A The minimal statistical interpretation is neither minimal nor statistical

[Demystifier]

This doesn't answer my question, what $\lambda$ is.

It's an abstract mathematical object satisfying axioms need to prove a Bell-like theorem. This also answers a question by @martinbn.

 

[Demystifier]

In the formalism there's no collapse

In most QM textbook there is.

 

[Demystifier]

The Bohmian trajectories are not observable. At least I don't have seen any measurement of the "Bohmian streamlines" behind a double slit for single electrons.

The same can be said for the wave function.

 

[Demystifier]

What is the logical inconsistency?

Read again the text you quoted. The first sentence shows that it must exist, while the second one considers the possibility that it doesn't exist. That's logical inconsistency, or more precisely a contradiction.

 

[AlexCaledin]

Just found this 50 year old H. Stapp paper. Stapp had read so many contradictory accounts of the Copenhagen interpretation that he became compelled to delineate it precisely.

- it's based on his correspondence with Heisenberg.

 

[vanhees71]

Could you give the source. Already the first paragraph of the above picture says it all! I guess the author had to clarify his mind after correspondence with Heisenberg, leading to such a clear and no-nonsense statement. SCNR.

 

[AlexCaledin]

Could you give the source.

- sorry - forgot to attach it! It's also in Mind, Matter and Quantum Mechanics

 

[StevieTNZ]

- sorry - forgot to attach it! It's also in Mind, Matter and Quantum Mechanics

Is the attached PDF subject to copyright?

 

[vanhees71]

- sorry - forgot to attach it! It's also in Mind, Matter and Quantum Mechanics

Already the abstract of the forwarded pdf makes no sense. Quantum theory does NOT say that its completeness were incompatible with the objective existence of classical spacetime. To the contrary the standard quantum theory builds on classical spacetime descriptions (Newtonian or special relativistic, depending on whether you do non-relativistic quantum mechanics or relativistic quantum (field) theory). The Rules of Quantum Mechanics, defined by the realization of the observable algebras are based on the spacetime structure as defined by classical physics. E.g., the commutation relations between the position and momentum operators and thus the entire construction of non-relativistic quantum theory, formulated in one of its standard representations like Schrödinger wave mechanics, follows from the Galilei symmetry of Newton-Galilei spacetime. The same holds for relativistic QFT and the Standard Model of elementary particle physics, which looks as it looks because of the Poincare symmetry of Minkowski spacetime.

The main difficulty to also quantize the gravitational interaction, as far as I understand it, seems to be the more complicated spacetime model of GR (or its extension to Einstein-Cartan theory which one needs already to formulate QFT for particles with spin in a given classical spacetime-manifold, i.e., without quantizing also the gravitational interaction). In GR the spacetime itself becomes part of the dynamics (that's why Wheeler dubbed the nice name "geometrodynamics" for it) and thus in a complete QT of gravitation spacetime itself must in some way be quantized.

 

[AlexCaledin]

- but the actual variant of spacetime, as well as everything we observe, is the outcome of the quantum dice throwing, right? That's why the pragmatic theory is working.

 

[vanhees71]

All we can say is that what we observe is consistent with our theoretical models, with a "classical" spacetime model and quantum theory for matter and all interactions except gravity. Quantum theory works well within and is based on the classical spacetime models, in not too complicated spacetimes of GR even in that case. What we don't know is how to quantize the gravitational interaction and thus, because in GR the gravitational interaction is reinterpreted as a dynamical spacetime geometry, spacetime itself. From the experimental point of view, it's of course also difficult to find hints for how to build a quantum theory of gravitation, because so far all observations where gravity plays a significant role are involving macroscopic (usually even astronomical) objects, which are well-described within classical (continuum) mechanics, and there are not quantum effects of the gravitational interaction seen. What's known to work right is the quantum theory of particles in the gravitational field of macroscopic objects (like the experiment with cold neutrons in the gravitational field on Earth, for which the energy-eigenvalue problem is a standard exercise in the QM 1 lecture).

 

[AlexCaledin]

What we don't know is how to quantize the ... spacetime itself.

Perhaps it's quite enough to know that a sort of Branching Spacetime interpretation is quite possible? or Hartle's Spacetime Alternatives? - anyway, the actual coarse grained reality is somehow chosen - with the spacetime - and it seems not very scientific to speculate how exactly the choice occurs - it makes the QM working, that's all...

 

[bhobba]

I would describe it as typical Einstein, who, of course, Ballentine got it from. Einstein was not the only one to believe in it, nor its originator. Einstein was what I call an opportunistic realist. He believed in realism but was agnostic to the various nuanced versions. He picked the version that suited his purposes the best. It may not really be statistical or minimal, but that was of no worry to him. It is those that followed in his footsteps that debate such concerns. For example, is probability real? The wave function can be looked at as a tool to calculate probabilities, so it is just as real or not real as probabilities. If not real, how can it collapse? We can debate that one for ages, but one must ask - to what end? I would classify myself as a Model Dependant Realist (a version of realism advocated by Hawking):
https://en.wikipedia.org/wiki/Model-dependent_realism

I do not worry about its various versions - yes, with realism, we have various versions. Those versions also have various versions - no wonder philosophers make slow progress - some would say no progress at all. Feynman, from my reading, was even worse - he didn't care what philosophy he used to make progress, was openly contemptuous of it, and just tried various ideas whether it involved a particular philosophy or not.

Thanks
Bill

 

[bhobba]

I always thought the minimal interpretation was the "shut up and calculate" interpretation: If you set up an ensemble of identically prepared systems and specify a measurement procedure that generates data, QM will report the frequencies and correlations that will be present in the data.

I would describe a couple of interpretations as minimal, e.g. I also think the Bayesian interpretation is minimal. In fact, I prefer it to Copenhagen, which has always seemed to come in various versions.

I would call Ballentine's interpretation minimal in the sense he takes the most common probability interpretation (frequentist) and applies it to the wave function (or state) but goes no further.

Thanks
Bill