Insights 9 Reasons Quantum Mechanics is Incomplete - Comments

[Demystifier]

Greg Bernhardt submitted a new blog post

9 Reasons Quantum Mechanics is Incomplete

Continue reading the Original Blog Post.

 

[thephystudent]

Looks interesting, I have two rather naïve questions.

1) What do you mean by completeness? Is it a term you use colloquially, or with a precise technical meaning? On wikipedia I see for example a definition a formal system is called complete with respect to a particular property if every formula having the property can be derived using that system. Which makes me wonder, is quantum mechanics (or its interpretations) a formal system?
2) Can Gödel incompleteness have anything to do with it?

 

[DarMM]

A possible variant of Old Copenhagen:
Everything can be described by quantum mechanics, but not everything at once, therefore QM is incomplete.

 

[Demystifier]

Looks interesting, I have two rather naïve questions.

1) What do you mean by completeness? Is it a term you use colloquially, or with a precise technical meaning?

I use it colloquially.

2) Can Gödel incompleteness have anything to do with it?

No.

 

[Demystifier]

A possible variant of Old Copenhagen:
Everything can be described by quantum mechanics, but not everything at once, therefore QM is incomplete.

This variant of old Copenhagen is quite in spirit of modern consistent histories.

 

[A. Neumaier]

''Bohmian mechanics: Only fundamental objects have trajectories.''

Electrons and photons in a medium (i.e., all electrons and photons we observe here on earth) are quasiparticles only. Do they have trajectories?

 

[Demystifier]

''Bohmian mechanics: Only fundamental objects have trajectories.''

Electrons and photons in a medium (i.e., all electrons and photons we observe here on earth) are quasiparticles only. Do they have trajectories?

Thanks for asking, they don't have trajectories in my view of BM (which somewhat differs from the standard view of BM).

 

[eltodesukane]

What mean a QM interpretation?
A classical version of QM? A classical understanding of QM?
There need not be such thing.

 

[A. Neumaier]

What means a QM interpretation?

https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics

 

[Demystifier]

What mean a QM interpretation?

Any explanation of QM beyond pure operationalism.

 

[haushofer]

What mean a QM interpretation?
A classical version of QM? A classical understanding of QM?
There need not be such thing.

An ontology, like any physics theory has. Of course, an ontology doesn't need to be classical.

 

[haushofer]

Electrons and photons in a medium (i.e., all electrons and photons we observe here on earth) are quasiparticles only. Do they have trajectories?

Mmm, can you elaborate on that? Why wouldn't a photon I observe be fundamental?

 

[A. Neumaier]

Mmm, can you elaborate on that? Why wouldn't a photon I observe be fundamental?

Because a photon in air or in glass is something different from a photon in vacuum (and similarly for an electron). Already their speed is different, and since all QED photons travel with the speed of light in vacuum, photons in a medium must have a different nature - they are quasiparticles only. Their nature changes each time they change the medium.

 

[Dr. Courtney]

Very nice article, well articulated and thought provoking. Thank you for writing this. After reflecting on the issues for a couple days, the question at the top of my mind is, Which physical theories are complete?

1. Classical mechanics?
2. Classical electrodynamics?
3. Classical thermodynamics?
4. Quantum statistical mechanics?
5. Classical (Newtonian) gravity?

My tendency is to consider classical mechanics as the shining example of excellence in a physical theory to which other scientific ideas should be compared. But by your criteria (2), the inability to clearly articulate a boundary between systems where classical is applied and where quantum is applied means that neither theory is complete. But if we are dogmatic about this criterion, are there any complete theories at all anywhere in science?

 

[bhobba]

I just want to mention Ensemble also has the same issue as Copenhagen - namely it assumes a classical world for the outcome to be an ensemble of.

Decoherent histories, while these days subsumed into Consistent Histories, tries to explain why some questions can't be asked - but it still has issues. Will those issues be resolved? Who knows.

Thanks
Bill

 

[bhobba]

Which physical theories are complete?

That's pretty much Dirac's view - it's simply just a progression of what's gone before rather than the paradigm shifting idea of Kuhn and advocated by Heisenberg and others. Its my view as well for what its worth.

To be clear - I think all physical theories are incomplete and likely always will be - we simply just keep fleshing them out more. Dirac for example believed that QM was just a natural outgrowth of classical physics where some of its assumptions are relaxed. Of course there is really no classical physics just QM so this view is reasonable under the idea espoused by Gell-Mann that its like peeling away layers of a onion skin:
https://www.ted.com/talks/murray_gell_mann_on_beauty_and_truth_in_physics

It's connection with beauty in physics is interesting as well. Dirac would be smiling.

Thanks
Bill

 

[atyy]

Very nice article, well articulated and thought provoking. Thank you for writing this. After reflecting on the issues for a couple days, the question at the top of my mind is, Which physical theories are complete?

1. Classical mechanics?
2. Classical electrodynamics?
3. Classical thermodynamics?
4. Quantum statistical mechanics?
5. Classical (Newtonian) gravity?

My tendency is to consider classical mechanics as the shining example of excellence in a physical theory to which other scientific ideas should be compared. But by your criteria (2), the inability to clearly articulate a boundary between systems where classical is applied and where quantum is applied means that neither theory is complete. But if we are dogmatic about this criterion, are there any complete theories at all anywhere in science?

The distinction between classical electrodynamics and quantum mechanics is that the former is intrinsically complete (detailed experimental data is needed to show it is incomplete), while the latter is intrinsically incomplete (even without deviations from detailed experimental data, we know it is incomplete because measurement is considered to be a special process).

Although the source of incompleteness is different, there is a similar distinction between classical electrodynamics and quantum general relativity. Quantum general relativity is intrinsically incomplete, even without deviations from detailed experimental data, because we can see that it is mathematically undefined at high energies. (I think Zee says something like this in his QFT text.)

Thus QM and quantum gravity provide open problems to theorists, even before they have been experimentally falsified. They are incomplete on almost purely "logical" grounds.

 

[bhobba]

The distinction between classical electrodynamics and quantum mechanics is that the former is intrinsically complete (detailed experimental data is needed to show it is incomplete), while the latter is intrinsically incomplete (even without deviations from detailed experimental data, we know it is incomplete because measurement is considered to be a special process).

That is the conventional wisdom. But we have some curios things classically indicating classical physics is incomplete eg the a-causal runaway solutions of the Dirac-Lorentz equation:
https://arxiv.org/abs/gr-qc/9912045

My view is that each layer of the onion has issues that can only be resolved by the next layer.

I am also expressing the view it is never ending - that may of course be wrong - there may be a final theory, but certainly we do not know it at present.

Thanks
Bill

 

[atyy]

That is the conventional wisdom. But we have some curios things classically indicating classical physics is incomplete eg the a-causal runaway solutions of the Dirac-Lorentz equation:
https://arxiv.org/abs/gr-qc/9912045

One can exclude point charges from the theory.

 

[bhobba]

One can exclude point charges from the theory.

Then how do you handle a blob of matter? It is usually done by breaking it into a lot of infinitesimal size bits. But even aside from that if you want to exclude point particles a theory that requires that is not complete.

Thanks
Bill

 

[OCR]

Then how do you handle a blob of matter?

...some questions can't be asked...

That's one of them... .

.

 

[atyy]

Then how do you handle a blob of matter? It is usually done by breaking it into a lot of infinitesimal size bits. But even aside from that if you want to exclude point particles a theory that requires that is not complete.

A point particle has infinite density. A blob of matter does not.

 

[bhobba]

A point particle has infinite density. A blob of matter does not.

Fair point. But many books use it.

Thanks
Bill

 

[bhobba]

Quantum general relativity is intrinsically incomplete, even without deviations from detailed experimental data, because we can see that it is mathematically undefined at high energies. (I think Zee says something like this in his QFT text.).

That is true. But some think the Standard Model is like that - its predictive power peters out at high energies thought to be about the Plank scale eg some think the standard model is trivial - personally I do not - but we really do not know - or at least from what I have read I think its still an open question.

Thanks
Bill

 

[Demystifier]

But by your criteria (2), the inability to clearly articulate a boundary between systems where classical is applied and where quantum is applied means that neither theory is complete.

Neither theory is complete only if you claim that there is a strict border of that form. But if you say (which is more common in physics) that there is no strict border, but one theory is just an approximation of the other, then the other theory can be considered complete.

 

[AlexCaledin]

What has science to do with any ontologic completeness, anyway? You ask what reality is made of and you hear about strings and things that are abstract mathematical objects.

 

[Jimster41]

@Demystifier loved this article. It's philosophy tho.

Question-ish: I'm bashing my way through Hofstadter's Godel, Escher, Bach. It's hard. And if he's got the answer I haven't received it yet.
So I'm intrigued as I think others here are by the question of what "completeness" would even look like? Why your answer was so decisively "No" regarding connection to Godel completeness.

Isn't QM's (real) physical incompleteness both the observed symptom and the cause for the "No halting" problem. I mean Isn't the Halting Problem deeply connected to incompleteness? Wouldn't completeness imply the decidability of halting?

 

[bhobba]

Isn't QM's (real) physical incompleteness both the observed symptom and the cause for the "No halting" problem. I mean Isn't the Halting Problem deeply connected to incompleteness? Wouldn't completeness imply the decidability of halting?

QM incompleteness, if it exists, it is unsure now if it is or not although there is ongoing research, is nothing like Godel Incompleteness. Godel Incompleteness is really just Cantors Diagonal augment applied to logical systems:
https://www.physicsforums.com/threads/non-computable-functions-and-godels-theorem.953250/

Thanks
Bill

 

[Demystifier]

Why your answer was so decisively "No" regarding connection to Godel completeness.

For that matter, I highly recommend https://www.amazon.com/dp/1568812388/?tag=pfamazon01-20

 

[G. E. Hunter]

Some things that exist may not be quantifiable. We need to stop trying to force everything into the math number mold. Some things are abstract. They appear and disappear or change from one state to another. Some things cannot be detected with existing instruments, YET. Big discoveries yet to come.

 

[Adur Alkain]

Quantum mechanics is not incomplete. It is a complete description of observation. Physics does nothing but describe observation. The laws of physics are the laws of observation.

Interpretations of quantum mechanics belong to philosophy, not to physics. It is philosophy that has failed so far, not physics. (I'm a philosopher, not a physicist, btw.)
In other words, "shut up and calculate" is good advice for physicsts. It's a preposterous advice for philosophers (but that's what logical positivism did, basically).

One doesn't have to be a professional philosopher to see the clear picture that quantum mechanics gives about the nature of reality. Einstein wasn't a philosopher, and yet he clearly saw the philosophical implications of quantum theory (in its Copenhagen version) and asked the candid question: "Do you really think the moon isn't there if you aren't looking at it?"

Einstein used this philosophical argument as an objection to the Copenhagen "interpretation" (which as you very well argued in "Against "interpretations"", should rather be called the Copenhagen theory): his contention was that the theory must be faulty. The theory, as far as I know, has been experimentally proven correct.

The philosophical conclusion is unavoidable: there is no physical world independent of observation. Quantum mechanics implies Idealism.

But again, this whole discussion lies on the realm of philosophy, not physics. (All alternative theories to Copenhagen can be understood as attempts to avoid Idealism, but as far as I'm aware they have failed so far.)

Yet one can imagine that most physicsts won't welcome the realization that physics is nothing but a specialised field of psychology: the study of observation (understanding observation as a special type of conscious experience that is bound by the laws of physics - the laws of observation).

This is a typical "the Emperor has no clothes" scenario, which I find rather amusing.

 

[bhobba]

Quantum mechanics is not incomplete. It is a complete description of observation.

It's a description of observations that occur in a classical world. But since everything is quantum how does a theory that assumes a classical world explain that world? That is the issue. A lot of progress has been made in resolving it, but it is not fully resolved yet. This means QM may or may not be complete - we just do not know yet.

Thanks
Bill

 

[ftr]

Quantum mechanics is not incomplete. It is a complete description of observation.

QM is a physics theory and theories in physics must include predictions and since it does not predict everything( like mass and couplings), hence it is incomplete.

 

[DarMM]

QM is a physics theory and theories in physics must include predictions and since it does not predict everything( like mass and couplings), hence it is incomplete.

I think this mixes up the incompleteness of the Standard Model (mass and coupling parameters) with the incompleteness of Quantum Theory in general (measurement problem, meaning of contextuality).

 

[ftr]

I think this mixes up the incompleteness of the Standard Model (mass and coupling parameters) with the incompleteness of Quantum Theory in general (measurement problem, meaning of contextuality).

SM is part of QM, measurement problem is an "interpretation" issue but mass and coupling is real/clear issue. I think understanding will come when the later is addressed first.

 

[microsansfil]

Hi,

is it not possible to verify the completeness of any mathematical axiomatization of quantum mechanics?

http://www.iecl.univ-lorraine.fr/~Wolfgang.Bertram/WB-TB.pdf

/Patrick

 

[Demystifier]

I think this mixes up the incompleteness of the Standard Model (mass and coupling parameters) with the incompleteness of Quantum Theory in general (measurement problem, meaning of contextuality).

In general that's true, but in my view of Bohmian mechanics those two types of incompleteness are closely related. See the paper linked in my signature.

 

[bhobba]

is it not possible to verify the completeness of any mathematical axiomatization of quantum mechanics?

It is not possible to verify the axiomatic completeness of any system as strong as arithmetic. Note - this is verifying completeness in the Godel sense because we always have true statements that can't be proven in the system. But that has nothing to do with if a system is not complete because its axioms may contain a hidden circularity with regard to observations, which is what people that talk about QM completeness mean. You are falling for a common semantic error - because two different things use the same name you context shift. Such reasoning is invalid.

Thanks
Bill

 

[DarMM]

SM is part of QM, measurement problem is an "interpretation" issue but mass and coupling is real/clear issue. I think understanding will come when the later is addressed first.

The measurement problem is a problem in QM that interpretations try to solve, but it is a real issue as much as the masses and couplings. It might be the case that the explanation of couplings and masses is related to the measurement problem or it might not, from where we stand now they are two separate problems.

 

[microsansfil]

It is not possible to verify the axiomatic completeness of any system as strong as arithmetic.

Some examples of complete theories are: https://en.wikipedia.org/wiki/Complete_theory

/Patrick

 

[microsansfil]

I use it colloquially.

How do we measure the distance between physical theory and the ontology of nature, without having access to it? So, therefore, any physical theory will be incomplete?

/Patrick

 

[lowlize]

"There is an objective reality out there". I don't think that applies to the relational interpretation. And what about the "new" Copenhagen interpretation with decoherence taken into account?

 

[Lord Jestocost]

Regarding “the incompleteness of QM interpretations”, there is, to my mind, a subtle hint given by David Bohm and Basil J. Hiley in “The Undivided Universe: An Ontological Interpretation of Quantum Theory”:

"Several physicists have already suggested that quantum mechanics and consciousness are closely related and that the understanding of the quantum formalism requires that ultimately we bring in consciousness in some role or other (e.g. Wigner [17], Everett [18] and Squires [19]). Throughout this book it has been our position that the quantum theory itself can be understood without bringing in consciousness and that as far as research in physics is concerned, at least in the present general period, this is probably the best approach. However, the intuition that consciousness and quantum theory are in some sense related seems to be a good one, and for this reason we feel that it is appropriate to include in this book a discussion of what this relationship might be." [emphasis added by LJ]

 

[jambaugh]

There is one reason that quantum mechanics is a complete physical theory. Quantum mechanics makes a class of predictions. Those are probabilistic predictions but since you can embed logic within probability by restricting to specific cases of p=0 or 1, this is not a failing on the part of QM. And quantum mechanics also specifies that there are no stronger predictions that can be made. The uncertainty principle defined the end of the question of what more can be known about what will happen.

So any improvement upon the predictions of QM must necessarily violate QM. That's fine, GR breaks SR except as a limiting case. SR breaks Newtonian mechanics except at a limiting case. QM is not necessarily the end of all theories but it is complete in the sense that no more exact theory can be given that incorporates all of QM's predictions.

Now if you feel it is "incomplete" because it doesn't provide for a specific observably distinguishable ontological model then I would point out to you that QM is not an ontological theory. It is a description of what happens (and how often) not of what is. That's the mistake people make in misinterpreting Copenhagen. Yes the wave function collapses but the wave function is not an ontological representative. It is a QM version of a classical probability distribution. Classical distributions collapse all the time.

The dissatisfaction people have with the Copenhagen interpretation which is the positivistic interpretation is the same sort of dissatisfaction they have with the non-absolute time in the Twins paradox which makes them one to throw in an aether (with necessarily screwy dynamical properties) in order to feel better about the relative ages of twins. The relativity of time and simultaneity is likewise the positivistic interpretation eliminating as meaningless that which cannot be observed, namely the luminiferous aether.

There is no fixed objective reality in QM. There are a set of relative frame dependent realities with well defined relativity transformations relating them. Fantasies about pilot waves and infinite worlds are no more helpful than questions about the unobservable properties of the aether.

 

[Avodyne]

Yes the wave function collapses

What is the mathematical description of the collapse process?

Let's say we're going to do a Stern-Gerlach experiment. We isolate the lab completely from any external environment. We put the lab (and everything in it, including the experimenters) in an initial pure state, with the experiment about to begin. We time-evolve forward unitarily with the hamiltonian of the Standard Model.

I claim that the state of the lab splits into an "up" branch (where the measured spin was up, the dial points up, the brains of the experimenters in the lab think they saw the dial point up, etc) plus a "down" branch. (I believe this part must be correct, but maybe you disagree.)

So then, when does collapse occur? And what is the mathematical description of it?

 

[DarMM]

What is the mathematical description of the collapse process?

If you look at @jambaugh 's post he's clearly taking an epistemic view of the wavefunction where collapse is just (generalized) Bayesian conditioning.

 

[Avodyne]

I don't see why it matters whether one views the quantum state as epistemic or ontological. QFT predicts a two-branched state for the post-measurement Stern-Gerlach lab (and the people in it). At what point in time, and according to what mathematical rule, do we throw away one branch?

 

[DarMM]

I don't see why it matters whether one views the quantum state as epistemic or ontological.

If the quantum state is epistemic then throwing away one branch doesn't correspond to a physical process which needs a more detailed mathematical description, it's simply (generalized) Bayesian updating.

 

[Avodyne]

What is "(generalized)" Bayesian updating? (I know what ordinary Bayesian updating is.) Do you have a reference?

 

[DarMM]

It's just how Lüders rule is viewed in epistemic approaches, i.e. it represents a generalized form of Bayesian conditioning.