In Nick Herbert's Quantum Reality, he describes an experiment in which light is sent through a calcite crystal which seperates the photons by their polarization. In the experiment he describes, the light has a 50/50 chance of either going up into a detector or down into a different detector. Later, when he is talking about when the wave functions representing the photons might collapse, he says they can't collapse at the calcite crystal because it would disagree with other experiments: Well this seems similar to the double slit experiment, but somehow I just can't wrap my mind around it. In the double slit experiment, atleast the photons don't touch anything, but in this experiment the photons hit this calcite crystal and are seperated by it according to their polarization, but apparently Herbert is saying the photons aren't really sent on a specific path when they hit the crystal because they can still interfere with themselves later... So I guess I really don't have much of a question but am just asking for someone to corroborate this claim. :grumpy: Is this true? Has this experiment been performed by sending single photons through the calcite crystal at a time so there's no chance of photons interfering with each other? Quantum theory is driving me insane.