Objects with mass always travel less than c with respect to other objects with mass. Objects without mass always travel at c with respect to objects with mass. But what speed do objects without mass travel with respect to each other? Do two massless photons travel at c with respect to the other's frame of reference even if they are going in the same direction? If so, do they perceive themselves as going in the same direction at different speeds or in opposite directions with respect to objects with mass?