In a complete theory there is an element corresponding to each element of reality. A sufficient condition for the reality of a physical quantity is the possibility of predicting it with certainty,… Expand

In 1921, five years after the appearance of his comprehensive paper on general relativity and twelve years before he left Europe permanently to join the Institute for Advanced Study, Albert Einstein… Expand

on the assumption of discrete portions of energy, from which quantum theory developed rapidly. It was then only natural that Wien’s argument, which had led to eq. (2), should have become forgotten.… Expand

Some time ago, R. W. Mandi paid me a visit and asked me to publish the results of a little calculation, which I had made at his request. This note complies with his wish.

Introduction. In this paper we investigate the fundamentally simple question of the extent to which the relativistic equations of gravitation determine the motion of ponderable bodies. Previous… Expand