By Amanda Gefter ALBERT EINSTEIN had many passions beyond his physics. He spent much time thinking, writing and speaking on nuclear disarmament, human rights, democracy, education reform, even reducing the conflict between Arabs and Jews. Less well known, however, are his contributions to philosophy. Einstein thought deeply about the nature of knowledge and of reality, about scientific theories and their relation to the world. He often wondered how the hidden, unseen world that his equations described was possible. How is it that the mind can venture into realms of knowledge divorced from our everyday experiences?