Using the "rays theory" of light, it's easy to see the reason for why an object becomes smaller when it gets more and more distant from us. I have always wondered what is the explanation for this phenomenon using a more sophisticated theory, like Maxwell or QFT theory. Some thoughts: In Maxwell theory: That the fields become more weak as they propagate through space sounds good? But wouldn't that necessarily imply other objects interacting with the original field? (No, it wouldn't.) In QFT: well, essentially the same thing as above: the system (the photons originally emmited by the distant object) interacts with other fields, and this causes photons to be anihilated. But this explanation doesn't seem to be right, because if photons are anihilated in their way to our eyes, photons could also be created through interactions equally well.