Early in his academic career, Sébastien Philippe realized the potential for his work to have a major societal impact. His research on the consequences of French nuclear weapon testing in the South Pacific led to him co-authoring the book Toxique, published in 2021.
Using hundreds of declassified French government documents, on-the-ground interviews in France and in Polynesia, and countless hours of advanced computer simulations, the book revealed that the human and environmental aftermath of the nuclear weapon tests conducted between 1966 and 1996 was much more damaging and far-reaching than had been believed based on existing government studies. Toxique received numerous awards and led French President Emmanuel Macron to publicly recognize that France owed a debt to French Polynesia, to improve victims’ compensation and open government archives.
“That experience was eye-opening. It showed me how I could draw on my technical expertise and scholarly training to generate real-world policy changes that benefit people and society,” says Philippe, who joined the UW-Madison Department of Nuclear Engineering and Engineering Physics in August 2025 as an assistant professor and an affiliate of the La Follette School of Public Affairs.
In his research, Philippe focuses on technical and policy solutions to assess, manage and reduce the risks to international peace and security associated with nuclear weapons and emerging technologies. He works across fields, partnering with social scientists and journalists, to make his research more impactful and brings his findings to policymakers and diplomats.
His work involves developing methods for monitoring nuclear weapons and verifying international agreements. He says it’s becoming increasingly challenging to get countries to allow foreign inspectors into their military facilities because such in-person inspections are seen as very intrusive and could reveal military secrets. To address this challenge, Philippe is working on new approaches to enable remote inspections of nuclear facilities and activities. These methods will harness technologies such as commercial satellite imagery, drones, radiation detection, cryptographic protocols and artificial intelligence to overcome verification challenges and enable new strategic arms control initiatives.
“Developing and integrating these technologies could help us better monitor nuclear activities from fissile materials production to verify new limits on deployed nuclear weapons,” he says.
Philippe also develops models of the effects of nuclear weapons, and he has used his models to reconstruct and analyze past nuclear weapon activities. By combining models of a radioactive mushroom cloud with models of atmospheric transport and dispersion, along with historical weather data, Philippe and his co-authors were the first to model the fallout of the 1945 Trinity test across the United States, an advance that garnered coverage by the New York Times.
Starting in fall 2025, Philippe will contribute his modeling expertise at the United Nations. Philippe and 20 other scientists were recently appointed by UN Secretary-General António Guterres to form an Independent Scientific Panel on the Effects of Nuclear War. The panel will examine the physical effects and societal consequences of nuclear war at local, regional and planetary scales from the first days to decades after and will present its findings to the UN General Assembly in 2027.
“I’m deeply honored and thankful for the opportunity to contribute to the panel’s work,” Philippe says. “It has been more than three decades since the United Nations last conducted a study on the consequences of nuclear war, and this new effort comes at a pivotal time. Amid growing geopolitical tensions, there has been an unraveling of international agreements in recent years, and the risks and threats of nuclear weapon use have also been increasing. We’re almost on the verge of a new nuclear arms race. A driving force for my work is to better inform policymakers and the public and help prevent it.”
Philippe earned his PhD in mechanical and aerospace engineering in 2018 from Princeton. Previously, he was a Stanton Nuclear Security postdoctoral fellow at the Harvard Kennedy School’s Belfer Center for Science and International Affairs, an associate faculty member in the Nuclear Knowledges Program at Sciences-Po, Paris, and a nuclear safety engineer for strategic deterrent systems in the French Ministry of Armed Forces. Prior to joining UW-Madison, Philippe was a research scholar at Princeton University’s Program on Science and Global Security in the School of Public and International Affairs.