QFT made Bohmian mechanics a non-starter: missed opportunities?

[WernerQH]

There's no problem whatsoever to apply the formalism to the fusion processes in the Sun.

We all know that. You are refusing to answer my question. Is it too embarrassing?

 

[vanhees71]

I obviously don't understand the question. The state of the matter in the Sun is that of a plasma close to thermal equilibrium, and you have thus a well-"prepared state" you can do calculations with. Where do you think contradicts this example in any way the here discussed statistical/ensemble interpreation of Q(F)T?

 

[WernerQH]

The state of the matter in the Sun is that of a plasma close to thermal equilibrium, and you have thus a well-"prepared state" you can do calculations with.

I thought state preparation is something physical, brought about by an experimenter in the real world. Apparently for you it can also be something that happens in the mind of a theorist. Never mind.

 

[vanhees71]

The Sun is also the result of a "preparation process" in the sense we are discussing it here. Of course, it's not prepared by a human being in the lab, but that is completely irrelevant to the discussion about the formal meaning of the quantum state within the ensemble interpretation.

 

[WernerQH]

The Sun is also the result of a "preparation process" in the sense we are discussing it here.

Your use of the term "preparation process" is so general as to render it meaningless. I don't see how this clarifies the "formal meaning of the quantum state". Merely reiterating these anthropomorphic terms doesn't make them precise. After decades of mutual indoctrination physicists have learned to apply quantum theory and have become accustomed to the required mental gymnastics. You may think that the formulation of the theory leaves nothing to be desired, but this is a view I do do not share.

 

[vanhees71]

So what's your "definition of the quantum state"? For me the ensemble interpretation is the most simple and close to what's really done in physics.

 

[WernerQH]

We agree on the mathematical definition. My concern is how it relates to the real world. But for you this is probably a merely philosophical question :-)

 

[PeterDonis]

I thought state preparation is something physical

Yes.

brought about by an experimenter in the real world.

This is way too restrictive. Natural processes that happen without humans being involved can count as state preparations. Otherwise QM would be limited to predicting what can happen in human laboratories.

 

[Demystifier]

"equivalence class of preparations" is quite vague, as it cannot be equivalent as defined by QM itself (no cloning).

Unknown state cannot be cloned. Known state can be cloned. When the preparation is known, the state is known.

 

[gentzen]

We agree on the mathematical definition. My concern is how it relates to the real world. But for you this is probably a merely philosophical question :-)

Statements like "that is merely philosophy" or "that is just mathematics" have the problem that both disciplines are huge, hence such a statement either contains very little information, or else risks to denigrate huge complex academic fields.
Pauli accusing Bohmian mechanics (and other opposition to Copenhagen) as resulting from "metaphysical prejudices" doesn't suffer from that problem. Not sure how helpful it would be to blame religion, psychology, or ethics (seen as subfield of philosophy) instead, to classify some unresolvable conflict. The risk to devalue serious human endeavors remains.

Still, I guess it would help me if "merely philosophical question" would be replaced by something more concrete, like metaphysics, metamathematics, linguistics, or maybe also postmodern nonsense, continental philosophy, ... whatever drew your scorn.

 

[vanhees71]

Parts of the Copenhagen doctrine is also pretty vague. A lot of all the confusion and apparent "weirdness" of QT is due to the "great Oracle" from Copenhagen rather then in the theory itself...

 

[Demystifier]

Still, I guess it would help me if "merely philosophical question" would be replaced by something more concrete, like metaphysics, metamathematics, linguistics, or maybe also postmodern nonsense, continental philosophy, ... whatever drew your scorn.

Those who say "that's just philosophy" are usually not interested in philosophy, so it's not to be expected that they distinguish different branches of it. All philosophy often sounds like "postmodern nonsense" to them.

risks to denigrate huge complex academic fields

In the case of philosophy it's not a risk, it's their intention.

The risk to devalue serious human endeavors remains.

They just don't think that philosophy is serious. Their own philosophy certainly isn't, and they don't think that philosophy of others can be more serious than that.

Perhaps their attitude towards philosophy can be compared to an attitude of anti-vaxxers and climate-change-denyers towards science. They don't understand it and don't appreciate it, but often they use a trivialized version of it to win an argument.

 

[vanhees71]

The difference between vaccination and philosophy is that the former is "evidence/science based" and the latter just free speculation of the human mind. SCNR.

 

[Demystifier]

The

The difference between vaccination and philosophy is that the former is "evidence/science based" and the latter just free speculation of the human mind. SCNR.

is a philosophy itself. SCNR.

 

[vanhees71]

Yes, and that's why it's just based on the subjective interpretation of my experience with reading philosophical papers :-).

 

[gentzen]

The

is a philosophy itself. SCNR.

But it is not a subfield of philosophy in the sense of philosophy as an academic field.

Those who say "that's just philosophy" are usually not interested in philosophy, so it's not to be expected that they distinguish different branches of it. All philosophy often sounds like "postmodern nonsense" to them.

And if analytic philosophy had never happened, this would be totally unproblematic. They tried to "save" philosophy from metaphysics and postmodern nonsense. But because of them, substantial parts of most structural sciences and linguistic are now part of philosophy. (Let me ignore philosophy of science here, because in this case the overlap was created intentionally.)

The different notions of what it means to be a theory, the different ways to construct models of a theory, the different notions of a model, the different possible satisfaction relations between theories and models, the different ways in which theories can be equivalent, or the notions how one theory can be stronger than another, or more expressive, all that is now part of analytic philosophy. For computer science, that stuff can be relevant in applications, so it is obvious that you cannot shrug it off as mere philosophy. For mathematics, as long as it stays sufficiently far away from computer science related questions, ignoring that stuff is harmless, and it is safely encapsulated as another subdiscipline of mathematics. For physics, the situation is weird, not completely sure why. My impression is that the splitting-off of subdisciplines from physics somehow didn't work as well as for mathematics. Perhaps it is because the typical physicists enjoys being a generalist much more than the typical mathematician.

 

[Demystifier]

The different notions of what it means to be a theory, the different ways to construct models of a theory, the different notions of a model, the different possible satisfaction relations between theories and models, the different ways in which theories can be equivalent, or the notions how one theory can be stronger than another, or more expressive, all that is now part of analytic philosophy.

Do you know a book that studies such stuff?

 

[Structure seeker]

The

is a philosophy itself. SCNR.

I think Demystifiers point is that vanhees' statement is not valid to dismiss philosophy, since it is itself a philosophic statement. It is therefore self-referential and, like the sentence "this sentence is false" cannot lead to a proof, it has no value in the discussion.

But the statement doesn't literally dismiss all philosophic discussion.

 

[vanhees71]

But it is not a subfield of philosophy in the sense of philosophy as an academic field.


And if analytic philosophy had never happened, this would be totally unproblematic. They tried to "save" philosophy from metaphysics and postmodern nonsense. But because of them, substantial parts of most structural sciences and linguistic are now part of philosophy. (Let me ignore philosophy of science here, because in this case the overlap was created intentionally.)

I'd say the category "structural sciences" was rather invented to distinguish math and informatics from the "metaphysical nonsense part" of philosophy.

The different notions of what it means to be a theory, the different ways to construct models of a theory, the different notions of a model, the different possible satisfaction relations between theories and models, the different ways in which theories can be equivalent, or the notions how one theory can be stronger than another, or more expressive, all that is now part of analytic philosophy. For computer science, that stuff can be relevant in applications, so it is obvious that you cannot shrug it off as mere philosophy. For mathematics, as long as it stays sufficiently far away from computer science related questions, ignoring that stuff is harmless, and it is safely encapsulated as another subdiscipline of mathematics. For physics, the situation is weird, not completely sure why. My impression is that the splitting-off of subdisciplines from physics somehow didn't work as well as for mathematics. Perhaps it is because the typical physicists enjoys being a generalist much more than the typical mathematician.

The split into subdisciplines is simply necessary because of the vast amount of wisdom generated by the sciences. You cannot oversee "all of physics" as was possible till the early 1900s.

 

[Demystifier]

For computer science, that stuff can be relevant in applications, so it is obvious that you cannot shrug it off as mere philosophy. For mathematics, as long as it stays sufficiently far away from computer science related questions, ignoring that stuff is harmless, and it is safely encapsulated as another subdiscipline of mathematics. For physics, the situation is weird, not completely sure why.

Physics is usually viewed as a natural science, based on empirical evidence. Computer science and math are formal sciences, based on pure thought. Since philosophy is also based on pure thought, this probably explains why philosophy is generally more accepted in the latter than in the former.

 

[gentzen]

Do you know a book that studies such stuff?

I don't know any book exclusively dedicated to those concepts and definitions in isolation. Such stuff is typically presented in introductory chapters or in appendices of books concerned with analysis or applications of specific logics (or other applications). Here is a typical example of (the beginning of) such a presentation:

Now that we have described the syntax of our language (that is, the set of well-formed formulas), we need semantics, that is, a formal model that we can use to determine whether a given formula is true or false. One approach to defining semantics is, as we suggested above, in terms of possible worlds, which we formalize in terms of (Kripke) structures. (In later chapters we consider other approaches to giving semantics to formulas.) A Kripke structure $M$ for $n$ agents over $\Phi$ is a tuple $(S, π, \mathcal{K}_1, . . . , \mathcal{K}_n )$, where $S$ is a nonempty set of states or possible worlds, $π$ is an interpretation which associates with each state in $S$ a truth assignment to the primitive propositions in $\Phi$ (i.e., $π(s) : \Phi → \{\bf{true}, \bf{false}\}$ for each state $s ∈ S$), and $\mathcal{K}_i$ is a binary relation on $S$, that is, a set of pairs of elements of $S$.

Note the highlighted words: "syntax", "semantics", "(Kripke) structures", "states", "possible worlds", and "interpretation". Those are highlighted in the original, because the intention of that paragraph is to define those words. I guess there is than more than just one word in this list passionately hated by vanhees71.

A good source for such material is SEP, but also here it is more often found in some appendix rather than the main article. One problem for me with suggesting specific books is also that "I like good readable (medium level) German books", at least as far as it concerns non-electronic books. For example, some of the books by Dirk W. Hoffmann helped me get an initial broad overview of that stuff.

Here is my attempt to suggest an electronic book in English related to logic:

Trying to read about Logic, which I never covered in much depth as a physicist. Currently on "First Steps in Modal Logic" by Sally Popkorn. I really recommend Schechter's "Classical and Nonclassical Logics: An Introduction to the Mathematics of Propositions"

Frank Pfenning's Automated Theorem Proving Handouts are a nice easily accessable resource for many topics in Logic from a non-philosophical engineering point of view.