“Oppenheimer” centers around the legacy of J. Robert Oppenheimer (Murphy), who is credited as the inventor of the atomic bomb. Based on the biographical novel “American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer,” the film follows the physicist as he works alongside a team of government scientists to develop nuclear weapons in the early 1940s.It looks at the key players of the Manhattan Project, as portrayed by a star-studded cast including Cillian Murphy, Florence Pugh, Emily Blunt, Robert Downey Jr., Matt Damon, Leslie Groves Jr. and Tom Conti, who appears briefly as a somber looking Albert Einstein.