Jaroslav Pelikan was professor of history at Yale University for four decades. He authored many books “Christian Tradition: A History of the Development of Doctrine” and “Credo.” This interview is edited and produced with music and other features in the On Being episode “Jaroslav Pelikan — The Need for Creeds.” Find more at onbeing.org.

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An astrophysicist who studies the shape of the universe, Janna Levin has also explored her science by writing a novel about two pivotal 20th-century mathematicians, Kurt Gödel and Alan Turing. Both men pushed at boundaries where mathematics presses on grand questions of meaning and purpose. Such questions, she says, help create the technologies that are now changing our sense of what it means to be human.

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Janna Levin is an astrophysicist and writer. She has contributed to an understanding of black holes, the cosmology of extra dimensions, and gravitational waves in the shape of spacetime. She is the author of “A Madman Dreams of Turing Machines,” which won the PEN/Bingham prize. This interview is edited and produced with music and other features in the On Being episode “Janna Levin — Mathematics, Purpose, and Truth.” Find more at onbeing.org.

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“There’s no question about the reality of evil, of injustice, of suffering, but at the center of this existence is a heart beating with love.”

South African Archbishop Emeritus Desmond Tutu on how his understanding of God and humanity has unfolded through the history he’s lived and shaped.

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“Let’s go back and look at our faith before it was reduced to a system, before it was reduced to a system of abstractions and beliefs. How can we rediscover our faith as a series of stories and as a series of encounters?” Brian McLaren on the evolution of Christianity and the meaning of progressive Evangelicalism.

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Brian McLaren is a leading Evangelical pastor and author of several books including “A Generous Orthodoxy,” “Why Did Jesus, Moses, the Buddha, and Mohammed Cross the Road?,” and the forthcoming “We Make the Road by Walking.” This interview is edited and produced with music and other features in the On Being episode “Brian McLaren — The Equation of Change.” Find more at onbeing.org.

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Dr. Sherwin Nuland died this week at the age of 83. He became well-known for his first book, “How We Die,” which won the National Book Award. For him, pondering death was a way of wondering at life — and the infinite variety of processes that maintain human life moment to moment. He reflects on the meaning of life by way of scrupulous and elegant detail about human physiology.

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