Levitt rarely interviews advocates, but the founder of the Good Food Institute is different. Once an outspoken — and sometimes outlandish — animal-rights activist, Bruce has come to believe that market-driven innovation and scientific advancement are the best ways to reduce global meat consumption. Steve and Bruce talk about the negative externalities of factory-farmed meat, and why Bruce gave up antics like streaking at Buckingham Palace.

As a neuroscientist and psychology professor at Columbia University who studies the immediate and long-term effects of illicit substances, Carl Hart believes that all drugs — including heroin, methamphetamines, and cocaine — should be legalized. Steve talks to Carl about his new book, Drug Use for Grown-Ups, and Carl tells Steve why decriminalizing drugs is as American as apple pie.

Nobel laureate, best-selling author, and groundbreaking psychologist Daniel Kahneman is also a friend and former business partner of Steve’s. In discussing Danny’s new book Noise: A Flaw in Human Judgment, the two spar over inconsistencies in criminal sentencing and Danny tells Steve that “Your attitude is unusual” — no surprise there.

He’s one of the world’s leading competitors, having won four U.S. memory tournaments and holding the record for most names memorized in 15 minutes (235!). But Nelson Dellis claims he was born with an average memory and that anyone can learn his tricks. Steve gives Nelson’s techniques a shot, without much hope — and is surprised by the result.

He’s a cognitive neuroscientist and philosopher who has written five best-selling books. Sam Harris also hosts the Making Sense podcast and helps people discover meditation through his Waking Up app. Sam explains to Steve how to become spiritual as a skeptic and commit to never lying again.

He graduated high school at 14, and by 23 had several graduate degrees and was a research assistant with Stephen Hawking. He became the first chief technology officer at Microsoft (without having ever studied computer science) and then started a company focused on big questions — like how to provide the world with clean energy and how to optimize pizza-baking. Find out what makes Nathan Myhrvold’s fertile mind tick, and which of his many ideas Steve Levitt likes the most.

She spent nearly a decade as an undercover C.I.A. operative working to prevent terrorism. More recently, she hosted The Business of Drugs on Netflix. Amaryllis Fox — now Kennedy — explains why intelligence work requires empathy, and she soothes Steve’s fears about weapons of mass destruction.

Former top-ranked golfer Greg Norman and data analysis expert Mark Broadie discuss improving the golf swing, the concept of strokes gained as a metric for evaluating performance, randomized experiments revealing the benefits of taking safe shots in golf, and proposing a new scoring system that emphasizes risk-taking and memorable shots.

Khan Academy grew out of Sal Khan’s online math tutorials for his extended family. It’s now a platform used by more than 115 million people in 190 countries. So what does Khan want to do next? How about reinventing in-school learning, too? Find out why Steve nearly moved to Silicon Valley to be part of Khan's latest venture.

He’s the chief creative officer of Pixar, and the Academy Award-winning director of Soul, Inside Out, Up, and Monsters, Inc. Pete Docter and Steve talk about Pixar’s scrappy beginnings, why it costs $200 million to make an animated film, and the movie moment that changed Steve’s life.