9 Reasons Quantum Mechanics is Incomplete - Comments

In summary: I don't know...the lead singer for a band that sounds like it borrows from Pink Floyd and Radiohead.In summary, Dirac believed that QM is just a natural outgrowth of classical physics where some of its assumptions are relaxed. However, because QM is still a physical theory, it is incomplete.
  • #1
Demystifier
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Greg Bernhardt submitted a new blog post

9 Reasons Quantum Mechanics is Incomplete
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  • #2
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?
 
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  • #3
A possible variant of Old Copenhagen:
Everything can be described by quantum mechanics, but not everything at once, therefore QM is incomplete.
 
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  • #4
thephystudent said:
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.

thephystudent said:
2) Can Gödel incompleteness have anything to do with it?
No.
 
  • #5
DarMM said:
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.
 
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  • #6
''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?
 
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  • #7
A. Neumaier said:
''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).
 
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  • #8
What mean a QM interpretation?
A classical version of QM? A classical understanding of QM?
There need not be such thing.
 
  • #10
eltodesukane said:
What mean a QM interpretation?
Any explanation of QM beyond pure operationalism.
 
  • #11
eltodesukane said:
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.
 
  • #12
A. Neumaier said:
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?
 
  • #13
haushofer said:
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.
 
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  • #14
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?
 
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  • #15
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
 
  • #16
Dr. Courtney said:
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
 
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  • #17
Dr. Courtney said:
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.
 
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  • #18
atyy said:
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
 
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  • #19
bhobba said:
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.
 
  • #20
atyy said:
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
 
  • #21
bhobba said:
Then how do you handle a blob of matter?
bhobba said:
...some questions can't be asked...
That's one of them... . :DD

.
 
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  • #22
bhobba said:
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.
 
  • #23
atyy said:
A point particle has infinite density. A blob of matter does not.

Fair point. But many books use it.

Thanks
Bill
 
  • #24
atyy said:
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
 
  • #25
Dr. Courtney said:
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.
 
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  • #26
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.
 
  • #27
@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?
 
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  • #28
Jimster41 said:
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
 
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  • #30
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.
 
  • #31
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.
 
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  • #32
Adur Alkain said:
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
 
  • #33
Adur Alkain said:
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.
 
  • #34
ftr said:
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).
 
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  • #35
DarMM said:
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.
 
<h2>1. What is quantum mechanics?</h2><p>Quantum mechanics is a branch of physics that studies the behavior of particles at the subatomic level. It explains how particles such as electrons and photons behave and interact with each other.</p><h2>2. What are the limitations of quantum mechanics?</h2><p>One of the main limitations of quantum mechanics is that it cannot fully explain the behavior of particles in certain situations, such as when they are observed or measured. This has led to the development of alternative theories, such as quantum field theory and string theory.</p><h2>3. What is the concept of quantum entanglement?</h2><p>Quantum entanglement is a phenomenon in which two or more particles become connected in such a way that the state of one particle affects the state of the other, even if they are separated by large distances. This concept is a fundamental aspect of quantum mechanics and has been demonstrated through various experiments.</p><h2>4. How does quantum mechanics challenge our understanding of reality?</h2><p>Quantum mechanics challenges our understanding of reality by introducing concepts such as superposition and wave-particle duality, which go against our classical understanding of how the world works. It also suggests that the act of observation can affect the behavior of particles, leading to questions about the nature of reality and consciousness.</p><h2>5. What are some potential implications of the incompleteness of quantum mechanics?</h2><p>The incompleteness of quantum mechanics has led to ongoing debates and research in the scientific community. Some potential implications include the search for a more complete theory that can unify quantum mechanics with other branches of physics, as well as the development of new technologies based on quantum principles, such as quantum computing and cryptography.</p>

1. What is quantum mechanics?

Quantum mechanics is a branch of physics that studies the behavior of particles at the subatomic level. It explains how particles such as electrons and photons behave and interact with each other.

2. What are the limitations of quantum mechanics?

One of the main limitations of quantum mechanics is that it cannot fully explain the behavior of particles in certain situations, such as when they are observed or measured. This has led to the development of alternative theories, such as quantum field theory and string theory.

3. What is the concept of quantum entanglement?

Quantum entanglement is a phenomenon in which two or more particles become connected in such a way that the state of one particle affects the state of the other, even if they are separated by large distances. This concept is a fundamental aspect of quantum mechanics and has been demonstrated through various experiments.

4. How does quantum mechanics challenge our understanding of reality?

Quantum mechanics challenges our understanding of reality by introducing concepts such as superposition and wave-particle duality, which go against our classical understanding of how the world works. It also suggests that the act of observation can affect the behavior of particles, leading to questions about the nature of reality and consciousness.

5. What are some potential implications of the incompleteness of quantum mechanics?

The incompleteness of quantum mechanics has led to ongoing debates and research in the scientific community. Some potential implications include the search for a more complete theory that can unify quantum mechanics with other branches of physics, as well as the development of new technologies based on quantum principles, such as quantum computing and cryptography.

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