To avoid week-long hiatuses, let me mention a new article by Philip Ball in the Quanta Magazine:
That's nice and it's true in some sense but it is not a new theory or a new piece of a theory that has to be added to quantum mechanics. Instead, it is just a story and a way to talk about some consequences of an underlying theory in a class of contexts. And the underlying theory must still be quantum mechanics for Quantum Darwinism to work. The rest is a straightforward, nearly tautological, derivation combined with marketing.
Indeed, there is no "hard science" behind the recommendation to promote the analogy between the emergence of a classical limit from quantum mechanics; and Darwin's theory about the origin of species. You may like or dislike this analogy. There is no testable way to find out whether this is the right way of thinking. The analogy is surely imperfect – it is not a precise equivalence – and whether the analogy is close enough to be interesting or worth repeating is up to your taste. Analogies between these vastly different fields are at most a matter of pop science, pedagogy, or marketing; they are not science.
So these experiments aren't really testing any new fundamental theory. They're just testing quantum mechanics because the rephrasing of the "story" in terms of "Quantum Darwinism" is nothing else than another consequence of quantum mechanics. As long as the derivation is done correctly, the predictions follow from normal quantum mechanics and their confirmation – which is pretty much guaranteed – is nothing else than another confirmation of quantum mechanics.
Like either Zurek's buzzwords, einselection and especially decoherence, these are just buzzwords conveying pretty much the same content. There is nothing interesting in these experiments to be seen – they're just technically undemanding trivialities whose performers are making living out of the fog that surrounds quantum mechanics in the eyes of the laymen. And it's this fog that is primary. While they always end up with the conclusion that "the theory has passed the tests", they always love to add their own misinterpretations and misunderstandings about what the theory – quantum mechanics – actually says.
Let me look at Ball's initial motivation and introduction.
Quantum Darwinism, an Idea to Explain Objective Reality, Passes First TestsThat's too bad if an idea linked to quantum mechanics "explains objective reality" because a primary fact proven in the quantum revolution is that the reality isn't "objective" – it is unavoidably observer-dependent and in this sense "subjective".
It’s not surprising that quantum physics has a reputation for being weird and counterintuitive. The world we’re living in sure doesn’t feel quantum mechanical.What's remarkably about these two first sentences of the article is that they are exactly what Sidney Coleman mocked in his 1994 talk Quantum Mechanics In Your Face (TRF 2010). Let me quote from my older text:
At the very end, Sidney paraphrases a wise comment by philosopher Ludwig Wittgenstein. People used to believe geocentrism. Wittgenstein asked why people had usually considered such a history "natural". His friend told him that it was because it "looks like" the Sun is revolving around the Earth. Wittgenstein replied with this key point:So nice! ;-) So Mr Ball, you're wrong about thousands of technicalities and your and your soulmates' proposals to replace quantum mechanics with something else. But at the root of all this misguided activity, there is this single, obvious, wrong assumption: you just believe that quantum mechanics is incompatible with our observations.
Well, what would it look like if it had looked as if the Earth were rotating? :-)
Obviously, it would look exactly like the world around us. ;-) It's natural for things to move - and people could have known for quite some time that "free motion" is indistinguishable from the rest (the old principle of relativity, perhaps combined with the equivalence of inertial and gravitational masses).
Some people try to justify the scientifically invalid approach of the geocentrists but they are just wrong. The conclusion that "it seems that geocentrism had to be valid" was always completely irrational. It couldn't have ever been justified by the scientific evidence. Geocentrism was always a naive emotional dogma that was spreading by the "consensus" of the blinded believers, not by rational arguments.
In the very same way, some people keep on saying that it "looks like" there must be a classical mechanism beneath the quantum phenomena - a real process corresponding to the reduction of the wave packet. But Coleman encouraged everyone to seriously consider the following question:
Well, what would it look like if it looked like that the world is really following the causal laws of quantum physics without any [objectively real, he meant] reductions of the wave packets - and not any laws of classical physics - at the fundamental level?
Needless to say, it would look exactly as our ordinary everyday life. Welcome home. :-) And thank you for your patience.
You never state this belief of yours in these clear words because you don't have the courage. You know that if you said quantum mechanics contradicts my observations, many more people would understand – and join me in pointing out – that you are completely misguided about the very basic points in physics. So you are obfuscating the belief of yours in various ways. But at the very end, you do believe that quantum mechanics is incompatible with observations.
But it isn't. It is perfectly compatible – otherwise physicists would have already thrown it away. Quantum mechanics is perfectly compatible with our observations of the very small, of the very big, and everything in between, too.
The vexing question then becomes: How do quantum probabilities coalesce into the sharp focus of the classical world?Well, the only correct answer is that it never does and you've been writing nonsense throughout your life. But for some reasons, you don't like this answer, do you? You would prefer a different one, wouldn't you?
Our world works according to probabilistic laws – and it's true not only in the intrinsically quantum situations. In practice, the laws are probabilistic even when a classical approximation of the laws looks good enough, like in the casinos. Every kid knows that some things occur by chance. Last night, I watched the 1968 crime soap opera The Sinful People of the City of Prague (the episode about a missing shoe) where the cops shared the quote After all, chance is God by Anatole France (the TV quote was simplified, the page I linked to says "Chance is perhaps the pseudonym of God when he did not want to sign."). Even very regular people know very well that chance is very important and omnipresent in our world!
Quantum mechanics adds the uncertainty principle which guarantees that some degree of uncertainty – i.e. some existence of probabilities that are strictly in between 0 and 100 percent – is unavoidable. And indeed, it is unavoidable in Nature.
Statements about big objects' properties may "look" certain because quantum mechanics may predict probabilities to be 99.9999% or higher for statements that are sufficiently trivial – vicinities of some dominant mean values of the predictions etc. If the vicinities are much broader than the error margin, the certainly may get very close to 100%. But quantum mechanics never allows the certainty to go to 100% for generic, non-tautological propositions (except for statements guaranteed by the conservation laws etc.).
But in fact there’s no reason to think that the large and the small have fundamentally different rules, or that there’s a sudden switch between them.Right. But the correct theory that holds for the small and the large is quantum mechanics, not a classical or objective theory as you believe.
Over the past several decades, researchers have achieved a greater understanding of how quantum mechanics inevitably becomes classical mechanics through an interaction between a particle or other microscopic system and its surrounding environment.Quantum mechanics can never "become" classical physics. Quantum mechanics is one in which \(FG-GF\) for a general pair of observables \(F,G\) is nonzero, proportional to Planck's reduced constant \(\hbar\). Classical physics is where \(FG-GF=0\). For this reason, quantum mechanics cannot become classical physics in the exact same sense in which a nonzero number such as two or pi can never become zero.
Ball's writing is a typical example of the manipulative pseudoscience. All of this garbage rhetoric, useless experiments, their interpretations, hopeless new alternative theories, would-be arguments for them etc. is motivated by the consumers' belief that quantum mechanics disagrees with the observation. But this fundamental assumption of this whole quantum flapdoodle industry is a dogma everyone must remain silent about. It's never properly tested by these people – if they tested it (they would first have to learn quantum mechanics and how to make predictions using it which they clearly misunderstand), they could see that the fundamental dogma of this industry, and therefore every single "research direction" motivated by it, is wrong. But they don't really want to settle this question because the anti-quantum zeal is a religion of a sort and the emitters of fog about quantum mechanics are religious bigots.