Particles do not Pass Both Slits

The double-slit experiment is often explained as particles going through both slits. Supposedly this quantum mechanics interpretation was made rigorous by R.P. Feynman's path integral formulation, where particles take all possible paths.

This is not really correct, as explained in a new video: Debunking Veritasium: The “All Possible Paths” Myth & What Feynman Really Showed

Curt Jaimungal rigorously debunks the viral myth popularized by Veritasium (that quantum particles literally take “all possible paths” has been proved) and clarifies the true mathematical purpose of Feynman's formalism. Learn why this concept is a computational tool in configuration space rather than a physical map of reality.

People doing quantum computing are always talking about an electron being in two places at once, like the Schroedinger Cat that is alive and dead at the same time. The many-worlds fans especially like to talk this way. It these things do not happen in standard textbook quantum mechanics. In textbook/Copenhagen QM, does not have a defined position until it is measured. It does not get observed in two places.