# Kenneth G. Wilson

Kenneth Geddes "Ken" Wilson (June 8, 1936 – June 15, 2013) was an American theoretical physicist and a pioneer in leveraging computers for studying particle physics. He was awarded the 1982 Nobel Prize in Physics for his work on phase transitions—illuminating the subtle essence of phenomena like melting ice and emerging magnetism. It was embodied in his fundamental work on the renormalization group.

## Quotes

* An especially intractable breed of problems in physics involves those with very many or an infinite number of degrees of freedom and in addition involve “renormalization.” Renormalization is explained as the existence of very many length or energy scales of importance in the physics of the problem. The renormalization group approach is a way of reducing the complexity of these problems to the point where numerical methods can be used to solve them. The Kondo problem (dilute magnetic alloys) is used as an illustration.
** (1975). "Renormalization group methods". Advances in Mathematics 16 (2): 170–186. ISSN 00018708. DOI:10.1016/0001-8708(75)90149-8.
* The fourth aspect of renormalization group theory is the construction of nondiagrammatic renormalization group transformations, which are then solved numerically, usually using a digital computer. This is the most exciting aspect of the renormalization group, the part of the theory that makes it possible to solve problems which are unreachable by Feynman diagrams. The Kondo problem has been solved by a nondiagrammatic computer method.
** "The renormalization group: Critical phenomena and the Kondo problem." Reviews of modern physics 47.4 (1975): 773.
* Asymptotic freedom arises as follows. The fundamental interactions of quarks and gluons are modified by “radiative” corrections of higher order in the quark-gluon coupling constant. These radiative corrections depend on the quark and gluon momenta. A careful analysis shows that the cumulative effect of radiative corrections to all orders can be characterized by a momentum-dependent effective coupling constant. The effective coupling is found to vanish in the limit of large momenta (to be precise, large momentum transfers between the quarks and gluons). This is called asymptotic freedom. As a result of asymptotic freedom the quarks can behave as nearly free particles at short distances; this is required to explain the high energy electron scattering experiments ... Meanwhile the interactions of quarks at long distances can be strong enough to bind the quarks into the observed bound states; protons, mesons, etc.
** Lévy M.; Mitter P. (eds.) (1977). "Chapter 6. Quantum Chromodynamics on a Lattice". New Developments in Quantum Field Theory and Statistical Mechanics Cargoes 1976. Nato Advanced Study Institutes Series, vol 26. Springer, Boston, MA.. doi:10.1007/978-1-4615-8918-1_6.
* Sometime toward the end of my second year, I started working with Gell-Mann. I went to Gell-Mann and he gave me a problem to work on and suggested I start working with fixed source theory of K-particles, where he wanted me to do things involving strong and weak interactions. And it's when I read about fixed source theory that I began to learn about renormalization group and realized it could be applied to fixed source theory, and I don't know whether there were papers that I read about renormalization group and fixed source theory, or I worked it out for myself, but in playing around with this, sort of trying to learn what was going on, I discovered that there were great simplifications that took place when you took the fixed source equation and took them to high energies, and when you did a leading log approximation. In the end, I discovered that those equations, simplified at the high energies -- you could get exact solutions. That was part of my thesis. And that was the initial thing that sparked my interest in the renormalization group. I remember when I presented my thesis to a seminar, and this was when Feynman was there, but not Gell-Mann. I went through all this exciting mathematics and toward the end, someone said, "Yes, that's fine, but what good is it?" I remember Feynman's answer as "Don't look a gift horse in the mouth!"
** Interview of Wilson conducted by Babak Ashrafi, Karl Hall, and Sam Schweber, edited by A. Martinez and S. S. Schweber. library.caltech.edu (6 July 2002).
* You shouldn’t choose a problem on the basis of the tool. You start by thinking about the physics problem, and the computational method should be a tool like any other. Maybe you’ll solve it using computer techniques, maybe using a contour integral; but it’s very important to approach it starting from the physics because otherwise you get lost in the use of the tool, and lose track of where you’re trying to go.
** as quoted by Paul Ginsparg in: (2014). "Kenneth G. Wilson: Renormalized after-dinner anecdotes". Journal of Statistical Physics 157 (4-5): 610-624. DOI:10.1007/s10955-014-1092-x. arXiv preprint (quote from p. 8 of preprint)

## Quotes about Wilson

    Arranged alphabetically by author
* The first efforts to turn quantum field theory into a rigorous mathematical subject occurred in the 1950s, when Wightman in particular formulated a set of axioms which define what we mean by a relativistic quantum field theory ... The subject took a significant step forward around 1970 largely through the work of Ken Wilson, who taught us to think of quantum field theory as a kind of second-order phase transition ... The Standard Model of particle physics was also formulated in the 1970s, and still stands as our best description of the strong and electroweak interactions after decades of thorough vetting in high-energy-physics experiments. ... Ken Wilson is a hero to me and many others because he provided a satisfying answer to the question: What is quantum field theory? (His was not the first answer, nor was it the complete and final answer, but nevertheless it transformed our understanding of the subject.) Wilson understood more deeply than his predecessors the meaning of renormalization.
** John Preskill in: (2018). "Simulating quantum field theory with a quantum computer". arXiv preprint arXiv:1811.10085. (quote from p. 5)
* Ken Wilson was one of a very small number of physicists who changed the way we all think, not just about specific phenomena, but about a vast range of different phenomena.
** Steven Weinberg as quoted by Dennis Overbye in: (June 20, 2013)"Kenneth Wilson, Nobel Physicist, Dies at 77". New York Times.
* Wilson was quick to appreciate the promise of QCD, but he realized that to calculate the theory’s consequences at (relatively) low energies or long distances would be a demanding task. Wilson’s approach ... was revolutionary in its directness: He formulated the theory in computer-friendly form, essentially as a complicated definite integral in a space of enormously large dimension, and then set out to perform the integral numerically. Many years passed before computers and algorithms were up to the job, but lattice gauge theory amply fulfilled Wilson’s vision. The highest award in the field, awarded annually at the major international conference in Lattice Field Theory, bears Wilson’s name.
** Frank A. Wilczek: (2013). "Ken Wilson: A scientific appreciation". Proceedings of the National Academy of Sciences 110 (32): 12855–12856. ISSN 0027-8424. DOI:10.1073/pnas.1312463110.