I find it useful to think of photons as vector clocks: https://en.wikipedia.org/wiki/Vector_clock https://en.wikipedia.org/wiki/Vector_clock Take a photon sta

I find it useful to think of photons as vector clocks: https://en.wikipedia.org/wiki/Vector_clock https://en.wikipedia.org/wiki/Vector_clock Take a photon starting from your chest and give it t1. * Assume that the speed of light is symmetrical. * When the photon hits the next person's eyes, it is t1 + distance/speed of light. Meaning, the photon is "from the past". Since all photons arriving are from the past, the photons travelling the shortest distance are the newest (representing the largest timestamp). So, the thing with the largest observable timestamp is yourself.