I Nature Physics on quantum foundations

[gentzen]

The only theory that's really both microscopic as macroscopic is QT, and Born's rule applies to both microscopic and macroscopic systems.

Do you have a reference for this?

Any textbook on quantum many-body theory will do.

No, it will not. This is exactly my point that you claim that your position would be generally accepted, even so it is not and would need to be defended.

What of my position contradicts what can be found in any quantum many-body textbook?

I didn't claim that your position would "contradict" information found in standard textbooks. What I said was that you claim your position would be generally accepted, even so they are not. Replying "Any textbook on quantum many-body theory will do." is exactly such a "it is generally accepted" claim.

For fun, I now checked whether
Wolfgang Nolting, "Grundkurs Theoretische Physik 7: Viel-Teilchen-Theorie"
has anything to say with respect to "The only theory that's really both microscopic as macroscopic is QT, and Born's rule applies to both microscopic and macroscopic systems." Of course, as expected, nothing at all was said about that topic.

What do you think contradicts the standard minimal interpretation?

Again here, the same issue. I didn't claim that your position would "contradict" the standard minimal interpretation. You make stronger statements than the minimal interpretation, and then claim that those would coincide with what is claimed by the minimal interpretation.

 

[vanhees71]

Which stronger claims do I make? You always claim, I'd made some claims beyond the "standard interpretation" but never concretely give an example.

The only additional piece in my argument is to take into account relativistic local QFT, which is not treated in detail in Ballentine's book, which adds the "locality by construction" to the discussion of correlations due to entanglement and the impossibility of "spooky actions at a distance" in Bell-test experiments. I think, also this is rather standard and not very controversial. For textbooks emphasizing the microcausality constraint, see Weinberg, QT of Fields and Duncan, The conceptual framework of QFT.

Nolting's book is pretty standard too, though very sloppy in the definition of "state" (vectors rather than stat. ops./rays), not clearly distinguishing "measurements" and "preparations". In addition, as most textbooks, he introduces the projection/collapse postulate, which goes beyond the minimal interpretation.

 

[Demystifier]

I am a bit suspicious whether "my" Durr et al school successfully notices that the quantum potential is "bad" (in the sense that some crucial argument would fail to hold for the quantum potential version of BM).

The Durr et al school also accepts that quantum potential is "bad". The following excerpt from the book "Bohmian Mechanics" by Durr and Teufel illustrates that very well.

 

[Demystifier]

impossibility of "spooky actions at a distance" in Bell-test experiments. I think, also this is rather standard and not very controversial.

If impossibility of "spooky actions at a distance" in Bell-test experiments is not controversial, then I don't know what is.

 

[martinbn]

If impossibility of "spooky actions at a distance" in Bell-test experiments is not controversial, then I don't know what is.

@vanhees71 means that "there are no signals that propagate from one to the other faster than light" is not contraversial.

 

[gentzen]

Which stronger claims do I make? You always claim, I'd made some claims beyond the "standard interpretation" but never concretely give an example.

I did provide concrete quotes. It is simply a bit of work to repeat those quotes, that is why I only did this for the first part with respect to "Any textbook on quantum many-body theory will do."

So on your request, I now also did this work for the second part "You make stronger statements than the minimal interpretation, and then claim that those would coincide with what is claimed by the minimal interpretation."

All there is to specify about a concrete physical system in the lab is the quantum state (represented by the statistical operator with the meaning to describe the result of a specific preparation procedure), and the meaning are probabilities for the outcome of specifically given measurement procedures, i.e., quantitative observations on the system with a given measurement device.

Together with locality (i.e., microcausality) of relativistic QFT this implies that ... These correlations are there due to the preparation in the entangled state, and (within local relativistic QFTs) no faster-than-light spooky action at a distance due to the choice of a measurement setup and observations on the values of the measured observables is needed to explain these correlations.

I didn't change my mind. The state represents a "preparation procedure" for a single system, implying probabilities for the outcomes of measurements via Born's rule, and as such the state refers to an ensemble of equally prepared systems since there's no other way to test the probabilistic predictions than by making repeated measurements on such equally prepared ensembles.

 

[vanhees71]

Again, for me these statements are pretty standard ;-).

 

[Demystifier]

Which stronger claims do I make? You always claim, I'd made some claims beyond the "standard interpretation" but never concretely give an example.

Here are some claims beyond the standard interpretation that you often claim:
1) There is no collapse.
2) Entanglement correlations are caused by local interactions.
3) Wave function only specifies an ensemble of similarly prepared systems, it doesn't specify an individual system.

Notes:
- 1) and 3) are claimed by the Ballentine interpretation, but not by the standard interpretation.
- In addition to 3) you also often say that
3') Wave function completely specifies an individual system,
which of course contradicts 3).
- 2) is not claimed by any published interpretation that I am aware of.

 

[martinbn]

Here are some claims beyond the standard interpretation that you often claim:
1) There is no collapse.
2) Entanglement correlations are caused by local interactions.
3) Wave function only specifies an ensemble of similarly prepared systems, it doesn't specify an individual system.

Notes:
- 1) and 3) are claimed by the Ballentine interpretation, but not by the standard interpretation.
- In addition to 3) you also often say that
3') Wave function completely specifies an individual system,
which of course contradicts 3).
- 2) is not claimed by any published interpretation that I am aware of.

By standard, he means standard minimal statistical interpretation.

About 2), why is that controversial? I thought that is just QM and interpretation independent?

 

[vanhees71]

Here are some claims beyond the standard interpretation that you often claim:
1) There is no collapse.

For me the minimal interpretation is the standard interpretation, but indeed the collapse in my opinion cannot be a general postulate, because what happens to the measured system depends on the specific measurement device.

2) Entanglement correlations are caused by local interactions.
3) Wave function only specifies an ensemble of similarly prepared systems, it doesn't specify an individual system.

Notes:
- 1) and 3) are claimed by the Ballentine interpretation, but not by the standard interpretation.
- In addition to 3) you also often say that
3') Wave function completely specifies an individual system,
which of course contradicts 3).
- 2) is not claimed by any published interpretation that I am aware of.

How can 3') contradict 3), when we are obviously preparing single systems to form the ensemble?

2) follows from local/microcausal QFT.

 

[Demystifier]

About 2), why is that controversial? I thought that is just QM and interpretation independent?

It is standard that entanglement is caused by local interactions, but it's not standard that resulting correlations are caused by local interactions. Entanglement is a property of the abstract state in the HiIlbert space, while correlation is a property of the concrete measurement outcomes. Creation of entanglement is clearly deterministic, while creation of outcomes is seemingly random. Some interpretations say that correlations are caused by non-local action at a distance, some that they are not caused at all, etc.

 

[vanhees71]

But entanglement implies the corresponding correlations. So if entanglement is caused by local interactions, then also the correlations, described by it, are caused by local interactions.

If one accepts standard micocausal relativistic QFT, there cannot be non-local action at a distance.

 

[martinbn]

It is standard that entanglement is caused by local interactions, but it's not standard that resulting correlations are caused by local interactions. Entanglement is a property of the abstract state in the HiIlbert space, while correlation is a property of the concrete measurement outcomes. Creation of entanglement is clearly deterministic, while creation of outcomes is seemingly random. Some interpretations say that correlations are caused by non-local action at a distance, some that they are not caused at all, etc.

How can there be a non-local action at a distance and no faster than light signaling at the same time?

 

[martinbn]

How can 3') contradict 3), when we are obviously preparing single systems to form the ensemble?

Because the state describes the ensemble not the single system.

 

[Demystifier]

For me the minimal interpretation is the standard interpretation,

Something called "standard" should be universal, not "for you".

How can 3') contradict 3), when we are obviously preparing single systems to form the ensemble?

If you don't accept Ballentine's argument that 3') contradict 3), there is no hope that you would accept mine.

2) follows from local/microcausal QFT.

Except that there is no reference claiming it, making the claim 2) nonstandard.

 

[vanhees71]

Then you imply that one member of the ensemble influences any other, but that can be excluded in modern experiments (e.g., only single diphotons in Bell-test experiments, building an ensemble of really independent single-system realizations).

 

[martinbn]

Then you imply that one member of the ensemble influences any other, ...

How is that implied?

 

[vanhees71]

Because then you say that the quantum state cannot be determined by preparing a single system, i.e., that the ensemble is defined by the probabilistic properties of a single-system preparation procedure. For me this contradicts the findings of many Bell-test experiments, where it is ensured that always single systems are measured.

 

[Demystifier]

How can there be a non-local action at a distance and no faster than light signaling at the same time?

Signal is transmitted by controlled action, while action in general does not need to be controlled. For example, non-local action at a distance may be transmitted by some hidden variables, and variables which are hidden obviously cannot be controlled. Another example is random collapse, which involves non-local action at a distance but cannot be controlled because it's random.

 

[martinbn]

Because then you say that the quantum state cannot be determined by preparing a single system, i.e., that the ensemble is defined by the probabilistic properties of a single-system preparation procedure. For me this contradicts the findings of many Bell-test experiments, where it is ensured that always single systems are measured.

It can but only after you know what state the procedure produces. How do you know that by just one preperation?

 

[Demystifier]

For me this contradicts the findings of many Bell-test experiments

"For me" is the key. It's your view, not standard view.

 

[martinbn]

Signal is transmitted by controlled action, while action in general does not need to be controlled. For example, non-local action at a distance may be transmitted by some hidden variables, and variables which are hidden obviously cannot be controlled. Another example is random collapse, which involves non-local action at a distance but cannot be controlled because it's random.

Ok, suppose we have the standard Alice and Bob scenario. We do it 1000 times, Alice makes a measurement on either the first 500 or on the last 500, the other 500 she does nothing. Bob's task is by measuring his particle to determine when Alice measured, in the first half of the trials or in the second. Can he do it?

 

[vanhees71]

It can but only after you know what state the procedure produces. How do you know that by just one preperation?

Of course, I can't know this, but I have to prepare ensembles and do statistics with them. To completely determine the state you need several different measurements on the ensembles. The ensembles are defined by prepratation procedures of single systems. That's why it is so important to clearly distinguish "states" and "measurements". A state is a preparation procedure (for single systems), allowing to form well-defined ensembles. The outcomes of measurements are random and the statistics of these outcomes is given by the corresponding statistical operator according to Born's rule.

 

[Demystifier]

Ok, suppose we have the standard Alice and Bob scenario. We do it 1000 times, Alice makes a measurement on either the first 500 or on the last 500, the other 500 she does nothing. Bob's task is by measuring his particle to determine when Alice measured, in the first half of the trials or in the second. Can he do it?

He can't do it. This demonstrates that Alice by performing measurement cannot send a signal to Bob. But it does not imply that measurement by Alice doesn't have any influence on Bob's results.

 

[vanhees71]

Ok, suppose we have the standard Alice and Bob scenario. We do it 1000 times, Alice makes a measurement on either the first 500 or on the last 500, the other 500 she does nothing. Bob's task is by measuring his particle to determine when Alice measured, in the first half of the trials or in the second. Can he do it?

No, all Bob will see is a stream of random results with statistics determined by the prepared state. The correlations due to entanglement can only be verified by exchanging information about A's and B's measurement results on each individual entangled system.

 

[vanhees71]

He can't do it. This demonstrates that Alice by performing measurement cannot send a signal to Bob. But it does not imply that measurement by Alice doesn't have any influence on Bob's results.

If the measurement events are space-like separated within relativistic microcausal QFT there cannot be any influence of one of the measurements on the other.

 

[Demystifier]

If the measurement events are space-like separated within relativistic microcausal QFT there cannot be any influence of one of the measurements on the other.

Yes, but this does not contradict my claim. Standard relativistic microcausal QFT is one possible model of reality consistent with existing experiments, but it's not the only possible model of reality consistent with existing experiments.

 

[martinbn]

He can't do it. This demonstrates that Alice by performing measurement cannot send a signal to Bob. But it does not imply that measurement by Alice doesn't have any influence on Bob's results.

What kind of influence can there be if you cannot find any!

(By the same logic you could claim that there is a little sprite that looks at Alice's results and changes Bob's accordingly.)

 

[martinbn]

Of course, I can't know this, but I have to prepare ensembles and do statistics with them. To completely determine the state you need several different measurements on the ensembles. The ensembles are defined by prepratation procedures of single systems. That's why it is so important to clearly distinguish "states" and "measurements". A state is a preparation procedure (for single systems), allowing to form well-defined ensembles. The outcomes of measurements are random and the statistics of these outcomes is given by the corresponding statistical operator according to Born's rule.

Yes, and that is why there is a difference between an ensemble and a single system representing the ensemble. The state describes the ensemble.

 

[Demystifier]

But entanglement implies the corresponding correlations.

No, entanglement + Born rule implies the corresponding correlations. The origin of Born rule is controversial, hence the origin of correlations is controversial.