India, Aug. 17 -- In Christopher Nolan's The Odyssey, a king returns from a long war to his hometown Ithaca to find his palace consumed by free-riders. Along the way, gods and monsters demand their price. Columbia University professor Adam Tooze quote-tweeted Nolan's film as a commentary on a world "where rules have collapsed." It is a powerful reading. When reciprocity weakens, cooperation becomes fragile. Enforcement eventually returns to its most primitive form- force.

The story is three thousand years old. Yet Nolan makes it feel contemporary. At its centre is Zeus's law-the film's condensed version of xenia, the ancient Greek obligation of hospitality between host and guest. Treat the stranger as you would wish to be treated. A trav...