He started working in the field of general relativity with the great German physicist Pascual Jordan in Hamburg, in 1952, and he earned his PhD there in 1955.
It is with P. Jordan that he found the locus of his life's work, namely the geometric aspects of general relativity and Einstein's field equations.
There, he started a group working on general relativity, comprising such first-rate physicists as Roger Penrose, Roy Kerr, Rainer K. Sachs, and Jürgen Ehlers.
In 1967, he was appointed as Professor of Physics at New York University, where he had many students, including some twenty successful PhD candidates.
[2] He died at the age of 88 on January 5, 2015, surrounded by family and friends in his Manhattan apartment in New York City, NY.