‘The Social Network’’ opens with a scene — already justly celebrated — in which a college-age couple sits in a darkened Cambridge restaurant and discusses their relationship. It’s not going well for the guy, a weedy, focused sort named Mark Zuckerberg (Jesse Eisenberg) who talks as if he’s trying to break the sound barrier and assumes his girlfriend, Erica (Rooney Mara), will keep up. She doesn’t, and after a while her eyes go dead and she’s not his girlfriend anymore.
