Thread by @skdh

Reading news about this year's #NobelPrize in physics. I haven't yet found a single article (!) that actually gets it right. This is incredibly depressing.

It's probably futile, but I'll try this once again. Entanglement is a type of correlation: it links particles together. It's locally created, it's just that you can move entangled particles apart from each other once it's been created. 2/

Entanglement is not what Einstein referred to as "spooky action at a distance" -- There is no action in entanglement to begin with. Einstein wasn't stupid. 3/

Instead, what he meant is this: According to the standard interpretation of quantum mechanics, both particles in an entangled pair can be in an indefinite state, until you make a measurement. If you measure one, you know the property of the other, too. 4/

If (<--- this "if" is super important) the standard interpretation was correct, then this update of the wave-function upon measurement (aka the "collapse" of the wave-function). would be a "spooky action at a distance". 5/

If, on the other hand, the state of the particles was already definite *before* the measurement and you just didn't know, then there's no spooky action. This option requires "hidden variables". (Hence Hans's demonstration with the envelopes!) 6/

The tests that Aspect, Clauser, and Zeilinger have done show that Bell's inequality is violated, which means that a local explanation with hidden variables is only possible if measurement independence is violated. 7/

A violation of measurement independence (aka "statistical independence") is known as superdeterminism and it's been rejected on metaphysical grounds by most physicists (different story). 8/

If you reject superdeterminism, then the experiments by Aspect, Clauser, and Zeilinger show that a local hidden variables explanation of the results is not possible. This is often said to mean that "nature is non-local" or something like this. 9/

To come to the point, manipulating (without measuring!) one of a pair of entangled particles does NOT influence the other particle. Quantum mechanics is perfectly local in that sense. The "spooky action" is the supposed update on measurement. 10/

This is why you can't use entangled particles to send information faster than light! And why, if you misunderstand what the "spooky action" is, you mistakenly think you can signal faster than light. 11/

So to sum up. Leaving aside superdeterminism (more about that in a second), the Nobel Prize - winning experiments can be said to show that Einstein's "spooky action" must be real. These experiments work WITH entangled particles, but the entanglement is not the spooky action. 12/

Okay, to finish, another word on superdeterminism. If you want a local explanation of the observations of Aspect, Clauser, and Zeilinger -- ie, one without "spooky action" -- then the only currently known way to do this is superdeterminism. 13/

And I'm in camp Einstein: I think it's correct to pick a local theory. The consequence of Aspect, Clauser, and Zeilinger's results is then that you have to look for evidence for superdeterminism. And I am pretty sure it'll be found eventually... 14/

... and if that happens, there'll be another Nobel Prize in physics. Just that then the headlines will say that Einstein was right in the end, and spooky action doesn't exist. /end

Okay, I have found an article that gets it right (written by David Kaiser, one of the top-experts on the topic). ht @bsgallagher

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