Austrian physicist Erwin Schrödinger is considered one of the founders of quantum mechanics. But he’s mostly known for something he never did. In a now famous thought experiment, he imagined sealing a cat inside a box with a quantum device that had a 50% chance of killing the cat within the next hour. At the end of that hour, he asked, what is the state of the cat? According to quantum physics, at the instant before the box is opened, the cat is both alive and dead at the same time. It’s only when you open the box that you see the cat in one state or the other. 

But in his new book, Something Deeply Hidden quantum physicist Sean Carroll offers a different ending for Schrödinger’s imaginary cat. Carroll ascribes to the “many worlds” interpretation of quantum mechanics, originally proposed by American physicist Hugh Everett in the 1950s. According to Everett, when you look inside the box you are also in two states at once. Now there are two worlds—one in which you saw the cat alive, and one in which you saw the cat dead.

If just thinking about this makes your head hurt, you’re not alone. Carroll joins Ira to talk about the “many worlds” interpretation of quantum mechanics, and why he thinks not enough physicists are taking on the challenge of trying to understand it.

Further Reading:

• Learn more about where quantum probability comes from in this article from Quanta Magazine.
• Find out more about how even physicists struggle to understand quantum mechanics in a column from New York Times.
• Get a copy of the book here