Thursday, November 27, 2014

An 1985 documentary on entanglement

If you have 40 spare minutes, here is a 1985 documentary about quantum entanglement. It begins with a rather cute discussion of the Einstein-Bohr debates.

I wanted to see what the people were saying in the documentary because it was shot shortly before I began to learn quantum mechanics myself – and it's "in the middle" between the 1950s when the professional physicists were sensible about the foundations of quantum mechanics and the 2010s when the idiocy seems to prevail.

So what will we get if we make an observation in the middle?

We get a mixed bag, as you may guess from the collection of physicists who are interviewed: Wheeler, Aspect, Bell, Bohm, Shimony, Holger Bech Nielsen (very energetic and dubbed)...

I do think that the basic issues and possible answers are explained more crisply than what the average documentaries that would be recorded nowadays would do.

John Wheeler is arguably the most reasonable guy – and the best physicist – and he tries to convey the key ideas which means Niels Bohr's understanding of quantum mechanics, one that Bohr was trying to convey to his confused friend Albert Einstein.

It is being explained that the violation of Bell's inequalities – to describe the different character of quantum mechanics using a clear, but not terribly important, example – may be due to the absence of realism or due to non-locality. The "main explanation" seems to admit that locality is a safely guaranteed condition due to Einstein's special relativity.

But Bohm and Bell are confusing the debate by their weird speculations that the preferred frame exists, after all, and trains are being synchronized only in that frame, and so on. What Bell is saying on the show is much more clearly wrong than what Bohm is saying. Around 28:00, Bell sounds devastated that Aspect's experiment confirmed quantum mechanics – which he admits – but he insists that there has to be an action at a distance if we want to explain the experiment because he doesn't consider quantum mechanics (a "non-realist theory") to be an explanation! Too embarrassing, Mr Bell.

Three decades later, broken physics that used to be represented by folks like Bohm and Bell became the "new normal". One could perhaps pessimistically suggest physicists of John Wheeler's caliber have gone extinct – they have either died or have been chased out of the environment that writes books or records documentaries about these questions.

But it's not just the likes of Wheeler who have disappeared (and the likes of Holger Bech Nielsen were no longer invited to English-speaking documentaries). The documentary above spends quite some time with proper, faithful explanations of what Bohr was saying and the principles that the Copenhagen school considered important. The filmmakers thought it was necessary for the narrator (and for Wheeler and, to a lesser extent, even Bohm – and Shimony) to present some (Copenhagen) textbook stuff on the meaning of quantum mechanics. These days, their successors no longer seems to think that it's needed. Presenting just the seemingly simple but demonstrably wrong, superficial, popular-book-level Bell-Bohmian crap seems to be enough for them – and for their viewers.

Lots of correct and lots of wrong things are said in the program. Some of the statements may be interpreted as "correct" but what people make out of them is almost guaranteed to be wrong. For example, Aspect says the usual thing that up to Bell, it was a matter of taste whether Bohr or Einstein was right. Well, there was a difference: Bohr actually had a theory that predicted all these entanglement measurements while Einstein didn't have a damn thing – I mean, he didn't have any competing theory. How can a "perfectly viable theory agreeing with observations" vs "no theory" may be "up to one's taste", I don't know. Moreover, it is not really true that it wasn't understood why the predictions of quantum mechanics were not imitable by any local classical theory. I am planning a blog post about the double slit experiment that not only shows this general "Bell's theorem" but makes it clear that all of its parts were fully appreciated decades before Bell.

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