What is the Copenhagen interpretation according to its originator(s)?

[dx]

I feel that contemporary authors' statements about the copenhagen interpretation don't really match with what the founders of quantum mechanics said. Also, different authors give seemingly contradictory statements about it is.

What do the members here think about this? What is the copenhagen interpretation according to people like Bohr and Heisenberg?

 

[BvU]

Hello @love_42, !

There is a lot that has already been said about this; perhaps you want to browse the threads listed at the bottom of the page, so you can -- if still desired -- come up with a more specific question than "what do you all think ?"

 

[dx]

Thanks for the welcome. I will browse some of the threads and try to come up with a more specific question.

 

[PeterDonis]

contemporary authors' statements about the copenhagen interpretation

Which ones? Please give specific references.

 

[PeterDonis]

What is the copenhagen interpretation according to people like Bohr and Heisenberg?

What do Bohr and Heisenberg say? There are plenty of writings by them on the subject.

 

[dx]

What do Bohr and Heisenberg say? There are plenty of writings by them on the subject.

As far as I understand, Bohr and Heisenberg argue as follows. We don't have to talk about measurement in classical physics because can always account for the influence of the measuring bodies on the objects under investigation. We can make the effect of the measuring bodies as small as we want, or if it is finite, we can take that finite effect into account in our description. This means that we can talk about the state of a system, for example the position of a particle, as something that exists independently of observation. This is not possible in quantum physics because the effect of the measuring bodies is uncontrollable. If a body is to serve as a clock, then there will be an uncontrollable exchange of energy with the clock, which cannot be separately taken into account in order to specify the state of the objects. Any attempt to do so would interfere with the capability of the body to serve its original purpose of functioning as a clock. Our inability to eliminate disturbances does not by itself imply a need to alter the classical concept of observation. The reason that the distinction between measuring agencies and the objects under investigation becomes important in quantum theory is because these disturbances have a closed and uncontrollable character. This creates an essential latitude in the fixation of the state of the system by mechanical variables such as position and momentum, which has its precise formulation in the so-called uncertainty principle. Since a causal account which predicts the future state of the system from its initial state requires an exact knowledge of position and momentum, the quantum mechanical description of the system can only make statistical predictions. There is no sharp distinction between an independent behavior of the system and the statistics of measurements attainable on the system.

 

[PeterDonis]

As far as I understand

From what sources? You don't have to guess. As I have already said, they both made many writings on the subject. Have you read any? If so, please give specific references.

 

[dx]

From what sources? You don't have to guess. As I have already said, they both made many writings on the subject. Have you read any? If so, please give specific references.

I get all this from Bohr's writings collected in Volume 6 and Volume 7 of Bohr's collected works. The title of these two volumes are "Foundations of Quantum Physics I" and "Foundations of Quantum Physics II"

Heisenberg has made similar comments in his book "The Physical Principles of The Quantum Theory."

 

[PeterDonis]

I get all this from Bohr's writings collected in Volume 6 and Volume 7 of Bohr's collected works. The title of these two volumes are "Foundations of Quantum Physics I" and "Foundations of Quantum Physics II"

Heisenberg has made similar comments in his book "The Physical Principles of The Quantum Theory."

Ok, good. Now, do you have any specific references to contemporary authors that you think are saying things that contradict what Bohr and Heisenberg said?

 

[dx]

Ok, good. Now, do you have any specific references to contemporary authors that you think are saying things that contradict what Bohr and Heisenberg said?

For example, David Mermin says

If I were forced to sum up in one sentence what the Copenhagen interpretation says to me, it would be `'Shut up and calculate!'

 

[PeterDonis]

David Mermin says

Please give a specific reference.

 

[dx]

Please give a specific reference.

N. David Mermin (2004). "Could Feynman Have Said This?". Physics Today. 57(5): 10–11. Bibcode:2004PhT...57e..10M. doi:10.1063/1.1768652

 

[Jarvis323]

Here is my understanding.

I think it was mostly a consensus amongst top authorities on quantum physics at the time that we could never find a more intrinsic model that explains the probabilistic aspects of quantum mechanics. The belief was that the probabilistic model and the Copenhagen interpretation were the very root of the "But why?" tree and at the pinnacle of prediction and explanation. Others wanted to keep searching for a more complete theory and an explanation (e.g. Einstein).

Then Von Neumann published his "Impossibility Proof" that purported to prove that it was impossible to better explain the probabilities that show up (no hidden variables). That sort of settled it and changed the course of physics research in support of the shut up and calculate side.

Meanwhile, Grete Hermann had pointed out an error in Von Neumann's proof, but she was ignored. It wasn't until 30 or so years passed that John Bell rediscovered the flaw Grete had found. Now we know that a probabilistic system isn't the only possible explanation. So now, the strict, authoritarian shut up and calculate ideology is more or less dead, and there is active research towards going deeper than a probabilistic model. However, there is still a problem testing them.

So all in all, I guess it's not the Copenhagen interpretation itself that means shut up and calculate, it's the belief that the Copenhagen interpretation is the way it is and as deep as it gets that suggests shut up and calculate. It marked the point in science that people decided to stop digging (as it turned out, for an invalid reason).

But now, the phrase is used commonly to quell demands for intuitive or more fundamental explanations in general, as many people argue that it is not the role of Physics (nor is it possible) to explain things, but we can only measure and predict/calculate things. This is sort of the view that was central to the famous debates about the Copenhagen Interpretation. I think it's a sort of polarizing issue and there are people here and everywhere all over the spectrum.

And finally, I think that ones perception that the Copenhagen interpretation "means" shut up and calculate, is not a contradiction to the more technical arguments made about what the interpretation is, especially if one is asked to sum it up in only a few words.

 

[atyy]

There is no well defined Copenhagen interpretation. Usually it means an operational or instrumental view of the quantum formalism, as can be found in Landau & Lifshitz, Messiah, or Weinberg, for example. When people wish to use the term Copenhagen to refer to the historical views of Bohr or Heisenberg, for example, the textbook Copenhagen interpretation is often called the Orthodox interpretation.
https://arxiv.org/abs/quant-ph/0209123
http://eng-web1.eng.famu.fsu.edu/~dommelen/quantum/style_a/stat.html

 

[PeterDonis]

N. David Mermin (2004). "Could Feynman Have Said This?". Physics Today. 57(5): 10–11. Bibcode:2004PhT...57e..10M. doi:10.1063/1.1768652

In that article (or more precisely, in the previous article by Mermin that he references in this article), Mermin was pointing out that this...

the quantum mechanical description of the system can only make statistical predictions

...is basically the same as saying "all QM can tell you is the statistical predictions it calculates, so quit trying to get it to tell you more and just shut up and calculate". In other words, according to this viewpoint, it is pointless to ask what QM says is "really happening", because QM doesn't tell you that. All it tells you is the statistical predictions for measurement results.

I don't think that's an unfair characterization of what Bohr and Heisenberg said in at least some of their published writings. I also don't think it's unfair to say that Bohr and Heisenberg weren't always consistent in their published writings.

 

[dx]

There is no well defined Copenhagen interpretation. Usually it means an operational or instrumental view of the quantum formalism, as can be found in Landau & Lifshitz, Messiah, or Weinberg, for example.

I think it's misleading to say that the copenhagen interpretation is just some kind of operational or instrumentalist viewpoint. Bohr's ideas are much more subtle and deep than that. For example, he once said that

" I felt also — but not to do anything with it — that it was more so that if one created a photon, then one had made a knot in existence, a knot which was of a very difficult kind to say, and only when that photon was absorbed, annihilated, that knot was untied. And that [view] I felt, was nothing, but [that] it had to be done in that kind of way was really something which was formidable. But now we know that these are solved by the non-commutation rules, and therefore, the non-commutation rules are certainly something great. But in order to understand what they mean — You cannot get over that problem of the particle and the wave. "

 

[Lord Jestocost]

For example, David Mermin says
If I were forced to sum up in one sentence what the Copenhagen interpretation says to me, it would be `'Shut up and calculate!'

In "Annotated Interview with a QBist in the Making“ (https://arxiv.org/abs/1301.6551), N. David Mermin writes:

Quantum states, in other words, are bookkeeping tools that enable one to calculate, from a knowledge of the initial preparation and the fields acting on a system, the probability of the outcomes of measurements on that system.¹³ This is what I take to be the Copenhagen interpretation of quantum mechanics. (I hereby renounce my earlier summary of Copenhagen, widely misattributed to Richard Feynman, as “shut up and calculate.”)

¹³My QBist friends don’t like this. At a minimum they would replace “knowledge of” with “belief about”

 

[Lord Jestocost]

I think it's misleading to say that the copenhagen interpretation is just some kind of operational or instrumentalist viewpoint.

To my mind, the Copenhagen view can be considered as an instrumentalist’s point of view.
Niels Bohr in: Atomic Theory and the Description of Nature, I, FOUR ESSAYS, With an Introductory Survey, CAMBRIDGE AT THE UNIVERSITY PRESS, 1961 (first published 1934)

“We meet here in a new light the old truth that in our description of nature the purpose is not to disclose the real essence of the phenomena but only to track down, so far as it is possible, relations between the manifold aspects of our experience.”

 

[EPR]

To my mind, the Copenhagen view can be considered as an instrumentalist’s point of view.
Niels Bohr in: Atomic Theory and the Description of Nature, I, FOUR ESSAYS, With an Introductory Survey, CAMBRIDGE AT THE UNIVERSITY PRESS, 1961 (first published 1934)

“We meet here in a new light the old truth that in our description of nature the purpose is not to disclose the real essence of the phenomena but only to track down, so far as it is possible, relations between the manifold aspects of our experience.”

The essence of his view on the CI(bolding mine). While still minimalist in nature, it goes beyond the usual 'we shall only speak about what can be measured /observed' in its operational form as it's saying something about the nature of the classical reality(speculation but not entirely groundless).
I think this is the reason why there is the MWI which substitutes the observer with the environment( and which makes no use of minimalism). It seems for most scientists who are deeply interested in these issues the choice most often boils down to whether it's the CI or the MWI(as they are structurally similar and the most popular interpretations).