“According to quantum mechanics, any two electrons must necessarily be completely identical. […] This is not merely to say that there is now way of telling the particles apart: the statement is considerably stronger than that. If an electron in a person’s brain were to be exchanged with an electron in a brick, then the state of the system would be exactly the same state as it was before, not merely indistinguishable from it! […] What distinguishes the person from his house is the pattern of how his constituents are arranged, not the individuality of the constituents themselves.”

—The Emperor’s New Mind by Roger Penrose