This is a slightly off topic question but commenters here might have an answer.
In the original double slit experiment, how do they actually know that they are emitting a just a single photon. The entire experiment depends on this being the case, but how is it done? Especially way back when it was first performed. How could they confidently say that have an apparatus that can reliably only emit a single photon, yet at the same not be clear about whether light was a wave or a particle.
The original experiment did not rely on the emission of individual photons. It just observed an interference pattern that classical particles would not exhibit.
Later experiments that relied on individual photons could detect them individually [0]
In the original double slit experiment, how do they actually know that they are emitting a just a single photon. The entire experiment depends on this being the case, but how is it done? Especially way back when it was first performed. How could they confidently say that have an apparatus that can reliably only emit a single photon, yet at the same not be clear about whether light was a wave or a particle.