A Statistical ensemble interpretation done right

[Morbert]

And what if it doesn't?

Then an orthodox interpretation could imply quantum theory is a complete physical theory, even of individual systems, while an ensemble interpretation would at least be that quantum theory is a complete theory of the statistics of ensembles.

 

[vanhees71]

How are you modelling the "microscopic sphere"? With a hidden variable state $\lambda$?

[edit to add] - You have to be careful about asserting properties of a microscopic system independent of measurement.

No, simply quantum mechanically. Instead of some ominous sphere, take a silver atom. Then you have Stern's and Gerlach's experiment of 1922.

 

[vanhees71]

No. It only gives an account of events ''that we can talk about at the breakfast table'' (according to the above paper) - not of dynamical processes that would qualify as measurement processes.

In particular, their discussion assumes measurement results that fall from heaven, given by a POM or POVM in addition to the untary dynamics of the system, rather than taking the state of the universe and deriving from it the distribution of the values read from a macroscopic detector that is part of the dynamics.

Thus everything is empty talk embellishing Born's rule.

Why is the minimal interpretation "empty talk"? It's all that's observed in real-world experiments. The outcomes of measurements are random, and the probabilities predicted by quantum theory, which of course includes Born's rule as one of its basic postulates, are confirmed. As any good theory QT simply describes, what's observed. If it wouldn't, one would look for another better theory.

 

[A. Neumaier]

Why is the minimal interpretation "empty talk"?

I wasn't talking about the minimal interpretation but about the decoherent histories paper cited.

The minimal interpretation (without your ''and nothing else'' addition to it) is the consensus among quantum physicists, and does not say anything about the observation of a quantum system (the solar system, say) by a subsystem (a laboratory on Earth, say).

Everything beyond the minimal interpretation (including your ''and nothing else'' addition to it) is controversial.

Decoherent histories is not minimal as it claims to say something about observations in quantum cosmology, where the quantum system is the whole universe. But all it says is empty talk, since it is silent about how the measurement results encoded in the POVMs are related to the macrostate of the detector (which encodes what can be read form it), as it would be described by the unitary dynamics of the state of the universe.

 

[vanhees71]

I wasn't talking about the minimal interpretation but about the decoherent histories paper cited.

The minimal interpretation (without your ''and nothing else'' addition to it) is the consensus among quantum physicists, and does not say anything about the observation of a quantum system (the solar system, say) by a subsystem (a laboratory on Earth, say).

It says everything that can be said in accordance with all observations known so far, and indeed we observe all the systems you mention, and what we observe is in accordance with the predictions of (minimally interpreted) QT.

Everything beyond the minimal interpretation (including your ''and nothing else'' addition to it) is controversial.

Indeed, because it's not based on empirical evidence.

Decoherent histories is not minimal as it claims to say something about observations in quantum cosmology, where the quantum system is the whole universe. But all it says is empty talk, since it is silent about how the measurement results encoded in the POVMs are related to the macrostate of the detector (which encodes what can be read form it), as it would be described by the unitary dynamics of the state of the universe.

I thought the POVMs are constructed to describe as best as one can the properties of the measurement device, or rather the other way, experiments construct measurement devices, which as good as possible realize a measurement described by a POVM.

 

[A. Neumaier]

I thought the POVMs are constructed to describe as best as one can the properties of the measurement device, or rather the other way, experiments construct measurement devices, which as good as possible realize a measurement described by a POVM.

There is a new thread for discussing this.

 

[Morbert]

No, simply quantum mechanically. Instead of some ominous sphere, take a silver atom. Then you have Stern's and Gerlach's experiment of 1922.

That's perfectly fine if we want to use quantum mechanics to relate measurements on silver atoms to preparations of silver atoms, but as an immediate ontic description, issues arise (see e.g. delayed-choice experiments).

 

[vanhees71]

I've no clue, what you mean. We can successfully predict what happens with silver atoms when going through a magnetic field. What, do you think, is missing?

 

[Morbert]

I've no clue, what you mean. We can successfully predict what happens with silver atoms when going through a magnetic field. What, do you think, is missing?

It's not that something is missing. It's that something is missing *if* we conceptualise the quantum state as having some correspondence to an ontic state, as opposed to as representing an ensemble of prepared systems.

Consider a delayed-choice experiment as described by wheeler. The meanignfulness of the statement "the electron went through slot A or the electron went through slot B" is determined by whether or not a measurement is made at a later time. This is not a problem if a quantum state is an ensemble and probabilities refer to detector response rates. But it is a problem if we want an ontic, contextless description of the course of the electron.

 

[vanhees71]

QT teaches you that the context of our observations matter. I don't know, what precisely you mean by "ontic" though.