Occasionally I remark about how illogical quantum mechanics is. Sometimes people either insist that it is logical, or simply assert some simple explanation that shows they don’t really get how utterly strange this stuff is.
This video of Jim Al-Khalili gives a relatively brief explanation of this experiment, including its freaky results.
If Al-Khalili doesn’t strike you as an authoritative enough source, or you’d like a more detailed explanation, here’s a classic lecture by Richard Feynman. Unfortunately, given how old it is, the quality of the video isn’t great, but experiencing a Feynman lecture is worth it.
Feynman is famous for saying that if you think you understand quantum mechanics, you don’t understand quantum mechanics. He makes a similar statement in this lecture.
Even if you don’t feel like watching the whole thing, Feynman’s musing at the end on the primacy in science of experiment and observation over logical reasoning is well worth checking out.
What’s really happening in quantum mechanics when an observation takes place? There are several “interpretations.” None of them currently have unique evidence. Those who feel certitude about their preferred interpretation may want to consider Feynman’s closing remarks.