Tthe older he gets, the less flexible he becomes in his thinking, and the more arrogant he becomes. He has a deeply flawed understanding of what science is and how it works and – like many esoterics – he'd abuse some scientific concepts to explain his world view, but reject other concepts if they don't fit the world view. E. g. Quantum Theory as a wishy-washy explanation for "supernatural phenomenons", if you know what I mean.
I know, it's impossible to change someone, if he isn't willing to do change himself. But maybe a good book could show him some flaws in his thinking and act as a trigger to at least reconsider some of his world views.
Does anyone have recommendations for books that teach basic rational thinking and core scientific concepts? Or any other tips for a situation like that when you find a family member detached from reality?