What separates good from bad troublemakers? Productive provocateurs from mere contrarians, bullshit artists, attention-seekers? This is the personalized equivalent of philosophy’s demarcation problem, which involves telling genuine from pseudo-science. Lee Smolin, a 59-year-old physicist at the Perimeter Institute in Canada, has always struck me as a good–even necessary–troublemaker. I first interviewed him in the early 1990s about loop quantum gravity. Conceived with Abhay Ashtekar, Carlo Rovelli and others, loop quantum gravity is an attempt to solve an abiding conundrum, the incompatibility of quantum mechanics with general relativity, Einstein’s theory of gravity. Smolin has contributed to string theory, a more popular quantum-gravity model, but in his controversial 2006 book The Trouble with Physics, he deplored the dominance of string theory and argued that physics needs more diverse, creative thinking. Smolin has presented creative ideas in physics and cosmology in four other books, including, most recently, The Singular Universe, which he co-authored. In his writings, Smolin invokes the philosophical, social and historical dimensions of physics in a way that seems both old-fashioned and fresh. I’ve recently posted Q&As with physicists George Ellis, Carlo Rovelli, Edward Witten, Garrett Lisi and Paul Steinhardt, and their remarks got me wondering what Smolin is up to. At the end of our email exchange, he urges young scientists to seek “that hot zone where you are in equal parts a rebel and a conservative.” Smolin lives in that zone.

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