QP Interpretation Hierarchy and Subclasses

[Feeble Wonk]

As an interested reader of the work done by you professional physicists, it sometimes seems a little murky to me as to where some subcategories of QP interpretation schools of thought belong in the theoretical hierarchy.

I'm curious if it's possible to definitively delineate these theoretical relationships in a logistical "flow chart" type of format. I'd think the attempt to do this by you guys that "get it" would be fertile ground for an interesting discussion and debate, and very educational for those of us that are still struggling with some of the general concepts in dispute.

I'm not even certain how I would try to logically organize the primary interpretive categories, let alone the theoretical subcategories. For example, I'd assume that primary categories would include Copenhagen, MW and dBB, but how would environmental decoherence, hidden variable and ensemble concepts apply to these, or would some of those be "higher" level hierarchal differentiations? Would the initial differentiation be between "realistic" vs. "idealistic" interpretations?

I suspect that this process would be difficult, if not impossible, because some of the concepts would apply to multiple subsets of theories in different ways, which might start divergent lines of thought that categorize differently depending on how you are considering them.

But, that's the kind of logical breakdown of interpretive schools of thought that I'm wondering about. I, at least, would find this exercise - by you guys qualified to do it - very interesting and informative. Perhaps the academics among you could even sprinkle in some chronological/historical background on the theoretical developments.

Any takers?

 

[Nugatory]

I suspect that this process would be difficult, if not impossible, because some of the concepts would apply to multiple subsets of theories in different ways, which might start divergent lines of thought that categorize differently depending on how you are considering them.

Good guess :)
Not that that will stop people from trying.

 

[bhobba]

Well just to start you might like to read what John Baez says about it:
http://math.ucr.edu/home/baez/bayes.html
'It turns out that a lot of arguments about the interpretation of quantum theory are at least partially arguments about the meaning of the probability'

I have an interest in interpretations, and if someone asked me to distil their differences it would be what John Baez wisely said.

Thanks
Bill

 

[Feeble Wonk]

I'm reading through the source you offered from Baez. Fascinating... but it's raising more questions, in my mind anyway, than providing answers. I hate it when that happens.

 

[bhobba]

I'm reading through the source you offered from Baez. Fascinating... but it's raising more questions, in my mind anyway, than providing answers. I hate it when that happens.

I thought it would

This interpretation stuff is rather subtle.

Thanks
Bill

 

[atyy]

It's easy.

If MWI works, then dBB is a good instrumental theory (reality is just a tool to calculate the probabilities of outcomes), so MWI will be above dBB.

In dBB, MWI is a good instrumental theory (if it works), so dBB will be above MWI.

 

[ddd123]

Well just to start you might like to read what John Baez says about it:
http://math.ucr.edu/home/baez/bayes.html
'It turns out that a lot of arguments about the interpretation of quantum theory are at least partially arguments about the meaning of the probability'

Then he continues: "For example, suppose you have an electron in a state where the probability to measure its spin being "up" along the z axis is 50%. Then you measure its spin and find it is indeed up. The probability now jumps to 100%. What has happened? Did we "collapse the wavefunction" of the electron by means of some mysterious physical process? Or did we just change our prior based on new information? Bayesianism suggests the latter. This seems to imply that the "wavefunction" of a specific individual electron is just a summary of our assumptions about it, not something we can ever measure. Some people find this infuriating; I find it explains a lot of things that otherwise seem mysterious."

More than a map, a book that explains the various arguments and counter-arguments with the experimental basis would be nice. If people are infuriated by this interpretation (just an example, it could be any other) they must have a reason to, but not enough hard evidence to disprove it. There have been numerous articles on Scientific American etc. talking about experimental observation of the wavefunction etc... If there's actually no consensus, the facts of the matter must be very messed up, so a book that explains what exactly the mess consists of would be nice.

 

[Swamp Thing]

Then (John Baez) continues: "For example, suppose you have an electron in a state where the probability to measure its spin being "up" along the z axis is 50%. Then you measure its spin and find it is indeed up. The probability now jumps to 100%. What has happened? Did we "collapse the wavefunction" of the electron by means of some mysterious physical process? Or did we just change our prior based on new information? Bayesianism suggests the latter.

This seems to imply that Nature (or God) knows something that the experimenters don't know -- and a measurement helps them to refine their information and converge towards a better knowledge about the system. And that sounds just like hidden variables. Does a Baysean viewpoint assume (or at least admit) hidden variables? Is there a Baysean school that manages without hidden variables?

 

[ddd123]

Afaik hidden variables are only non-probabilistic variables. Finding out the exact probability spectrum isn't like finding the hidden variables, that would be meta-hidden variables or something.

 

[bhobba]

Afaik hidden variables are only non-probabilistic variables.

They are any variables not directly observable a theory is supposed to depend on - probabilistic or otherwise.

Its not only the usual hidden variable ones such as BM or Nelson Stochastics - it includes theories like Feynman's path integral approach (the path is the hidden variable). Even the modern Consistent Histories approach is technically a hidden variable theory - a history is (like a path in Feynmans approach) is a hidden variable - in that interpretation QM is the stochastic theory about histories. It must be said Griffiths doest think its a hidden variable theory - which just goes to show the controversy in this stuff.

Unfortunately I know of no text or paper that does what you want.

The closest I know of is the following:
https://www.amazon.com/dp/3540357734/?tag=pfamazon01-20

Thanks
Bill

 

[Demystifier]

Feeble Wonk, I think the table at wikipedia may be very helpful:
http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics#Tabular_comparison

 

[Feeble Wonk]

Feeble Wonk, I think the table at wikipedia may be very helpful:
http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics#Tabular_comparison

Thanks DM. I had actually already read that wiki source. In fact, I've got it bookmarked. It's very informative, and I think it does a really good job of summarizing some of the major schools of interpretive thought, but it's not quite organized in the hierarchal format I was curious about.

Plus... I thought it would be fun to watch you experts debate about how it should be arranged. [emoji39]

 

[bhobba]

I thought it would be fun to watch you experts debate about how it should be arranged.

Its a huge area which is likely why what you want doesn't exist.

Even just one interpretation, the ensemble, is a big area:
http://www.kevinaylward.co.uk/qm/eis.pdf

From the above, and very similar to John Baez (and I tend to agree):
'More generally, Jammer suggests. “the different interpretations of probability in quantum mechanics may even be taken as a kind of criterion for the classification of the various interpretations of quantum mechanics”

Really that's the classification IMHO.

Couple that with, while interpretations fascinate non-physicists, most physicists are in the shut up and calculate camp so its an area that goes at a rather leisurely pace anyway - it doesn't have these huge breakthroughs like the discovery of the Higg's that gets everyone excited. Every now and then you get something like Bell and Aspect - but otherwise its basically a lot of discussion about opinions rather than fact.

Thanks
Bill

 

[Swamp Thing]

http://www.kevinaylward.co.uk/qm/
The Ensemble Interpretation does not attempt any explanation as to why Quantum Mechanics is the way it is. It simply states a rational way of interpreting and calculating results without introducing the conceptual difficulties that are inherent in the Copenhagen Interpretation. It is essentially still, a shut up and calculate method.

Rather than being an interpretation, is it not a decree not to interpret?

 

[bhobba]

Rather than being an interpretation, is it not a decree not to interpret?

Its an actual interpretation - but a minimalist one.

Its interpretation of probability is frequentest, which is different to Copenhagen which is Bayesian.

As I, and links I gave, have alluded to, much of QM interpretations is an argument about what probability means.

Thanks
Bill

 

[Feeble Wonk]

As I, and links I gave, have alluded to, much of QM interpretations is an argument about what probability means.

This is being increasingly clear to me. But it does seem to leave some much open to speculation regarding what's actually going on.

 

[Feeble Wonk]

...On the other hand. It also appears to be an honest concession that we really don't know "what" is going on, and limit the discussion to what we "do" know.

 

[bhobba]

This is being increasingly clear to me. But it does seem to leave some much open to speculation regarding what's actually going on.

Its not the only thing. But another big factor is related to it. From the Ensemble paper:
'Einstein was an early supporter of the view, which he maintained until the end of his life, that quantum theory represented a correct and complete statistical theory of ensembles, but not a theory of elementary processes. In other words he regarded the theory as incomplete'

Is QM probabilities a complete description?

Thanks
Bill

 

[Demystifier]

much of QM interpretations is an argument about what probability means.

Perhaps even more is about what properties, if any, a system has when they are not measured.

 

[bhobba]

...On the other hand. It also appears to be an honest concession that we really don't know "what" is going on, and limit the discussion to what we "do" know.

Here you are falling into a trap - we simply do not know if there is more - that was the exact point Einstein argued with Bohr about. It wasn't what the popular press portray it as - early on Einstein had doubts about QM's validity - but later he accepted it as a complete statistical description - but those statistics depended on 'what's really going on'.

Thanks
Bill

 

[Feeble Wonk]

Is QM probabilities a complete description?

Well... It would appear to be an "accurate" description in terms of its predictive power within the probabilistic constraints of the theory. Yet, not at all complete if you are asking about "what" is actually occurring.

 

[Feeble Wonk]

Perhaps even more is about what properties, if any, a system has when they are not measured.

Here you are falling into a trap - we simply do not know if there is more - that was the exact point Einstein argued with Bohr about. It wasn't what the popular press portray it as - early on Einstein had doubts about QM's validity - but later he accepted it as a complete statistical description - but those statistics depended on 'what's really going on'.

These are both good points that illustrate why my silly idea about a logical flow chart of interpretational theories won't work. These questions would appear to apply to ALL of the interpretations, other than possibly dBB, as it at least seems to posit a definitive physical process... regardless of how compellingly is does so.

For instance, how would you classify Copenhagen? It could be viewed as either "realistic" or "idealistic" depending on how you view the nature of the wave vector.

 

[bhobba]

Yet, not at all complete if you are asking about "what" is actually occurring.

Why must more be happening?

That was the crux of the magnificent Einstein Bohr debates. For years it was thought Bohr won - but from our vantage we know that's not the case - either view is valid.

Really it's nothing new:
https://www.amazon.com/dp/0387715193/?tag=pfamazon01-20

The two masters have trod the path before and it is wise to be aware of what they did.

Thanks
Bill

 

[bhobba]

For instance, how would you classify Copenhagen?

Bayesian.

Thanks
Bill

 

[avarmaavarma]

Try this text by John Wheeler...it is out of print..but still a classic. It attempts to categorize the various interpretations based on both underlying principles as well as ( not so recent) experiments.

https://www.amazon.com/dp/0691613168/?tag=pfamazon01-20

If you need a quick read, look into this collection of essays - one of them summarizes the interpretations well.

https://www.amazon.com/dp/020150393X/?tag=pfamazon01-20

A popular science book - ' quantum reality' by Nick Herbert is also a good read.