This is not a straw man, and here is another guy stuck in 19th century physics.
Physicist Lee Smolin explains his view of physics:
Then there's a small number, and I'm one of them, that take the problems in quantum mechanics as evidence that the theory is wrong, or at least incomplete. ...No, this is just a misunderstanding of basic physics. Once separated, the two particles are independent. Nothing you do to one can possibly have any effect on the other.
There is a key idea that underlies my work in that area, and that's the problem of what's called nonlocality. This is a very important hint. Nonlocality is the phenomenon — also sometimes called entanglement — that if you have two quantum systems and they interact and then separate, they share properties, in that the choice of what property we measure on one of those particles, even if they're very far away from each other, affects what's measurable in the other particle. That's a statement of what's sometimes called Bell's theorem, and it's been put in a form where it can be tested experimentally. The experiments clearly show that the assumption that the two particles are independent because they're far away from each other is wrong. If you want a complete description of the results of experiments on these kinds of systems, and not a statistical description in terms of probabilities, which is all that quantum theory gives in these situations, you have to posit explicit interactions and communication between the two particles.
I believe that's right. That's what would be called a nonlocal theory. Traditionally, we call it a nonlocal hidden variable theory. There are a number of these — Louis de Broglie invented the first, called pilot-wave theory. It was laughed out of town by people in the late 1920s. There were theorems that showed it was impossible in the early thirties, and it was basically dropped by de Broglie and everybody else and then rediscovered by David Bohm. That's the first nonlocal hidden variable theory we have, and there are others.
Hidden variable theories were laughed out of town because they were throwbacks to outmoded theories that had been discarded as wrong. Bell's theorem and subsequent experiments showed that they were impossible, unless you adopt some mystical views. Sensible physicists concluded that the conventional wisdom of the 1920s was correct. Instead, Smolin takes the theorem as encouragement to become a mystic.
Dear Roger,
ReplyDeleteI wrote something here but it became too big, so I posted an entry at my own blog, of the title:
"Entanglement, nonlocality, and the slickness of the MSQM folks".
The URL is:
https://ajitjadhav.wordpress.com/2020/01/03/entanglement-nonlocality-and-the-slickness-of-the-msqm-folks/
Best,
--Ajit
No Roger, Smolin has a very fine understanding of basic physics, and even more relevantly here, of its problems.
ReplyDeleteYou say that:
“Once separated, the two particles are independent. Nothing you do to one can possibly have any effect on the other.”
Einstein thought the same. And a lot of other people would like to be able to agree with you on that, including I suspect Smolin himself.
But John Bell showed that no theory consistent with local causality can reproduce the predictions of quantum mechanics in all circumstances.
That famous Theorem of Bell has been widely accepted as irrefutable. And unfortunately a series of Bells experiments including several allegedly loophole-free experiments have seemed to confirm that quantum mechanics is correct and that Nature is indeed nonlocal
But quantum mechanics departs from the local realism of classical physics, not only in implying nonlocality, but also in assuming that a particle might subsist in a probabilistic superposition of alternative states, and thus in no particular state at all until measured or observed.
The attractive feature of de Broglie-Bohm theories is in their assertion that the particle is always in one place at a time. These pilot wave theories are nonlocal but unfortunately it seems to be widely accepted now that Nature is non local.
But if someone could prove that all those complicated Bells experiments are incorrect and that Nature is in fact locally causal, I expect that Smolin would be delighted. Bell and Einstein would also be cheering from wherever they are now.
Bell's theorem is only accepted as proving that quantum mechanics is inconsistent with classical theories of local hidden variables. That's all.
ReplyDeleteIf you assume the electron is a classical particle, as in de Broglie-Bohm, then there are nonlocal effects. However, the electron is not a classical particle.
These theories are just refusals to accept textbook quantum mechanics.
But unfortunately it is textbook quantum mechanics that is implying that nonlocality, and the experimentalists are now asserting that in this respect, quantum mechanics has been proved correct, see for instance, H. Wiseman, Death by experiment for local realism, in News and views, Nature, 526, 649 (2015)
ReplyDeleteHere is the Nature article.
ReplyDeleteAs anyone can see by reading the article, it argues that classical theories are more intuitive than quantum theories, but the Bell-inspired experiments have confirmed what everyone has thought since 1925. That is, the quantum theory is correct, and the classical theory is incorrect.
Nowhere does this article or any reputable textbook say that nonlocality has been proved, or that local causality has been disproved.
Yes, nonlocality is a horrible idea, but the experimentalists claim they have proved it. See the references to the Hansen, Shalm and Giustina experiments in the Wikpedia entry under Quantum nonlocality.
ReplyDeleteThose experimentalists would have received a Nobel Prize, and textbooks would be rewritten, if they had really proved nonlocality. That Wikipedia article only says that the experiment does not admit a classical physics interpretation.
ReplyDeleteBelieving in nonlocality is like believing in witchcraft. Believe in it if you want, but there is no scientific backing for it.