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, the
seat of government of the Netherlands. 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,
an elite 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, 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 ===
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
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.
== Bibliography ==
=== 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
== See also ==
Anomaly matching condition
Feynman–'t Hooft gauge
Minimal subtraction scheme
Naturalness (physics)
Renormalon
't Hooft symbol
Mars One (Gerard 't Hooft is a main supporter
of the project)
== References ==
== External links ==
Gerard 't Hooft (homepage)
How To Become a Good Theoretical Physicist
The Nobel Prize in Physics 1999
A Confrontation with Infinity, Nobel Lecture
Publications from Google Scholar
Publications on the Arxiv
TVO.org video - Gerard t'Hooft lectures on
Science Fiction and Reality Lecture delivered
at the Perimeter Institute in Waterloo, Ontario,
Canada on May 7, 2008
Gerard 't Hooft on INSPIRE-HEP
