But Bohr’s distinction helps to focus us on the right question. What has changed crucially, he says, is the way we look. So instead of trying to figure out what has made the difference to the outcome in terms of ‘where the particle went’, we should be asking ‘Why does it matter how we look?’ This in turn prompts a deeper question: ‘What information have we gained in this case that we did not have in that case?’ I believe that it is this question, not ‘Which path is the particle taking?’, that may eventually lead us to a better understanding of quantum mechanics.
