"observation" isn't important, it's enough interaction to decohere the superposition, or in another sense, entangle it with the environment. A polarization filt

"observation" isn't important, it's enough interaction to decohere the superposition, or in another sense, entangle it with the environment. A polarization filter could be considered an "observer" in some sense, but I think focusing on observation results in a less clear and truthful understanding of what a measurement is. A polarization filter rather interacts with the light in a strong enough way to force conditional behavior based on its polarization. This results in photos that have a superposition of different polarizations to probabilistically become one of the polarizations, wrt the respective amplitudes of each polarization for that photon.