The impossible is possible. We understand the concept in theory; films like “Free Solo” remind us of the thrilling truth. The movie documents climber Alex Honnold’s attempt to scale Yosemite’s iconic El Capitan cliff face — more than 3,000 feet of virtually perpendicular rock — without ropes, clamps, or nets, using only his claw-like hands, Spiderman feet, and a reservoir of willpower possibly unmatched in human history. “Free Solo” isn’t easy to watch. Filmed by professional climbers using drones and telescoping lenses, the viewer feels like she’s there on the wall, one meager slip away from oblivion, clinging to life by a fingernail. Seldom has watching a movie made us feel so alive.