When the planes hit the Twin Towers on the morning of September 11, 2001, Facebook hadn’t been invented, nor had Twitter, or What’s App, or the so-called “dark web.” Fewer than half of Americans had cell phones, and less than 9 percent of people around the world were online. Now, 15 years later, the internet—and its ubiquitous social networks—reach to every corner of the globe, changing the way terrorists communicate and plan, and also how terrorist plots can be unearthed, monitored, and stopped. How can the power of big data be harnessed to combat terrorism, and what will it take to get us there? Physicist Neil Johnson explains in this riveting and timely ’Cane Talk.