Human Flow is not a documentary by a journalist, or a traditional activist. If it were, it might be 25 hours long, with abundant background on the history of the world’s current refugee disasters and a guidebook on how these terrible problems—the worst since the end of World War II, with 65 million people displaced—can be addressed. Instead, Human Flow is a film by an artist, albeit one famous for his dissidence against his country’s government. This is Ai Weiwei, whose art-world celebrity has only been enhanced by his battles with Chinese officials (he’s now based in Berlin). With Human Flow, Ai does something that has recently ignited debate in documentary circles: He takes a terrible subject and makes it beautiful.