Peter Bergmann

Peter Gabriel Bergmann (Berlin, 24 March 1915 – Seattle, 19 October 2002) was a German-American physicist best known for his work with Albert Einstein on a unified field theory encompassing all physical interactions. He also introduced primary and secondary constraints into mechanics. After obtaining his Ph.D at the German University in Prague in 1936 under the direction of Philipp Frank he went to work with Einstein, as his research assistant, at the Institute for Advanced Study between 1936 and 1941. In 1942, Bergmann published the first textbook on general relativity, Introduction to the Theory of Relativity, with a foreword by Einstein. The second edition of this book was published by Dover Publications in 1976. His other textbooks were:
The Riddle of Gravitation (Dover Publications, 1993)
Basic Theories of Physics (Prentice Hall, 1951)
He also co-wrote Albert Einstein: His Influence on Physics, Philosophy and Politics, together with Peter C. Aichelburg and Roman Ulrich Sexl (Vieweg, 1979).
When Edward P. Tryon came out in 1973 with a paper in Nature titled "Is the Universe a Vacuum Fluctuation," Tryon mentions how he learned from Bergmann how our universe could have started with zero energy and not contradict the conservation of energy law because mass energy is positive and gravitational energy is negative and they cancel each other out and so our universe then could begin with zero energy.
Bergmann was a professor at Syracuse University from 1947 to 1982 and at New York University. He was posthumously awarded the first Einstein Prize in 2003. His doctoral students include Joel Lebowitz, Pantur Silaban, John Boardman and Rainer K. Sachs.
Bergmann has an Erdős number of 2(via Ernst G. Straus to Paul Erdős).