Revisiting the Completeness of Quantum Theory: A Scientist's Perspective

[computerphys]

I am sorry if this issue has been already addressed previously in this forums, but I have been looking for old threads on the subject and I haven't found any specific to the matter. If anyone knows about any, please let me know and sorry again.

Otherwise, this is my question: "Is Quantum theory complete?"

If I am not wrong, this was Einstein's point in the famous letter to Bohr in 1920. According to Bohr quantum theory is complete because what is to supposed to be left in the theory (hidden variables) is also left in the very reality. Ok. I understand it, and I already know and accept that there are important reasons to debunk hidden variables.

Nevertheless, I still have a doubt. When a measurement takes place an unpredictable value is obtained (under certain circumstances of uncertainty). How can we say that quantum theory is complete and at the same time that quantum theory cannot predict accurately the outcomes of a measurement? This is the very point I don't understand. Reality is given us the accurate outcome, whilst quantum theory is not, so reality is in fact "more complete" than quantum theory!

Call me "retro" and "stubborn" but I sincerely still think Einstein was right about this point, but at the same time I am ready to open my mind to reasonable statements about the completeness of Quantum Theory.

Thanks in advance.

 

[Dickfore]

Define what you mean by "complete".

 

[GeorgCantor]

We have to know what reality is and how reality is, then we will be able to say if qm is a complete description of reality. If there is no underlying reality, qm is complete. But such questions should be relegated to God(Nostradamus comes as a second option).

 

[computerphys]

Define what you mean by "complete".

I am going to try it: a complete theory means to me that every outcome of a given experiment (*) could be accurately calculated using that theory.

* under the scope of application of that theory.

I assume that the position of a free electron, for example is inside the scope of quantum theory.

 

[GeorgCantor]

I am going to try it: a complete theory means to me that every outcome of a given experiment (*) could be accurately calculated using that theory.

This is not enough. You need to elaborate if "accurately calculated" includes probabilities or not.

 

[computerphys]

If there is no underlying reality, qm is complete.

First of all, thanks for the answer, GeorgCantor, I am kind of a fan of your posts, by the way.

I still don't understand how can we see QM as complete, even in the case that there is no underlying reality. My concern is that a simple quantum experiment outcome is showing certain information that the theory is unable to render, as for example the exact location of an electron.

So, if the theory is unable to render the outcome of an experiment, would be correct to say the theory to be complete?

Thanks!

 

[Dickfore]

I am going to try it: a complete theory means to me that every outcome of a given experiment (*) could be accurately calculated using that theory.

* under the scope of application of that theory.

I assume that the position of a free electron, for example is inside the scope of quantum theory.

Then it is complete. QM predicts that the outcomes of a measurement of an observable are the eigenvalues of the operator associated with that observable.

 

[computerphys]

You need to elaborate if "accurately calculated" includes probabilities or not.

No probabilities. The outcome of an experiment is not a probability, but a value. The outcome of a complete theory should also be a value, not a probability. Sorry if I am too naive.

The same way that thermodynamics is not a complete theory of the microstates, could we say the same about QM?

Thanks!

 

[GeorgCantor]

First of all, thanks for the answer, GeorgCantor, I am kind of a fan of your posts, by the way.

I still don't understand how can we see QM as complete, even in the case that there is no underlying reality. My concern is that a simple quantum experiment outcome is showing certain information that the theory is unable to render, as for example the exact location of an electron.

You can't know the location of the electron simultaneously with the momentum of the electron.

So, if the theory is unable to render the outcome of an experiment, would be correct to say the theory to be complete?

Thanks!

The theory would be complete even if there exists a deterministic underlying reality(to which we wouldn't have access).

 

[GeorgCantor]

No probabilities. The outcome of an experiment is not a probability, but a value. The outcome of a complete theory should also be a value, not a probability. Sorry if I am too naive.

Then this universe isn't for you . The probability "thing" comes as a result of the wave nature of matter. Waves aren't well localized in space.

The same way that thermodynamics is not a complete theory of the microstates, could we say the same about QM?

Thanks!

If you push it that far, there isn't ever going to be a complete theory of anything.

 

[Dickfore]

No probabilities. The outcome of an experiment is not a probability, but a value. The outcome of a complete theory should also be a value, not a probability. Sorry if I am too naive.

The same way that thermodynamics is not a complete theory of the microstates, could we say the same about QM?

Thanks!

Hmmm. It seems you have objections to the probabilistic interpretation of the wavefunction. I will refer you to Sakurai's introductory section.

Let's look at polarization of light. An unpolarized light beam passes through a polarizer. As a result, the light becomes linearly polarized in the direction of the polarizer's optical axis. Then we put another polarizer at an angle different from 90^o to the first one. Some light still passes, but it is now polarized in the direction of the second polarizer's axis.

But, then, we use yet a third analyzer. Its axis is parallel to the first one's. The question is: Will some light still pass through?

 

[Pythagorean]

It's definitely not complete in the sense that it's a unified theory of everything.

But of course, no theory is complete like this, or we'd have a unified theory of everything and science would be dead and applied science would be the new thing.

I don't personally think a TOE is even possible, because:

You're trying to model reality. Reality consists of a lot of stuff (virtually infinite bits of matter and interactions between that mater). Anytime you want to model that reality, you have to use stuff to do it (whether it's your neurons, pencil and paper, computers, or actual 3d models) and those models aren't going to have anywhere near the infinite resources that reality have, so they're always going to be missing information.

All you can do is scale your model from general to specific, taking on the flaws of one, or compromising for a little of the flaws of both for a more balanced model.

 

[computerphys]

Hmmm. It seems you have objections to the probabilistic interpretation of the wavefunction

I think I haven't, honestly. The theory says that there could be several eigenvalues with given probabilities and I accept (even believe) that it is due to the very nature of the world and not a flaw of QM.

Nevertheless, my concern is the information that an experiment give us (a single, accurate and certain value) but the theory does not (theory gives us values and probabilities). How can QM explain that information?

QM cannot tell us which one of the eigenvalues is going to be detected. QM cannot predict completely the event happening when doing the measurement. The event is that certain eigenvalue is the outcome, but not that a set of eigenvalues with certain probabilities are the outcome.

The fact is that we measure a value, whilst QM only renders sets of values and probabilities.

Facts don't match completely with QM predictions. Is that correct?

Thanks!

 

[computerphys]

Then it is complete. QM predicts that the outcomes of a measurement of an observable are the eigenvalues of the operator associated with that observable.

Yes, eigenvalues, plural. But the experiment outcome is not a set of eigenvalues, but only one single eigenvalue. Nature in someway has chosen that one and not any other of the set. The process by which nature makes that choice is not addressed by QM. Right?

Thanks!

 

[Hurkyl]

By your definitions, if nature happens to be nondeterministic, then I think every scientific theory must be incomplete by your definition.


Have you tried your hand at understanding some of the non-collapse interpretations, like MWI or Bohm?

 

[Dickfore]

Yes, eigenvalues, plural. But the experiment outcome is not a set of eigenvalues, but only one single eigenvalue. Nature in someway has chosen that one and not any other of the set. The process by which nature makes that choice is not addressed by QM. Right?

Thanks!

So, you object that the position or momentum can have any possible value?

 

[computerphys]

If you push it that far, there isn't ever going to be a complete theory of anything.

When a theory predicts an experiment outcome under its scope, we should say it is complete, as for example, Newtonian Mechanics. Of course, NM gets out of its scope when relativistic corrections are needed. So, at least we have a complete theory of something here.

In contrast, my point is that QM seems to me to be a theory that cannot predict an experiment outcome under its own scope, as for example the position of a free electron (after measuring its momentum).

Do you agree?

Thanks!

 

[computerphys]

By your definitions, if nature happens to be nondeterministic, then I think every scientific theory must be incomplete by your definition.

Not exactly. If you consider the proper scope/range of a given theory, NM would be complete but QM wouldn't be.

Have you tried your hand at understanding some of the non-collapse interpretations, like MWI or Bohm?

Do you think that a non-collapse interpretation could "fix" the QM incompleteness?

Thanks!

 

[Dickfore]

What principle of Nature requires that we should simultaneously know the position and momentum of a particle?

QM says that the state of a system is described by a wave function. It also provides an equation that gives the time-evolution of the wave function. It is true that we cannot solve this equation for all but the simplest cases, but that does not mean that the theory is incomplete. A similar situation arises in classical mechanics, where the three-body problem is unsolvable, but that does not mean the theory is incomplete.

 

[computerphys]

So, you object that the position or momentum can have any possible value?

I am not sure if I understand what you are asking me ... but according to the experiment of measuring the position of a free electron you get one and only one eigenvalue. Do you agree with it?

Of course, according to QM, you get a set of eigenvalues, not just one. So, I must conclude that QM cannot predict a fact, an event, a measurement (under proper QM scope/range).

Einstein called it an incomplete theory. I just would like to know whether he was wrong or not, and where is the flaw in this way of reasoning.

Thanks!

 

[Hurkyl]

Not exactly. If you consider the proper scope/range of a given theory, NM would be complete but QM wouldn't be.

Explain how Newtonian Mechanics could be complete if reality is nondeterminstic.

Do you think that a non-collapse interpretation could "fix" the QM incompleteness?

It seems you are already predisposed to reject the idea, no matter whether or not it has merit.

MWI, for example, is complete and deterministic. Bohm as well. (whether it's accurate at a macroscopic scale is another question)


Nature-is-wavefunctions-collapse-is-nondeterministic-and-there's-nothing-else is also complete. Nondeterminsitic, though.

 

[computerphys]

What principle of Nature requires that we should simultaneously know the position and momentum of a particle?

None, of course. As I said, I accept the uncertainty of QM and of the very nature.

My point is that what we measure in the laboratory cannot be predicted by QM completely. Nature can render it, but QM cannot. So, QM is not as complete as nature. Where is my flaw?

It is true that we cannot solve this equation for all but the simplest cases, but that does not mean that the theory is incomplete. A similar situation arises in classical mechanics, where the three-body problem is unsolvable, but that does not mean the theory is incomplete.

I agree with you about this point. The reason why Einstein told Bohr that QM is incomplete wasn't related to the integrability of its equations.

Thanks!

 

[Evo]

Computerphys, please respond to Hurkyl.

Thanks!

 

[Dickfore]

Computerphys, please respond to Hurkyl.

Thanks!

Why should he respond to someone?

 

[computerphys]

Explain how Newtonian Mechanics could be complete if reality is nondeterminstic.

The non-determinisc correction is out of NM scope. So, NM is effectively complete.

It seems you are already predisposed to reject the idea, no matter whether or not it has merit.

Sorry, then. No intention to offend or ignore merit. In fact I strongly believe QM interpretations are essential to the understanding of the world.

Nature-is-wavefunctions-collapse-is-nondeterministic-and-there's-nothing-else is also complete. Nondeterminsitic, though.

If you tell me that nature is complete, of course I agree with it.

If you tell me that nature is non-deterministic at this level, I also agree with you.

The problem is not about nature. The problem is about QM when saying QM is complete.

Einstein's point is:

Nature gives us results that QM cannot predict (inside the quantum scope, of course), so QM is incomplete.

Thanks!

 

[Evo]

Why should he respond to someone?

Because Hurkyl knows what he is talking about and is trying to keep this thread in line so it doesn't get closed.

That's why.

 

[Dickfore]

Because Hurkyl knows what he is talking about and is trying to keep this thread in line so it doesn't get closed.

That's why.

Why would it get closed?

 

[GeorgCantor]

When a theory predicts an experiment outcome under its scope, we should say it is complete, as for example, Newtonian Mechanics. Of course, NM gets out of its scope when relativistic corrections are needed. So, at least we have a complete theory of something here.

In contrast, my point is that QM seems to me to be a theory that cannot predict an experiment outcome under its own scope, as for example the position of a free electron (after measuring its momentum).

Do you agree?

Thanks!

If nature is that way(electrons not having a definite position and momentum at the same time), then qm is complete.

If you want to posit some hidden variables theory about an underlying hidden reality, make it a non-local one(i.e. a pilot wave that instructs/directs the particle).

 

[Pythagorean]

The non-determinisc correction is out of NM scope. So, NM is effectively complete.

"non-deterministic correction" is a bit of an oxymoron isn't it? I mean, if you're making a correction to a model of a reality, aren't you implying determinism, given that the whole applying of a correction is, on some level, validation of the model? And models don't really have any purpose outside of determinism.

 

[Pythagorean]

It is possible, computerphys, that you're confusing chaotic, nonlinear, or stochastic processes with non-determinism.

 

[computerphys]

If nature is that way(electrons not having a definite position and momentum at the same time), then qm is complete.

If you want to posit some hidden variables theory about an underlying hidden reality, make it a non-local one(i.e. a pilot wave that instructs/directs the particle).

No, I don't need any hidden variables to get the conclusion that QM is incomplete. As I said before, I do believe in the uncertainty as a fundamental feature of the nature, and I know they are debunked due to Bell and Aspect, so forget hidden variables.

I still don't see why you say QM is complete while you agree with the empirical fact that the outcome of a measurement is a single eigenvalue, and at the same time knowing that QM is not capable of render/predict such a single eigenvalue, but a bunch of them.

Einstein's point in short words:

How can we say that QM is complete when it cannot render accurately experimental outcomes?

Thanks!

 

[computerphys]

It is possible, computerphys, that you're confusing chaotic, nonlinear, or stochastic processes with non-determinism.

Thanks for the hints, but no. Independently of these uncertainty sources, there is a fact we cannot avoid: the nature renders a single eigenvalue but QM renders a lot of them. So, nature is not completely described by QM. QM is incomplete.

By the way, chaotic or nonlinear cases belong to the Hidden Variables scheme, if I am not wrong. So, we should avoid them.

And models don't really have any purpose outside of determinism

I agree with you, but it does not change Einstein's point:

QM is incomplete because it cannot renders accurately eigenvalues as nature does.

 

[GeorgCantor]

No, I don't need any hidden variables to get the conclusion that QM is incomplete. As I said before, I do believe in the uncertainty as a fundamental feature of the nature, and I know they are debunked due to Bell and Aspect, so forget hidden variables.

I still don't see why you say QM is complete while you agree with the empirical fact that the outcome of a measurement is a single eigenvalue, and at the same time knowing that QM is not capable of render/predict such a single eigenvalue, but a bunch of them.

I didn't say qm was complete, look at my first post. In order for me to know this, i would have to know if there exist at the fundamental level such a thing as an electron with a defnite momentum and definite position at the same time. I don't know if this is true, hence i am not taking a side.

Einstein's point in short words:

How can we say that QM is complete when it cannot render accurately experimental outcomes?

Thanks!

Einstein didn't know that lhv would be refuted so any underlying model has to either be non-realistic(counterfactual), non-local or the observers have no free will.

You seem to insist that fundamental particles must have a definite position and momentum at the same time, but what is the justification for this, except a classical mindset?

 

[computerphys]

Just for the sake of clarity, when I say that QM is incomplete, I am not implying that it should exist a deeper theory that would "fix" QM. In fact, I believe that deeper theory cannot exist.

What I mean by incomplete is fairly simple: nature is given us more information in the experimental outcomes than QM can render/predict. Just that.

The key concept in this thread should be the completeness, its meaning and its applicability to QM. I hope that clarifies my point which I think it is the same that Einstein's.

Thanks again!

 

[computerphys]

I didn't say qm was complete, look at my first post. In order for me to know this, i would have to know if there exist at the fundamental level such a thing as an electron with a defnite momentum and definite position at the same time. I don't know if this is true, hence i am not taking a side.

I apologize for my misunderstanding. I respect you taking no side.

Einstein didn't know that lhv would be refuted so any underlying model has to either be non-realistic(counterfactual), non-local or the observers have no free will.

Yes, Einstein believed in hidden variables as a solution to the incompleteness of QM. But I don't share that point with him. Nevertheless it seems to me that Einstein was right when telling Bohr that QM is not complete due to the lack of accuracy in QM predictions as opposed to the accuracy nature give us in the measurement process.

You seem to insist that fundamental particles must have a definite position and momentum at the same time, but what is the justification for this, except a classical mindset?

I don't know where I have said that, but I don't think that fundamental particles must have a definite position and momentum at the same time.

What I say is just that what you measure in the laboratory cannot be rendered by QM.

I think that is equivalent to say that QM is not complete, but not meaning there should exist another alternative, deeper and more complete theory.

Just would like to know if this point could be a sound argument under a scientific and philosophical basis.

Thanks!

 

[computerphys]

"non-deterministic correction" is a bit of an oxymoron isn't it?

Yes, you are right. Call it instead "quantum uncertainty". Then, the sentence would be:

Quantum uncertainty is out of NM scope. So, NM is effectively complete.

 

[GeorgCantor]

I don't know where I have said that, but I don't think that fundamental particles must have a definite position and momentum at the same time.

What I say is just that what you measure in the laboratory cannot be rendered by QM.

Hundreds of experiments confirm the validity of the uncertainty principle. There is no experiment to my knowledge that doesn't agree with the mathematical formalism to date. In fact, qm and qft are the most 'complete' theories we currently have and present a much fuller and more valid picture of what it is that is actually going on.

 

[computerphys]

Hundreds of experiments confirm the validity of the uncertainty principle. There is no experiment to my knowledge that doesn't agree with the mathematical formalism to date. In fact, qm and qft are the most 'complete' theories we currently have and present a much fuller and more valid picture of what it is that is actually going on.

I agree with you. The point is that "the most 'complete' theories we currently have" are not fully complete. I have heard a lot of times that QM is complete, and Einstein was wrong. That is the problem. There is no way to justify that QM is complete. As a matter of fact, I think that when we compare nature's outcome with QM's outcome, it becomes evident that QM is not complete. So, saying QM is not complete is justifiable, but saying the contrary is not.

We can say that QM is our most complete theory, yes, but we cannot say QM is complete or fully complete, because it is false, with all my respects. (If I am wrong, please tell me why, where is the flaw in this argument).

To say that QM is not complete is not an aggression toward the QM mathematical formalism, nor any experiment. It is just to establish the limits of QM and be conscious that nature is more than QM (at the very QM scope). There is not an "homomorphical" or "bijective" relation between nature and QM. This is another way to express that QM is not complete.

We cannot say seriously that a theory is complete if nature's outcome does not correspond (*) to theory's prediction.

* Through a relation of homomorphism/bijection.

Thanks!

 

[computerphys]

MWI, for example, is complete and deterministic

I have followed your advice and read a little bit about MWI. My conclusion seems to be that the predictive power of MWI is the same as QM plain formalism. Well, actually that is not a surprise due to MWI being just an interpretation of QM. Tell me if I am wrong:

1.- MWI cannot predict the position of a free electron, just only a set of eigenvalues.

2.- QM plain formalism, exactly the same.

3.- Nature gives us the exact position of the free electron.

So, comparing the information got from the outcomes of the 3 of them we may say that:

MWI = QM < Nature

Nature renders more information, so nature is complete, but QM is incomplete and MWI as well.

MWI cannot tell us where exactly we are going to find the electron, but nature can.

Other equivalent way to understand the word "complete" is defining it roughly as "that where nothing is left". In QM, somebody telling us which eigenvalue will be the outcome of the experiment is the part that is left (and I say it is left because we expect a theory like QM to be a model for the nature, rendering the same values for every measurement). In Nature, nothing is left, because nature give us only one eigenvalue as the result of the measurement.

I am not telling we need an additional theory for the part that is left (the man telling us which eigenvalue is the outcome). I know (according to Bell and Aspect) that an additional theory cannot exist. I accept Heisenberg principle as something unavoidable.

I am just telling that something (not necessarily a theory) is left because nature has it, but neither MWI nor QM has it. Suppose that QM had that "thing", then and only then we could say QM is complete.

It seems to me that substituting wavefunction collapse (non-determinist process) for world branching (also a non-determinist process, if I am not wrong ...) doesn't change the fact that QM cannot render outcomes as accurately as nature does.

If nature does a thing that the theory doesn't (under its own scope), I think the correct word to describe that situation is "incomplete".

Thanks!

 

[computerphys]

I have just run into something interesting at:

http://en.wikipedia.org/wiki/Incompleteness_of_quantum_physics

Incompleteness, it seems, is here to stay: The theory prescribes that no matter how much we know about a quantum system—even when we have maximal information about it—there will always be a statistical residue. There will always be questions that we can ask of a system for which we cannot predict the outcomes. In quantum theory, maximal information is simply not complete information [Caves and Fuchs 1996]. But neither can it be completed.

 

[ThomasT]

By your definitions, if nature happens to be nondeterministic, then I think every scientific theory must be incomplete by your definition.

Even if nature happens to be deterministic, or maybe especially so, then I agree that every current scientific theory is incomplete.

 

[ConradDJ]

I have just run into something interesting at:

http://en.wikipedia.org/wiki/Incompleteness_of_quantum_physics

"Incompleteness, it seems, is here to stay: The theory prescribes that no matter how much we know about a quantum system—even when we have maximal information about it—there will always be a statistical residue. There will always be questions that we can ask of a system for which we cannot predict the outcomes. In quantum theory, maximal information is simply not complete information [Caves and Fuchs 1996]. But neither can it be completed."

I wanted to mention Carlo Rovelli's attempt ("Relational Quantum Mechanics") to derive the formalism of QM from these two postulates:

> There is a maximum amount of information that can be obtained about a system.

> Having obtained the maximum information, one can always interact with a system in a way that produces new information about it.

These may sound contradictory, but essentially the idea is that reality itself is not "complete" -- it's an interactive information system that's always creating new answers to new questions in new situations. The idea of "completeness" seems to assume a notion of reality in which all the answers are already there, whether or not any question is asked.

 

[computerphys]

... reality itself is not "complete" -- it's an interactive information system that's always creating new answers to new questions in new situations. The idea of "completeness" seems to assume a notion of reality in which all the answers are already there, whether or not any question is asked.

That "interactive information system" is a nature's process.

The description of this process, by which this new information is added to the system, is unknown and unknowable (according to Bell and Aspect).

So, the process exists in nature, but the theory that describes it will never exist. So, again, theory doesn't reach nature and won't ever.

* I admit QM is "scientifically complete" in the sense that science cannot create a more complete theory that would predict accurate eigenvalues.

* But I also think is quite obvious that QM is "naturally incomplete" in the sense that QM cannot successfully describe nature (the how) when rendering eigenvalues.

Am I wrong concluding that ...?: Einstein was right: Nature can do it, QM cannot.

 

[Dickfore]

> There is a maximum amount of information that can be obtained about a system.

> Having obtained the maximum information, one can always interact with a system in a way that produces new information about it.

In Shannon's Information Theory, concepts of information and entropy are defined for random variables. What is the meaning of information about a system?

 

[GeorgCantor]

Am I wrong concluding that ...?: Einstein was right: Nature can do it, QM cannot.

Aha, i now see the point you were making from the beginning.

Yes, Einstein was right imo that Nature can do it but qm cannot, but for a different reason - the reason being that Nature(whatever it is) is hollistic. I guess this isn't news in any way to those involved the foundational issues of physics(think about it in terms of background-independence and space and time being emergent).

Outcomes are sellected for in a way to preserve a kind of determinism that is explicit on the macro scale. Nature is definitely more than the sum of its parts.

And if you think about it, so are we, regardless of what compatibilists(i am told they exist ) might say.


Perhaps, that's Nature's way of observing itself(if i start sounding like Wheeler, that's a coincidence).

 

[computerphys]

Nature(whatever it is) is hollistic ...
Nature is definitely more than the sum of its parts.

Sorry, but I don't get the point about the relation between holism, "non-reductionism" and QM completeness.

Are you meaning that holism and "non-reductionism" must fill the gap left by QM incompleteness?

Sorry in advance if I understood wrong

 

[GeorgCantor]

Sorry, but I don't get the point about the relation between holism, "non-reductionism" and QM completeness.

Reality simply is, it can't be reduced from the fundamental interactions. Look at the interpretations - none of them solve the problem of outcomes, namely why we get the outcomes we observe. Reality is holistic(more than the sum of its parts) and a case can be made that it strives towards observers, hence why the fundamental constants seem fine tuned for life(silly idea but what do we know?). The "gap" is filled with what you might wish to call "self-organization at different levels" or alternatively "mind of god", "a universe that's alive in some sense", etc. The theory of everything is a mirage, a naive human invention.

 

[computerphys]

Reality simply is, it can't be reduced from the fundamental interactions. Look at the interpretations - none of them solve the problem of outcomes, namely why we get the outcomes we observe. Reality is holistic(more than the sum of its parts) and a case can be made that it strives towards observers, hence why the fundamental constants seem fine tuned for life(silly idea but what do we know?). The "gap" is filled with what you might wish to call "self-organization at different levels" or alternatively "mind of god", "a universe that's alive in some sense", etc. The theory of everything is a mirage, a naive human invention.

I am very glad to hear that. I agree with you 100%.

Thanks for sharing your point of view!

 

[imiyakawa]

Reality simply is, it can't be reduced from the fundamental interactions. Look at the interpretations - none of them solve the problem of outcomes, namely why we get the outcomes we observe. Reality is holistic(more than the sum of its parts) and a case can be made that it strives towards observers, hence why the fundamental constants seem fine tuned for life(silly idea but what do we know?). The "gap" is filled with what you might wish to call "self-organization at different levels".

If materialism, how do we know that the whole is greater than the sum of its parts? Who are we to say that ostensible self-organization at the "higher" levels isn't run by strict laws at the base of reality? Even if something like Navier-Stokes fluid dynamics can't be deduced from our current host of 'base' formalisms, do we really have to infer "greater than the sum of its parts"? It would just mean that either we don't have all the base laws figured out yet, or there's laws that 'kick in' at the higher levels, perhaps interference of self-gravitation onto the system that isn't seen on the singular wavefunction level.. Maybe I'm being tripped up on what you mean by "whole is greater than sum of its parts".

I know apeiron will step in here - I wait to be educated!

And, assuming a non-local hidden variable interp. is false, why does random collapse to discrete-state give credence to the notion that the whole is > the sum of its parts? Sure, we could engage in a debate of whether this entails acausality or not, and the consequences of this..[a debate I don't wish to have :D]

When a theory predicts an experiment outcome under its scope, we should say it is complete, as for example, Newtonian Mechanics. Of course, NM gets out of its scope when relativistic corrections are needed. So, at least we have a complete theory of something here.

Prediction vs. Explanation.

In contrast, my point is that QM seems to me to be a theory that cannot predict an experiment outcome under its own scope, as for example the position of a free electron (after measuring its momentum).

Doesn't mean that it's an incomplete theory. The very failure of the measurement could be a confirmation of the theory.

 

[computerphys]

Doesn't mean that it's an incomplete theory. The very failure of the measurement could be a confirmation of the theory.

We are not doubting about the validity of QM, so another "confirmation of the theory" is not necessary.

We are discussing the completeness of QM. QM can be a very good theory, but at the same time an incomplete one.

The fact that QM cannot yield accurate measurement predictions is the proof of QM incompleteness. Incompleteness doesn't mean a new theory is left. It only means that QM cannot explain/predict the nature we observe. It can explain part of it, but not the whole of it. So, it is logical to say that it is incomplete.

Heisenberg principle is telling us what is the empirical part that nature can render but QM cannot. Accepting Heisenberg principle is accepting that QM is incomplete.

How do we fill that gap, is another question.