Early Gedanken Experiments of Quantum Mechanics Revisited

The famous gedanken experiments of quantum mechanics have historically played crucial roles in trying to understand quantum mechanics and in developing the Copenhagen interpretation. They are re-examined here from the perspective of standard quantum mechanics, without a mix of any ontological interpretation. It is shown that, in most of these gedanken experiments, entanglement plays a crucial role. In an interference experiment, even if momentum exchanges are involved, the loss of interference is due to the entanglement with other degrees of freedom. Bohr’s analyses of these gedanken experiments, based on the uncertainty relation with his interpretation, are not consistent with fully quantum mechanical accounts.