Leonard Susskind

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https://en.wikipedia.org/wiki/Leonard_Susskind

 

Leonard Susskind
Leonard Susskind
Born	1940 South Bronx, New York City, US
Residence	United States
Nationality	United States
Citizenship	United States
Alma mater	City College of New York Cornell University
Known for	Holographic principle String theory Matrix theory (physics) String theory landscape Color confinement Hamiltonian lattice gauge theory RST model Susskind–Glogower operator Kogut–Susskind fermions Fischler–Susskind mechanism ER=EPR
Awards	Pomeranchuk Prize (2008) American Institute of Physics' Science Writing Award Sakurai Prize (1998) Boris Pregel Award, New York Academy of Sciences (1975)[1]
Scientific career
Fields	Physics, mathematics
Institutions	Yeshiva University Tel Aviv University Stanford University Stanford Institute for Theoretical Physics Korea Institute for Advanced Study Perimeter Institute for Theoretical Physics
Thesis	Quantum mechanical approach to strong interactions (1965)
Doctoral advisor	Peter A. Carruthers
Doctoral students	Eduardo Fradkin

Leonard Susskind (/ˈsʌskɪnd/; born 1940) is an American physicist, who is a professor of theoretical physics at Stanford University, and founding director of the Stanford Institute for Theoretical Physics. His research interests include string theory, quantum field theory, quantum statistical mechanics and quantum cosmology. He is a member of the US National Academy of Sciences, and the American Academy of Arts and Sciences, an associate member of the faculty of Canada's Perimeter Institute for Theoretical Physics,^[6] and a distinguished professor of the Korea Institute for Advanced Study.

Susskind is widely regarded as one of the fathers of string theory. He was the first to give a precise string-theoretic interpretation of the holographic principle in 1995 and the first to introduce the idea of the string theory landscape in 2003.

Susskind was awarded the 1998 J. J. Sakurai Prize, and the 2018 Oskar Klein Medal.

Early life and education

Leonard Susskind was born to a Jewish family from the South Bronx in New York City. He began working as a plumber at the age of 16, taking over from his father who had become ill. Later, he enrolled in the City College of New York as an engineering student, graduating with a B.S. in physics in 1962. In an interview in the Los Angeles Times, Susskind recalls the moment he discussed with his father that changed his career path: "When I told my father I wanted to be a physicist, he said, 'Hell no, you ain’t going to work in a drug store.' I said, 'No, not a pharmacist.' I said, 'Like Einstein.' He poked me in the chest with a piece of plumbing pipe. 'You ain’t going to be no engineer,' he said. 'You're going to be Einstein.'" Susskind then studied at Cornell University under Peter A. Carruthers where he earned his Ph.D. in 1965. 

Career

Susskind giving 2014 Messenger Lecture at Cornell.

 

Susskind was an assistant professor of physics, then an associate professor at Yeshiva University (1966–1970), after which he went for a year to the Tel Aviv University (1971–72), returning to Yeshiva to become a professor of physics (1970–1979). Since 1979 he has been professor of physics at Stanford University, and since 2000 has held the Felix Bloch professorship of physics.

Susskind was awarded the 1998 J. J. Sakurai Prize for his "pioneering contributions to hadronic string models, lattice gauge theories, quantum chromodynamics, and dynamical symmetry breaking." Susskind's hallmark, according to colleagues, has been the application of "brilliant imagination and originality to the theoretical study of the nature of the elementary particles and forces that make up the physical world."

In 2007, Susskind joined the faculty of Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, as an associate member. He has been elected to the National Academy of Sciences and the American Academy of Arts and Sciences. He is also a distinguished professor at Korea Institute for Advanced Study.

Scientific career

Susskind was one of at least three physicists, alongside Yoichiro Nambu and Holger Bech Nielsen, who independently discovered during or around 1970 that the Veneziano dual resonance model of strong interactions could be described by a quantum mechanical model of oscillating strings,^[16] and was the first to propose the idea of the string theory landscape. Susskind has also made important contributions in the following areas of physics:

• The independent discovery of the string theory model of particle physics
• The theory of quark confinement
• The development of Hamiltonian lattice gauge theory known as Kogut-Susskind fermions
• The theory of scaling violations in deep inelastic electroproduction
• The theory of symmetry breaking sometimes known as "technicolor theory"
• The second, yet independent, theory of cosmological baryogenesis (Andrei Sakharov's work was first, but was mostly unknown in the Western hemisphere)
• String theory of black hole entropy
• The principle of black hole complementarity
• The causal patch hypothesis
• The holographic principle
• M-theory, including development of the BFSS matrix model 
• Introduction of holographic entropy bounds in physical cosmology
• The idea of an anthropic string theory landscape
• The Census Taker's Hat (FRW/CFT duality)
• Most recently, application of ideas from information and computation theory, such as quantum complexity, to the physics and thermodynamics of black holes, and holographic theories in general.
  

Books

Susskind is the author of several popular science books. 

The Cosmic Landscape

The Cosmic Landscape: String Theory and the Illusion of Intelligent Design is Susskind's first popular science book, published by Little, Brown and Company on December 12, 2005. It is Susskind's attempt to bring his idea of the anthropic landscape of string theory to the general public. In the book, Susskind describes how the string theory landscape was an almost inevitable consequence of several factors, one of which was Steven Weinberg's prediction of the cosmological constant in 1987. The question addressed here is why our universe is fine-tuned for our existence. Susskind explains that Weinberg calculated that if the cosmological constant was just a little different, our universe would cease to exist. 

The Black Hole War

The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics is Susskind's second popular science book, published by Little, Brown, and Company on July 7, 2008. The book is his most famous work and explains what he thinks would happen to the information and matter stored in a black hole when it evaporates. The book sparked from a debate that started in 1981, when there was a meeting of physicists to try to decode some of the mysteries about how particles of particular elemental compounds function. During this discussion Stephen Hawking stated that the information inside a black hole is lost forever as the black hole evaporates. It took 28 years for Leonard Susskind to formulate his theory that would prove Hawking wrong. He then published his theory in his book, The Black Hole War. Like The Cosmic Landscape, The Black Hole War is aimed at the lay reader. He writes: "The real tools for understanding the quantum universe are abstract mathematics: infinite dimensional Hilbert spaces, projection operators, unitary matrices and a lot of other advanced principles that take a few years to learn. But let's see how we do in just a few pages". 

The Theoretical Minimum book series

Susskind co-authored a series of companion books to his lecture series The Theoretical Minimum. The first of these, The Theoretical Minimum: What You Need to Know to Start Doing Physics, was published in 2013 and presents the modern formulations of classical mechanics. The second of these, Quantum Mechanics: The Theoretical Minimum, was published in February 2014. The third book, Special Relativity and Classical Field Theory: The Theoretical Minimum (September 26, 2017), introduces readers to Einstein's special relativity and Maxwell's classical field theory. 

The Theoretical Minimum lecture series

Susskind teaches a series of Stanford Continuing Studies courses about modern physics referred to as The Theoretical Minimum. The title of the series is a clear reference to the Landau's famous comprehensive exam called the "Theoretical Minimum" which students were expected to pass before admission to his school. The Theoretical Minimum lectures later formed the basis for the books of the same name. The goal of the courses is to teach the basic but rigorous theoretical foundations required to study certain areas of physics. The sequence covers classical mechanics, relativity, quantum mechanics, statistical mechanics, and cosmology, including the physics of black holes.

These courses are available on The Theoretical Minimum website, on iTunes, and on YouTube. The courses are intended for the mathematically literate public as well as physical science/mathematics students. Susskind aims the courses at people with prior exposure to algebra, and calculus. Homework and study outside of class is otherwise unnecessary. Susskind explains most of the mathematics used, which form the basis of the lectures. 

Cornell Messenger Lectures

Susskind gave 3 lectures "The Birth of the Universe and the Origin of Laws of Physics" April 28-May 1, 2014 in the Cornell Messenger Lecture series which are posted on a Cornell website.

Smolin–Susskind debate

The Smolin–Susskind debate refers to the series of intense postings in 2004 between Lee Smolin and Susskind, concerning Smolin’s argument that the "anthropic principle cannot yield any falsifiable predictions, and therefore cannot be a part of science." It began on July 26, 2004, with Smolin's publication of "Scientific alternatives to the anthropic principle." Smolin e-mailed Susskind asking for a comment. Having not had the chance to read the paper, Susskind requested a summarization of his arguments. Smolin obliged, and on July 28, 2004, Susskind responded, saying that the logic Smolin followed "can lead to ridiculous conclusions." The next day, Smolin responded, saying that "If a large body of our colleagues feels comfortable believing a theory that cannot be proved wrong, then the progress of science could get stuck, leading to a situation in which false, but unfalsifiable theories dominate the attention of our field." This was followed by another paper by Susskind which made a few comments about Smolin's theory of "cosmic natural selection." The Smolin-Susskind debate finally ended with each of them agreeing to write a final letter which would be posted on the edge.org website, with three conditions attached: (1) No more than one letter each; (2) Neither sees the other's letter in advance; (3) No changes after the fact. 

Personal life

He has been married twice, first in 1960, and has four children. Susskind is a great-grandfather.

Scientific wager

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Scientific_wager

 

A scientific wager is a wager whose outcome is settled by scientific method. They typically consist of an offer to pay a certain sum of money on the scientific proof or disproof of some currently-uncertain statement. Some wagers have specific date restrictions for collection, but many are open. Wagers occasionally exert a powerful galvanizing effect on society and the scientific community.

Notable scientists who have made scientific wagers include Stephen Hawking and Richard Feynman. Stanford Linear Accelerator has an open book containing about 35 bets in particle physics dating back to 1980; many are still unresolved.

Notable scientific wagers

• In 1870, Alfred Russel Wallace bet a flat-Earth theorist named John Hampden that he could prove the flat Earth hypothesis incorrect. The sum staked was £500 (equivalent to about £47000 in present-day terms^[1]). A test (now known as the Bedford Level experiment) involving a stretch of the Old Bedford River, in Norfolk, was agreed on: Wallace measured the curvature of the canal's surface using two markers separated by about 5 kilometres (3.1 mi) and suspended at equal heights above the water's surface. Using a telescope mounted 5 km from one of the markers, Wallace established that the nearer one appeared to be the higher of the two. An independent referee agreed that this showed the Earth's surface to curve away from the telescope, and so Wallace won his money. However, Hampden never accepted the result and made increasingly unpleasant threats to Wallace.
• In 1975, cosmologist Stephen Hawking bet fellow cosmologist Kip Thorne a subscription to Penthouse magazine for Thorne against four years of Private Eye for him that Cygnus X-1 would turn out to not be a black hole. In 1990, Hawking acknowledged that he had lost the bet. Hawking's explanation for his position was that if black holes didn't actually exist much of his research would be incorrect, but at least he'd have the consolation of winning the bet.
• In 1978, chess International Master David Levy won £1250 from four artificial intelligence experts by never losing a match to a chess program in a ten-year span from 1968 to 1978.
• In 1980, biologist Paul R. Ehrlich bet economist Julian Lincoln Simon that the price of a portfolio of $200 of each of five mineral commodities (copper, chromium, nickel, tin, and tungsten) would rise over the next 10 years. He lost, and paid the amount the total price had declined: $576.07.
• In 1997, Stephen Hawking and Kip Thorne made a bet with John Preskill on the ultimate resolution of the apparent contradiction between Hawking radiation resulting in loss of information, and a requirement of quantum mechanics that information cannot be destroyed. Hawking and Thorne bet that information must be lost in a black hole; Preskill bet that it must not. The formal wager was: "When an initial pure quantum state undergoes gravitational collapse to form a black hole, the final state at the end of black hole evaporation will always be a pure quantum state". The stake was an encyclopaedia of the winner's choice, from which "information can be recovered at will". Hawking conceded the bet in 2004, giving a baseball encyclopaedia to John Preskill. Thorne has not formally conceded. See: Thorne-Hawking-Preskill bet
• In 2005, British climate scientist James Annan proposed bets with global warming denialists concerning whether future temperatures will increase. Two Russian solar physicists, Galina Mashnich and Vladimir Bashkirtsev, accepted the wager of US$10,000 that the average global temperature during 2012–2017 would be lower than during 1998–2003. Previously, Annan first directly challenged Richard Lindzen. Lindzen had been willing to bet that global temperatures would drop over the next 20 years. Annan says that Lindzen wanted odds of 50–1 against falling temperatures. Lindzen, however, says that he asked for 2–1 odds against a temperature rise of over 0.4 °C. Annan and other proponents of global warming state they have challenged other denialists to bets over global warming that were not accepted, including Annan's attempt in 2005 to accept a bet that had been offered by Patrick Michaels in 1998 that temperatures would be cooler after ten years. Annan made a bet in 2011 with Doctor David Whitehouse that the Met Office temperature would set a new annual record by the end of the year. Annan was declared to have lost on January 13, 2012.
• In 2005, The Guardian columnist George Monbiot challenged Myron Ebell of the Competitive Enterprise Institute to a GB£5,000 bet of global warming versus global cooling.
• In 2012, Stephen Hawking lost $100 to Gordon Kane of the University of Michigan because of the Higgs boson discovery.
• Zvi Bern has won many bets connected to quantum gravity.
• On July 8, 2009, at a FQXi conference in the Azores, Antony Garrett Lisi made a public bet with Frank Wilczek that superparticles would not be detected by July 8, 2015. On Aug 16, 2016, after agreeing to a one-year delay to allow for more data collection from the Large Hadron Collider, Frank Wilczek conceded the superparticle bet to Lisi.
• In 2000 roughly 40 physicists made a bet about the existence of supersymmetry to be settled in 2011, but because LHC was delayed the bet was extended to 2016. As of Summer 2016 there had been no signs of superparticles, and the losers delivered "good cognac at a price not less than $100" each to the winners.
• Also in 2016 David Gross lost a separate wager about supersymmetry, but he continues to believe in the theory.

Black hole thermodynamics

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Black_hole_thermodynamics

 

In physics, black hole thermodynamics is the area of study that seeks to reconcile the laws of thermodynamics with the existence of black-hole event horizons. As the study of the statistical mechanics of black-body radiation led to the advent of the theory of quantum mechanics, the effort to understand the statistical mechanics of black holes has had a deep impact upon the understanding of quantum gravity, leading to the formulation of the holographic principle.

An artist's depiction of two black holes merging, a process in which the laws of thermodynamics are upheld

 

Overview

The second law of thermodynamics requires that black holes have entropy. If black holes carried no entropy, it would be possible to violate the second law by throwing mass into the black hole. The increase of the entropy of the black hole more than compensates for the decrease of the entropy carried by the object that was swallowed. 

Starting from theorems proved by Stephen Hawking, Jacob Bekenstein conjectured that the black hole entropy was proportional to the area of its event horizon divided by the Planck area. In 1973 Bekenstein suggested ${\displaystyle (\pi \ln {2})/8}$ as the constant of proportionality, asserting that if the constant was not exactly this, it must be very close to it. The next year, in 1974, Hawking showed that black holes emit thermal Hawking radiation corresponding to a certain temperature (Hawking temperature). Using the thermodynamic relationship between energy, temperature and entropy, Hawking was able to confirm Bekenstein's conjecture and fix the constant of proportionality at ${\displaystyle 1/4}$:

${\displaystyle S_{\text{BH}}={\frac {k_{B}A}{4\ell _{\text{P}}^{2}}},}$

where ${\displaystyle A}$ is the area of the event horizon, ${\displaystyle k_{B}}$ is Boltzmann's constant, and ${\displaystyle \ell _{\text{P}}={\sqrt {G\hbar /c^{3}}}}$ is the Planck length. This is often referred to as the Bekenstein–Hawking formula. The subscript BH either stands for "black hole" or "Bekenstein–Hawking". The black-hole entropy is proportional to the area of its event horizon ${\displaystyle A}$. The fact that the black-hole entropy is also the maximal entropy that can be obtained by the Bekenstein bound (wherein the Bekenstein bound becomes an equality) was the main observation that led to the holographic principle. This area relationship was generalized to arbitrary regions via the Ryu-Takayanagi formula, which relates the entanglement entropy of a boundary conformal field theory to a specific surface in its dual gravitational theory.

Although Hawking's calculations gave further thermodynamic evidence for black-hole entropy, until 1995 no one was able to make a controlled calculation of black-hole entropy based on statistical mechanics, which associates entropy with a large number of microstates. In fact, so called "no-hair" theorems appeared to suggest that black holes could have only a single microstate. The situation changed in 1995 when Andrew Strominger and Cumrun Vafa calculated the right Bekenstein–Hawking entropy of a supersymmetric black hole in string theory, using methods based on D-branes and string duality. Their calculation was followed by many similar computations of entropy of large classes of other extremal and near-extremal black holes, and the result always agreed with the Bekenstein–Hawking formula. However, for the Schwarzschild black hole, viewed as the most far-from-extremal black hole, the relationship between micro- and macrostates has not been characterized. Efforts to develop an adequate answer within the framework of string theory continue.

In loop quantum gravity (LQG) it is possible to associate a geometrical interpretation to the microstates: these are the quantum geometries of the horizon. LQG offers a geometric explanation of the finiteness of the entropy and of the proportionality of the area of the horizon. It is possible to derive, from the covariant formulation of full quantum theory (spinfoam) the correct relation between energy and area (1st law), the Unruh temperature and the distribution that yields Hawking entropy. The calculation makes use of the notion of dynamical horizon and is done for non-extremal black holes. There seems to be also discussed the calculation of Bekenstein–Hawking entropy from the point of view of LQG. 

The laws of black hole mechanics

The four laws of black hole mechanics are physical properties that black holes are believed to satisfy. The laws, analogous to the laws of thermodynamics, were discovered by Brandon Carter, Stephen Hawking, and James Bardeen. 

Statement of the laws

The laws of black-hole mechanics are expressed in geometrized units. 

The zeroth law

The horizon has constant surface gravity for a stationary black hole. 

The first law

For perturbations of stationary black holes, the change of energy is related to change of area, angular momentum, and electric charge by

${\displaystyle dE={\frac {\kappa }{8\pi }}\,dA+\Omega \,dJ+\Phi \,dQ,}$

where ${\displaystyle E}$ is the energy, ${\displaystyle \kappa }$ is the surface gravity, ${\displaystyle A}$ is the horizon area, ${\displaystyle \Omega }$ is the angular velocity, ${\displaystyle J}$ is the angular momentum, ${\displaystyle \Phi }$ is the electrostatic potential and ${\displaystyle Q}$ is the electric charge. 

The second law

The horizon area is, assuming the weak energy condition, a non-decreasing function of time:

${\displaystyle {\frac {dA}{dt}}\geq 0.}$

This "law" was superseded by Hawking's discovery that black holes radiate, which causes both the black hole's mass and the area of its horizon to decrease over time. 

The third law

It is not possible to form a black hole with vanishing surface gravity. That is, ${\displaystyle \kappa =0}$ cannot be achieved. 

Discussion of the laws

The zeroth law

The zeroth law is analogous to the zeroth law of thermodynamics, which states that the temperature is constant throughout a body in thermal equilibrium. It suggests that the surface gravity is analogous to temperature. T constant for thermal equilibrium for a normal system is analogous to ${\displaystyle \kappa }$ constant over the horizon of a stationary black hole. 

The first law

The left side, ${\displaystyle dE}$, is the change in energy (proportional to mass). Although the first term does not have an immediately obvious physical interpretation, the second and third terms on the right side represent changes in energy due to rotation and electromagnetism. Analogously, the first law of thermodynamics is a statement of energy conservation, which contains on its right side the term ${\displaystyle TdS}$. 

The second law

The second law is the statement of Hawking's area theorem. Analogously, the second law of thermodynamics states that the change in entropy in an isolated system will be greater than or equal to 0 for a spontaneous process, suggesting a link between entropy and the area of a black-hole horizon. However, this version violates the second law of thermodynamics by matter losing (its) entropy as it falls in, giving a decrease in entropy. However, generalizing the second law as the sum of black-hole entropy and outside entropy, shows that the second law of thermodynamics is not violated in a system including the universe beyond the horizon. 

The generalized second law of thermodynamics (GSL) was needed to present the second law of thermodynamics as valid. This is because the second law of thermodynamics, as a result of the disappearance of entropy near the exterior of black holes, is not useful. The GSL allows for the application of the law because now the measurement of interior, common entropy is possible. The validity of the GSL can be established by studying an example, such as looking at a system having entropy that falls into a bigger, non-moving black hole, and establishing upper and lower entropy bounds for the increase in the black hole entropy and entropy of the system, respectively. One should also note that the GSL will hold for theories of gravity such as Einstein gravity, Lovelock gravity, or Braneworld gravity, because the conditions to use GSL for these can be met.

However, on the topic of black hole formation, the question becomes whether or not the generalized second law of thermodynamics will be valid, and if it is, it will have been proved valid for all situations. Because a black hole formation is not stationary, but instead moving, proving that the GSL holds is difficult. Proving the GSL is generally valid would require using quantum-statistical mechanics, because the GSL is both a quantum and statistical law. This discipline does not exist so the GSL can be assumed to be useful in general, as well as for prediction. For example, one can use the GSL to predict that, for a cold, non-rotating assembly of ${\displaystyle N}$ nucleons, ${\displaystyle S_{BH}-S>0}$, where ${\displaystyle S_{BH}}$ is the entropy of a black hole and ${\displaystyle S}$ is the sum of the ordinary entropy.

The third law

Extremal black holes have vanishing surface gravity. Stating that ${\displaystyle \kappa }$ cannot go to zero is analogous to the third law of thermodynamics, which states that the entropy of a system at absolute zero is a well defined constant. This is because a system at zero temperature exists in its ground state. Furthermore, ${\displaystyle \Delta S}$ will reach zero at zero temperature, but ${\displaystyle S}$ itself will also reach zero, at least for perfect crystalline substances. No experimentally verified violations of the laws of thermodynamics are known yet.

Interpretation of the laws

The four laws of black-hole mechanics suggest that one should identify the surface gravity of a black hole with temperature and the area of the event horizon with entropy, at least up to some multiplicative constants. If one only considers black holes classically, then they have zero temperature and, by the no-hair theorem, zero entropy, and the laws of black-hole mechanics remain an analogy. However, when quantum-mechanical effects are taken into account, one finds that black holes emit thermal radiation (Hawking radiation) at a temperature

${\displaystyle T_{\text{H}}={\frac {\kappa }{2\pi }}.}$

From the first law of black-hole mechanics, this determines the multiplicative constant of the Bekenstein–Hawking entropy, which is

${\displaystyle S_{\text{BH}}={\frac {A}{4}}.}$

Beyond black holes

Gary Gibbons and Hawking have shown that black-hole thermodynamics is more general than black holes—that cosmological event horizons also have an entropy and temperature. 

More fundamentally, 't Hooft and Susskind used the laws of black-hole thermodynamics to argue for a general holographic principle of nature, which asserts that consistent theories of gravity and quantum mechanics must be lower-dimensional. Though not yet fully understood in general, the holographic principle is central to theories like the AdS/CFT correspondence.

There are also connections between black-hole entropy and fluid surface tension.

Gerard 't Hooft

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Gerard_'t_Hooft

 

Gerard 't Hooft
November 2008
Born	July 5, 1946 (age 73) Den Helder, Netherlands
Nationality	Dutch
Alma mater	Utrecht University
Known for	Quantum field theory, Quantum gravity, 't Hooft–Polyakov monopole, 't Hooft symbol, 't Hooft operator, Holographic principle, Renormalization, Dimensional regularization
Awards	Heineman Prize (1979) Wolf Prize (1981) Lorentz Medal (1986) Spinoza Prize (1995) Franklin Medal (1995) Nobel Prize in Physics (1999) Lomonosov Gold Medal (2010)
Scientific career
Fields	Theoretical physics
Institutions	Utrecht University
Doctoral advisor	Martinus J. G. Veltman
Doctoral students	Robbert Dijkgraaf Herman Verlinde

Gerardus (Gerard) 't Hooft (Dutch: [ˈɣeːrɑrt ət ˈɦoːft]; born July 5, 1946) is a Dutch theoretical physicist and professor at Utrecht University, the Netherlands. He shared the 1999 Nobel Prize in Physics with his thesis advisor Martinus J. G. Veltman "for elucidating the quantum structure of electroweak interactions".

His work concentrates on gauge theory, black holes, quantum gravity and fundamental aspects of quantum mechanics. His contributions to physics include a proof that gauge theories are renormalizable, dimensional regularization and the holographic principle.

Personal life

He is married to Albertha Schik (Betteke) and has two daughters, Saskia and Ellen.

Biography

Early life

Gerard 't Hooft was born in Den Helder on July 5, 1946, but grew up in The Hague. He was the middle child of a family of three. He comes from a family of scholars. His grandmother was a sister of Nobel prize laureate Frits Zernike, and was married to Pieter Nicolaas van Kampen, who was a well-known professor of zoology at Leiden University. His uncle Nico van Kampen was an (emeritus) professor of theoretical physics at Utrecht University, and while his mother did not opt for a scientific career because of her gender, she did marry a maritime engineer. Following his family's footsteps, he showed interest in science at an early age. When his primary school teacher asked him what he wanted to be when he grew up, he boldly declared, "a man who knows everything."

After primary school Gerard attended the Dalton Lyceum, a school that applied the ideas of the Dalton Plan, an educational method that suited him well. He easily passed his science and mathematics courses, but struggled with his language courses. Nonetheless, he passed his classes in English, French, German, classical Greek and Latin. At the age of sixteen he earned a silver medal in the second Dutch Math Olympiad. 

Education

After Gerard 't Hooft passed his high school exams in 1964, he enrolled in the physics program at Utrecht University. He opted for Utrecht instead of the much closer Leiden, because his uncle was a professor there and he wanted to attend his lectures. Because he was so focused on science, his father insisted that he join the Utrechtsch Studenten Corps, a student association, in the hope that he would do something else besides studying. This worked to some extent, during his studies he was a coxswain with their rowing club "Triton" and organized a national congress for science students with their science discussion club "Christiaan Huygens". 

In the course of his studies he decided he wanted to go into what he perceived as the heart of theoretical physics, elementary particles. His uncle had grown to dislike the subject and in particular its practitioners, so when it became time to write his 'doctoraalscriptie' (Dutch equivalent of a master's thesis) in 1968, 't Hooft turned to the newly appointed professor Martinus Veltman, who specialized in Yang–Mills theory, a relatively fringe subject at the time because it was thought that these could not be renormalized. His assignment was to study the Adler–Bell–Jackiw anomaly, a mismatch in the theory of the decay of neutral pions; formal arguments forbid the decay into photons, whereas practical calculations and experiments showed that this was the primary form of decay. The resolution of the problem was completely unknown at the time, and 't Hooft was unable to provide one. 

In 1969, 't Hooft started on his doctoral research with Martinus Veltman as his advisor. He would work on the same subject Veltman was working on, the renormalization of Yang–Mills theories. In 1971 his first paper was published. In it he showed how to renormalize massless Yang–Mills fields, and was able to derive relations between amplitudes, which would be generalized by Andrei Slavnov and John C. Taylor, and become known as the Slavnov–Taylor identities. 

The world took little notice, but Veltman was excited because he saw that the problem he had been working on was solved. A period of intense collaboration followed in which they developed the technique of dimensional regularization. Soon 't Hooft's second paper was ready to be published,^[3] in which he showed that Yang–Mills theories with massive fields due to spontaneous symmetry breaking could be renormalized. This paper earned them worldwide recognition, and would ultimately earn the pair the 1999 Nobel Prize in Physics. 

These two papers formed the basis of 't Hooft's dissertation, The Renormalization procedure for Yang–Mills Fields, and he obtained his PhD degree in 1972. In the same year he married his wife, Albertha A. Schik, a student of medicine in Utrecht.

Career

Gerard 't Hooft at Harvard

 

After obtaining his doctorate 't Hooft went to CERN in Geneva, where he had a fellowship. He further refined his methods for Yang–Mills theories with Veltman (who went back to Geneva). In this time he became interested in the possibility that the strong interaction could be described as a massless Yang–Mills theory, i.e. one of a type that he had just proved to be renormalizable and hence be susceptible to detailed calculation and comparison with experiment. 

According to 't Hooft's calculations, this type of theory possessed just the right kind of scaling properties (asymptotic freedom) that this theory should have according to deep inelastic scattering experiments. This was contrary to popular perception of Yang–Mills theories at the time, that like gravitation and electrodynamics, their intensity should decrease with increasing distance between the interacting particles; such conventional behaviour with distance was unable to explain the results of deep inelastic scattering, whereas 't Hooft's calculations could. 

When 't Hooft mentioned his results at a small conference at Marseilles in 1972, Kurt Symanzik urged him to publish this result; but 't Hooft did not, and the result was eventually rediscovered and published by Hugh David Politzer, David Gross, and Frank Wilczek in 1973, which led to their earning the 2004 Nobel Prize in Physics.

In 1974, 't Hooft returned to Utrecht where he became assistant professor. In 1976, he was invited for a guest position at Stanford and a position at Harvard as Morris Loeb lecturer. His eldest daughter, Saskia Anne, was born in Boston, while his second daughter, Ellen Marga, was born in 1978 after he returned to Utrecht, where he was made full professor. In the academic year 1987-1988 't Hooft spent a sabbatical in the Boston University Physics Department along with Howard Georgi, Robert Jaffe and others arranged by the then new Department chair Lawrence Sulak.

In 2007 't Hooft became editor-in-chief for Foundations of Physics, where he sought to distance the journal from the controversy of ECE theory. 't Hooft held the position until 2016.

On July 1, 2011 he was appointed Distinguished professor by Utrecht University.

Honors

In 1999 't Hooft shared the Nobel prize in Physics with his thesis adviser Veltman for "elucidating the quantum structure of the electroweak interactions in physics". Before that time his work had already been recognized by other notable awards. In 1981, he was awarded the Wolf Prize, possibly the most prestigious prize in physics after the Nobel prize. Five years later he received the Lorentz Medal, awarded every four years in recognition of the most important contributions in theoretical physics. In 1995, he was one of the first recipients of the Spinozapremie, the highest award available to scientists in the Netherlands. In the same year he was also honoured with a Franklin Medal.

Since his Nobel Prize, 't Hooft has received a slew of awards, honorary doctorates and honorary professorships. He was knighted commander in the Order of the Netherlands Lion, and officer in the French Legion of Honor. The asteroid 9491 Thooft has been named in his honor, and he has written a constitution for its future inhabitants.

He is a member of the Royal Netherlands Academy of Arts and Sciences (KNAW) since 1982, where he was made academy professor in 2003. He is also a foreign member of many other science academies, including the French Académie des Sciences, the American National Academy of Sciences and American Academy of Arts and Sciences and the Britain and Ireland based Institute of Physics.

Research

't Hooft's research interest can be divided in three main directions: 'gauge theories in elementary particle physics', 'quantum gravity and black holes', and 'foundational aspects of quantum mechanics'.

Gauge theories in elementary particle physics

't Hooft is most famous for his contributions to the development of gauge theories in particle physics. The best known of these is the proof in his PhD thesis that Yang–Mills theories are renormalizable, for which he shared the 1999 Nobel Prize in Physics. For this proof he introduced (with his adviser Veltman) the technique of dimensional regularization.

After his PhD, he became interested in the role of gauge theories in the strong interaction, the leading theory of which is called quantum chromodynamics or QCD. Much of his research focused on the problem of color confinement in QCD, i.e. the observational fact that only color neutral particles are observed at low energies. This led him to the discovery that SU(N) gauge theories simplify in the large N limit, a fact which has proved important in the examination of the conjectured correspondence between string theories in an Anti-de Sitter space and conformal field theories in one lower dimension. By solving the theory in one space and one time dimension, 't Hooft was able to derive a formula for the masses of mesons.

He also studied the role of so-called instanton contributions in QCD. His calculation showed that these contributions lead to an interaction between light quarks at low energies not present in the normal theory. Studying instanton solutions of Yang–Mills theories, 't Hooft discovered that spontaneously breaking a theory with SU(N) symmetry to a U(1) symmetry will lead to the existence of magnetic monopoles. These monopoles are called 't Hooft–Polyakov monopoles, after Alexander Polyakov, who independently obtained the same result.

As another piece in the color confinement puzzle 't Hooft introduced 't Hooft operators, which are the magnetic dual of Wilson loops. Using these operators he was able to classify different phases of QCD, which form the basis of the QCD phase diagram.

In 1986, he was finally able to show that instanton contributions solve the Adler–Bell–Jackiw anomaly, the topic of his master's thesis.

Quantum gravity and black holes

When Veltman and 't Hooft moved to CERN after 't Hooft obtained his PhD, Veltman's attention was drawn to the possibility of using their dimensional regularization techniques to the problem of quantizing gravity. Although it was known that perturbative quantum gravity was not completely renormalizible, they felt important lessons were to be learned by studying the formal renormalization of the theory order by order. This work would be continued by Stanley Deser and another PhD student of Veltman, Peter van Nieuwenhuizen, who later found patterns in the renormalization counter terms, which led to the discovery of supergravity.

In the 1980s, 't Hooft's attention was drawn to the subject of gravity in 3 spacetime dimensions. Together with Deser and Jackiw he published an article in 1984 describing the dynamics of flat space where the only local degrees of freedom were propagating point defects. His attention returned to this model at various points in time, showing that Gott pairs would not cause causality violating timelike loops, and showing how the model could be quantized. More recently he proposed generalizing this piecewise flat model of gravity to 4 spacetime dimensions.

With Stephen Hawking's discovery of Hawking radiation of black holes, it appeared that the evaporation of these objects violated a fundamental property of quantum mechanics, unitarity. 'T Hooft refused to accept this problem, known as the black hole information paradox, and assumed that this must be the result of the semi-classical treatment of Hawking, and that it should not appear in a full theory of quantum gravity. He proposed that it might be possible to study some of the properties of such a theory, by assuming that such a theory was unitary.

Using this approach he has argued that near a black hole, quantum fields could be described by a theory in a lower dimension. This led to the introduction of the holographic principle by him and Leonard Susskind.

Fundamental aspects of quantum mechanics

't Hooft has "deviating views on the physical interpretation of quantum theory". He believes that there could be a deterministic explanation underlying quantum mechanics. Using a speculative model he has argued that such a theory could avoid the usual Bell inequality arguments that would disallow such a local hidden variable theory. In 2016 he published a book length exposition of his ideas which, according to 't Hooft, has encountered mixed reactions.

Popular publications

• Playing With Planets, Oct 30, 2008, doi:10.1142/6702
• In Search of the Ultimate Building Blocks, Nov 28, 1996, doi:10.1017/CBO9781107340855
• Time in Powers of Ten. Natural Phenomena and Their Timescales. May 19, 2014, doi:10.1142/8786