Seems to me that in deep space real photons collide often with virtual particles. Is that a reasonable theory? If so, what are the (approximate or ball-park) statistics? What does happen? Does the putative virtual particle involved in a collision with a real photon become real? What are the consequences that we can observe, such as "tired light"? I see that heisenberg posted questions like the above already. My apologies to him. They never got replies, though.