Like small children, scientists are always asking the question ‘why?’. One question they’ve yet to answer is why nature picked quantum physics, in all its weird glory, as a sensible way to behave.
Researchers Corsin Pfister and Stephanie Wehner at the Centre for Quantum Technologies at the National University of Singapore tackle this perennial question in a paper published 14 May in Nature Communications.
We know that things that follow quantum rules, such as atoms, electrons or the photons that make up light, are full of surprises. They can exist in more than one place at once, for instance, or exist in a shared state where the properties of two particles show what Einstein called “spooky action at a distance”, no matter what their physical separation. Because such things have been confirmed in experiments, researchers are confident the theory is right. But it would still be easier to swallow if it could be shown that quantum physics itself sprang from intuitive underlying principles.
One way to approach this problem is to imagine all the theories one could possibly come up with to describe nature, and then work out what principles help to single out quantum physics. A good start is to assume that information follows Einstein’s special relativity and cannot travel faster than light.
However, this alone isn’t enough to define quantum physics as the only way nature might behave. Pfister and Wehner think they have come across a new useful principle. “We have found a principle that is very good at ruling out other theories,” says Pfister. In short, the principle to be assumed is that if a measurement yields no information, then the system being measured has not been disturbed. Quantum physicists accept that gaining information from quantum systems causes disturbance. Pfister and Wehner suggest that in a sensible world the reverse should be true, too. If you learn nothing from measuring a system, then you can’t have disturbed it.
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