  Recalling the discussion sketched in the Introduction, if we were to create a twin using some kind of Star trek replicator, say, then in the classical domain such a twin could insist that ‘I’m here and she’s there’ or, more generally, ‘I’m in this state and she’s in that one’ and ‘swapping us over makes a difference’. In the classical domain each (indistinguishable) twin has a metaphysical ‘alibi’ grounded in their individuality. Weyl’s point is that in quantum mechanics, they do not. 