What happens when you see something? Say, for the sake of argument, this sentence you are now reading. Dismissing the whole business of how the brain processes visual stimuli, let’s set our focus on the travel time of the information you receive. And to simplify matters even further, let’s also ignore how atoms absorb and reemit light, taking only into account the classical propagation of photons (or the basic units of all light).

We can then agree that photons of light are bouncing around the room you’re currently at. Either because a window is open or a lamp is on (or maybe a…