It consists in the missed fourth implication of his epoch-making “equivalence principle” of 1907.
The completed 4-set reads:
1) Gravitational redshift
2) Gravitational light bending
3) Gravitational light-creeping downstairs
4) Optically masked gravitational size increase downstairs
The added fourth point follows from the fact that a horizontally propagating light ray downstairs is locally slanted relative to the tip (owing to the constant recession of the bottom from the tip which also causes point 1).
Without the newly added point 4, point 3 amounted to a logical contradiction-in-terms in view of the constant c assumed axiomatically at the outset since only special relativity with its global c is presupposed in the equivalence principle. This logical contradiction explains Einstein’s falling silent on the topic of gravitation for 4 years until 1911 when he grudgingly accepted the inconsistency as an element to be included in general relativity.
The new “global-c general relativity” GCGR implicit in point 4 is only waiting to be written down explicitly. It will bring instant fame to the first lucky student.
For J.O.R.
January 19, 2019