Einstein could not but accept the criticism by Kretschmann that the basic general covariance postulate of general relativity is without physical content:
- I believe Kretschmann’s argument to be correct, but…of two theoretical systems compatible with experience, the one is to be preferred that is the simpler and more transparent from the standpoint of the absolute differential calculus.
This connects to the standpoint of S. Weinberg (Nobel Prize in Physics 1979):
- I believe that the general acceptance of general relativity was due in large part to the attractions of the theory itself– in short, to its beauty.
- By the beauty of a physical theory, I certainly do not mean merely the mechanical beauty of its symbols on the printed page…. Simplicity is part of what I mean by beauty…
- The equations of general relativity are notoriously difficult to solve except in the simplest situations, but this does not detract from the beauty of the theory itself….In Einstein’s theory there are fourteen equations, In Newton’s three…
The criticism (expressed by many physicists) that Einstein’s theory of relativity is vacuous of physical content, is thus met with an argument of aesthetics: The theory is beautiful because it is simple, and a beautiful theory is to be preferred.
But relativity theory is so simple that nobody can understand it , and that may be its real beauty.