In 1966, relatively early in his career, Israel analyzed the dynamics of thin shells of matter in general relativity.[1] Partly because many interesting examples can be constructed using such thin shells, this has become Israel's most cited paper, with thousands of citations. Interest in this paper has increased over time; it has been cited most heavily since the year 2000.[2] Israel returned to the topic of thin shells in general relativity many years later.[3]
In 1972, Israel and G. A. Wilson discovered a new class of stationary solutions of Einstein-Maxwell theory,[9] also discovered by Perjés.[10] Variants of these solutions have been important in recent work counting quantum states of black holes in string theory models.[11]
What was perhaps Israel's deepest work, published in 1976, concerned a black hole in equilibrium with the Hawking radiation that it emits. A quantum system in thermal equilibrium at a nonzero temperature is most directly described by a thermal density matrix. However, it is possible to "purify" such a thermal density matrix as a pure state of a doubled system—two copies of the original system. This pure state of a doubled system is nowadays usually called the thermofield double state. In view of Stephen Hawking's fundamental discovery of thermal radiation from black holes, a black hole at the quantum level is an example of a thermal system and one can ask how to describe a black hole in thermal equilibrium with radiation. Israel showed that the thermal equilibrium state of a (non-rotating) black hole has a natural geometric description in a two-sided "wormhole" version of the black hole spacetime. The two sides of the wormhole correspond to the two copies in the thermofield double state.[12] This was in parallel with well known work by Hartle and Hawking[13] and the state of a black hole in equilibrium with radiation is sometimes called the Hartle-Hawking-Israel state.[14][15]
Standard formulations of dissipativethermodynamics are inconsistent with relativity theory as they predict instantaneous propagation of signals. In the 1970s, Israel reformulated dissipative thermodynamics to be consistent with relativity. As in the case of Israel's work on the thin shells, interest in this work has increased over time and Israel's papers in this area[16][17] have been heavily cited since the year 2000.
In 1989, together with Eric Poisson, Israel pioneered the study of black hole interiors and, following up a suggestion of Roger Penrose, discovered the phenomenon of “mass inflation'' which can occur near the Cauchy horizon of a black hole.[18][19] This work has a bearing on the question of “strong cosmic censorship'' in general relativity and influenced research on strong cosmic censorship in the following decades.[20]
Together with Stephen Hawking, Werner Israel co-edited two volumes on gravitational physics.[21][22]
^Dafermos, Mihalis; Rendall, Alan D. (2007). "Strong cosmic censorship for surface-symmetric cosmological spacetimes with collisionless matter". arXiv:gr-qc/0701034.
^S. W. Hawking and W. Israel, General Relativity: an Einstein Centenary Survey (Cambridge University Press, 1979).
^S. W. Hawking and W. Israel, Three Hundred Years of Gravitation (Cambridge University Press, 1987).
Werner Israel. Astronomy, Astrophysics and Space Science. "Physicist and cosmologist: Wrote the first logically precise theory for the simplicity of black holes (1967)”, science.ca. https://www.science.ca/scientists/scientistprofile.php?pID=9
