What’s more, no one really knows what a wavefunction is. It was long considered to be just a mathematical convenience, but now some researchers believe it is a real, physical thing. Some think that collapse of the wavefunction during measurement is also a real process, like the bursting of a bubble; others see it as just a mathematical device put into the theory “by hand” – a kind of trick. The Austrian poll showed that these questions about whether or not the act of measurement introduces some fundamental change to a quantum system still cause deep divisions among quantum thinkers, with opinions split quite evenly in several ways.
Bohr, Heisenberg and their collaborators put together an interpretation of quantum mechanics in the 1920s that is now named after their workplace: the Copenhagen interpretation. This argued that all we can know about quantum systems is what we can measure, and this is all the theory prescribes – that it is meaningless to look for any “deeper” level of reality. Einstein rejected that, but nearly two-thirds of those polled in Austria were prepared to say that Einstein was definitely wrong. However, only 21% felt that Bohr was right, with 30% saying we’ll have to wait and see.
Nonetheless, their responses revealed the Copenhagen interpretation as still the favourite (42%). But there are other contenders, one of the strongest being the Many Worlds interpretation formulated by Hugh Everett in the 1950s. This proposes that every possibility expressed in a quantum wavefunction corresponds to a physical reality: a particular universe. So with every quantum event – two particles interacting, say – the universe splits into alternative realities, in each of which a different possible outcome is observed. That’s certainly one way to interpret the maths, although it strikes some researchers as obscenely profligate.
One important point to note is that these debates over the meaning of quantum theory aren’t quite the same as popular ideas about why it is weird. Many outsiders figure that they don’t understand quantum theory because they can’t see how an object can be in two places at once, or how a particle can also be a wave. But these things are hardly disputed among quantum theorists. It’s been rightly said that, as a physicist, you don’t ever come to understand them in any intuitive sense; you just get used to accepting them. After all, there’s no reason at all to expect the quantum world to obey our everyday expectations. Once you accept this alleged weirdness, quantum theory becomes a fantastically useful tool, and many scientists just use it as such, like a computer whose inner workings we take for granted. That’s why most scientists who use quantum theory never fret about its meaning – in the words of physicist David Mermin, they “shut up and calculate”, which is what he felt the Copenhagen interpretation was recommending.
So will we ever get to the bottom of these questions? Some researchers feel that at least some of them are not really scientific questions that can be decided by experiment, but philosophical ones that may come down to personal preference. One of the most telling questions in the Austrian poll was whether there will still be conferences about the meaning of quantum theory in 50 years time. Forty-eight percent said “probably yes”, only 15% said “probably no”. Twelve percent said “I’ll organize one no matter what”, but that’s academics for you.