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Kenneth W. Ford – The Quantum World (2004)

Physicists themselves often say that their heads swim when they think too hard about quantum mechanics. As I have stated earlier in this book, quantum mechanics is eerie not just because it violates common sense. It is strange for deeper reasons: it deals with unobservable quantities; it shows that nature’s fundamental laws are probabilistic; it permits particles to be in two or more states of motion at the same time; it allows a particle to interfere with itself; it says that two widely separated particles can be entangled.