Accusations of serial plagiarism against one of France’s best-known scientists have shaken the country’s scientific community and the media. Physicist and philosopher Étienne Klein, a gifted popularizer of science, stands accused of appropriating passages from other scientists, philosophers, and famous writers. Some of the authors are long dead, such as novelists Émile Zola and Stefan Zweig. Klein has admitted making mistakes but says he hasn’t knowingly committed plagiarism.

Klein is a researcher at the Alternative Energies and Atomic Energy Commission, where he leads a lab for material sciences in Saclay, France. In September, he was also named president of the Institute of High Studies for Science and Technology (IHEST), which seeks to foster debate about the role of science in society and to buttress public trust in the scientific enterprise. Klein is the author of many popular science books, a columnist, and the host of a radio show every Saturday on France Culture. He has won a long list of awards. “The French adore him,” the weekly journal L’Express wrote in a 30 November story.

But many passages from Klein’s recent Einstein biography Le pays qu’habitait Albert Einstein appear to have been lifted almost verbatim, without attribution or quotation marks, from other sources, L’Express reported. “Strangely, it’s the most personal, most literary passages, those where Étienne Klein puts himself on the scene, the ones that bring the reader happiness, that often don’t come from his own pen,” L’Express wrote.

The journal cited other examples as well. A column about the “art of the free kick,” published during last summer’s European soccer championship in the newspaper La Croix, seems to have borrowed heavily from a 1986 book by physicists Gilles Cohen-Tannoudji and Michel Spiro. (The monthly magazine Sciences et Avenir put the two passages side by side to show the resemblance.)

Klein, who did not respond to a request for comment today from Science Insider, defended himself in a response posted on his own website and at Le Monde newspaper on Monday. He didn’t deny the similarities but said physicists don’t always cite each other when they discuss well-established science: “When one writes that Earth revolves around the sun, one doesn’t use quotation marks or cite the names of Copernicus, Galileo, and [Léon] Foucault.”

He noted that Cohen-Tannoudji did not consider Klein’s reuse of his ideas in La Croix as plagiarism, and said he had used some short quotes from his favorite writers in the Einstein book without attribution because he had “internalized” them after “reading and rereading them for decades.” As to longer passages from three other authors, however, he acknowledged they were “mistakes that I regret.”

“To write this book, I have taken ample notes, gathered in numerous files, so much so that I may have lost certain sources or gotten mixed up,” Klein wrote.

The response only made L’Express dig deeper. In a story published today, the magazine produced seven more instances of alleged plagiarism. Perhaps the most ironic example comes from Klein’s 2013 book about Italian theoretical physicist Ettore Majorana. In the very first lines, Klein reflected on the art of writing itself, which he compared to “an illness” or even “madness.” The passage comes almost verbatim from a 1995 book by philosopher Clément Rosset, according to L’Express.

Klein has not yet responded to today’s charges; neither did IHEST. In a story published earlier by Sciences et Avenir, Klein said that he has no plans to resign from his prestigious post at the institute.