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.
And yet, it attracts both publicity and extraordinarily confident endorsement. Why? To understand that, we need to see why, more than 100 years after quantum theory was first conceived, experts are still gathering to debate what it means.
If the MWI were supported by some sound science, we would have to deal with it – and to do so with more seriousness than the merry invention of Doppelgängers to measure both quantum states of a photon. But it is not. It is grounded in a half-baked philosophical argument about a preference to simplify the axioms. Until Many Worlders can take seriously the philosophical implications of their vision, it’s not clear why their colleagues, or the rest of us, should demur from the judgment of the philosopher of science Robert Crease that the MWI is ‘one of the most implausible and unrealistic ideas in the history of science’. Here, after all, is a theory that seems to allow everything conceivable to happen. To pretend that its only conceptual challenge is that it leads to scenarios like the plot of Sliding Doors(1998) shows a puzzling lacuna in the formidable minds of its advocates. Perhaps they should stop trying to tell us that philosophy is dead.
An electron is going through two slits and is interfering with itself because it is a wave? After it (the wave) hits the screen (or any other macroscopic object), it makes point-like impact. And no measuring problem arises. How does it happen? Simply we have created two descriptions, two incomplete models of one reality. IOW all elementary particles are the waves (otherwise there would be no interference in many slits) which, when interfering with macroscopic world (or, in other many particle experiments), behave like particles. For some experiments the particle model works better, for some other – the wave model does. Just like we observe them in our experiments. IV.