Jürgen Ehlers
Jürgen Ehlers | |
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Born | Hamburg, Germany | 29 December 1929
Died | 20 May 2008 Potsdam, Brandenburg, Germany | (aged 78)
Nationality | German |
Alma mater | University of Hamburg |
Known for | General relativity Mathematical physics |
Awards | Max Planck Medal (2002) |
Scientific career | |
Fields | Physics |
Institutions | University of Hamburg Max Planck Institute for Astrophysics Max Planck Institute for Gravitational Physics |
Doctoral advisor | Pascual Jordan |
Part of a series on |
Physical cosmology |
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Jürgen Ehlers (German:
Ehlers' research focused on the foundations of general relativity as well as on the theory's applications to
Biography
Early life
Jürgen Ehlers was born in Hamburg on 29 December 1929.
Prior to Ehlers' arrival, the main research of Jordan's group had been dedicated to a
In 1961, as Jordan's assistant, Ehlers earned his
Munich
In 1970, Ehlers received an offer to join the
One of Ehlers'
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.[11] 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.[12]
Ehlers continued to work at the institute until his death on 20 May 2008.[13] He left behind his wife Anita Ehlers, his four children, Martin, Kathrin, David, and Max, as well as five grandchildren.[14]
Research
Ehlers' research was in the field of general relativity. In particular, he made contributions to
Exact solutions
For his doctoral thesis, Ehlers turned to a question that was to shape his lifetime research. He sought exact solutions of
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".[17] 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
The following papers in the series were treatises on
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
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
Ehlers group
In physics,
In his doctoral thesis, Ehlers pointed out a duality symmetry between different components of the
The duality discovered by Ehlers was later expanded to a larger symmetry corresponding to the special linear group . This larger
Cosmology: Ehlers–Geren–Sachs theorem
The Ehlers–Geren–Sachs theorem, published in 1968, shows that in a given universe, if all freely falling observers measure the
Fundamental concepts in general relativity
In the 1960s, Ehlers collaborated with
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.[28]
Gravitational lensing
With Peter Schneider, Ehlers embarked on an in-depth study of the foundations of
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
General relativity is 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.[33]
His work on the Newtonian limit, particularly in relation to cosmological solutions, led Ehlers, together with his former doctoral student Thomas Buchert, to a systematic study of 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.[34]
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.[35] In particular, he explored Pascual Jordan's seminal contributions to the development of quantum field theory between 1925 and 1928.[36] 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.[37]
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 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.[38] 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.[39]
Honours and awards
Ehlers became a member of the
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 and is awarded triennially, at the society's international conference, to the best doctoral thesis in the areas of mathematical and numerical general relativity.[43] Issue 9 of volume 41 of the journal General Relativity and Gravitation was dedicated to Ehlers, in memoriam.[44]
Selected publications
- Börner, G.; Ehlers, J., eds. (1996), Gravitation, Spektrum Akademischer Verlag, ISBN 3-86025-362-X
- Ehlers, Jürgen (1973), "Survey of general relativity theory", in Israel, Werner (ed.), Relativity, Astrophysics and Cosmology, D. Reidel, pp. 1–125, ISBN 90-277-0369-8
- Schneider, P.; Ehlers, J.; Falco, E. E. (1992), Gravitational lenses, Springer, ISBN 3-540-66506-4
Notes
- ISBN 978-1-58603-990-5. Retrieved 28 December 2022.
- ^ The dissertation is Ehlers 1957; cf. Ellis 2009.
- ISBN 3-540-67073-4
- ^ As described in Ellis & Krasiński 2007 and Sachs 2009.
- ^ Ellis 2009
- ^ Huisken, Nicolai & Schutz 2009, cf. the English version online as Huisken, Nicolai & Schutz 2008, and the associated CV, Lebenslauf von Prof. Dr. Jürgen Ehlers (PDF), Max Planck Institute for Gravitational Physics, 27 May 2008, archived from the original (PDF) on 19 May 2009, retrieved 27 May 2008 (in German, English translation of title: "CV for Prof. Dr. Jürgen Ehlers"). Dates and positions also summarized in Weber & Borissoff 1998.
- ^ Henning & Kazemi 2011, p. 472
- ^ Henning & Kazemi 2011, p. 634
- ^ As described in Breuer 2008
- ^ Breuer 2008
- ^ Henning & Kazemi 2011, p. 676
- ^ Henning & Kazemi 2011, p. 737
- ^ See p. 520 in the Max Planck Society's annual report for 2000, Jahrbuch 2000, Max-Planck-Gesellschaft, 2000. Time as emeritus and death cf. Braun 2008.
- ^ Huisken, Nicolai & Schutz 2009; English version online as Huisken, Nicolai & Schutz 2008
- ^ Schücking 2000
- ^ B. Schmidt, Preface to Schmidt 2000
- ^ Ellis 2009, p. 2180
- ^ A later version of this paper is Ehlers & Kundt 1962. For an assessment, see J. Bicak, p. 14f. in Schmidt 2000
- ^ Ehlers-Sachs theorem see sec. 5.3 in Frolov & Novikov 1998. An assessment of the work and its connection with Kerr solution is given by J. Bicak on p. 14f. of Schmidt 2000. The original work with Sachs is Jordan, Ehlers & Sachs 1961.
- ^ The English translation, by G. F. R. Ellis, is Ehlers 1993. The quotation can be found on p. 1225 in the editor's comments section.
- ^ The changing views of what eventually be regarded as black holes can be found in Israel 1987. Ehlers' thesis is Ehlers 1957.
- ^ Olive 1996
- ^ Cf. Dieter Maison's contribution "Duality and Hidden Symmetries in Gravitational Theories", pp. 273–323 in Schmidt 2000.
- ^ Maison op. cit., Geroch 1971, and, for various applications, Mars 2001.
- ^ Hawking & Ellis 1973, p. 351ff. The original work is Ehlers, Geren & Sachs 1968.
- ^ E.g. Liddle 2003, p.2
- ^ See Ehlers, Pirani & Schild 1972; a summary can be found in Ehlers 1973.
- ^ See Köhler & Schattner 1979. The original publication is Ehlers & Rudolph 1977.
- ^ A review of the book itself is 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. Perlick 2005 and Bozza 2005; see also the assessment of Trümper 2009, p. 154.
- ^ Seitz, Schneider & Ehlers 1994, cf. section 3.5 of Annual Report 1994, Max Planck Institute for Astrophysics, 1995, archived from the original on 19 May 2009
- ^ Ehlers 1997; a description can be found on p. 216f. in Luc Blanchet's contribution "Post-Newtonian Gravitational Radiation", pp. 225–271 in Schmidt 2000.
- ^ Oliynyk & Schmidt 2009
- ^ A description that includes the historical context can be found in Schutz 1996. The original work is Ehlers et al. 1976.
- ^ See Buchert & Ehlers 1993, Buchert & Ehlers 1997a and Buchert & Ehlers 1997b. The current status of Buchert's further work is summarized in Buchert 2008.
- ^ Cf. Braun 2008. Details about the project can be found on its website.
- ^ Ehlers 2007
- ^ See Ehlers 2006a and Breuer & Springer 2001 as well as its later English translation Breuer & Springer 2009, as well as Ehlers 2005.
- ^ Public lectures: Biennial Report 2004/2005 (PDF), Max Planck Institute for Gravitational Physics, 2006, archived from the original (PDF) on 11 June 2007, lists 25 popular talks (p. 158f.) for that time-frame alone. The compilation of articles is Börner & Ehlers 1996, listed under Selected Publications. An example for a popular article is Ehlers & Fahr 1994.
- ^ Biennial Report 2004/2005 (PDF), Max Planck Institute for Gravitational Physics, 2006, archived from the original (PDF) on 11 June 2007 lists 11 talks to teachers or in an interdisciplinary setting (p. 147f., p. 154f.). Mathematics and physics Ehlers 2006b
- ^ Berlin: Huisken, Nicolai & Schutz 2009; initial membership date in brief note on p.35 of the same publication. Mainz: p. 13 of Lütjen-Drecoll 2008. Leopoldina: listed as member on Mitgliederverzeichnis, Deutsche Akademie der Naturforscher Leopoldina, retrieved 28 May 2012 (in German, English translation of title: Members list). Bavarian Academy: Trümper 2009.
- ^ GRG Society History, International Society on General Relativity and Gravitation, retrieved 28 May 2013.
- ^ Max Planck Medal: Press release about the 2002 awards, Physikalische Spitzenleistung, Deutsche Physikalische Gesellschaft, 17 December 2001, archived from the original on 13 February 2007, retrieved 27 May 2008 (in German, English translation of title: Top achievement in physics), and Rogalla 2001. Volta Medal: "Namen: Prof. Dr. Jürgen Ehlers", Berliner Zeitung, 18 May 2005, retrieved 27 May 2008 (in German) and "Medaille für Golmer Forscher", Märkische Allgemeine Zeitung, 19 May 2005 (in German, English translation of title: Medal for researcher from Golm). Charles University Medal: Trümper 2009, p. 154.
- ^ The Jürgen Ehlers Thesis Prize, Website of the International Society on General Relativity and Gravitation, retrieved 28 May 2013
- ^ Nicolai, Ellis & Schmidt 2009
References
- Bleyer, U. (1993), "Book-Review - Gravitational Lenses", Astronomische Nachrichten, 314 (4): 314–315,
- Bozza, Valerio (2005), "Book review: Silvia Mollerach, Esteban Roulet: Gravitational Lensing and Microlensing", General Relativity and Gravitation, 37 (7): 1335–1336, S2CID 120764050
- Braun, Rüdiger (27 May 2008), "Wo Zeit und Raum aufhören. Der Mitbegründer des Golmer Max-Planck-Instituts für Gravitationsphysik, Jürgen Ehlers, ist unerwartet verstorben", Märkische Allgemeine Zeitung, retrieved 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)
- Breuer, Reinhard; Springer, Michael (2001), "Die Wahrheit in der Wissenschaft", Spektrum der Wissenschaft, 7: 70 (in German)
- Breuer, Reinhard; Springer, Michael (2009), "The truth in science", General Relativity and Gravitation, 41 (9): 2159–2167, S2CID 123226152
- Breuer, Reinhard (26 May 2008), Jürgen Ehlers und die Relativitätstheorie, Spektrum der Wissenschaft Verlagsgesellschaft mbH, archived from the original on 28 September 2008 (in German, English translation of title Jürgen Ehlers and the Theory of Relativity)
- Buchert, Thomas (2008), "Dark Energy from Structure—A Status Report", General Relativity and Gravitation, 40 (2–3): 467–527, S2CID 17281664
- Buchert, Thomas; Ehlers, Jürgen (1993), "Lagrangian theory of gravitational instability of Friedmann-Lemaître cosmologies – second-order approach: an improved model for nonlinear clustering", Mon. Not. R. Astron. Soc., 264 (2): 375–387,
- Buchert, Thomas; Ehlers, Jürgen (1997a), "Averaging inhomogeneous Newtonian cosmologies", Astron. Astrophys., 320: 1–7, Bibcode:1997A&A...320....1B
- Buchert, Thomas; Ehlers, Jürgen (1997b), "Newtonian cosmology in Lagrangian formulation: foundations and perturbation theory", General Relativity and Gravitation, 29 (6): 733–764, S2CID 15670330
- Ehlers, Jürgen (1957), Konstruktionen und Charakterisierungen von Lösungen der Einsteinschen Gravitationsfeldgleichungen, University of Hamburg (dissertation, in German; title in English translation: Constructions and characterizations of solutions to Einstein's gravitational field equations)
- Ehlers, J. (1993), "Contributions to the relativistic mechanics of continuous media", Gen. Rel. Grav., 25 (12): 1225–1266, S2CID 122689869
- Ehlers, Jürgen (January 1997), "Examples of Newtonian limits of relativistic spacetimes" (PDF), S2CID 250804865
- Ehlers, Jürgen (2005), "Modelle in der Physik", Modelle des Denkens, Berlin-Brandenburgische Akademie der Wissenschaften, pp. 35–40 (in German, English translation of contribution title: Models in physics; English translation of title: Models of thinking)
- Ehlers, Jürgen (2006a), "Physikalische Erkenntnis, dargestellt am Beispiel des Übergangs von Newtons Raumzeit zu Einsteins spezieller Relativitätstheorie", in Balsinger, Philipp W.; Kötter, Rudolf (eds.), Die Kultur moderner Wissenschaft am Beispiel Albert Einstein, Elsevier/Spektrum Akademie Verlag, pp. 1–16, archived from the original on 24 March 2018, retrieved 8 July 2008 (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)
- Ehlers, Jürgen (2006b), "Mathematik als "Sprache" der Physik", Praxis der Naturwissenschaften – Physik in der Schule, 55, archived from the original on 20 April 2017, retrieved 8 July 2008 (in German, English translation of title: Mathematics as the "language" of physics)
- Ehlers, Jürgen (2007), "Pascual Jordan's Role in the Creation of Quantum Field Theory", in Ehlers, J.; Hoffmann, D.; Renn, Jürgen (eds.), Pascual Jordan (1902–1980). Mainzer Symposium zum 100. Geburtstag. Preprint Nr. 329, Max Planck Institute for the History of Science, pp. 23–35
- Ehlers, J.; Fahr, H. J. (1994), "Urknall oder Ewigkeit", Bild der Wissenschaft, June: 84
- Ehlers, J.; Geren, P.; Sachs, R. K. (1968), "Isotropic solutions of Einstein-Liouville equations", J. Math. Phys., 9 (9): 1344–1349,
- Ehlers, Jürgen; Kundt, Wolfgang (1962), "Exact Solutions of the Gravitational Field Equations", in Witten, Louis (ed.), Gravitation: An Introduction to Current Research, New York: John Wiley & Sons, pp. 49–101
- Ehlers, Jürgen; Pirani, F. A. E.; Schild, Alfred (1972), "The geometry of free fall and light propagation", in O'Raifeartaigh, L. (ed.), General Relativity. Papers in Honor of J. L. Synge, Clarendon Press, pp. 63–84, ISBN 0-19-851126-4
- Ehlers, J.; Rosenblum, A.; Goldberg, J. N.; Havas, Peter (1976), "Comments on gravitational radiation damping and energy loss in binary systems", Astrophys. J., 208: L77, .
- Ehlers, Jürgen; Rudolph, Ekkart (1977), "Dynamics of extended bodies in general relativity center-of-mass description and quasirigidity", General Relativity and Gravitation, 8 (3): 197–217, S2CID 59429452, archived from the originalon 28 September 2019, retrieved 13 July 2019.
- S2CID 121554142, archived from the originalon 3 March 2016, retrieved 8 July 2008
- Henning, Eckart; Kazemi, Marion (2011), Chronik der Kaiser-Wilhelm-/Max-Planck-Gesellschaft zur Förderung der Wissenschaften 1911–2011, Berlin: Dunker & Humblot, ISBN 978-3-428-13623-0(in German)
- Frolov, Valeri P.; ISBN 0-7923-5145-2
- Geroch, R. (1971), "A method for generating new solutions of Einstein's field equation. I", J. Math. Phys., 12 (6): 918–924,
- ISBN 0-521-09906-4
- Schutz, Bernard (2008), Obituary: Jürgen Ehlers (PDF), Max Planck Institute for Gravitational Physics, archived from the original(PDF) on 11 May 2011
- Schutz, Bernard (2009), "Zum Tod von Jürgen Ehlers", in Berlin-Brandenburgische Akademie der Wissenschaften (ed.), Jahrbuch 2008(PDF), Oldenbourg, pp. 92–96 (in German)
- Israel, Werner (1987), "Dark stars: the evolution of an idea", in Hawking, Stephen W.; Israel, Werner (eds.), 300 Years of Gravitation, Cambridge University Press, pp. 199–276, ISBN 0-521-37976-8
- Bibcode:1961MAWMN...1....1J(in German, English translation of title: Contributions to the theory of pure gravitational radiation)
- Köhler, Egon; Schattner, Ruprecht (1979), "Some results on pseudorigid motions", General Relativity and Gravitation, 10 (8): 709–716, S2CID 121458325
- Liddle, Andrew (2003), An Introduction to Modern Cosmology (2nd ed.), John Wiley & Sons, ISBN 978-0-470-84835-7
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- Mars, Marc (2001), "Space-time Ehlers group: Transformation law for the Weyl tensor", Class. Quantum Grav., 18 (4): 719–738, S2CID 16943248
- Olive, D. I. (1996), "Exact Electromagnetic Duality", Nucl. Phys. B Proc. Suppl., 45A (1): 88–102, S2CID 8584458
- Nicolai, Hermann; Ellis, George; Schmidt, Bernd (2009), "Editorial", General Relativity and Gravitation, 41 (9): 1897,
- Oliynyk, Todd Andrew; Schmidt, Bernd (2009), "Existence of families of spacetimes with a Newtonian limit", General Relativity and Gravitation, 41 (9): 2093–2111, S2CID 12396713
- Perlick, Volker (2005), "Book review:Petters, A.O., Levine, H., Wambsganss, J.: Singularity theory and gravitational lensing", Gen. Relativ. Gravit., 37 (2): 435–436, S2CID 122607061
- Sachs, Rainer (2009), "Some memories of Juergen", General Relativity and Gravitation, 41 (9): 1903–1904,
- Rogalla, Thomas (28 December 2001), "Namen: Prof. Dr. Jürgen Ehlers", Berliner Zeitung, retrieved 28 May 2013 (in German)
- Schmidt, Bernd, ed. (2000), Einstein's Field Equations and their Physical Implications. Selected Essays in Honour of Jürgen Ehlers, Springer, ISBN 3-540-67073-4
- Schücking, Engelbert (2000), "Jürgen Ehlers:Work and Style", Annual Report 2000 (PDF), Max Planck Institute for Gravitational Physics, pp. 46–47, archived from the original (PDF) on 11 June 2007
- Schutz, B. F. (1996), "Making the Transition from Newton to Einstein: Chandrasekhar's Work on the Post-Newtonian Approximation and Radiation Reaction" (PDF), J. Astrophys. Astron., 17 (3–4): 183–197, S2CID 73579437
- Seitz, S.; Schneider, P.; Ehlers, J. (1994), "Light propagation in arbitrary spacetimes and the gravitational lens approximation", Class. Quantum Grav., 11 (9): 2345–2383, S2CID 18176981
- Trümper, Joachim (2009), "Nachruf auf Jürgen Ehlers", Jahrbuch der Bayerischen Akademie der Wissenschaften 2008 (PDF), pp. 152–154
- Weber, Peter; Borissoff, Irene, eds. (1998), Handbuch der Wissenschaftlichen Mitglieder, Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V., p. 38 (in German, English translation of title: Handbook of Scientific Members).
External links
- Jürgen Ehlers at the Mathematics Genealogy Project
- Jürgen Ehlers in the German National Library catalogue
- Pages In Memoriam Jürgen Ehlers at the Albert Einstein Institute