For and Against the Copenhagen Interpretation

[Lynch101]

TL;DR Summary

What are the things in the plus column for the Copenhagen Interpretation and what are the things in the minus colum?

Given the various different interpretations of quantum mechanics, I am interested in getting a general overview of most/all of them. I think it would be interesting to hear what people list as the positives of each interpretation as well as issues they perceive with each. I was thinking that, if people so choose, they could reply with what they would say both for and against a particular interpretation.

I'm thinking it might be best to go one theory at a time, so that it's easier to keep track of the information. The Copenhagen Interpretation is probably as good a place to start as any. To give an idea of the format I had in mind, I will outline what little I know in the for and against format. My own post will likely not be completely accurate, which is one of the reasons for starting this thread. I'm hoping to learn more from what other members think of the different interpretations, and then have some topics for further learning.

I understand that some of the positives and negatives will apply equally to the different interpretaions.

For
- The success of QM predictions (although this probably applies to all interpretations).
- It doesn't postulate any unobserved physical variables.
- It attempts to take the mathematical formalism at face value

Against
- the "measurement problem" (it doesn't specify the boundary between the quantum and macro worlds - is that accurate?)
- It doesn't tell us what happens in individual experiments (applies equally to all interpreations?)
- It gives rise to "Schroedinger's cat" type scenarios, which are not easily explained

 

[Demystifier]

- It doesn't tell us what happens in individual experiments (applies equally to all interpreations?)

Most of what you have written is correct, but the part in the bracket above is not. Some interpretations, most notably the Bohmian interpretation, tell what happens in individual experiments.

 

[Lynch101]

Most of what you have written is correct, but the part in the bracket above is not. Some interpretations, most notably the Bohmian interpretation, tell what happens in individual experiments.

Of course! I was thinking along the lines that such interpretations attempt to tell us what's going on, but ultimately can't - is that correct? Is that the import of one of the no go theorems?

Are there any other "positives" or "negatives" that people point to, with regard to the Copenhagen Interpretation, or perhaps any other features of it that are noteworthy?

Does the Copenhagen Interpretation rely on the freedom of choice of the experimenter i.e. "free will"?

 

[Demystifier]

Of course! I was thinking along the lines that such interpretations attempt to tell us what's going on, but ultimately can't - is that correct? Is that the import of one of the no go theorems?

No, there is no no-go theorem that says that it's impossible.

Does the Copenhagen Interpretation rely on the freedom of choice of the experimenter i.e. "free will"?

No, not really.

 

[Lord Jestocost]

Does the Copenhagen Interpretation rely on the freedom of choice of the experimenter...

To abandon freedom means to abandon science. In his book “Dance of the photons”, Anton Zeilinger remarks the following:

“The second important property of the world that we always implicitly assume is the freedom of the individual experimentalist. This is the assumption of free will. It is a free decision what measurement one wants to perform. In the experiment on the entangled pair of photons, Alice and Bob are free to choose the position of the switch that determines which measurement is performed on their respective particles. It was a basic assumption in our discussion that that choice is not determined from the outside. This fundamental assumption is essential to doing science. If this were not true, then, I suggest, it would make no sense at all to ask nature questions in an experiment, since then nature could determine what our questions are, and that could guide our questions such that we arrive at a false picture of nature.”

And Hans Primas in „Hidden Determinism, Probability, and Time’s Arrow“:

„At present the problem of how free will relates to physics seems to be intractable since no known physical theory deals with consciousness or free will. Fortunately, the topic at issue here is a much simpler one. It is neither our experience of personal freedom, nor the question whether the idea of freedom could be an illusion, nor whether we are responsible for our actions. The topic here is that the framework of experimental science requires a freedom of action in the material world as a constitutive presupposition. In this way “freedom” refers to actions in a material domain which are not governed by deterministic first principles of physics.

To get a clearer idea of what is essential in this argument we recall that the most consequential accomplishment by Isaac Newton was his insight that the laws of nature have to be separated from initial conditions. The initial conditions are not accounted for by first principles of physics, they are assumed to be “given”. In experimental physics it is always taken for granted that the experimenter has the freedom to choose these initial condition, and to repeat his experiment at any particular instant. To deny this freedom of action is to deny the possibility of experimental science.

In other words, we assume that the physical system under investigation is governed by strictly deterministic or probabilistic laws. On the other hand, we also have to assume that the experimentalist stands out of these natural laws. The traditional assumption of theoretical physics that the basic deterministic laws are universally and globally valid for all matter thus entails a pragmatic contradiction between theory and practice. A globally deterministic physics is impossible.“ [Italics in original, LJ]

 

[Demystifier]

Concerning free will, motivated (and somewhat irritated) by the opinions quoted in the post above, I think the essential points can be explained in a rather non-controversial way. There is a physical system studied, there is a measuring apparatus that measures this system, and there is an experimentalist who prepares all this. All three, together with their environment, constitute a closed physical system. Any of those subsystems alone, however, is an open system, so its behavior depends also on other subsystems. In particular, the behavior of the experimentalist depends not only on the experimentalist itself, but also on the other subsystems, especially the environment. So, when we want that the experimentalist has a "free will", all what we really require is that the behavior of the experimentalist is not much influenced by the measured system and the apparatus, so that for practical purposes their influence can be neglected. Such a requirement is a rather weak requirement and should not be considered controversial at all.

 

[Lord Jestocost]

For me, the experimentalist is more than a physical system. He/she posseses a mind which is free to will.

 

[Demystifier]

For me, the experimentalist is more than a physical system. He/she posseses a mind which is free to will.

Fine, but this is
(i) controversial from the physical point of view,
and more importantly
(ii) irrelevant to quantum foundations.

But still, I'll bite the bullet and ask: Do you think that some laws of physics are violated in the brain?

 

[Lord Jestocost]

Do you think that some laws of physics are violated in the brain?

Why?? What has this question to do with "mind" and "freedom to will"? All is said in post #5!

 

[Lord Jestocost]

Against
- the "measurement problem" (it doesn't specify the boundary between the quantum and macro worlds - is that accurate?)
- It doesn't tell us what happens in individual experiments (applies equally to all interpreations?)
- It gives rise to "Schroedinger's cat" type scenarios, which are not easily explained

What you subsume under “Against Copenhagen” are to my mind merely “artificially created problems” by those who insist on thinking about quantum phenomena with classical ideas. As Werner Heisenberg remarks in his book “Physics and Philosophy”:

“However, all the opponents of the Copenhagen interpretation do agree on one point. It would, in their view, be desirable to return to the reality concept of classical physics or, to use a more general philosophic term, to the ontology of materialism. They would prefer to come back to the idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them.”

 

[Lynch101]

To abandon freedom means to abandon science. In his book “Dance of the photons”, Anton Zeilinger remarks the following:

“The second important property of the world that we always implicitly assume is the freedom of the individual experimentalist. This is the assumption of free will. It is a free decision what measurement one wants to perform. In the experiment on the entangled pair of photons, Alice and Bob are free to choose the position of the switch that determines which measurement is performed on their respective particles. It was a basic assumption in our discussion that that choice is not determined from the outside. This fundamental assumption is essential to doing science. If this were not true, then, I suggest, it would make no sense at all to ask nature questions in an experiment, since then nature could determine what our questions are, and that could guide our questions such that we arrive at a false picture of nature.”

And Hans Primas in „Hidden Determinism, Probability, and Time’s Arrow“:

„At present the problem of how free will relates to physics seems to be intractable since no known physical theory deals with consciousness or free will. Fortunately, the topic at issue here is a much simpler one. It is neither our experience of personal freedom, nor the question whether the idea of freedom could be an illusion, nor whether we are responsible for our actions. The topic here is that the framework of experimental science requires a freedom of action in the material world as a constitutive presupposition. In this way “freedom” refers to actions in a material domain which are not governed by deterministic first principles of physics.

To get a clearer idea of what is essential in this argument we recall that the most consequential accomplishment by Isaac Newton was his insight that the laws of nature have to be separated from initial conditions. The initial conditions are not accounted for by first principles of physics, they are assumed to be “given”. In experimental physics it is always taken for granted that the experimenter has the freedom to choose these initial condition, and to repeat his experiment at any particular instant. To deny this freedom of action is to deny the possibility of experimental science.

In other words, we assume that the physical system under investigation is governed by strictly deterministic or probabilistic laws. On the other hand, we also have to assume that the experimentalist stands out of these natural laws. The traditional assumption of theoretical physics that the basic deterministic laws are universally and globally valid for all matter thus entails a pragmatic contradiction between theory and practice. A globally deterministic physics is impossible.“ [Italics in original, LJ]

Thank you LJ, I am familiar with the above quotes about the import of the denial of free will, with regard to the practice of science, but I'm not entirely sure what point they try to make. I'm not sure they are particularly compelling arguments in favour of free will.

That the practice of science would not be what we believe it to be, would just a direct consequence of us not doing precisely what we believe we are doing . It wouldn't change anything about how science is done and it wouldn't invalidate any experimental findings. It's equally possible that we don't stand outside the laws of nature and that we are just nature exploring itself. Science would proceed as normal.

 

[Demystifier]

Why?? What has this question to do with "mind" and "freedom to will"? All is said in post #5!

For a start, it is not clear how the laws of physics (either deterministic or probabilistic), when applied to the brain, can be compatible with the idea that the brain has a free will.

 

[Demystifier]

For me, the experimentalist is more than a physical system. He/she posseses a mind which is free to will.

Is a cat more than a physical system? If no, then how about a few days old baby? If yes, then how about an insect?

 

[Lord Jestocost]

For a start, it is not clear how the laws of physics (either deterministic or probabilistic), when applied to the brain, can be compatible with the idea that the brain has a free will.

The mind is free to will (at the end, nobody understands the relationship between thought in the human mind, and the brain as part of the physical body).

Is a cat more than a physical system? If no, then how about a few days old baby? If yes, then how about an insect?

As a physicist, I have no objective access to the subjective character of the experiences of other beings. So, I don't know and will never know what it is like for a cat to be a cat. So, I don't know and will never know what it is like for you to be you. In case you regard yourself merely as a physical system which follows the laws of physics, either deterministic or probabilistic ones, why should I deal with your comments. A physical systems does what it has to do in a probabilistic or deterministic way, so what?

 

[Demystifier]

What you subsume under “Against Copenhagen” are to my mind merely “artificially created problems” by those who insist on thinking about quantum phenomena with classical ideas. As Werner Heisenberg remarks in his book “Physics and Philosophy”:

“However, all the opponents of the Copenhagen interpretation do agree on one point. It would, in their view, be desirable to return to the reality concept of classical physics or, to use a more general philosophic term, to the ontology of materialism. They would prefer to come back to the idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them.”

I have two objections on that.

First, Copenhagen interpretation does not get rid of classical ideas. Just the opposite, it claims that the classical macroscopic world is a necessary part of the formulation of physics, for otherwise it cannot explain where do the quantum measurement outcomes come from. In this sense, other interpretations attempt to reformulate QM such that classical ideas have a less important role (not a more important one) than classical ideas in the Copenhagen interpretation.

Second, Copenhagen interpretation claims that classical objects, that is the objective real world, exists only on the macroscopic level. This is a very problematic statement, well illustrated by the Schrodinger cat paradox, because it doesn't tell where exactly the borderline between the classical macroscopic and quantum microscopic worlds is.

 

[Demystifier]

The mind is free to will (at the end, nobody understands the relationship between thought in the human mind, and the brain as part of the physical body).

As a physicist, I have no objective access to the subjective character of the experiences of other beings. So, I don't know and will never know what it is like for a cat to be a cat. So, I don't know and will never know what it is like for you to be you. In case you regard yourself merely as a physical system which follows the laws of physics, either deterministic or probabilistic ones, why should I deal with your comments. A physical systems does what it has to do in a probabilistic or deterministic way, so what?

To me, it looks as if you are saying: Nobody knows the solution of the problem, therefore we should not even consider the problem, therefore there is no problem.

 

[Lord Jestocost]

Thank you LJ, I am familiar with the above quotes about the import of the denial of free will, with regard to the practice of science, but I'm not entirely sure what point they try to make. I'm not sure they are particularly compelling arguments in favour of free will.

That the practice of science would not be what we believe it to be, would just a direct consequence of us not doing precisely what we believe we are doing . It wouldn't change anything about how science is done and it wouldn't invalidate any experimental findings. It's equally possible that we don't stand outside the laws of nature and that we are just nature exploring itself. Science would proceed as normal.

In case a scientist seriously believes him-/herself to be a determined material machine, why would he/she take him-/herself and his/her ideas and writings so seriously? Some ideas should be thought right to the end.

 

[PeterDonis]

The mind is free to will

You cannot possibly know this since you go right on to say:

nobody understands the relationship between thought in the human mind, and the brain as part of the physical body

Exactly. But "nobody understands" (although plenty of people are working on it) does not mean "we know the mind is a separate thing not bound by the laws of physics", which is what you are claiming.

 

[PeterDonis]

In case a scientist seriously believes him-/herself to be a determined material machine, why would he/she take him-/herself and his/her ideas and writings so seriously?

Because being a determined material machine is not necessarily the same as having no mind.

You should take some time to familiarize yourself with the extensive literature on this topic before making such dogmatic pronouncements.

Some ideas should be thought right to the end.

Please take your own advice.

 

[Lynch101]

In case a scientist seriously believes him-/herself to be a determined material machine, why would he/she take him-/herself and his/her ideas and writings so seriously? Some ideas should be thought right to the end.

Firstly, if they were to do so, that would be explained by determinism i.e. they do so, because the chain of causal determinism is such that they do. That is probably somewhat unsatisfactory, I know, but whether or not a scientist takes their work seriously does not change how science is done and it doesn't change experimental results. It simply affects how those results are interpreted and indeed one's own self-perception.

The validity of an experimental result is, in no way, dependent on the experimenter's beliefs about their own free will.

 

[Lord Jestocost]

Because being a determined material machine is not necessarily the same as having no mind.

Agreed! Let us assume that there is "mind" bound by the laws of physics which rule the "material machine". What is in this context of a "determined physical system with mind" (the experimenter) now the role of mind?

 

[Lord Jestocost]

@PeterDonis

Nevertheless, please, read my ironic question in comment #17 carefully:

"In case a scientist seriously believes him-/herself to be a determined material machine, why would he/she take him-/herself and his/her ideas and writings so seriously?"

To "believe" is a mental act, presupposing that the considered scientist is aware of his/her mind.

 

[PeterDonis]

Let us assume that there is "mind" bound by the laws of physics which rule the "material machine". What is in this context of a "determined physical system with mind" (the experimenter) now the role of mind?

Whatever the role of the mind was before. None of this affects the role of the mind at all.

To "believe" is a mental act, presupposing that the considered scientist is aware of his/her mind.

Yes. So what?

You seem to believe that having a mind is somehow inconsistent with being a deterministic mechanical system. It isn't. At least, that is the belief of a large number of people who have written a lot of literature on this topic. As I said, you should take the time to familiarize yourself with that literature. Your obvious ignorance of all the previous thought on this topic is not helpful for this discussion. As a result, I am banning you from further posting in this thread.

 

[EPR]

Agreed! Let us assume that there is "mind" bound by the laws of physics which rule the "material machine". What is in this context of a "determined physical system with mind" (the experimenter) now the role of mind?

It could be a mere 'observer'(passive witness).

 

[PeterDonis]

It could be a mere 'observer'(passive witness).

Please do not clutter the thread with further discussion of the mind-body problem. That is off topic for this discussion. Please focus on the OP question, which was about the pros and cons of the Copenhagen Interpretation of QM.

 

[Lynch101]

Please do not clutter the thread with further discussion of the mind-body problem. That is off topic for this discussion. Please focus on the OP question, which was about the pros and cons of the Copenhagen Interpretation of QM.

Thank you for your efforts in trying to keep this on topic.

My original thinking was to start a thread for each of the interpretations and see what arguments there are for and against each of them, but I recently discovered your insights article The Fundamental Difference in [URL="https://www.physicsforums.com/insights/fundamental-difference-interpretations-quantum-mechanics/"]Interpretations of Quantum Mechanics[/URL] and I think that frames the question I had in mind, in a much more concise manner. Would it be OK to start a new thread on the pros and cons of instrumentalist interpretations vs non-instrumentalist ones?

Your article gives great insight into the question but I would love to ask a few more questions in that direction. I don't want to spam the forum with multiple threads but the thread title of this wouldn't really capture the broader question.

 

[PeterDonis]

Would it be OK to start a new thread on the pros and cons of instrumentalist interpretations vs non-instrumentalist ones?

As long as you're specific about which interpretations fall into each category, that should be OK. Giving specific references to support your classification of the interpretations would also be very helpful; I'm not sure there is a single "standard" version of any interpretation, so it's always good to give a specific reference to whatever source you are using as a basis for your understanding.

 

[Ian J Miller]

Regarding the pros, my feeling is the success, one way or the other, is the success of the Schrödinger equation. The problem with it, as I see it, is that the variable is ψ, which leaves open the question, what does it represent. Copenhagen takes the Born interpretation wherein ψ.ψ* represents probability, but while this is generally successful I dispute it is a pro because often it leads to the need for renormalization, and while I understand this need, I feel it is a bit of a fudge. I would be curious to know what others think of this. The fact it does not postulate hidden variables is an advantage but I still think there are uncomfortable aspects and I think every interpretation has the odd dead rat that must be swallowed. I don't see the fact that it complies with the mathematical formalism as an advantage because the formalism could be argued to be a means of carrying out calculations, and is therefore not really part of the interpretation. No formalism would be acceptable if it did not give correct answers.

As for the cons, I don't really see the measurement problem as a con, but rather just that - a problem. As I see it, measurement is not part of the interpretation - you cannot formulate an operator for ψ. However, the cat is a problem. To simplify the problem as I see it, and maybe someone can explain, if I see the cat alive and if A is an amplitude of ψ, and let me oversimplify, I can write P (probability)= (A^2) = 1. If I see a dead cat, I write P= (D^2) = 1. If I put the cat in the box, and oversimplifying to illustrate, classically I would write P = (A^2 + D^2)/2 =1, i.e. there is one cat and we don't know. But with this interpretation, it seems we write P = (A^2 + D^2 + 2AB)/x = 1. This is because we add amplitudes, not probabilities, and x renormalizes. What bothers me is, in this example, what does 2AB represent physically? Maths is clear, and in this oversimplified state I would assume x = 4, but it leaves the cat a quarter alive, a quarter dead and half something else. Which leaves two problems when I open the box. One is well-known - the so-called collapse of the wave function (where do the other probabilities go?), but what happens to the "something else"? It obviously disappears, but how does it know to disappear. If we replace cats with spin we have the question, what is the angular momentum contribution of the 2AB? If the wave interference is physical, then the total angular momentum "disappears" until measurement, although if it is statistical, it is, "before measurement we did not know, after, we did" which is the Einstein view, but that is not part of Copenhagen.

Just thinking. Maybe not clearly enough. Anyone care to help?

 

[EPR]

These type of questions will likely not be resolved in the current framework.
'Particles' are a set of relationships in SR and QFT. Although we can make statistical predictions, we seem to be missing a huge part of the underlying mechanism which leads to definite outcomes. This isn't something minor that can be overlooked.
I doubt any interpretation is even close to how this comes about(and the Copenhagen rightly says almost nothing about it which i find it's not a real interpretation per se).