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.