New ideas of space and time

There are reasons for believing that the gravitational constant, expressed in terms of atomic units, is not accurately constant, but varies slowly with the age of the universe. This requires a modification of Einstein's theory of gravitation. One may suppose that the element of distance occurring in Einstein's theory is not the same as that measured by atomic apparatus. It becomes possible to revive Weyl's geometry, a generalization of that used by Einstein, to account for the electromagnetic field. There is then no exact symmetry between positive and negative electric charge, or between past and future.