status=dead}} (in German, English translation of title: ''Mathematics as the "language" of physics'')
*{{Citation|last=Ehlers|first=Jürgen|contribution=Pascual Jordan's Role in the Creation of Quantum Field Theory|editor-last=Ehlers|editor-first=J.|editor2-last=Hoffmann|editor2-first=D.|editor3-last=Renn|editor3-first=Jürgen|title=Pascual Jordan (1902–1980). Mainzer Symposium zum 100. Geburtstag. Preprint Nr. 329|publisher=Max Planck Institute for the History of Science|year=2007|pages=23–35}}
*{{Citation|last1=Ehlers|first1=J.|last2=Fahr|first2=H. J.|title=Urknall oder Ewigkeit|journal=Bild der Wissenschaft|pages=84|year=1994|volume=June}}
*{{Citation| last1=Ehlers| first1=J.| last2=Geren| first2=P.| last3=Sachs| first3=R. K.| title=Isotropic solutions of Einstein-Liouville equations| journal=J. Math. Phys.| volume=9| year=1968| pages=1344–1349| doi=10.1063/1.1664720| bibcode=1968JMP.....9.1344E| issue=9| hdl=11858/00-001M-0000-0013-5EFE-8| hdl-access=free}}
*{{Citation | last1=Ehlers| first1=Jürgen| last2=Kundt| first2=Wolfgang | contribution=Exact Solutions of the Gravitational Field Equations | title=Gravitation: An Introduction to Current Research | editor-last=Witten| editor-first=Louis | location=New York| publisher=John Wiley & Sons| year=1962 | pages=49–101}}
*{{Citation | last1=Ehlers | first1=Jürgen | last2=Pirani | first2=F. A. E. | last3=Schild | first3=Alfred | contribution = The geometry of free fall and light propagation
 | editor-last=O'Raifeartaigh | editor-first=L. | title=General Relativity. Papers in Honor of J. L. Synge | publisher=Clarendon Press | year=1972 | pages=63–84 | isbn=0-19-851126-4 }}
*{{Citation|last1=Ehlers|first1=J.|last2=Rosenblum|first2=A.|last3=Goldberg|first3=J. N.|last4=Havas|first4=Peter|journal=Astrophys. J.|volume=208|page=L77|bibcode=1976ApJ...208L..77E|doi=10.1086/182236|title=Comments on gravitational radiation damping and energy loss in binary systems|year=1976|hdl=11858/00-001M-0000-0013-5EC4-8|hdl-access=free}}.
*{{Citation|last1=Ehlers|first1=Jürgen|last2=Rudolph|first2=Ekkart|title=Dynamics of extended bodies in general relativity center-of-mass description and quasirigidity|journal=General Relativity and Gravitation|doi=10.1007/BF00763547|volume=8|issue=3|year=1977|pages=197–217|bibcode=1977GReGr...8..197E|url=http://edoc.mpg.de/335128|hdl=11858/00-001M-0000-0013-5EBF-5|s2cid=59429452|access-date=13 July 2019|archive-url=https://web.archive.org/web/20190928081656/http://edoc.mpg.de/335128|archive-date=28 September 2019|url-status=dead|hdl-access=free}}.
*{{Citation|last=Ellis|first=George|author-link =George Francis Rayner Ellis|title=Editorial note to: Pascual Jordan, Jürgen Ehlers, and Wolfgang Kundt, Exact solutions of the field equations of the general theory of relativity|journal=General Relativity and Gravitation|volume=41|issue=9|year = 2009|pages=2170–2189|doi=10.1007/s10714-009-0868-9|bibcode = 2009GReGr..41.2179E |doi-access=free}}
*{{Citation|last1=Ellis|first1=George|author-link=George Francis Rayner Ellis|last2=Krasiński|first2=Andrzej|title=Editors' comment|journal=General Relativity and Gravitation|volume=39|issue=11|year=2007|pages=1941–1942|url=http://edoc.mpg.de/335066|doi=10.1007/s10714-007-0448-9|bibcode=2007GReGr..39.1929S|access-date=8 July 2008|archive-url=https://web.archive.org/web/20160303195249/http://edoc.mpg.de/335066|archive-date=3 March 2016|url-status=dead|hdl=11858/00-001M-0000-0013-47A1-D|s2cid=121554142|hdl-access=free}}
*{{Citation|last1=Henning|first1=Eckart|first2=Marion|last2=Kazemi|title=Chronik der Kaiser-Wilhelm-/Max-Planck-Gesellschaft zur Förderung der Wissenschaften 1911–2011|publisher=Dunker & Humblot|location = Berlin|year=2011|isbn=978-3-428-13623-0}} (in German)
*{{Citation|last1=Frolov|first1=Valeri P.|last2=Novikov|first2=I. D.|author2-link=Igor Dmitriyevich Novikov|title=Black Hole Physics|publisher=Kluwer|year=1998|isbn=0-7923-5145-2}}
*{{Citation|last=Geroch|first=R.|title=A method for generating new solutions of Einstein's field equation. I|journal=J. Math. Phys.|volume=12|year=1971|issue=6|pages=918–924|doi=10.1063/1.1665681|bibcode = 1971JMP....12..918G }}
*{{Citation | last1=Hawking | first1=Stephen W. | author1-link = Stephen Hawking | last2=Ellis | first2=George F. R. | author2-link=George Francis Rayner Ellis | title=The large scale structure of space-time | publisher=Cambridge University Press | isbn=0-521-09906-4 | year=1973 | title-link=The large scale structure of space-time }}
*{{Citation|last1=Huisken|first1=Gerhard|author-link=Gerhard Huisken|last2=Nicolai|first2=Hermann|last3=Schutz|first3=Bernard|title=Obituary: Jürgen Ehlers|url=http://www.aei.mpg.de/pdf/pm_news/2008/ObituaryJuergenEhlers.pdf|publisher=[[Max Planck Institute for Gravitational Physics]]|year=2008|author-link3=Bernard Schutz|url-status=dead|archive-url=https://web.archive.org/web/20110511232243/http://www.aei.mpg.de/pdf/pm_news/2008/ObituaryJuergenEhlers.pdf|archive-date=11 May 2011}}
*{{Citation|last1=Huisken|first1=Gerhard|author-link=Gerhard Huisken|last2=Nicolai|first2=Hermann|last3=Schutz|first3=Bernard|contribution=Zum Tod von Jürgen Ehlers|editor=Berlin-Brandenburgische Akademie der Wissenschaften|title=Jahrbuch 2008|url=http://edoc.bbaw.de/volltexte/2010/1503/pdf/Jahrbuch_2008.pdf|publisher=Oldenbourg|pages=92–96|year=2009|author-link3=Bernard Schutz|access-date=28 May 2013|archive-date=2 May 2013|archive-url=https://web.archive.org/web/20130502062250/http://edoc.bbaw.de/volltexte/2010/1503/pdf/Jahrbuch_2008.pdf|url-status=dead}} (in German)
*{{Citation | last=Israel | first=Werner | contribution=Dark stars: the evolution of an idea | editor2-last=Israel | editor2-first=Werner | editor1-last=Hawking | editor1-first=Stephen W. | title=300 Years of Gravitation | publisher=Cambridge University Press | year=1987 | pages=199–276 | isbn=0-521-37976-8 }}
*{{Citation|journal=Akad. Wiss. Lit. Mainz, Abh. Naturwiss. Kl.|last1=Jordan|first1=P.|author-link=Pascual Jordan|last2=Ehlers|first2=J.|last3=Sachs|first3=R. K.|year=1961|title=Beiträge zur Theorie der reinen Gravitationsstrahlung|volume=1|page=1 |bibcode=1961MAWMN...1....1J }} (in German, English translation of title: ''Contributions to the theory of pure gravitational radiation'')
*{{Citation|last1=Köhler|first1=Egon|last2=Schattner|first2=Ruprecht|title= Some results on pseudorigid motions|journal=General Relativity and Gravitation|doi=10.1007/BF00756906|volume=10|issue=8|year=1979|pages=709–716|bibcode = 1979GReGr..10..709K |s2cid=121458325}}
*{{Citation| last = Liddle|first=Andrew |title=An Introduction to Modern Cosmology (2nd ed.) |isbn=978-0-470-84835-7 |year=2003 |publisher=John Wiley & Sons}}
*{{Citation|editor-last=Lütjen-Drecoll|editor-first=Elke|title=Newsletter 1/08|publisher=Akademie der Wissenschaften und der Literatur Mainz|year=2008|url=http://www.adwmainz.de/fileadmin/adwmainz/Newsletter/Newsletter_1_08.pdf}}{{dead link|date=September 2017 |bot=InternetArchiveBot |fix-attempted=yes }} (in German)
*{{Citation|last=Mars|first=Marc|title= Space-time Ehlers group: Transformation law for the Weyl tensor|journal=Class. Quantum Grav.|volume=18|issue=4|pages=719–738|year=2001|doi= 10.1088/0264-9381/18/4/311|arxiv = gr-qc/0101020 |bibcode = 2001CQGra..18..719M |s2cid=16943248}}
*{{Citation|last=Olive|first=D. I.|title=Exact Electromagnetic Duality|journal=Nucl. Phys. B Proc. Suppl.|volume=45A|year=1996|issue=1|pages=88–102|doi=10.1016/0920-5632(95)00618-4|arxiv = hep-th/9508089 |bibcode = 1996NuPhS..45...88O |s2cid=8584458}}
*{{Citation|last1=Nicolai|first1=Hermann|last2=Ellis|first2=George|last3=Schmidt|first3=Bernd|title=Editorial|journal=General Relativity and Gravitation|volume=41|year=2009|issue=9|doi=10.1007/s10714-009-0867-x|pages=1897|bibcode = 2009GReGr..41.1897. |doi-access=free}}
*{{Citation|last1=Oliynyk|first1=Todd Andrew|last2=Schmidt|first2=Bernd|title=Existence of families of spacetimes with a Newtonian limit|journal=General Relativity and Gravitation|volume=41|issue=9| year = 2009|pages=2093–2111 |doi=10.1007/s10714-009-0843-5|arxiv = 0908.2832 |bibcode = 2009GReGr..41.2093O |s2cid=12396713}}
*{{Citation|last=Perlick|first=Volker|title=Book review:Petters, A.O., Levine, H., Wambsganss, J.: Singularity theory and gravitational lensing|journal=Gen. Relativ. Gravit.|year=2005|volume=37|issue=2|pages=435–436|doi=10.1007/s10714-005-0033-z|bibcode = 2005GReGr..37..435P |s2cid=122607061}}
*{{Citation|last=Sachs|first=Rainer|title=Some memories of Juergen|journal=General Relativity and Gravitation|volume=41|issue=9|year=2009|pages=1903–1904 |doi=10.1007/s10714-009-0784-z|bibcode = 2009GReGr..41.1903S |doi-access=free}}
*{{Citation|last=Rogalla|first=Thomas|title=Namen: Prof. Dr. Jürgen Ehlers|url=http://www.berliner-zeitung.de/archiv/prof--dr--juergen-ehlers,10810590,9961958.html|newspaper=Berliner Zeitung|date=28 December 2001|access-date=28 May 2013}} (in German)
*{{Citation|editor-last=Schmidt|editor-first=Bernd|title=Einstein's Field Equations and their Physical Implications. Selected Essays in Honour of Jürgen Ehlers|publisher=Springer|isbn=3-540-67073-4|year=2000}}
*{{Citation|last=Schücking|first=Engelbert|author-link=Engelbert Schücking|contribution=Jürgen Ehlers:Work and Style|title=Annual Report 2000|publisher=Max Planck Institute for Gravitational Physics|pages=46–47|url=http://www.aei.mpg.de/pdf/illustrationsDocs/annual2000.pdf|year=2000|url-status=dead|archive-url=https://web.archive.org/web/20070611023427/http://www.aei.mpg.de/pdf/illustrationsDocs/annual2000.pdf|archive-date=11 June 2007}}
*{{Citation|last=Schutz|first=B. F.|title=Making the Transition from Newton to Einstein: Chandrasekhar's Work on the Post-Newtonian Approximation and Radiation Reaction|journal=J. Astrophys. Astron.|volume=17|issue=3–4|pages=183–197|url=http://www.ias.ac.in/jarch/jaa/17/183-197.pdf|year=1996|doi=10.1007/BF02702303|bibcode=1996JApA...17..183S|hdl=11858/00-001M-0000-0013-7535-E|s2cid=73579437|hdl-access=free}}
*{{Citation|last1=Seitz|first1=S.|last2=Schneider|first2=P.|last3=Ehlers|first3=J.|title=Light propagation in arbitrary spacetimes and the gravitational lens approximation|journal=Class. Quantum Grav.|volume=11|issue=9|pages=2345–2383|year=1994|doi=10.1088/0264-9381/11/9/016|arxiv = astro-ph/9403056 |bibcode = 1994CQGra..11.2345S |s2cid=18176981}}
*{{Citation|last=Trümper|first=Joachim|contribution=Nachruf auf Jürgen Ehlers|title=Jahrbuch der Bayerischen Akademie der Wissenschaften 2008|year=2009|pages=152–154|url=http://www.badw.de/publikationen/sonstige/nachrufe/2008/ehlers.pdf}}{{Dead link|date=August 2024 |bot=InternetArchiveBot |fix-attempted=yes }}
*{{Citation|editor-last=Weber|editor-first=Peter|editor2-last=Borissoff|editor2-first=Irene|publisher=Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V.|title=Handbuch der Wissenschaftlichen Mitglieder|page=38|year=1998}} (in German, English translation of title: ''Handbook of Scientific Members'').
{{refend}}

== External links ==
*{{MathGenealogy |id=51076}}
*{{DNB portal|121317374|TYP=}}
* Pages [https://www.aei.mpg.de/299871/ehlers In Memoriam Jürgen Ehlers] at the [[Albert Einstein Institute (Germany)|Albert Einstein Institute]]

{{relativity}}
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{{DEFAULTSORT:Ehlers, Jurgen}}
[[Category:1929 births]]
[[Category:2008 deaths]]
[[Category:Mathematical physicists]]
[[Category:German cosmologists]]
[[Category:German relativity theorists]]
[[Category:Scientists from Hamburg]]
[[Category:University of Hamburg alumni]]
[[Category:Winners of the Max Planck Medal]]
[[Category:Max Planck Institute directors]]