Quantum Mechanics Gets Even Weirder. Or Maybe Less Weird.


I don’t know if this is firm enough to be worth blogging about, but even if it’s not, it’ll be interesting to hear physicists cautioning us in comments not to go overboard about what this means. So here it is: three physicists have produced a theorem implying that the quantum wavefunction is not merely a mathematical abstraction that tells us the probability of subatomic particles being in certain locations and having certain properties. The Copenhagen interpretation, they say, is wrong. The wavefunction is an actual physical thing:

“I don’t like to sound hyperbolic, but I think the word ‘seismic’ is likely to apply to this paper,” says Antony Valentini, a theoretical physicist specializing in quantum foundations at Clemson University in South Carolina.

Valentini believes that this result may be the most important general theorem relating to the foundations of quantum mechanics since Bell’s theorem, the 1964 result in which Northern Irish physicist John Stewart Bell proved that if quantum mechanics describes real entities, it has to include mysterious “action at a distance”.

Action at a distance occurs when pairs of quantum particles interact in such a way that they become entangled. But the new paper, by a trio of physicists led by Matthew Pusey at Imperial College London, presents a theorem showing that if a quantum wavefunction were purely a statistical tool, then even quantum states that are unconnected across space and time would be able to communicate with each other. As that seems very unlikely to be true, the researchers conclude that the wavefunction must be physically real after all.

….Their theorem effectively says that individual quantum systems must “know” exactly what state they have been prepared in, or the results of measurements on them would lead to results at odds with quantum mechanics. They declined to comment while their preprint is undergoing the journal-submission process, but say in their paper that their finding is similar to the notion that an individual coin being flipped in a biased way — for example, so that it comes up ‘heads’ six out of ten times — has the intrinsic, physical property of being biased, in contrast to the idea that the bias is simply a statistical property of many coin-flip outcomes.

So if this is true, what does it mean? In my vague and probably confused understanding of things, I always understood that the wavefunction of Bell’s Theorem traveled faster than light. However, that was OK since it wasn’t a physical thing and didn’t convey any information. But if it’s a physical thing, even a massless physical thing, how can that be?

Or does this result mean that entanglement doesn’t really operate over long distances in the first place, that particles know their own states all along and don’t react to observations of their entangled twin? Help!

In other, probably unrelated news, those Italian researchers who say that neutrinos travel faster than light have doubled down. They now claim to have reproduced their initial results.

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