“ Light ” is an imponderable 4-D electroMagnetic field
propagating in an imponderable 4-D gravitational field.

Depending on how much of it you might be able to observe,
it might be a semi-random spec of radiation pressure.

Nothing is acausal. Randomness is ignorance.
For a black body at room temperature with a meter^2 surface area,
a photon in the visible range appears every thousand years or so.

Quoting WikiPedia on “ Planck's law ”:
“ Although Planck's formula predicts that
a black body will radiate energy at all frequencies, the formula is
only practically applicable when many photons are being measured. ”.

In an Ideal laser beam, it's a pure wave ( perfectly coherent ),
hitting both slits at the same time, yet undetectable at either one.