Hello Thomas.

I’ll try to answer to your questions.

1 & 2 — We should stop thinking of photons as being created, then travelling through the universe, then arriving somewhere else (or loosing energy during the trip), because from their own point of view, the whole emission-flight-detection process is a single, indivisible event.

So only the full emission-flight-detection process is real. There are no photons “in flight”, no “born” but “not detected yet”. A photon is only real when it interacts with the material world, causing a detectable effect. So, in a sense, a photon that has not been detected has not been born yet. Whenever a photon is detected, it fulfils all the conditions that should be met in order to say it came from where it came from, following all possible paths that link the emission event to the interaction event, and also “travelling” exactly at the speed of light.

Photons (and other quanta at c) always feel they are instantaneous, so they can not evolve. What evolves is the material world, and then, that particular “photon coming from the edge of the universe” would materialize as an energy or momentum transference in a particular matter detector placed somewhere in the universe, if the condition “coming at the speed of light” is met at that particular spacetime coordinate. If the condition is not met, then, that photon is not real at that place/moment. That energy transference would materialize later, on another detector at another spacetime coordinate that fulfills the required condition for the emitter-detector interaction to happen.

2 — As I said before, there are no photons in flight. They become real only at detection. So the “photon from the edge of the universe” will only be REALLY real when detected. Until then, it is nonexistent, it is just a probability of interaction at each spacetime coordinate that complies with the c speed rule starting from the emitter, but nothing real exists or “propagates”, until it REALLY “happens”. And when it does, it is fully equivalent to the “evolution” we envisioned for the probability of interaction.

So whenever/wherever a photon gets detected, it always comply with the c speed rule that links emitter and detector, so that’s why we think they “travelled” at that speed. The way photons develop is so consistent with the “c speed” rule, that it seems the photon really “travelled” through space undetected during that interval. But it’s more like a recurrent draw, and when the conditions are met, the photon materializes: A single point/instant of existence that, somehow, fulfills all the spacetime conditions that the detector says took place from its particular frame of reference.

3 — That’s right. It can take nanoseconds, or billions and billions of years, but any “real” photon will be absorbed somewhere else, some time later, no matter what.

Only the complete emission-flight-absorption sequence is what defines a real photon, because only the complete process is what the photon experiences as an instant point-like event. In order for the photon to REALLY exist, there can no be part of the process left out.

I hope I have answered your questions. Don’t hesitate to contact again if there are new questions coming to your mind. I know it takes some time to get used to these ideas, but the more I look at things from this viewpoint, the more things fit into place and make sense.