Dirac said "A photon only interferes with itself."

[confused2]

For reasons unknown the English seem to accept this and the rest of the world not so much.
The first requirement for interference is being in the right place at the right time. Obviously a single photon is always at roughly the right place and the same time as itself - other photons not so likely. Is that enough already? If anyone is interested in a deeper dive .. post your thoughts/evidence.

[Syne]

https://en.wikipedia.org/wiki/Two-photon_physics

[confused2]

https://en.wikipedia.org/wiki/Two-photon_physics

Thanks Syne - yes he was wrong.

The (my) original context was of a 'classroom' experiment

This is a single photon experiment but with lots of them.

There are 'some claims' of two (or more) photon interference even at low energies which would refute what I wrote in the context I wrote it.