Philip Ball writes: In July 2011, participants at a conference on the placid shore of Lake Traunsee in Austria were polled on what they thought the meeting was about. You might imagine that this question would have been settled in advance, but since the broad theme was quantum theory, perhaps a degree of uncertainty was to be expected. The title of the conference was ‘Quantum Physics and the Nature of Reality’. The poll, completed by 33 of the participating physicists, mathematicians and philosophers, posed a range of unresolved questions about the relationship between those two things, one of which was: ‘What is your favourite interpretation of quantum mechanics?’

The word ‘favourite’ speaks volumes. Isn’t science supposed to be decided by experiment and observation, free from personal preferences? But experiments in quantum physics have been obstinately silent on what it means. All we can do is develop hunches, intuitions and, yes, cherished ideas. Of these, the survey offered no fewer than 11 to choose from (as well as ‘other’ and ‘none’).

The most popular (supported by 42 per cent of the very small sample) was basically the view put forward by Niels Bohr, Werner Heisenberg and their colleagues in the early days of quantum theory. Today it is known as the Copenhagen Interpretation. More on that below. You might not recognise most of the other alternatives, such as Quantum Bayesianism, Relational Quantum Mechanics, and Objective Collapse (which is not, as you might suppose, just saying ‘what the hell’). Maybe you haven’t heard of the Copenhagen Interpretation either. But in third place (18 per cent) was the Many Worlds Interpretation (MWI), and I suspect you do know something about that, since the MWI is the one with all the glamour and publicity. It tells us that we have multiple selves, living other lives in other universes, quite possibly doing all the things that we dream of but will never achieve (or never dare). Who could resist such an idea?

Yet resist we should. We should resist not just because MWI is unlikely to be true, or even because, since no one knows how to test it, the idea is perhaps not truly scientific at all. Those are valid criticisms, but the main reason we should hold out is that it is incoherent, both philosophically and logically. There could be no better contender for Wolfgang Pauli’s famous put-down: it is not even wrong. [Continue reading…]