This is my very first post, so here it goes. I've had this idea for a while but this is my first attempt at putting it into words. We've all heard of the hypothetical demonstration that tries to put gravity into perspective by pitting a fired bullet against a simple falling bullet. The idea is that if you fired a bullet parallel to the ground and at the exact same time you dropped a bullet from the same height, they would hit the ground at the same time. This thought experiment is 'similar' and starts with two perfectly parallel, perfectly plumb and perfectly reflective mirrors. Between these two mirrors exists a perfect vacuum and you have the ability to fire, or release, a single photon that is perfectly parallel to the ground, thus making its trajectory absolutely perpendicular to the opposing mirror. Now using classical physics, a single photon fired perfectly perpendicularly between two perfectly parallel and perfectly reflective mirrors should 'bounce' back and forth ad infinitum (I believe that this is precisely how Einstein's 'photon clock' is constructed). All is well and good out side of any gravitational field, but now lets consider gravity and general relativity. Our imaginary mirror apparatus is constructed on the surface of Earth in a very real gravitational field. Here is my question, will the photon 'fall' towards earth? And if so, will it 'accelerate'? If one were to drop an object at the exact moment as the photon was released, negating any air resistance, would the photon and outside object reach the ground at the same time? This is how I imagine the experiment would go because as I understand it gravity and acceleration are indistinguishable experimentally.