First off, before I get a bit ponderous, I really, really enjoyed this.
It’s interesting, predictability. Because, if the writer has let it be predictable in a charming, well-written way, I don’t mind – in fact, I find it quite comforting, knowing where something is going, but enjoying the ride there anyway.
I really enjoyed this. I love it when some hard science gets used in a story. My only qualm is that the journey is too short. It would have been more entertaining to describe more aspects of the photon’s trip through the universe, like how it traveled billions of miles through absolutely nothing, then flew past some of the planets in our solar system before shooting through our atmosphere and hitting the diamond earring.