Physicist Shevek leaves his anarchist homeworld of Anarres—a society of austere collective equality—to visit its twin capitalist planet Urras, and the novel alternates between his life on both worlds as he seeks to complete a unified theory of time that neither world can produce alone. A rigorous and searching novel that takes both anarchism and capitalism seriously as systems with genuine costs and benefits. One of science fiction's most politically and philosophically substantial works.