When companies tore down office walls in the 2010s, the pitch was collaboration: more spontaneous conversation, faster idea sharing, a flatter culture. Then Harvard researchers Ethan Bernstein and Stephen Turban actually measured it. Tracking two Fortune 500 headquarters as they converted to open plan, they found face-to-face interaction fell by roughly 70%. Instead of talking more, employees put in headphones, opened a messaging app, and found a way to disappear.