This week Iran agreed to an outline of a nuclear deal, which the U.S. says would shift the amount of “breakout time” to a nuclear weapon to a full year, up from just several months today. But behind that number lies the complexity of nuclear physics: uranium stockpiles, enrichment rates, number of centrifuges. You’d need a nuclear physicist to figure it all out—which is why energy secretary Ernest Moniz has been at the negotiating table alongside Secretary of State John Kerry. Moniz joins us here to talk about the science behind the diplomacy.