Existence is a difficult concept for something moving at the speed of light.
Light follows a null geodesic through space-time with zero (space-time) length and no proper time. Past, future, and causality have no meaning to a photon. We think of photons travelling through space because our symmetry is broken, we have mass, and we and experience time and space.
Observers like us will see light follow the same world-line from its source to its target. It cannot interact with anything else, and some might say it was only ever emitted so that it could interact with its target.
So from a certain point of view the “existence” of a photon is entirely bound up in its interaction with source and target, and it’s not really useful to speak of it in other terms. The quantised interaction is the photon.
Light follows a null geodesic through space-time with zero (space-time) length and no proper time. Past, future, and causality have no meaning to a photon. We think of photons travelling through space because our symmetry is broken, we have mass, and we and experience time and space.
Observers like us will see light follow the same world-line from its source to its target. It cannot interact with anything else, and some might say it was only ever emitted so that it could interact with its target.
So from a certain point of view the “existence” of a photon is entirely bound up in its interaction with source and target, and it’s not really useful to speak of it in other terms. The quantised interaction is the photon.