The story of the 'double slit' experiment: how a piece of paper with two holes in it changed the way we understand light and the fabric of reality - and is still doing so two hundred years later. 'Through Two Doors at Once' celebrates physics at its most elegantly simple and profound. Anil Ananthaswamy travels around the world and through history, introducing readers to visionary contemporary physicists such as Roger Penrose and Leonard Susskind who are still developing this experiment, as well as revolutionaries like Albert Einstein and Niels Bohr. It is a journey readers will never forget.