Exquisite vintage pearl-finish 8 x 10 photo of Einstein at the blackboard taken by a press photographer at Cal Tech’s Mount Wilson Observatory in Pasadena in 1931, signed in fountain pen, "A. Einstein, 1933." Einstein had lectured on Unified Field Theory to a small group of scientists at the Observatory, and written on the blackboard is one of the fundamental equations of General Relativity theory: Rik = 0, the equation for a vanishing Ricci Curvature Tensor. In fine condition.
The Ricci Curvature Tensor measures the deviation of a curved spacetime from a Euclidean framework, and it is a concept of central importance for both General Relativity and Unified Field Theory. When the Ricci Curvature Tensor is equal to a zero value, the equation betokens a spacetime that is stable and static (neither expanding nor contracting).
“Rik = 0” has been called 'Einstein’s favorite equation' and Einstein spent the second half of his life and career attempting to fine tune the precise value of this equation. As a result of his work on Unified Field Theory, Einstein was in fact considering possible modification to this equation at the time of his Wilson Observatory lecture. And given that the lecture was attended by Edwin Hubble, the scientist who had recently demonstrated that the universe was expanding, it is entirely likely that Einstein was discussing the equation’s future validity in context of Hubble’s expanding universe—hence the probable reason for the question mark (“?”) after the equation.
One of the most significant scientific photographs ever taken—capturing Einstein at a critical moment for his thought: pondering the implications of Hubble’s expanding universe for his own Theory of General Relativity. To our knowledge, this is the only known signed copy of this important image.
Terms and abbreviations used in our descriptions.