Is quantum theory really as random as it seems?

The maths suggests the reality we get from quantum probabilities is random, but there might be some hidden determinism at play – or perhaps the present can influence the past

Physics 25 August 2021

New Scientist Default Image

Skizzomat

THE quantum realm of atoms and particles has randomness at its core. At least that’s what the maths of probabilistic quantum wave functions implies. Our knowledge of the quantum world is rather like a die throw – in the air it takes many values at once, before landing on one. Until then, the result is unknowable. Or is it?

Quantum randomness is “just odd”, says Sabine Hossenfelder, a theorist at the Frankfurt Institute for Advanced Studies in Germany, contradicting our intuitive understanding of cause and effect. Unlike most of her peers, she’s not convinced the quantum world is an incorrigible gambler. “I don’t think one should give up trying to find an explanation,” she says.

She favours an idea known as superdeterminism, that what we ultimately see on measuring a quantum object is somehow predetermined by factors we can’t observe. The idea has been around for a while, but has remained pretty unloved, partly because it seems to undermine the notion of scientific experiment: if undetectable initial conditions somehow predetermine outcomes so that experimenters cannot use their free will, how can we trust science? Many also argue that superdeterminism is “fine-tuned” to an absurd extent: to make any sense of the data we collect in the physical world, we need to know about the initial conditions from which the world arose.

Hossenfelder recently published a paper stating the first problem need not be an issue, because it wouldn’t apply to humans or macroscopic apparatuses – these still follow the predictable rules of classical physics. Regarding the second argument, she reckons that you can actually calculate how a certain quantum …