The “Fama–French model” is a Nobel laureate-designed tool for predicting the stock market. It guides hundreds of billions in investments. The problem? Its numbers keep shifting. For this Money Talks, Felix Salmon chats with Planet Money host Mary Childs about her deep dive for Bloomberg into finance mathematics. They question the nature of investing, markets, and reality itself. If you enjoy this show, please consider signing up for Slate Plus. Slate Plus members get an ad-free experience across the network and an additional segment of our regular show every week. You’ll also be supporting the work we do here on Slate Money. Sign up now at slate.com/moneyplus to help support our work. Podcast production by Jared Downing and Cheyna Roth. Learn more about your ad choices. Visit megaphone.fm/adchoices