Giorgio Parisi

Giorgio Parisi
Parisi in 2006
Giorgio Parisi
Born	4 8, 1948
Birthplace	Rome, Italy
Nationality	Italian
Occupation	Theoretical physicist
Employer	Sapienza University of Rome
Known for	Altarelli–Parisi (DGLAP) equations, replica symmetry breaking in spin glasses, Kardar–Parisi–Zhang equation, study of complex systems
Education	Sapienza University of Rome (Laurea)
Awards	Nobel Prize in Physics (2021), Max Planck Medal (2011), Dirac Medal (1999)
Website	[Official homepage Official site]

Giorgio Parisi (born 4 August 1948) is an Italian theoretical physicist whose work spans quantum field theory, statistical mechanics, and the science of complex systems. Over a career stretching more than five decades, Parisi has made contributions that have reshaped understanding in several distinct areas of physics — from the behaviour of subatomic particles to the collective motion of flocks of starlings. He is perhaps best known for his co-development of the Altarelli–Parisi equations (also called the DGLAP equations), which describe the evolution of parton densities in quantum chromodynamics; for providing the exact solution to the Sherrington–Kirkpatrick model of spin glasses through his method of replica symmetry breaking; and for his role in formulating the Kardar–Parisi–Zhang equation, which describes the dynamic scaling of growing interfaces. In 2021, Parisi was awarded the Nobel Prize in Physics jointly with Klaus Hasselmann and Syukuro Manabe "for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales." He became the sixth Italian scientist to receive the Nobel Prize in Physics. Parisi has served as president of the Accademia dei Lincei, one of the oldest scientific academies in the world, and has held academic positions at institutions including Sapienza University of Rome, Columbia University, the Institut des Hautes Études Scientifiques, and the University of Rome Tor Vergata.

Early Life

Giorgio Parisi was born on 4 August 1948 in Rome, Italy. In interviews, Parisi has recalled that his curiosity about the natural world began at a young age, with an early fascination for numbers and reading forming the foundation of his later scientific interests. He grew up in Rome during the post-war period, a time when Italian scientific institutions were rebuilding and expanding their research capacity. The intellectual environment of Rome, with its concentration of universities and research centres, provided a fertile setting for Parisi's developing interest in physics and mathematics.

Parisi has spoken about the importance of his early academic environment in shaping his approach to scientific problems. In a 2022 interview with the Nobel Prize organization, he reflected on the role that self-confidence played in his development as a young scientist, noting that "self-confidence is an important ingredient" in pursuing difficult research questions. He also mentioned his love of reading and dancing as lasting personal interests that complemented his scientific pursuits.

His formative years coincided with a period of significant development in Italian theoretical physics. The generation of physicists who preceded him — building on the legacy of Enrico Fermi and the Italian school of physics — created an academic culture that valued both mathematical rigour and creative problem-solving. This tradition would deeply influence Parisi's own approach to research, which has been characterised by a willingness to move between different subfields and to apply methods from one area of physics to seemingly unrelated problems.

Education

Parisi pursued his undergraduate studies at the Sapienza University of Rome, where he earned his Laurea (the Italian equivalent of a master's degree). At Sapienza, he studied under Nicola Cabibbo, the distinguished Italian physicist known for his work on the weak interaction and the Cabibbo angle in particle physics. Cabibbo served as Parisi's academic advisor and was a formative influence on his scientific development. The academic environment at Sapienza during this period was intellectually stimulating, with a number of leading physicists working on problems in particle physics and field theory. Parisi's training under Cabibbo gave him a strong foundation in quantum field theory, which would become one of the central pillars of his research career. The mentorship of Cabibbo also appears to have instilled in Parisi an appreciation for the broader implications of theoretical work, encouraging him to think beyond the narrow confines of any single subfield.

Career

Early Research and Quantum Field Theory

Parisi began his research career in the field of quantum field theory and particle physics, areas in which he made several significant early contributions. Working with Guido Altarelli, he developed what became known as the Altarelli–Parisi equations (also referred to as the DGLAP equations, after Dokshitzer, Gribov, Lipatov, Altarelli, and Parisi). These equations describe how the parton density functions — the probability distributions of quarks and gluons inside hadrons — evolve as a function of the energy scale at which they are probed. The Altarelli–Parisi equations became a foundational tool in quantum chromodynamics (QCD), the theory of the strong force, and are essential for interpreting experimental results from particle colliders.

This work was carried out during a period of rapid development in QCD during the 1970s, and it placed Parisi at the forefront of theoretical particle physics. The equations have been used extensively in the analysis of data from high-energy experiments, including those at CERN's Large Hadron Collider, and remain a standard part of the theoretical framework used by experimentalists and theorists alike.

Parisi also made contributions to the theory of stochastic quantization, developing what became known as the Parisi–Sourlas stochastic quantization approach. This work explored deep connections between statistical mechanics and quantum field theory, providing new mathematical tools for understanding the behaviour of quantum fields.

Spin Glasses and Replica Symmetry Breaking

Perhaps Parisi's most celebrated contribution to physics is his solution of the Sherrington–Kirkpatrick (SK) model of spin glasses. Spin glasses are disordered magnetic systems in which the interactions between magnetic moments (spins) are randomly distributed, leading to frustration — a condition in which not all interactions can be simultaneously satisfied. The SK model, proposed in 1975, was a mean-field approximation designed to capture the essential physics of spin glasses, but solving it proved extremely difficult.

Parisi's breakthrough came through the development of the replica symmetry breaking (RSB) scheme. The replica method involves introducing multiple copies (replicas) of the system and performing calculations that exploit the mathematical structure of these copies. Earlier attempts using the replica method had assumed that the replicas were symmetric — that is, interchangeable. Parisi showed that this assumption was incorrect for the spin glass phase and proposed a hierarchical scheme of replica symmetry breaking that captured the correct physics of the system.

The Parisi solution revealed that the spin glass phase possesses an extraordinarily complex energy landscape, with a vast number of metastable states organized in an ultrametric hierarchical structure. This insight had implications far beyond condensed matter physics. The mathematical framework of replica symmetry breaking found applications in computer science (particularly in optimization problems and neural networks), biology, and information theory. The concept of a complex energy landscape with many competing states became a powerful metaphor and analytical tool for understanding systems as diverse as protein folding, combinatorial optimization, and machine learning.

The mathematical rigour of Parisi's solution was later confirmed through the work of mathematicians Francesco Guerra and Michel Talagrand, the latter of whom received the Abel Prize in part for his proof of the Parisi formula. The Nobel committee specifically cited Parisi's work on spin glasses as the primary basis for his 2021 award, describing it as "the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales."

Complex Systems and the Kardar–Parisi–Zhang Equation

Parisi's interests extended well beyond spin glasses into the broader science of complex systems. In 1986, together with Mehran Kardar and Yi-Cheng Zhang, he formulated the Kardar–Parisi–Zhang (KPZ) equation, which describes the dynamic scaling behaviour of growing interfaces. The KPZ equation captures how surfaces roughen over time when subjected to random fluctuations and nonlinear growth effects. It applies to a wide range of physical phenomena, including the growth of bacterial colonies, the spreading of fire fronts, and the deposition of thin films.

The KPZ equation became one of the central objects of study in non-equilibrium statistical mechanics. Its universality — the fact that it describes the behaviour of many different physical systems — made it a powerful theoretical tool. The KPZ universality class, defined by the scaling exponents predicted by the equation, has been confirmed in numerous experimental and computational studies.

Flocking Behaviour and Biological Physics

In a departure from traditional condensed matter physics, Parisi turned his attention to the study of collective animal behaviour, specifically the flocking patterns of starlings over Rome. Together with collaborators, he studied the large-scale coordinated movements of thousands of starlings forming intricate aerial patterns known as murmurations. This work combined field observations, high-speed photography, and statistical physics methods to understand how individual birds coordinate their movements to produce coherent group behaviour without a central leader or organizer.

Parisi and his team discovered that the correlations between the movements of individual birds extend across the entire flock, regardless of its size — a phenomenon known as scale-free correlation. This finding drew direct parallels to critical phenomena in statistical physics, where correlations between components of a system become long-ranged near a phase transition. The work demonstrated that the same mathematical frameworks developed for understanding physical systems could be applied to biological collective behaviour, establishing new connections between physics and biology.

In a 2023 interview with The Guardian, Parisi discussed his approach to explaining complex systems in accessible terms, using analogies of birds and bus rides to convey the principles underlying his branch of science. He expressed concern about a "lack of trust in science" in contemporary society and argued for the importance of demonstrating how scientific research is conducted.

Academic Positions and Leadership

Throughout his career, Parisi held positions at several leading research institutions. His primary academic home was the Sapienza University of Rome, where he served as a professor of theoretical physics. He also held positions at Columbia University in New York, the Institut des Hautes Études Scientifiques (IHES) in France, and the University of Rome Tor Vergata.

In June 2018, Parisi was elected president of the Accademia dei Lincei, the prestigious Italian scientific academy founded in 1603. The Accademia dei Lincei is one of the oldest scientific institutions in the world, counting Galileo Galilei among its early members. Parisi's election to the presidency reflected both his standing in the Italian scientific community and his broader engagement with science policy and public communication of science.

Parisi is also a member of the French Academy of Sciences and a member of the United States National Academy of Sciences.

Recent Activities

In May 2025, it was reported that Parisi had taken up a senior position in complexity sciences at a university in eastern China, continuing his international engagement with the field of complex systems research.

Parisi has also engaged with public discourse on the future of work and technology. In 2025, he was reported to have expressed views aligned with those of Elon Musk regarding the potential for work as traditionally understood to be fundamentally transformed by technological change, suggesting that future generations may have more free time but fewer regular employment opportunities.

Personal Life

Parisi has described himself as a person with wide-ranging interests beyond physics. In his 2022 interview with the Nobel Prize organization, he spoke of his love of reading and dancing as lifelong pursuits. He has also been involved in public advocacy for science funding and science education in Italy, using his platform as a Nobel laureate and president of the Accademia dei Lincei to address what he perceives as insufficient investment in scientific research.

In his public appearances, Parisi has expressed concern about the public understanding of science. Speaking to The Guardian in 2023, he argued that there is a "lack of trust in science" and that scientists bear a responsibility to show the public "how it's done" — that is, to make the process of scientific inquiry transparent and accessible. He has written popular science works aimed at conveying the principles of complex systems to a general audience, including a book that uses the metaphor of starling murmurations to explain the science of complexity.

Parisi resides in Rome, the city where he was born and where he has spent the majority of his career.

Recognition

Giorgio Parisi has received numerous awards and honours throughout his career, reflecting the breadth and depth of his contributions to physics.

His most prominent recognition is the 2021 Nobel Prize in Physics, which he shared with Syukuro Manabe and Klaus Hasselmann. Parisi received half of the prize, with the other half shared between Manabe and Hasselmann. The Nobel committee cited his work "for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales."

Other major awards include:

• Dirac Medal (1999), awarded by the International Centre for Theoretical Physics (ICTP) for his contributions to theoretical physics.
• Boltzmann Medal, awarded by the Commission on Statistical Physics of the International Union of Pure and Applied Physics (IUPAP).
• Max Planck Medal (2011), awarded by the German Physical Society (DPG), the highest honour for theoretical physics in Germany.
• Dannie Heineman Prize for Mathematical Physics (2005), awarded by the American Physical Society.
• Lars Onsager Prize (2016), awarded by the American Physical Society for outstanding research in statistical physics.
• Enrico Fermi Award, given by the Italian Physical Society.
• Lagrange Prize, awarded by the CRT Foundation.
• Nature Award for Mentoring in Science (Italy).

Parisi has also been recognized for his role as a mentor. The Nature Award for Mentoring in Science acknowledged his contributions to nurturing the next generation of physicists in Italy.

Legacy

Giorgio Parisi's legacy in theoretical physics is multifaceted. His work has connected fields that were previously considered separate, demonstrating that the mathematical tools of statistical mechanics could illuminate problems ranging from particle physics to biology.

The Altarelli–Parisi equations remain a standard tool in high-energy physics, used daily by researchers analysing collider data. The equations are incorporated into the computational frameworks that underpin modern experimental particle physics, making them one of Parisi's most widely applied contributions.

His solution of the Sherrington–Kirkpatrick model through replica symmetry breaking opened an entirely new chapter in the study of disordered systems. The methods he developed have been adopted across disciplines. In computer science, concepts from spin glass theory have influenced the study of optimization problems, constraint satisfaction, and neural networks. The connection between the physics of disorder and computational complexity has become an active area of research, with Parisi's work serving as a foundational reference.

The KPZ equation, formulated with Kardar and Zhang, has become one of the defining equations of non-equilibrium statistical mechanics. It established a universality class that encompasses a wide variety of growth and interface phenomena, and research on the KPZ equation and its extensions continues to generate new results in both physics and mathematics.

Parisi's work on flocking behaviour demonstrated that the methods of statistical physics could be applied to biological systems, contributing to the growing field of biological physics. His studies of starling murmurations attracted public attention and helped communicate the idea that physics can address questions about the natural world that extend well beyond the traditional boundaries of the discipline.

A 2021 article in Nature examining Parisi's early work emphasized the importance of the academic environment at Sapienza University in fostering his research, noting that the tradition of Italian theoretical physics — with its emphasis on both technical skill and conceptual imagination — was instrumental in enabling his contributions.

Parisi's involvement with the Simons Foundation's collaboration on "Cracking the Glass Problem" further attests to the ongoing relevance of his work to contemporary research.

As of 2025, Parisi continues to be active in research and public engagement, having taken a position in complexity sciences in China and contributing to public discussions about the societal implications of scientific and technological progress.