A physicist’s fresh look at the ‘prisoner’s dilemma’ reveals hope for cooperation
A Rutgers-led study offers a hopeful twist on a classic game theory problem
The “prisoner’s dilemma” is one of the most famous ideas in game theory. It even appeared in the Oscar-winning film A Beautiful Mind, which told the story of mathematician John Nash.
For decades, this game has been used to explain why selfishness often beats cooperation.
In the prisoner’s dilemma, two players can either cooperate or cheat. Cheating always seems to pay off more, so both players end up cheating and losing out even though working together would have given them the biggest reward.
Scientists have long used this idea to understand everything from microbes sharing resources to human societies negotiating peace. The takeaway message? In the evolutionary race, cheaters win.
A new study led by Rutgers physicist Alexandre Morozov turns that assumption upside down. His research, published in the Proceedings of the National Academy of Sciences, shows that cooperation can emerge naturally without special rules or genetic ties.
“The prisoner’s dilemma has told us for 75 years that cheaters always take over in the long run,” said Morozov, a professor in the Department of Physics and Astronomy at the Rutgers School of Arts and Sciences. “The end point of any society, based on this, is complete breakdown. But that’s not at all the case. Even in a very simple scenario, cheaters don’t always win. In fact, it’s easier for cooperation to rise.”
Morozov and his collaborator, Alexander Feigel of the Hebrew University of Jerusalem, discovered that the key to cooperation is keeping track of your opponents. If individuals can recognize others, cooperation starts to flourish.
“All you have to do is remember who you interacted with and react in the same way,” said Morozov, who is also director of the Rutgers Center for Quantitative Biology. “That’s enough for cooperation to emerge by itself in many scenarios. It’s what physicists call an emergent property.”
This finding is striking because previous theories required extra conditions such as helping relatives or sticking with your group. Morozov’s model works without those assumptions. It suggests that, even in simple organisms such as microbes or insects, cooperation can evolve if these organisms are able to tell each other apart, perhaps through chemical signals or physical traits.
Game theory underpins this research. A game, in the mathematical sense, is a situation in which players make rational decisions according to defined rules to receive some sort of payoff. Game theory is the branch of mathematics that studies these interactions and helps explain why strategies such as cooperation or cheating emerge in nature and society.
Cooperation is the foundation of complex life, Morozov said. Without it, cells wouldn’t form tissues and societies wouldn’t exist. Yet Darwinian evolution seems to favor selfishness. Morozov’s work offers a new way of understanding how life overcame that hurdle.
“Evolution likes shaping things over long periods of time if it has some material to work with,” Morozov said. “If cooperation always dies off, there’s nothing to evolve. But if there’s a chance, evolution will refine it and make it more stable.”
The implications go beyond biology. Morozov said that his model shows periods of stability interrupted by upheaval, patterns that might sound familiar in human history.
“Cheaters don’t always win,” he said. “Cooperation can persist, and it does persist in many systems scientists look at, such as multi-cellular organisms in which individual cells have to cooperate to survive.”
Morozov started his career as a physicist focusing on protein folding and statistical mechanics, which deals with predicting the behavior of complex systems. Later, he realized those same mathematical tools could help explain how living things evolve. For years, he has explored evolutionary dynamics, building models that show how traits spread in populations under evolutionary forces such as mutation and natural selection.
That experience, Morozov said, gave him the foundation for his latest work. When he encountered game theory during a sabbatical at the Hebrew University, he saw a connection. The same methods he used to study molecules and genes, he realized, could also reveal why cooperation, rather than selfishness, sometimes wins in the prisoner’s dilemma.
The team used mathematical models and computer simulations, including populations of neural networks playing repeated games. A neural network is a computer system modeled after the human brain that teaches patterns and makes predictions by processing information through layers of interconnected nodes.
The scientists also produced a new theoretical result, a generalization of a classic evolutionary principle called Fisher’s fundamental theorem of natural selection.
Morozov said he hopes the work will spark new research on how cooperation evolves in nature and maybe even inspire fresh thinking about cooperation in human societies.
Explore more of the ways Rutgers research is shaping the future.
Journal
Proceedings of the National Academy of Sciences
Article Title
Emergence of cooperation due to opponent-specific responses in Prisoner's Dilemma
Article Publication Date
22-May-2026
Busseiron and the formation of a discipline in Japanese physics
University of Chicago Press Journals
The middle of the twentieth century was a period of significant scientific advancement, particularly in the realm of physics. Within this rapidly changing landscape, academic disciplines emerged and evolved to keep pace with scientific discoveries. The new subdiscipline of solid-state physics gained prominence in the United States, but it was later subsumed by the broader category of condensed matter physics. In Japan, however, physics research since the 1940s has included a unique branch called Busseiron—a discipline concerning the study of matter that has no direct English equivalent but that has remained in use nonetheless. A new article by Hiroto Kono in Isis: A Journal of the History of Science Society explores the historical formation of Busseiron and how it was shaped by its specific national context.
The article presents a history of Busseiron as an evolving concept: the word Busseiron was initially used in a pedagogical context in the late nineteenth and early twentieth centuries, but by World War II, the landscape of Japanese physics had expanded greatly and Busseiron came to describe a cluster of research areas. These included magnetism, metal physics, and the emerging field of quantum theory. In a 1942 article, a physicist named Hidetosi Takahasi positioned Busseiron as a counterpart to Soryûshiron (the theory of elementary particles)—a distinction that would continue to shape discourse around the discipline and its boundaries.
Kono describes how Busseiron became more organized throughout the 1940s, with the establishment of several colloquia and a new journal (Busseiron Kenkyû). The field continued to broaden in scope, incorporating new topics such as polymers and low temperatures. This expansion, in part, reflected scientific advances related to wartime technologies. In contrast to the division between academia and engineering that characterized the physics landscape in the United States, Japanese physicists saw Busseiron as a field that bridged the gap between these two spheres.
In the article, Kono surveys various textbooks and other publications from this period that mention Busseiron and finds that a diversity of topics fell within the scope of the field. In fact, by the late 1940s the term Busseiron had become an “umbrella discipline” that incorporated a variety of new and existing topics related to matter. Despite a lack of consensus on what exactly should be included, the dichotomy between Busseiron and Soryûshiron (sometimes characterized as a rivalry) was widely referenced in attempts to classify the field. By the end of the 1940s, the founders of the original Busseiron discipline attempted to corral the expansion of the term by replacing it with the label “chemical physics”—a field growing in popularity overseas. This attempt was largely a failure, as Busseiron already had a foothold in the scientific community and the term was widely accepted. Its definition expanded even further by 1950, with a scope encompassing “almost any research that dealt with matter.”
Kono describes various debates over Busseiron’s structure that arose within the Japanese scientific community in the 1950s and argues that the lack of consistency in defining the term was partly what allowed it to endure into the present day. The name had firmly lodged itself in physicists’ nomenclature and the contentious discussion around it only served to further legitimize its status. As Kono states in the article’s conclusion, “names matter and deserve greater attention in the disciplinary and transnational histories of science.” By tracing discourse around the name Busseiron, this article explores how the Japanese cultural context influenced the genesis of a unique field.
Since its inception in 1912, Isis has featured scholarly articles, research notes, and commentary on the history of science, medicine, and technology and their cultural influences. Review essays and book reviews on new contributions to the discipline are also included. An official publication of the History of Science Society, Isis is the oldest English-language journal in the field.
Founded in 1924, the History of Science Society is the world’s largest society dedicated to understanding science, technology, medicine, and their interactions with society in historical context.
Journal
Isis
Article Title
Coining a Discipline: The Formation and Perpetuation of a Japanese Branch of Physics of Matter
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