ICTP Announces 2023 Dirac Medallists

ICTP has awarded its 2023 Dirac Medal to four physicists who have made wide-ranging contributions to string theory, a mathematical framework in fundamental physics that aims to describe the entirety of the whole universe. 

The 2023 Dirac Medallists are:

• Jeffrey Harvey, University of Chicago, USA
• Igor Klebanov, Princeton University, USA  
• Stephen Shenker, Stanford University, USA 
• Leonard Susskind, Stanford University, USA 

The award cites "their pioneering contributions to perturbative and non-perturbative string theory and quantum gravity, in particular, to the aspects related to anomalies, duality, black holes and holography".

"This year's medallists have made many original contributions to developing the theoretical framework of string theory, with the goal of unifying all physical interactions including gravity," said ICTP Director Atish Dabholkar. "Their work has led to deep, new insights about the physics of black holes and to major conceptual breakthroughs through the realization of new principles of duality and holography."

ICTP's Dirac Medal is given in honour of Paul Dirac, one of the greatest physicists of the 20th century and a staunch friend of the Centre. It is awarded every year on Dirac's birthday, 8 August, to scientists who have made significant contributions to theoretical physics.

A unified theory of physics

Physicists consider string theory to be a unified theory of physics, one that unites Einstein’s general theory of relativity (which describes gravity) and quantum mechanics (which  describes the fundamental elements of matter). It does this by re-imagining the fundamental building blocks of matter as tiny vibrating strings. Just like the different vibration patterns of a violin string produce different musical notes, the different vibrational states of strings produce different fundamental particles, such as electrons or neutrinos, by determining their properties, like mass or charge. 

String theory is of great importance in addressing several questions in fundamental physics, and has been applied in various fields, such as the study of black holes, the early universe, and condensed matter. It has enabled major developments in pure mathematics, thanks to its complex and rigorous formulation.

ICTP Director Atish Dabholkar gives a non-technical explanation of string theory in the following video:

"We presently understand nature using two main ideas, quantum physics and general relativity," explained Juan Maldacena, a theoretical physicist at the Institute for Advanced Study who serves on the Dirac Medal selection committee. "We apply the first to describe matter, light, atoms and subatomic particles, and the second to describe spacetime, the expanding universe and gravity. String theory is a theory under construction with the goal of  providing a quantum description for spacetime; it has provided a mathematical framework for taking important steps towards this goal," said Maldacena.

Maldacena highlighted that string theory has given important insights into quantum aspects of black holes. "For example, in string theory, a black hole seen from the outside is subject to the usual rules of quantum mechanics.  Black holes were observed in the 1970s to obey some relations that were similar to those of thermodynamics. String theory demonstrated that these can be given the standard statistical interpretation in the full quantum theory. These include the explanation of the entropy in terms of the number of states, as well as the statistical origin of the Hawking radiation."

About the 2023 Dirac Medallists

Jeffrey Harvey is the Enrico Fermi Distinguished Service Professor of Physics at the University of Chicago, USA. He is an elected fellow of the American Academy of Arts and Sciences and the American Physical Society, and a member of the National Academy of Sciences. He is a member of ICTP's Scientific Council, and a former trustee at the Institute for Advanced Study in Princeton, New Jersey. He obtained a PhD from Caltech in 1981 and was a postdoc and faculty member at Princeton University before moving to the University of Chicago in 1989. 

Igor Klebanov is the Eugene Higgins Professor of Physics and the Director of the Princeton Center for Theoretical Science at Princeton University, USA. He is also the Director of the Simons Collaboration on Confinement and Quantum Cromodynamics Strings at Simons Foundation. He earned a PhD in theoretical high-energy physics at Princeton University, followed by post-doctoral research at the Stanford Linear Accelerator Center. He is a fellow of the American Academy of Arts and Sciences and a member of the National Academy of Sciences. His honors include the 2014 Tomassoni Prize from the Sapienza University of Rome. 

Stephen Shenker is the Richard Herschel Weiland Professor of Physics at Stanford University, USA. He received his PhD from Cornell University, and was a postdoctoral fellow at the University of Chicago and the Institute for Theoretical Physics in Santa Barbara. Shenker is a fellow of the American Academy of Arts and Sciences and a member of the National Academy of Sciences. From 1998 to 2008 he was Director of the Stanford Institute for Theoretical Physics. In 2010 he received the Lars Onsager Prize from the American Physical Society.

Leonard Susskind is the Felix Bloch Professor of Theoretical Physics at Stanford University, USA. He is a member of the 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, and a distinguished professor of the Korea Institute for Advanced Study. Susskind received his PhD from Cornell University.  In 1997, he was awarded the J.J. Sakurai Prize for his "pioneering contributions to hadronic string models, lattice gauge theories, quantum chromodynamics, and dynamical symmetry breaking". Susskind is widely regarded as one of the founders of string theory.

Scientific Summaries, Dirac Medallists' Contributions to String Theory

The wide-ranging contributions that this year's Dirac Medallists have made to string theory reflect the broad scope of the framework. Below is a summary of the Medallists' string theory related work.

Jeffrey Harvey (with Gross, Martinec and Rohm) discovered the heterotic string theory which naturally leads to grand unified theories that can incorporate the standard model of particle physics. His work on orbifolds (with Dixon, Vafa and Witten) provided exact world-sheet constructions of such models.  He pioneered the study of solitons and branes which has played a crucial role in the discovery and understanding of duality symmetries. His work on anomaly inflow (with Callan) has found important applications in condensed matter physics. 

In a foundational paper on the subject, Igor Klebanov (with Gubser and Polyakov) developed a precise dictionary for the holographic AdS/CFT correspondence. He constructed examples of holographic gravitational duals of confining gauge theories (with Strassler) which have had many applications to model building. 

Stephen Shenker and Leonard Susskind (with Banks and Fischler) developed the first non-perturbative formulation of M-theory and string theory by providing a limiting procedure that describes the S-matrix. 

Other influential contributions by Shenker include analysis of the phase structure of lattice gauge theories (with Fradkin), classification of unitary two-dimensional conformal field theories (with Friedan and Qiu), covariant formulation of superstring theory (with Friedan and Martinec), non-perturbative formulations of string theory in low dimensions (with Douglas), and novel connections between chaos and black holes (with Saad and Stanford). 

Susskind was among the first to recognize that dual models could be interpreted in terms of  strings. His other influential contributions include his work on Hamiltonian lattice gauge theories (with Kogut), baryogenesis and technicolor (with Dimopoulos), holography, and connections between complexity theory and black holes.

About the ICTP Dirac Medal

ICTP's Dirac Medal was first awarded in 1985. Recipients comprise the world’s top physicists, many of whom have proceeded to win Nobel Prizes, Fields Medals or Wolf Prizes. An international committee of distinguished scientists selects the winners from a list of nominated candidates. An award ceremony, during which the 2023 winners will present lectures on their work, will take place in 2024. For more details about the prize and a list of past winners, visit the web page.