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A paradox turns out not to be real. Whew.




Quantum mechanics seems a little bit less weird and counter-intuitive now than it did before November. Since around last Thanksgiving a scientific paper has been making the rounds, and gradually it has become grist for science journalists

Now the idea has come to you, via my humble blog. The Cheshire cat and its smile do not actually separate in the quantum world. 

It has long been thought that certain subatomic particles can be in one place and that certain of their properties can be in another. Ah, what a mystical idea! what a contribution to the reputation of quantum mechanics for sheer weirdness!  Indeed, no less a physicist than Albert Einstein objected to the "spooky stuff" in quantum mechanics in its early development. 

Einstein wasn't wrong. There is spooky stuff and it does make quantum physics look like something less-than-ultimate, something that will be explained by something else deeper as thought progresses. If Einstein turns out to be right about that, though, the process of demystification may take a while yet. 

And here there is a provisional victory for Einstein's skepticism. Cats do not zig while their smiles zag. Likewise subatomic particles do not zig when their properties (spin or polarization) zag.  The polarization is merely a fact about the particle and, so far as we know, the polarization is wherever the particle is. Here is the peer-reviewed paper, in THE NEW JOURNAL OF PHYSICS, that explains why the results of experiments on the subject, previously cited as evidence of the Cheshire car effect, do not really make any such thing evident.

 https://iopscience.iop.org/article/10.1088/1367-2630/ad0bd4  

And, okay, the prose there is a little dense.  If you want a more straightforward explanation, Sabine Hossenfelder offers one here: 

  https://backreaction.blogspot.com/2024/01/another-famous-quantum-mystery-was-just.html  

My sense of irony is piqued by the fact that the scientists involved in debunking the Cheshire cat paradox appear to work out of Hiroshima University, in Japan. No doubt a place where there are firm opinions about subatomic physics, and about who ought to win the next Academy Award for Best Picture. 

"I am become death for a Cheshire cat," said no physicist ever.   

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