With the advent of modern physics in the twentieth century changing the world radically, both Einstein and Oppenheimer grappled with metaphysics that can provide an ethical framework for human actions. Einstein turned to the philosophical works of Spinoza and Schopenhauer, along with an attachment to the European enlightenment heritage. Oppenheimer became engrossed in the eastern philosophy, with particular interest in the Bhagavad Gita, and an affinity with the American philosophical tradition of pragmatism.