In quantum realism, a photon “exists” as processing running on the quantum network regardless of how that processing is distributed. Whether a photon is just starting at a point or spread out in space as a quantum wave that is larger than a galaxy doesn’t matter. For processing, where it runs is irrelevant as long as it does run. What exists is neither quantum states nor physical states but processing that never stops and is in our terms “immortal”. To say a photon has wave function is to maintain the stubborn illusion that it is a singular thing with a wave function property. Quantum realism says that the photon is the quantum wave and the “particle” we see is just a view created on demand when a physical event occurs. The particle is just the view we get while the quantum wave is the photon in itself. If “all the world’s a stage“, then classical mechanics describes the stage but quantum mechanics describes what is really going on backstage.
A physical realist might ask “If a photon is a wave of instances that can go through both Young’s slits at once, which one is the photon?” The question again betrays the assumption that a photon is a “thing”. The world of matter we see supports this view but the world that quantum theory describes doesn’t. We see a photon hit a screen at a point like a particle but that it traveled in the same way is just an assumption tacked onto the facts. Knowing how a photon arrives isn’t the same as knowing how it travels. Quantum theory tells us that photons travel as quantum waves but interact as point particles. Its critics couldn’t fault this logic because there is no fault. What can travel like a wave but arrive like a point particle? The next section suggests that quantum processing can.