Got the maths, not the meaning Dereje Belachew/Alamy Stock Photo

IF YOU find the quantum world confusing you’re not alone. A recent survey shows that physicists disagree over the picture of reality that quantum mechanics describes – and that many of them don’t even care.

There was no consensus among the 149 survey participants. While 39 per cent supported the so-called Copenhagen interpretation, the conventional picture of quantum mechanics, 25 per cent supported alternatives and 36 per cent had no preference at all. In addition, many weren’t sure they understood what certain interpretations described.

“I don’t think the debate will resolve soon,” says Sujeevan Sivasundaram, a recent graduate of Aarhus University in Denmark who conducted the survey. “I could see us still discussing this 100 years from now.”


The conventional interpretation, which is often the first and only one a physicist is taught, may have been the most popular in the survey, but that doesn’t indicate it’s right, says Charles Sebens at the University of California, San Diego. “It’s what physicists go on believing because it’s the first way they’re introduced to the theory,” he says. “But it’s a disservice to only learn one interpretation.”

This interpretation uses the Schrödinger equation to accurately predict the results of quantum experiments. But it includes a problem: if you measure or observe a particle, you abruptly change its trajectory in defiance of this equation.

Critics point out that nothing else we know of makes such a weird instant switch, and it seems to be inconsistent with other established laws of nature. In addition, making “measurements” is poorly defined, says Aephraim Steinberg at the University of Toronto, Canada. “If a fly looks at it, if a bacteria interacts with it, if a dog looks at it – what constitutes a measurement?” he says.

“In a survey, 32 per cent of respondents didn’t understand enough to have an opinion”

Alternatives approach things differently. For example, the many interacting worlds interpretation, published by Howard Wiseman at Australia’s Griffith University and colleagues in 2014, says quantum phenomena arise from multiple universes interacting with each other under consistent physical laws. “It’s very strange, I admit,” says Wiseman. But to him, parallel universes that consistently obey a set of laws are far less strange than a single universe with exceptions to the rules, as with Copenhagen.

Despite some enthusiasm for alternatives, 32 per cent of respondents didn’t understand the interpretations enough to have an opinion, and 23 per cent thought interpretations were irrelevant. “One physicist wrote in the comments that he found the survey a complete and utter waste of time,” says Sivasundaram. Furthermore, some thought that certain interpretations couldn’t be experimentally verified, and thus belonged more in philosophy than physics.

The number of diverging ideas suggests that maybe all of them are off the mark, says Sabine Hossenfelder of Germany’s Frankfurt Institute for Advanced Studies. “There doesn’t seem to be two people who can come to any agreement on anything,” she says. “It seems to me that they’re just discussing the wrong things or in the wrong way.”

This article appeared in print under the headline “Physicists cannot agree about quantum world”