Werner Israel, (October 4, 1931 – May 18, 2022) was a theoretical physicist known for his contributions to gravitational theory, and especially to the understanding of black holes.

Biography

Israel was born in Berlin, Germany in 1931. His family fled

Nazi Germany Nazi Germany, officially known as the German Reich and later the Greater German Reich, was the German Reich, German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a Totalit ...

in 1936 and settled in Cape Town, South Africa, where he was raised. He was interested in

astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...

and

cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe, the cosmos. The term ''cosmology'' was first used in English in 1656 in Thomas Blount's ''Glossographia'', with the meaning of "a speaking of the wo ...

from a young age. For four years, when his parents were seriously ill, Israel and his brother lived in an orphanage. Israel received his B.Sc. and M.Sc. from the

University of Cape Town The University of Cape Town (UCT) (, ) is a public university, public research university in Cape Town, South Africa. Established in 1829 as the South African College, it was granted full university status in 1918, making it the oldest univer ...

, and his Ph.D. from Trinity College, Dublin, under the direction of John Synge. In 1958, Israel accepted a faculty position at the University of Alberta in

Edmonton Edmonton is the capital city of the Provinces and territories of Canada, Canadian province of Alberta. It is situated on the North Saskatchewan River and is the centre of the Edmonton Metropolitan Region, which is surrounded by Central Alberta ...

, where he remained as professor until his retirement in 1996. Following his retirement, Israel was Adjunct Professor of Physics and Astronomy at the University of Victoria in

Victoria, British Columbia Victoria is the capital city of the Provinces and territories of Canada, Canadian province of British Columbia, on the southern tip of Vancouver Island off Canada's Pacific Ocean, Pacific coast. The city has a population of 91,867, and the Gre ...

. He remained active in research for another two decades. During the Dublin years, Werner Israel met and married Inge Margulies. They had a son Mark and a daughter Pia.

Scientific Work

Werner Israel is primarily known for his work on

general relativity General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the differential geometry, geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of grav ...

, especially on

black hole A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...

theory. In 1966, relatively early in his career, Israel analyzed the dynamics of thin shells of

matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic pa ...

in general relativity, providing a geometrical description in terms of the second fundamental form of the hypersurface on which the matter is supported. 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. Israel returned to the topic of thin shells in general relativity many years later. Israel's first important contribution to black hole theory came in 1967 when he showed that the Schwarzschild solution, which describes a spherically symmetric, uncharged black hole, is the unique static black hole solution of Einstein's equations (without matter fields). Israel extended this result to Einstein-Maxwell theory, showing that in that case, the unique static black hole solution is the Reissner-Nordstrom solution. It was soon shown by Carter that similar statements hold for black hole solutions that are stationary (not necessarily static). These results have been summarized by the expression " a black hole has no hair." The hypothesis that gravitational collapse in the real world always leads to a Kerr-Newman black hole (which requires an assumption about cosmic censorship in addition to the theorems of Israel and Carter about stationary solutions) is sometimes called the Carter-Israel conjecture. In 1972, Israel and G. A. Wilson discovered a new class of stationary solutions of Einstein-Maxwell theory, also discovered by Perjés. It was later found that, in a large class of supergravity theories, all supersymmetric black hole solutions are of the Israel-Wilson-Perjés form, generalized to include scalar fields. This has been important in subsequent work on the counting of black hole states in supersymmetric theories. 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 Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Addison-Wesley, 1989, It is ...

in thermal equilibrium at a nonzero

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

is most directly described by a mixed state -- 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. The pure state of a doubled system that describes thermal equilibrium of the original system is nowadays usually called the thermofield double state. (Israel's terminology was slightly different.) In view of Stephen Hawking's fundamental discovery of thermal

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

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 spherically symmetric (Schwarzschild) black hole has a natural geometric interpretation in terms of the maximal analytic extension of the Schwarzschild solution. This extension is “two-sided'' -- it describes a pair of asymptotically flat universes, each containing a black hole, with the two black holes being connected by a " wormhole." Israel interpreted the two sides of the wormhole as the two copies in the thermofield double state. This was in parallel with well known work by Hartle and Hawking and the state of a black hole in equilibrium with radiation is sometimes called the Hartle-Hawking-Israel state. Standard formulations of dissipative

thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed b ...

are inconsistent with relativity theory as they predict instantaneous propagation of thermal and viscous effects. 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 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 Sir Roger Penrose (born 8 August 1931) is an English mathematician, mathematical physicist, Philosophy of science, philosopher of science and Nobel Prize in Physics, Nobel Laureate in Physics. He is Emeritus Rouse Ball Professor of Mathematics i ...

, discovered the phenomenon of “mass inflation'' which can occur near the Cauchy horizon of a black hole. This work has a bearing on the question of “ strong cosmic censorship'' in

and influenced research on strong cosmic censorship in the following decades. Together with Stephen Hawking, Werner Israel co-edited two volumes on gravitational physics.S. W. Hawking and W. Israel, ''Three Hundred Years of Gravitation'' (Cambridge University Press, 1987)''.''

Honors

* 1972: Fellow of the

Royal Society of Canada The Royal Society of Canada (RSC; , SRC), also known as the Academies of Arts, Humanities, and Sciences of Canada (French: ''Académies des arts, des lettres et des sciences du Canada''), is the senior national, bilingual council of distinguishe ...

* 1974-75: Sherman-Fairchild Distinguished Scholar, CALTECH * 1981: Medal of Achievement in Physics of Canadian Association of Physicists * 1983: University of Alberta Research Prize in Natural Sciences and Engineering * 1984: Izaak Walton Killam Memorial Prize * 1986: Fellow of the

Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...

, London * 1986-91: Senior Research Fellow at the Canadian Institute for Advanced Research * 1994: Officer of the

Order of Canada The Order of Canada () is a Canadian state order, national order and the second-highest Award, honour for merit in the system of orders, decorations, and medals of Canada, after the Order of Merit. To coincide with the Canadian Centennial, ce ...

Biography

Scientific Work

Honors

References

Further reading