What makes the interpretations of Quantum Mechanics so important?

[RUTA]

Summary: Provided it's correct that the interpretations of Quantum Mechanics can be neither proved nor disproved why then do researchers invest so much time and talent in this field?

Adam Becker wrote an entire book answering that question. Some people believe foundations is worthless for physics, but as Adam points out in his book, the converse is rather true. https://www.physicsforums.com/threads/interview-with-astrophysicist-adam-becker-comments.943015/

 

[Jimster41]

So it's the pure joy of participating in an intellectual challenge with no quantifiable outcome.

I think that's sometimes called "curiosity".

 

[timmdeeg]

I think that's sometimes called "curiosity".

You mean the "curisity" to learn which interpretation is the "true" one? Will we ever know?

But wait, how about the "curiosity" how to get rid of assumptions which seem to contradict each other, e.g. the ugly collapse and the bizarre MWI? Would this be a preferred interpretation, perhaps the "true" one? I haven't been following up the Thermal Interpretation of @Neumaier closely. Isn't this interpretation formulated without recourse to the collapse of the wavefunction and to the Many Words? If yes, has it the potential to be the "true" interpretation then?

 

[Michael Price]

... how to get rid of assumptions which seem to contradict each other, e.g. the ugly collapse and the bizarre MWI?

Not sure what "bizarre" means here, but MWI is just QM without the ugly collapse postulate.

 

[ftr]

The QCD langragian is a component of the Standard Model Lagrangian. However conclusions about particles in QCD alone are not strictly accurate for the full Standard Model. This is basic enough QFT however, I'd suggest reading an introductory textbook.

apparently that is true, however, I have read a lot of textbooks for QFT, standard models, QCD( which are mostly about the formalism) but this fact did not seem obvious. I did check these books again and googled but I did not find any clear specific statement in that regard, maybe I should try harder.

 

[timmdeeg]

Not sure what "bizarre" means here,

Isn't the story told in #1 here a bit bizarre?

 

[vanhees71]

It's not bizarre, it's simply a misleading formulation you read quite often. I've never understood what the intention of the authors making it may be. It's said "a quantum state can be in a superposition". That's just a meaningless intellectual-sounding phrase.

QT is mathematically formulated using a certain kind of vector space, the socalled Hilbert space, i.e., a complex vector space with a scalar product, inducing a norm according to which it is complete (i.e., all Cauchy sequences of vectors converge), i.e., it's a Banach space. Usually one also assumes that the Hilbert space is separable, i.e., that there exist countable complete orthonormal sets. As for any vector space, each vector can be written as a superposition (generalized also to infinite series) with respect to any such complete orthonormal set. That's a mathematical feature and not very bizarre but simply natural for any Hilbert space.

Further a certain special kind of states, the socalled pure states, can be represented by a normalized state vector $|\psi \rangle$. The true representatives of states are always statistical operators, i.e., self-adjoint positive semidefinite operators with trace one. For a pure state represented by a state vector $|\psi \rangle$ that statistical operator is the projection operator $\hat{\rho}_{\psi}=|\psi \rangle \langle \psi|$.

The observables are described by self-adjoint operators, defined on a dense subspace of Hilbert space, which define a complete set of eigenvectors, sometimes including generalized states, living in the dual of the domain of the operator. If an observable is represented by such an operator $\hat{A}$ the possible values it can take are the (generalized) eigenvalues (or spectral values) $a$ of this operator. If the system is prepared in a pure state, for which the observable takes a determined value $a$, it must be represented by an eigenvector of this eigenvalue, i.e., $\hat{A} |\psi \rangle=a |\psi \rangle$. Any vector, representing a pure state can be written as a superposition wrt. the eigenbasis of $\hat{A}$. If it's not a eigenstate of $\hat{A}$ the observable $A$ doesn't take a determined value, and then measuring $A$ you only know the probabilities to get each of the possible values $a$. That's it.

There's nothing bizarre with this, it's simply how physicists over the last 119 years have figured out nature behaves.

 

[timmdeeg]

Thanks for your detailed response.

It's not bizarre, it's simply a misleading formulation you read quite often. I've never understood what the intention of the authors making it may be. It's said "a quantum state can be in a superposition". That's just a meaningless intellectual-sounding phrase.

Perhaps "bizarre" is the wrong wording. What puzzles me is the multiple existence of the observer. Claus Kiefer says in "Der Quantenkosmos" Das mehrfache und gleichzeitige Vorhandensein desselben makroskopischen Beobachters erscheint freilich so ungeheuerlich, daß es nicht verwundert, wenn Alternativen untersucht werden." That's what I intended to express in my recent post.

 

[vanhees71]

Well, esoterics sells, and since the "hippies saved physics" in the 1960ies quantum esoterics is a pretty well selling kind, particularly since people think it would have to do something with science...

I'm a bit surprised that Claus Kiefer nowadays also writes such stuff...

 

[timmdeeg]

I'm a bit surprised that Claus Kiefer nowadays also writes such stuff...

So what's the reason that physicists prefer other alternatives? I don't think that Kiefer is wrong here.

 

[timmdeeg]

It's said "a quantum state can be in a superposition". That's just a meaningless intellectual-sounding phrase.

Quantum mechanics says that the state of the particle can be a superposition of both possible measurement outcomes. It’s not that we don’t know whether the spin is up or down; it’s that it’s really in a superposition of both possibilities, at least until we observe it.

To understand you correctly is this "meaningless intellectual-sounding phrase" just a didact tool?

 

[vanhees71]

I don't know what it is. I never could make any sense of it. It's like saying "this vector in Euclidean 3D space is a superposition". Can you tell, what I want to say with this? I don't know, what sense it should make at all!

 

[vanhees71]

So what's the reason that physicists prefer other alternatives? I don't that Kiefer is wrong here.

Who prefers which alternatives? I know quite many physicists, but I've never met one who takes such esoterical pseudo-science (aka popular-science) writing seriously.

 

[Michael Price]

Thanks for your detailed response.

Perhaps "bizarre" is the wrong wording. What puzzles me is the multiple existence of the observer. Claus Kiefer says in "Der Quantenkosmos" Das mehrfache und gleichzeitige Vorhandensein desselben makroskopischen Beobachters erscheint freilich so ungeheuerlich, daß es nicht verwundert, wenn Alternativen untersucht werden." That's what I intended to express in my recent post.

tut tut. This forum is meant to be in English. Translation:
"The quantum cosmos. The multiple and simultaneous presence of the same macroscopic observer seems so monstrous, however, that it is not surprising that alternatives are investigated."
The MWI idea may seem "monsterous", but so have many new scientific ideas. If it fits the data, and is not magical, then it should be accepted. The MWI is a return to the classical certainties, where physical things are real.

 

[vanhees71]

LOL. So just observing this computer screen, i.e., registering the electromagnetic field with the retina of my eyes and processing it in my brain multiplies myself into zillions of copies. Where are all these copies of myself? Can I talk to them or see them or what? It's even a "return to classical certainties" to have all these copies? Last but not least, where in Everett's original writings are all these copies?

 

[Michael Price]

LOL. So just observing this computer screen, i.e., registering the electromagnetic field with the retina of my eyes and processing it in my brain multiplies myself into zillions of copies. Where are all these copies of myself? Can I talk to them or see them or what? It's even a "return to classical certainties" to have all these copies? Last but not least, where in Everett's original writings are all these copies?

The language of "timelines" is more helpful here. Each of the possible outcomes (near copies of you, in this example) are each actualized in their own timeline, which result from the splitting.
The language of splitting is in Everett's writing, even in his Wheeler-censored PhD thesis summary publication (see the footnote he was able to insert).

 

[vanhees71]

Do you have a reference? I only know the 9-page RMP paper (but I've to admit that I've not read it for a long time), which I remember not to have any esoteric statements like the creation of multiple copies of observers.

 

[Michael Price]

Do you have a reference? I only know the 9-page RMP paper (but I've to admit that I've not read it for a long time), which I remember not to have any esoteric statements like the creation of multiple copies of observers.

Since I have the article open in front of me,
"note added in proof"
... all the separate elements of the superposition individually obey the wave equation with complete indifference to the presence or absence ("actuality" or not) of any other elements. This total lack of effect of one branch on another also implies no observer will ever be aware of any "splitting" process...

But it is irrelevant what Everett said. It follows from quantum theory minus the collapse postulate.

 

[Quanundrum]

But it is irrelevant what Everett said. It follows from quantum theory minus the collapse postulate.

What follows Quantum Theory minus the Collapse Postulate is the 'Bare Theory' not MWI though.

 

[Michael Price]

What follows Quantum Theory minus the Collapse Postulate is the 'Bare Theory' not MWI though.

The bare theory has no way of making the other elements of the superposition disappear.

 

[Quanundrum]

The bare theory has no way of making the other elements of the superposition disappear.

If you assume the bare theory is fundamental, then indeed, but you do not get splitting worlds from this without additional assumptions, rendering it on par with Bohmian Mechanics and GRW

 

[Michael Price]

If you assume the bare theory is fundamental, then indeed, but you do not get splitting worlds from this without additional assumptions, rendering it on par with Bohmian Mechanics and GRW

Reference?

 

[Mentz114]

The bare theory has no way of making the other elements of the superposition disappear.

How can one prove they existed at all ? MWI is all speculation.

 

[Michael Price]

How can one prove they existed at all ? MWI is all speculation.

You need the all the elements in a superposition to make physics work at the microscale. If you're saying the laws of physics don't extrapolate to the macroscale, you'll need a dawn good reason to convince me.

 

[Mentz114]

You need the all the elements in a superposition to make physics work at the microscale.

MWI needs macroscopic superpositions as well, if I recall correctly.

If you're saying the laws of physics don't extrapolate to the macroscale, you'll need a darn good reason to convince me.

Huh ?
No, I'm saying MWI is not the laws of physics.

[edit]
@Michael Price - reading this I think am expressing my skepticism rather disrespectfully considering that you have studied these things to a level I cannot reach. I will let it rest and refrain from what are probably nit-picking objections.

 

[PeterDonis]

What follows Quantum Theory minus the Collapse Postulate is the 'Bare Theory' not MWI though.

Please give a reference for the "Bare Theory". I have only seen it used in philosophy books (and ones for lay people, not textbooks), such as Albert's Quantum Mechanics and Experience (at least I think that's the one where he uses that term).

 

[Quanundrum]

Please give a reference for the "Bare Theory". I have only seen it used in philosophy books (and ones for lay people, not textbooks), such as Albert's Quantum Mechanics and Experience (at least I think that's the one where he uses that term).

I am traveling atm. so pulling up references is cumbersome. Simply google: "Bare Theory" + "Jeffrey Barrett" and you will find the most comprehensive literature on both Everett's original thesis, as well as what David Albert indeed coined as 'Bare Theory'

 

[PeterDonis]

Simply google: "Bare Theory" + "Jeffrey Barrett"

This turned up a number of papers, including this one:

http://www.socsci.uci.edu/~jabarret/bio/publications/FixBareTheory.pdf
However, I'm not finding any actual physicists who either advocate for or use the "bare theory", only philosophers discussing it.

 

[Quanundrum]

This turned up a number of papers, including this one:

http://www.socsci.uci.edu/~jabarret/bio/publications/FixBareTheory.pdf
However, I'm not finding any actual physicists who either advocate for or use the "bare theory", only philosophers discussing it.

The same goes for MWI :)

 

[PeterDonis]

The same goes for MWI :)

One could say that physicists don't "use" any particular interpretation to actually analyze experiments, other than the minimal "shut up and calculate" interpretation, but many physicists have written papers on the MWI. That's why I was wondering if any physicists had written papers on the Bare Theory.

 

[Michael Price]

MWI needs macroscopic superpositions as well, if I recall correctly.

Huh ?
No, I'm saying MWI is not the laws of physics.

[edit]
@Michael Price - reading this I think am expressing my skepticism rather disrespectfully considering that you have studied these things to a level I cannot reach. I will let it rest and refrain from what are probably nit-picking objections.

I simply say that MWI is the extension of the microscale laws.to the macroscale, and leave it there.

 

[forcefield]

I simply say that MWI is the extension of the microscale laws.to the macroscale, and leave it there.

How does that relate to saying that there is a nearly infinite number of laws that change when the scale (or size/complexity) changes until Newton's laws ?

 

[Michael Price]

How does that relate to saying that there is a nearly infinite number of laws that change when the scale (or size/complexity) changes until Newton's laws ?

The laws don't change with the scale.

 

[forcefield]

The laws don't change with the scale.

From the Feynman Lectures here: "As we apply quantum mechanics to larger and larger things, the laws about the behavior of many atoms together do not reproduce themselves, but produce new laws, which are Newton’s laws, which then continue to reproduce themselves from, say, micro-microgram size, which still is billions and billions of atoms, on up to the size of the earth, and above."

 

[Michael Price]

From the Feynman Lectures here: "As we apply quantum mechanics to larger and larger things, the laws about the behavior of many atoms together do not reproduce themselves, but produce new laws, which are Newton’s laws, which then continue to reproduce themselves from, say, micro-microgram size, which still is billions and billions of atoms, on up to the size of the earth, and above."

He doesn't mean what you think he means.