Joseph Gerard Polchinski Jr. (; May 16, 1954 – February 2, 2018) was an American

theoretical physicist Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experimen ...

and

string theorist In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and intera ...

Biography

Polchinski was born in White Plains, New York, the elder of two children to Joseph Gerard Polchinski Sr. (1929–2002), a financial consultant and manager, and Joan (née Thornton), an office worker and homemaker. Polchinski was primarily of Irish descent with his paternal grandfather being Polish. Polchinski graduated from

Canyon del Oro High School Canyon del Oro High School (CDO) is a comprehensive public high school in Oro Valley, Arizona, located north of Tucson at the base of Pusch Ridge. Established in 1964, CDO is one of three high schools of Amphitheater Public Schools and serves ...

Tucson, Arizona , "(at the) base of the black ill , nicknames = "The Old Pueblo", "Optics Valley", "America's biggest small town" , image_map = , mapsize = 260px , map_caption = Interactive map ...

in 1971, obtained his B.S. degree from

Caltech The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

in 1975, and his Ph.D. from the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...

in 1980 under the supervision of

Stanley Mandelstam Stanley Mandelstam (; 12 December 1928 – 23 June 2016) was a South African theoretical physicist. He introduced the relativistically invariant Mandelstam variables into particle physics in 1958 as a convenient coordinate system for formulating ...

. He did not publish any papers as a graduate student. After postdoctoral positions at

SLAC SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center, is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Departm ...

(1980–82) and Harvard (1982–84) he was a professor at the

University of Texas at Austin The University of Texas at Austin (UT Austin, UT, or Texas) is a public research university in Austin, Texas. It was founded in 1883 and is the oldest institution in the University of Texas System. With 40,916 undergraduate students, 11,075 ...

from 1984 to 1992. From 1992 to March 2017 he was a professor in the Physics Department at the

University of California, Santa Barbara The University of California, Santa Barbara (UC Santa Barbara or UCSB) is a Public university, public Land-grant university, land-grant research university in Santa Barbara County, California, Santa Barbara, California with 23,196 undergraduate ...

and a permanent member of the

Kavli Institute for Theoretical Physics The Kavli Institute for Theoretical Physics (KITP) is a research institute of the University of California, Santa Barbara. KITP is one of the most renowned institutes for theoretical physics in the world, and brings theorists in physics and rela ...

there.

Contributions

Polchinski wrote the two-volume textbook ''String Theory'', published in 1998. Among his many contributions to

theoretical physics Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experim ...

D-branes In string theory, D-branes, short for ''Dirichlet membrane'', are a class of extended objects upon which open strings can end with Dirichlet boundary conditions, after which they are named. D-branes were discovered by Jin Dai, Leigh, and Polchi ...

are the best known. In 2008 he won the

Dirac Medal The Dirac Medal is the name of four awards in the field of theoretical physics, computational chemistry, and mathematics, awarded by different organizations, named in honour of Professor Paul Dirac, one of the great theoretical physicists of the 20 ...

for his work in

superstring theory Superstring theory is an attempt to explain all of the particles and fundamental forces of nature in one theory by modeling them as vibrations of tiny supersymmetric strings. 'Superstring theory' is a shorthand for supersymmetric string theor ...

. He was awarded the 2017

Fundamental Physics Prize The Breakthrough Prize in Fundamental Physics is one of the Breakthrough Prizes, awarded by the Breakthrough Prize Board. Initially named Fundamental Physics Prize, it was founded in July 2012 by Russia-born Israeli entrepreneur, venture capita ...

in recognition of his contributions to theoretical physics.

D-branes

Polchinski's contributions to

D-brane In string theory, D-branes, short for ''Dirichlet membrane'', are a class of extended objects upon which open strings can end with Dirichlet boundary conditions, after which they are named. D-branes were discovered by Jin Dai, Leigh, and Polchi ...

physics were a primary trigger of the

2nd superstring revolution The history of string theory spans several decades of intense research including two superstring revolutions. Through the combined efforts of many researchers, string theory has developed into a broad and varied subject with connections to quantum ...

and the physics of holographic gauge-gravity dualities. After co-discovering D-branes in 1989, his 1995 work conjectured and partially demonstrated the equivalence between D-branes and black p-branes. The duality between these objects was soon understood to be a demonstration of holography, in which a theory of quantum gravity (the black p-branes) is equivalent to a lower-dimensional theory without gravity (the D-branes), as later demonstrated in Maldacena's AdS-CFT duality.

Polchinski's paradox

In an unpublished communication to

Kip Thorne Kip Stephen Thorne (born June 1, 1940) is an American theoretical physicist known for his contributions in gravitational physics and astrophysics. A longtime friend and colleague of Stephen Hawking and Carl Sagan, he was the Richard P. Fey ...

circa 1990, commenting on the

Novikov self-consistency principle The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture and Larry Niven's law of conservation of history, is a principle developed by Russian physicist Igor Dmitriyevich Novikov in the mid-1980s. Novikov inten ...

(in relation to sending objects or people through a

traversable wormhole A wormhole (Einstein-Rosen bridge) is a hypothetical structure connecting disparate points in spacetime, and is based on a special solution of the Einstein field equations. A wormhole can be visualized as a tunnel with two ends at separate po ...

into the past, and the

time paradox A temporal paradox, time paradox, or time travel paradox is a paradox, an apparent contradiction, or logical contradiction associated with the idea of time and time travel. The notion of time travel to the future complies with current understanding ...

es that could result), Polchinski raised a potentially paradoxical situation involving a

billiard ball A billiard ball is a small, hard ball used in cue sports, such as carom billiards, pool, and snooker. The number, type, diameter, color, and pattern of the balls differ depending upon the specific game being played. Various particular ball p ...

sent through a wormhole which sends it back in time. In this scenario, the ball is fired into a

wormhole A wormhole (Einstein-Rosen bridge) is a hypothetical structure connecting disparate points in spacetime, and is based on a special Solutions of the Einstein field equations, solution of the Einstein field equations. A wormhole can be visualize ...

at an angle such that, if it continues along that path, it will exit the wormhole in the past at just the right angle to collide with its earlier self, thereby knocking it off course and preventing it from entering the wormhole in the first place. Thorne dubbed this problem "Polchinski's paradox" in 1994. Later students of the whimsical problem came up with solutions which managed to avoid any inconsistencies, by having the ball emerge from the future at a different angle than the one used to generate the paradox, and deliver its younger self a glancing blow instead of knocking it completely away from the wormhole, a blow which changes its trajectory in just the right way so that it will travel back in time with the angle required to deliver its younger self this glancing blow.

2012 paper on black holes

In July 2012, Polchinski, with two of his students, James Sully and Ahmed Almheiri, and fellow string theorist Donald Marolf at the University of California, Santa Barbara (UCSB), published a paper whose calculations about

black hole radiation Hawking radiation is theoretical black body radiation that is theorized to be released outside a black hole's event horizon because of relativistic quantum effects. It is named after the physicist Stephen Hawking, who developed a theoretical arg ...

suggested that either

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

equivalence principle In the theory of general relativity, the equivalence principle is the equivalence of gravitational and inertial mass, and Albert Einstein's observation that the gravitational "force" as experienced locally while standing on a massive body (suc ...

is wrong, or else a key tenet of quantum mechanics is incorrect."Astrophysics: Fire in the hole!"
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Personal life and death

Polchinski had two sons, Steven and Daniel, with his wife, Dorothy Maria Chun, whom he married in 1980. He died at his home in Santa Barbara, California on February 2, 2018 of

brain cancer A brain tumor occurs when abnormal cells form within the brain. There are two main types of tumors: malignant tumors and benign (non-cancerous) tumors. These can be further classified as primary tumors, which start within the brain, and secondar ...

, at the age of 63.

Bibliography

* * *. Autobiographical memoir.

References

External links

Personal website
* Mentioned in the episode of The Big Bang Theory, The Paintball Scattering, season 12. {{DEFAULTSORT:Polchinski, Joseph 1954 births 2018 deaths American people of Polish descent California Institute of Technology alumni Harvard University staff People from White Plains, New York American string theorists Members of the United States National Academy of Sciences University of California, Berkeley alumni University of Texas at Austin faculty University of California, Santa Barbara faculty Deaths from brain tumor Scientists from New York (state)