Monday, December 17, 2018

When terms, phrases, slogans don't repay the time needed to learn them

Most of the interpreters of quantum mechanics aren't natural scientists; they belong to humanities. This proposition holds because they don't search for theories that work and for the ideally quantitative evidence to strengthen such theories. Instead, they prefer qualitative assertions, the nurturing of words, and the reviews of other people who have said such words in the history.

Physicsnut has found a nice example of this talkative approach, a 504-page review of the quantum by Christopher Fuchs, a Quantum Bayesian guy, written in 2001. You may see that it is a historical book that pretends to be a scientific paper. The physics isn't at the center. Instead, "he said she said" plays the key role.

While Fuchs and other QBism guys may say some correct things about the meaning of quantum wave functions, they still push the thinking about the field in a wrong direction.



David Mermin – who is probably the actual originator of the "shut up and calculate" phrase to describe the prevailing attitude of quantitative physicists to the foundations of quantum mechanics (while Feynman is the originator of the content) – has also learned how to love Niels Bohr (2003).

Previously, in 1996 and in 1998 (the newer paper is expanded), he presented his "Ithaca interpretation" of quantum mechanics – which was named in this way because he wasn't fortunate enough to work in the Danish capital but only in a New York State campus of Cornell.



Now, like the QBists, Mermin has said lots of correct things about quantum mechanics – and has contradicted lots of wrong assertions about quantum mechanics. And I have said the very same things not only about the QBists and Mermin but also about Wojciech Zurek, the most famous proponent of decoherence.

But despite the correct statements, all these people still apparently love the production of the word salad. Quantum mechanics dramatically differs from classical physics – while it's more than analogous from other perspectives – but this new mixture of the "very new" and "very old" may still be seen to be rather straightforward. You shouldn't need hundreds of pages to understand the basic rules and concepts, the universal postulates of quantum mechanics. But even the people who are most reasonable concerning the meaning of quantum mechanics write lots of redundant stuff and they must like it.

In a 2014 blog post, I discussed the approximate synonyms of decoherence that Wojciech Zurek has generated over the years, including:
  • (his behavior of the) pointer states
  • decoherence
  • envariance
  • einselection
  • quantum Darwinism
From the viewpoint of the linguists or other people in social sciences and humanities, these terms sound completely different. But the physics ideas he is trying to address by these catchwords are almost identical. Pointer states are meant to be the states of the pointer, a part of the measurement apparatus, and when you describe them as parts of the measurement apparatus or the whole apparatus, you really want to assume that the different possible final states of the apparatus may be considered mutually exclusive classical outcomes, so they decohere from each other.

Decoherence itself is a natural enough word – it is the loss of coherence which means the disappearance of the information about the relative phases of some quantum mechanical probability amplitudes. But this irreversible process is spun differently if you call a part of this process "envariance" or "einselection" (mutations of some standard words) – and this apparent proliferation of the increasingly classical information is given an evolutionary flavor if you call it "quantum Darwinism".

You know, a person who is high feels differently when she hears any of these terms. But a person who actually cares "how the theory works" knows that all these feelings are irrelevant for the understanding and usage of the actual theory and there is only one theory. Decoherence is one phenomenon and the other terms are just linguistically different ways to describe the same idea.

Just like Zurek, Mermin has produced lots of similar catchwords. It's not surprising that if someone writes hundreds of pages filled with word salad, it must also contain some new catchwords and redundant terminology with useless definitions. Mik has pointed out that David Mermin and Ron Garret have coined:
  • correlations without correlata
  • the zero worlds interpretation
Just like Zurek's phrases, these may be considered good pieces of the marketing. Just to be sure, these two very differently sounding phrases are supposed to convey the exact same idea, whatever it is supposed to be. You know, inventing catchy names, titles, and slogans is an entertaining activity. I know that, too. I do admit of having spent joyful hours with inventing names for physics discoveries that sometimes hadn't even been done and papers that hadn't been ready to be written and published. It's so intriguing to invent witty slogans and titles, isn't it? ;-)

"Correlation without correlata" is assumed to be witty because it's a borderline oxymoron – but the very existence of the phrase is meant to say that there is no actual sharp, full-blown contradiction. And that's why it's supposed to be funny. You must have heard other slogans that (almost) sound like contradictions but they are meant to describe something that is possible, right? Can you give me a few examples?

Similarly, "the zero worlds interpretation" is widely viewed as witty because it's a variation of some widespread terminology in which the variations – in this case, the replacement of the numeral "one" or "many" by "zero" – claims to show the author's "thinking outside the box".

All these terms are good enough marketing. People employed in corporate P.R. departments may be doing similar things and they are often receiving good salaries for that. But if it's good marketing, is it good physics? Well, my answer is Usually no. And it is not good physics in these cases.

These phrases and slogans are close to being "worthless for physics" because they carry no content that may be usefully exploited in many situations.

Compare the phrases to some terminology in quantum mechanics and the relevant mathematics that actually makes sense, such as:
  • the uncertainty principle
  • operators
  • observables
"The uncertainty principle" sounds interesting but there's actually some content. It may be expressed as an inequality and the inequality may be generalized to any pair of observables. Observables and (linear Hermitian) operators should be identified within quantum mechanics – but "observables" is supposed to describe the conceptual and physical aspects of the concept while "operators" is mainly the name for the mathematical object that represents them in the formalism.

All of quantum physics is actually composed of observables/operators and their algebras. We have operators of position, momentum, angular momentum, parity etc.; field operators, picture-changing operators, and hundreds of other examples of subclasses of operators. The applications of the terms above are innumerable. They cover very technical detailed research as well as the talk about the universal rules and foundations.

Richard Feynman has been rather extreme about it but I do believe that it's a natural part of the brilliant physicist's attitude that he or she simply dislikes redundant terminology and talk that is vacuous or baloney. When someone introduces a new phrase, there should better be some content that makes sense – otherwise the creator or proponent of the phrase seems like a crackpot or a snake oil salesman. As soon as one has some justified doubts whether the introduction of a new phrase is justified, the real physicist is likely to become suspicious about the proponent of the new cliché.

Now, "correlations without correlata" and the "zero worlds interpretation" are just deeply misleading slogans that cannot be useful for anything. Why? First, it is simply not true that the correlations in quantum mechanics lack the "correlata". A correlation is just a statistical relationship between random variables; in a narrower sense, the correlation describes the proximity to a linear relationship.

If you understand the basic definition of correlations, you must immediately know what the "correlata" must mean if this word is used at all. The random variables are the correlata! Does quantum mechanics include the correlata whose correlations are calculable using the formalism of quantum mechanics? You bet. Quantum mechanics is full of random variables. Every observable quantity is a random variable according to quantum mechanics. The theory predicts that almost every observable is random – involving some uncertainty – in almost every situation. If you have a singlet state of two spins, the two qubits are random variables that are perfectly anticorrelated (only up-down or down-up are possible).

It's simply wrong to say that the "correlata don't exist" according to quantum mechanics. They – e.g. the values of \(j_z\) – exist in the sense that they are as measurable as they were in a world governed by classical physics. After all, it's still the same world – we just use a better (quantum) theory to describe it now. The only correct statement that the slogan "correlata don't exist" could mean is that the correlated random variables don't obey the laws of classical physics – so they don't "exist" in the sense of existence that was allowed in classical physics. But that doesn't mean that they don't exist at all. They are measurable so of course they exist.

The problem with the "zero worlds interpretation" is almost the same. This slogan is meant to convey the misleading viewpoint that the observables that may be measured "don't really exist" (the correct statement is that their values must be considered uncertain, according to the quantum rules that also allow interference, before the measurement). And because the information according to classical physics was all about the coordinates and momenta, "nothing exists" or "no world exists".

"The many worlds interpretation" is supposed to solve some psychological or psychiatric problems that some people have with quantum mechanics by imagining that the being is composed of infinitely "many worlds" and all those worlds are "real" in some sense of classical physics. Because classical physics is rejected even in the single world we believe to inhabit, there are zero worlds that obey classical physics (according to the rules of quantum mechanics). So every proper description of quantum mechanics implies the existence of "zero worlds" – but they really mean "zero classical worlds".

The only correct interpretation of the "zero worlds interpretation" that also makes the name sound "logical" is the observation that according to the user of this slogan, the number of worlds that obey the laws of classical physics is zero. Great. Is that a good enough observation to describe the foundations of quantum mechanics?

Clearly, the answer is No. To discover quantum mechanics, Werner Heisenberg and pals couldn't just deny classical physics. It wasn't enough to say that the number of worlds governed by the old laws was zero. They had to find the ingenious replacement – quantum mechanics itself! The "zero worlds interpretation" only captures the denial, the destructive part of the process, but it simply contains nothing from the constructive part. And the constructive part is really the nontrivial part we celebrate – the part that brought them all those "greater than average" Nobel prizes in physics.

The phrase "zero worlds interpretation" only captures a trivial, not terribly specific, part of quantum mechanics, namely that it isn't classical physics. There's another equivalent way to articulate this complaint of mine. "Zero worlds interpretation" looks like a special case of "\(N\) worlds interpretation" where we substitute \(N=0\). We also know the "many worlds interpretation" that is obtained by substituting \(N={\rm many}\) – recall that many tribes of savages have simplified the counting to "one, two, three, many" and some tribes have omitted "three", too.

Well, a problem with the "\(N\) worlds interpretation" is that it isn't well-defined for general values of \(N\), not even the integer values of \(N\in\ZZ\), and if you decided to associate these phrases with specific values of \(N\) with some meaning, they couldn't really be generated out of a general template to build "\(N\) worlds". So this whole terminology is cheating. It sounds like there is some general theory that allows you to pick \(N\) such that you get the proper quantum mechanics for \(N=0\). But there is no such generalized theory. The simple reason is that if you substituted \(N=0\) into a template, you would probably get a very empty or dull object (think about a wallet with zero banknotes) – but quantum mechanics is far from that.

There are really just two possible kinds of theories, the quantum mechanical ones and the classical ones. You may call them \(N=0\) and \(N=1\) theories but they are so qualitatively different that it isn't useful to conflate them into a "generalized theory" labeled by the parameter \(N\). These are the reasons why the terminology doesn't really work. And because it doesn't really work, no genuine scientist who knows what she is talking about will use this terminology. It is useless for people who know what they're talking about. The phrase may only be useful for people who don't know what they're talking about!

When I am exposed to some new terminology, I always – consciously or subconsciously – do something that almost every person should do. I am estimating how much time (in minutes), energy (in kilocalories), and memory (in bytes) has to be invested to learn the letters and words that make up the phrase as well as a proposed "definition" or some "basic rules to operate with the phrase" that are hopefully provided by the champion. This time, energy, and memory is considered the initial investment. And then I am trying to predict – or, later, observe – the situations in which the new phrase is being used in a way that makes it useful, e.g. because it would be much more cumbersome and time-consuming to express the same ideas without that new phrase.

If a phrase doesn't simplify the articulation of ideas and propositions in particular examples, or if the number of such cases is too small, the phrase is a waste of time, a waste of energy, and/or a waste of memory! Virtually everything that the "interpreters" of quantum mechanics have written about that field is a waste of time, energy, and memory. And sadly, that includes a great majority of the stuff written and promoted by those rare "interpreters" who actually have some clue what's going on.

In the text above, I have discussed the redundant phrases sold by Mermin, Garret, and Zurek. But the Quantum Bayesianists have produced lots of their examples, too. Well, the very term "Quantum Bayesianism" is redundant. To make things worse, they renamed it to "QBism" while insisting that those two things aren't even equivalent. Needless to say, all the probabilities used by an observer have always been subjective and therefore "Bayesian" – so as long as one is sane, this is nothing else than the Copenhagen Interpretation once again. On top of that, the Quantum Bayesianists have filled their papers with phrases such as "Dutch book" and other special terms imported from the world of bookmakers (or from the applied probability calculus, if you wish).

Now, Bayesian probabilities are also useful in betting but that does not mean that physics papers should include many pages or whole sections copied from the textbooks for bookmakers, does it? Because both quantum mechanics and bookmakers use subjective probabilities, they are analogous to a certain extent. But importing too much special stuff from one application to the other (e.g. from betting to quantum mechanics) is bound to be a waste of time, energy, and memory, too.

Maybe someone is clueless about the meaning of probabilities and odds or their basic relationships and methods to calculate the odds needed to bet that a soccer team wins or anything like that. It may be useful if this person learns how it works because it's useful and it's fun. But the teaching of this stuff is just a pedagogic effort, it is not a part of physics research. Moreover, it is a pedagogic effort not directly related to physics.

The long books about the foundations of quantum mechanics are therefore full of:
  • wrong views held by the author, usually caused by his blind belief that the world is fundamentally classical
  • quotes from similarly deluded authors in the past
  • tons of useless phrases coined to express some wrong ideas, usually in many different ways
  • some phrases designed to express mostly correct ideas – but most of such phrases are useless and redundant
  • teaching of useful and, more often, useless ideas – without appreciating that the teaching of some basic prerequisites isn't really research yet
  • analogies with other disciplines such as betting – which often go way too far and most of the stuff is useless for the original discipline
The industry of "interpreters" of quantum mechanics is a field that has allowed all these pathologies and a few others because it hasn't worked as a natural science. In fact, it hasn't worked as a field of critical thought at all. The Maudlins and similar talkative crackpots have almost never been told that they were talkative crackpots. Instead, they were able to hire other crackpots who have licked their rectums which is how the amount of wrong and redundant stuff could exponentially proliferate.

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