If no one’s around to sweep the sidewalks, weed Central Park, or turn the power grid on, nature would move in—and quick. Mold starts to form on the walls,” says architect Jana Horvat of the University of Zagreb, who studies building decay. Image: Getty Images Bob KristFrom Year 1 to Year 10: Decay Sets InIn a year without people, many of New York’s buildings would start to deteriorate. By Year 50: A One-of-a-Kind EcosystemIn the decades since humans abandoned New York, a “novel ecosystem” would emerge, says Tredici. Even without humans, pieces of New York would endure—a fragile legacy for the future to either uncover or forget.