Among other things, Noah Baumbach's very funny While We're Young is a rumination on the Long Tail, the theory that pop culture remains accessible long after it's originally created. Cornelia (Naomi Watts) and Josh (Ben Stiller) are fortysomething New York professionals who befriend the twentysomething couple Darby (Amanda Seyfried) and Jamie (Adam Driver), free spirits who represent the kind of youthful impetuousness that Cornelia and Josh long to return to, whether or not they ever had it in the first place. (The picture avoids dropping the H-Bomb ["hipster"] until the end.) Generation X-er Josh has reservations about Millennial Jamie's appropriation of 1980s pop culture (if you didn't grow up watching Tom Carvel commercials on TV, do you have the right to name your band after the ice-cream cake icon Cookie Puss because you saw it on YouTube? Discuss), and they're also both documentarians at different stages of their careers, with different ethics. As such, While We're Young also considers changing notions of authenticity in nonfiction filmmaking, though an early scene of college professor Josh showing his class Robert Flaherty's 1922 documentary Nanook of the North — in which many elements were staged or entirely fictionalized — suggests that reality is what you make it, and there's nothing new under the sun, whatever your age.