Hany Farid is an expert on photo fakery and develops tools for detecting whether and how much pictures have been ginned up by, say, advertisers hawking beauty products. He's testified about the veracity of photos in court cases, uncovered audacious forgeries, and helped authenticate some iconic images. We had a fascinating conversation about truth and deception in the age of Photoshop: the ways digital retouching has altered our relation to photography, sowed confusion in the legal system, altered our body images, and sparked a race between the technologies of authentication and tools for photo manipulation.

First broadcast in Jan. 2009: physicist and master explainer Brian Greene on the space-, time-, and mind-bending properties of black holes. This originally aired as part 1 of a black hole double-header. Part 2 was with the physicist Leonard Susskind, also available as a podcast.

First broadcast in Jan. 2009: physicist and master explainer Brian Greene on the space-, time-, and mind-bending properties of black holes. This originally aired as part 1 of a black hole double-header. Part 2 was with the physicist Leonard Susskind, also available as a podcast.

The Pulitzer-winning writer Tony Horwitz has a new book out about anti-slavery crusader John Brown (Midnight Rising: John Brown and the Raid that Sparked the Civil War), and we consider the challenge that Brown still poses for American history. Was Brown right to spill blood fighting slavery? When is violent resistance to manifest inhumanity justified? I talk history and morality with Tony Horwitz, with my friend and John Brown buff Andrea Monroe, and with ethicist Peter Singer.

The Pulitzer-winning writer Tony Horwitz has a new book out about anti-slavery crusader John Brown (Midnight Rising: John Brown and the Raid that Sparked the Civil War), and we consider the challenge that Brown still poses for American history. Was Brown right to spill blood fighting slavery? When is violent resistance to manifest inhumanity justified? I talk history and morality with Tony Horwitz, with my friend and John Brown buff Andrea Monroe, and with ethicist Peter Singer.

Peter Singer may be the world's best-known ethicist. He's regarded as the intellectual father of the animal liberation movement and has staked out prominent positions on euthanasia, abortion, the use of military force and economic inequality. We talked about those and other sticky moral questions, as well as Peter's brand of utilitarianism, which aims to provide a single logical framework for all ethical decision making. Originally broadcast in 2006.

Peter Singer may be the world's best-known ethicist. He's regarded as the intellectual father of the animal liberation movement and has staked out prominent positions on euthanasia, abortion, the use of military force and economic inequality. We talked about those and other sticky moral questions, as well as Peter's brand of utilitarianism, which aims to provide a single logical framework for all ethical decision making. Originally broadcast in 2006.

Steven Pinker, celebrated for his books on language and the workings of the mind, ventures into big history with his latest volume, "The Better Angels of Our Nature: Why Violence Has Declined." He unloads a truckload of evidence to argue that humans have been getting more peaceful, more cooperative and less murderous, on scales large and small, for quite some time. Among the reasons: civilization really has made us more civil. That might seem a surprising conclusion for a card-carrying evolutionary psychologist, but Pinker hasn't gone all liberal artsy on us. Historicity has a role to play, he says, but so do biology and game theory.

Steven Pinker, celebrated for his books on language and the workings of the mind, ventures into big history with his latest volume, "The Better Angels of Our Nature: Why Violence Has Declined." He unloads a truckload of evidence to argue that humans have been getting more peaceful, more cooperative and less murderous, on scales large and small, for quite some time. Among the reasons: civilization really has made us more civil. That might seem a surprising conclusion for a card-carrying evolutionary psychologist, but Pinker hasn't gone all liberal artsy on us. Historicity has a role to play, he says, but so do biology and game theory.

Errol Morris's passion for sleuthing dates back at least to his days as a private detective and runs through his work as a documentary filmmaker in movies like "The Thin Blue Line" and his most recent, "Tabloid." In his new book, "Believing is Seeing," he turns his magnifying glass on photography. He and I discussed (and occasionally debated) the veridical nature of photography, the impact of digital retouching and the truth value of his own films. Then, in the second half of the show, an excerpt from my 2009 interview with documentarist Jonathan Stack on his film Iron Ladies of Liberia. It's about the presidential administration of Liberia's Ellen Johnson Sirleaf, who shared in this year's Nobel Peace Prize.