My understanding is that a light beam will bend in an upward accelerating elevator. I told my uncle this. He responded that the velocity of the elevator cannot be added to the velocity of light since light's velocity always remains the same no matter the motion of the source or the observer. Therefore, he says, that an upward accelerating elevator would not bend the light beam since you cannot add the velocity of the elevator to the velocity of the light beam. He is essentially arguing that bending the path of the light beam by adding the upward velocity of the elevator is attempting to add to the velocity of the light beam. Since light's velocity remains constant, the path of the light beam should therefore remain straight he says. Is he correct? Or am I correct?