Also to what extent does “beginning and end” apply to a photon, which exists on a null geodesic? I realize that a photon can have no perspective, so I won’t try to talk about what a photon “sees,” and from our perspective a photon is emitted, travels, and is absorbed. Still, if you look at a spacetime diagram emission and absorption exist along the null axis.

Talking about photons hurts my brain. ><