In mid-1912, Einstein realizes that the force of gravity can be described as the curvature of space and time. Together with Marcel Grossmann, a friend and mathematician, he attempts to develop a new theory of gravity on this basis. Einstein\u2019s calculations are documented in his Zurich notebook. Einstein alternates between more mathematical and more physical approaches. Ultimately he hits on the correct approach, but then rejects it because it does not correspond to his physical expectations.