The photon slit experiment has been problematical since it was 1st done. The Born 'Copenhagen' interpretation asserts that each outcome of a measurement has a specific probability and that, while an aggregate of measurements matches that distribution, there is no way to determine the outcome of specific measurement. Booring! :)

What Hugh Everett said is the the results are better described in that each outcome, each and EVERY quantum event represents the spliting off of another, new parallel universe where that particular result 'happened'. It's great for alternate universe sci-fi universes or self fantasies like the improbable but possible where I sold all my stock investments Jan 1st.