Why is the Copenhagen interpretation so popular?

[Bender]

I have read in several books and articles that the Copenhagen interpretation is the most common among physicists (latest is a physics textbook from Giancoli). Is that true? If so, why?

 

It requires a boundary between the "quantum world" and the "macroscopic world": when is a system too large and do the wave functions collapse? To me that seems to be adding unnecessary complexity, but I may be missing something.

 

As a side note: a while ago I read about an experiment where they wanted to bring a tiny mirror (i.e. a macroscopic object) in superposition. Does anyone know whether that experiment was ever performed?

[Itoero]

According to the Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured, and quantum mechanics can only predict the probabilities that measurements will produce certain results. The act of measurement affects the system, causing the set of probabilities to reduce to only one of the possible values immediately after the measurement. This feature is known as wave function collapse.

 

This is imo an easy to understand interpretation which is applicable to the macroscopic or observable world.

This probably causes its popularity.

Edited February 4, 2017 by Itoero

[Bender]

According to the Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured, and quantum mechanics can only predict the probabilities that measurements will produce certain results. The act of measurement affects the system, causing the set of probabilities to reduce to only one of the possible values immediately after the measurement. This feature is known as wave function collapse.

 

This is imo an easy to understand interpretation which is applicable to the macroscopic or observable world.

This probably causes its popularity.

But "easy to understand" shouldn't be an issue for quantum physicists.

[Itoero]

But "easy to understand" shouldn't be an issue for quantum physicists.

That's true but I mean it's understandable because it's applicable to the macroscopic or observable world.

'understanding' is a wrong word....it's easy to imagine.

[Bender]

I guess I was hoping that it was more than just that.

Edited February 6, 2017 by Bender

[Itoero]

According to the Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured and the act of measurement affects the system.

 

This is just like the wave-particle duality and like Heisenberg's uncertainty.

Edited February 6, 2017 by Itoero

[Bender]

According to the Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured and the act of measurement affects the system.

 

This is just like the wave-particle duality and like Heisenberg's uncertainty.

The "act of measurement" is ill-defined, which is what bothers me, personally, about the Copenhagen interpretation. Clearly "interaction with other particles" doesn't qualify, because atoms and even molecules have been shown to be able to exist in superposition. Where is the "boundary" between the "quantum world" and the "macroscopic world"?

[Eise]

The "act of measurement" is ill-defined, which is what bothers me, personally, about the Copenhagen interpretation. Clearly "interaction with other particles" doesn't qualify, because atoms and even molecules have been shown to be able to exist in superposition. Where is the "boundary" between the "quantum world" and the "macroscopic world"?

 

'Decoherence' might be a solution. Or not...

 

From here:

 

Erich Joos and Heinz-Dieter Zeh claim that the phenomenon of quantum decoherence, which was put on firm ground in the 1980s, resolves the problem. The idea is that the environment causes the classical appearance of macroscopic objects. Zeh further claims that decoherence makes it possible to identify the fuzzy boundary between the quantum microworld and the world where the classical intuition is applicable. Quantum decoherence was proposed in the context of the many-worlds interpretation[citation needed], but it has also become an important part of some modern updates of the Copenhagen interpretation based on consistent histories. Quantum decoherence does not describe the actual process of the wavefunction collapse, but it explains the conversion of the quantum probabilities (that exhibit interference effects) to the ordinary classical probabilities.

(Bold by me)

On the other side, in the first link:

 

Specifically, decoherence does not attempt to explain the measurement problem.

 

Maybe this helps.

[studiot]

For those that like reading,

 

Roger Penrose devotes a whole chapter (chapter 29) of his book The Road to Reality to this question.

 

He examines 6 different interpretations, including Copenhagen, in some (mathematical) detail.

[Mordred]

Good book I also have a copy

[timo]

The "act of measurement" is ill-defined, which is what bothers me, personally, about the Copenhagen interpretation. Clearly "interaction with other particles" doesn't qualify, because atoms and even molecules have been shown to be able to exist in superposition. Where is the "boundary" between the "quantum world" and the "macroscopic world"?

I share your feelings that the understanding of the measurement process is not satisfactory on the conceptual level. But my gut feeling is that this might actually lead to the answer to your original question, namely why the Copenhagen interpretation is/became so popular:

 

Physics is all about creating a quantitative description of reality and testing it in experiments. Putting the conceptual annoyance in-between "this is how the system behaves" and "this is how my measurement device works" may be very practical for experiments. You can use your quantum world picture for the system you are investigating and your knowledge of your measurement device for your setup. And you have some magic rule that allows you to calculate what your measurement device sees depending on the state in the quantum world. Putting the annoyance of QM not making sense anywhere else in the interpretation (I am not familiar with other interpretations, but I assume they all have their weirdnesses) may be less suitable for practical work.

Edited February 6, 2017 by timo

[Bender]

 

'Decoherence' might be a solution. Or not...

 

From here:

 

(Bold by me)

On the other side, in the first link:

 

 

Maybe this helps.

I'll need some time to process this decoherence concept. What role does it play in (updated) Copenhagen interpretation? At first glance, it seems to be mentioned mostly in the context of the multiverse interpretation.

For those that like reading,

 

Roger Penrose devotes a whole chapter (chapter 29) of his book The Road to Reality to this question.

 

He examines 6 different interpretations, including Copenhagen, in some (mathematical) detail.

Thanks for the tip. The university library has a copy, so I think I'll have a look.

I share your feelings that the understanding of the measurement process is not satisfactory on the conceptual level. But my gut feeling is that this might actually lead to the answer to your original question, namely why the Copenhagen interpretation is/became so popular:

 

Physics is all about creating a quantitative description of reality and testing it in experiments. Putting the conceptual annoyance in-between "this is how the system behaves" and "this is how my measurement device works" may be very practical for experiments. You can use your quantum world picture for the system you are investigating and your knowledge of your measurement device for your setup. And you have some magic rule that allows you to calculate what your measurement device sees depending on the state in the quantum world. Putting the annoyance of QM not making sense anywhere else in the interpretation (I am not familiar with other interpretations, but I assume they all have their weirdnesses) may be less suitable for practical work.

Sounds reasonable. So the popularity would be practical rather than philosophical?

[KipIngram]

Copenhagen may be popular simply because it got a big momentum behind it from it's support by the "big guys" back in the day. I don't really know.

 

But all of these interpretations make the same experimental predictions, so there's no way to choose amongst them with a completely scientific process. I think it really comes down to a matter of "what appeals." How do the various perspectives fit into your personal "outlook" on the world.

 

For example, I believe there is more to consciousness than a "brain computer." Whatever you want to call them, I think we have "minds" or "spirits" or whatever that go beyond our material selves. So it's easy for me to fit Copenhagen into that - collapse occurs when a conscious mind demands an outcome. Possibilities become real in sort of a "just in time" manner when something has to be presented to a thinking mind.

 

Some of the other interpretations just offend my sensibilities. Many worlds, for example - when "all possible outcomes" occur and we suddenly have that many more new universes, where does all that mass and energy come from? Many universes full of mass and energy? I'm not saying there's an explicit violation of any conservation law - just that it's an awfully "big outcome" to get from a single quantum event. Also (and I'm not sure how rigorous my understanding is here), the "macro" outcome of many worlds seems ridiculous - in theory you should be able to find a universe that contains any possible physical outcome. So somewhere you've got a universe that's an awful lot like "The Sopranos" or "Days of Our Lives." Um, no - can't stretch my credulity that far.

 

Bohm gave us an interpretation where everything happening now is deterministic - all the uncertainty about the future is bundled up in an unobservable internal state at the beginning of time. But I believe we have real free will, so that doesn't fly for me either.

 

These examples - they're just to underline how the science of quantum theory gives us results that we can count on, but the interpretation really isn't a matter of scientific investigation, because the results are the same in every test and so no test distinguishes. And in the end it really doesn't matter, as long as we do the math right.

 

So the next time you're arguing with your buddy about which quantum interpretation is "right," just remember that you're having a philosophical debate, not a scientific one. And just to keep the argument from getting too heated, remember that you can't know that you're right. It's like arguing over Ginger vs. Mary Ann, or Mounds vs. Almond Joys.

Edited March 24, 2017 by KipIngram