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THE quantum realm of atoms and particles has randomness at its core. At least that鈥檚 what the maths of probabilistic quantum wave functions implies. Our knowledge of the quantum world is rather like a die throw 鈥� 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 鈥渏ust odd鈥�, says , 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鈥檚 not convinced the quantum world is an incorrigible gambler. 鈥淚 don鈥檛 think one should give up trying to find an explanation,鈥� 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鈥檛 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 鈥渇ine-tuned鈥� 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 stating the first problem need not be an issue, because it wouldn鈥檛 apply to humans or macroscopic apparatuses 鈥� these still follow the predictable rules of classical physics. Regarding the second argument, she reckons that you can actually calculate how a certain quantum system behaves deterministically without taking into account everything that has ever happened.

She hasn鈥檛 convinced many of her colleagues, but that hasn鈥檛 stopped her drawing up plans to put the basic idea to the test. If you measure the position, say, of a quantum object in short enough time intervals, with minimal noise, enough times, you might see that particles starting out in a similar state end up in a similar state, contrary to what quantum theory predicts. The randomness might appear, says Hossenfelder, because this underlying determinism gets lost in the noise and long measurement intervals.

Or it might be because the present and the future can influence the past. This is admittedly 鈥渁 very strange idea鈥�, says Matthew Pusey at the University of York, UK. But he has shown that backwards causation is, at the smallest scales at least, a necessary consequence of the fact that the equations of quantum mechanics work just as well both forward and backwards in time.

And it sounds 鈥渓ess crazy鈥�, says Pusey, when you consider that time in general relativity is just another dimension alongside the three spatial ones. This gives rise to a four-dimensional 鈥渂lock universe鈥� 鈥� mapping all locations at all times 鈥� with past, present and future being equally real, and the 鈥渘ow鈥� losing its special status. Advocates for retrocausality, then, just like superdeterminists, believe that randomness is an illusion caused by our partial, naive view of the world 鈥� in this case, our misconceived idea of how time works.

Think back to the die throw, they might say. Dice can be loaded, and throws masterfully controlled. Ultimately, even specks of dust or fluctuations in air temperature can influence the result. We only think of it as random because it is so hard to work out these details. Is the same true for the quantum world? You wouldn鈥檛 want to bet on it either way