The single photon / single electron double slit experiment shows particles appearing as dots on the screen. This is explained as being due to the collapse of their wavefunctions.
However, if they were point particles, we would not be able to see them at all. Instead, they have a radius upto which they appear as bright. That would mean there is some intensity of light emitted by the screen after absorption of the photon.
The light will not have the same intensity throughout that radius, and would decline along the radius. How can we quantitatively measure either the intensity of the incoming radiation along the surface of the screen or the intensity of light emitted by the screen?