photon in the box is very poorly written please a delete b correct in order to contain a correct explanation of what is going on the correct explanation of the photon in a box issue is that the trajectory of the photon inside the box gets slightly curved in the gravitational field such that there is a vertical component of the photon momentum p tangential p sin theta where p e c is the momentum and theta is a very small angle at each collision with the vertical walls of the box the photon transmits a downward force dp dp tangential dt to the box that can be mis construed as an increase of mass equal to dp g where g is the gravitational constant please remove any misleading references to m e c such ridiculous stuff can only further the misconception that the photon has non zero mass that can be measured thank you