Quantum Mechanics: The Debate Over "State

[Robert Shaw]

The term "state" in quantum mechanics is not generally agreed across the physics community.

Some physicists consider it to be synonymous with "state preparation procedure".

Others find this too restrictive, as it would exclude states not prepared in a laboratory. For example my nose is not subject to a state preparation procedure.

 

[bhobba]

Why do you think your nose is not subject to a state preparation procedure?

Thanks
Bill

 

[dextercioby]

"State preparation procedure" as it stands assumes the existence of the omnipresent "classical observer (the experimentalist in a laboratory) who does something to alter the "state of being" of a physical system subject to the laws of quantum mechanics. So, by this natural logic, the (state of the) nose can only be prepared by an esthetician (surgeon).

 

[Jilang]

Hmm, the nose grows to its present condition. Is that not a state preparation?

 

[Mentz114]

The term "state" in quantum mechanics is not generally agreed across the physics community.

Some physicists consider it to be synonymous with "state preparation procedure".

Others find this too restrictive, as it would exclude states not prepared in a laboratory. For example my nose is not subject to a state preparation procedure.

Why do you think that your macroscopic nose should have a 'quantum state' ? I cannot think of any definition of 'quantum state' that can be applied to it.

[]
So, by this natural logic, the (state of the) nose can only be prepared by an esthetician (surgeon).

Is this a 'nose operator' ?

 

[Nugatory]

Others find this too restrictive, as it would exclude states not prepared in a laboratory.

A citation for this claim would be helpful. What is an example of one of these "others" who restrict themselves by requiring that "state preparation procedure" is limited to states prepared in a laboratory?

 

[bhobba]

A citation for this claim would be helpful. What is an example of one of these "others" who restrict themselves by requiring that "state preparation procedure" is limited to states prepared in a laboratory?

Exactly. I mentioned in another thread a dust particle that is given a position by interacting with a few stray photons from the CBMR. It obviously was prepared by that interaction.

As for the nose - its caught up in all sorts of other issues that complicate it greatly eg exactly at point does the nose end and other parts of the face begin. As Feynman explains in his lectures in a discussion about a table even where the table begins and the air starts is far from well defined. But assuming you can untangle all these issues, your nose is interacting with the environment and that interaction, like all classical objects we see around us, is basically what gives it its classical properties ie definite position and momentum etc. Its state is prepared by that interaction so it has the properties of everyday objects.

The book that goes into this, Ballentine (obviously not the only one - but the one I know well) uses an example of that looks like straight from a laboratory - its the same as in fig 1 of the following:
https://arxiv.org/pdf/quant-ph/0101012.pdf

Of course the way its presented makes it look like its only relevant to a laboratory - but nothing is ever said it is and its quite easy to see how it can be applied outside it.

Thanks
Bill

 

[Robert Shaw]

Exactly. I mentioned in another thread a dust particle that is given a position by interacting with a few stray photons from the CBMR. It obviously was prepared by that interaction.

As for the nose - its caught up in all sorts of other issues that complicate it greatly eg exactly at point does the nose end and other parts of the face begin. As Feynman explains in his lectures in a discussion about a table even where the table begins and the air starts is far from well defined. But assuming you can untangle all these issues, your nose is interacting with the environment and that interaction, like all classical objects we see around us, is basically what gives it its classical properties ie definite position and momentum etc. Its state is prepared by that interaction so it has the properties of everyday objects.

The book that goes into this, Ballentine (obviously not the only one - but the one I know well) uses an example of that looks like straight from a laboratory - its the same as in fig 1 of the following:
https://arxiv.org/pdf/quant-ph/0101012.pdf

Of course the way its presented makes it look like its only relevant to a laboratory - but nothing is ever said it is and its quite easy to see how it can be applied outside it.

Thanks
Bill

I think Ballentine is correct.

Limiting the term is sensible. Widening it to any procedure at all strips it of purpose.

The reason why the term was introduced was to ensure replicability of the state.

Any old procedure is useless...it must prepare a replicable state.

Regarding the example of my nose, I find it hard to believe that you have discovered a procedure for preparing perfect copies of my nose.

If you have, then send me the procedure and we can become tycoons and set up a nose factory.

 

[Robert Shaw]

Why do you think that your macroscopic nose should have a 'quantum state' ? I cannot think of any definition of 'quantum state' that can be applied to it.Is this a 'nose operator' ?

So macroscopic objects do not have a "quantum state" ?

Please tell me where is the point at which microscopic states stop being quantum states? I'm assuming you can give me an answer that's accurate to 10 decimal places.

 

[atyy]

A citation for this claim would be helpful. What is an example of one of these "others" who restrict themselves by requiring that "state preparation procedure" is limited to states prepared in a laboratory?

It's basically a restatement of the measurement problem and related issues. In a purely operational sense, the state of the universe is not meaningful. However, there are efforts to make the state of the universe meaningful, eg. MWI.

 

[Robert Shaw]

It's basically a restatement of the measurement problem and related issues. In a purely operational sense, the state of the universe is not meaningful. However, there are efforts to make the state of the universe meaningful, eg. MWI.

Knowledge and lack of it are key issues.

We believe that the laws of physics including quantum mechanics are universally applicable.

We don't however know how to apply them to most situations.

A game of football we assume follows the laws of physics but do not know how to apply them.

Almost everything we do in physics involves toy models. These are idealisations where we know everything we need to apply the laws of physics.

"State preparation procedures" are needed to produce the same state again and again. "The same state" means we have perfect knowledge.

Many states exist for which we we have imperfect knowledge. There is not a known "state preparation procedure" for such states because we have imperfect knowledge of them.

 

[bhobba]

If you have, then send me the procedure and we can become tycoons and set up a nose factory.

Fair enough - exactly where the boundary lies is for me not clear.

Thanks
Bill

 

[Mentz114]

So macroscopic objects do not have a "quantum state" ?

Please tell me where is the point at which microscopic states stop being quantum states? I'm assuming you can give me an answer that's accurate to 10 decimal places.

Nobody appears to have an answer to that.
How do you define the part of the body that is the nose. Your example is absurd as is a lot of your speculation.

 

[StevieTNZ]

Exactly. I mentioned in another thread a dust particle that is given a position by interacting with a few stray photons from the CBMR. It obviously was prepared by that interaction.

As for the nose - its caught up in all sorts of other issues that complicate it greatly eg exactly at point does the nose end and other parts of the face begin. As Feynman explains in his lectures in a discussion about a table even where the table begins and the air starts is far from well defined. But assuming you can untangle all these issues, your nose is interacting with the environment and that interaction, like all classical objects we see around us, is basically what gives it its classical properties ie definite position and momentum etc. Its state is prepared by that interaction so it has the properties of everyday objects.

Only FAPP.

In principle, for example, the dust particle only entangles with the photons and is still in superposition.

 

[AlexCaledin]

Leaving the quantum nose alone, it's still interesting how the quantum brain is treated by Dr. H. Stapp:

By adopting a quantum-theoretical approach we open the way, of course, to a quantum treatment of various chemical processes that are important to the functioning of the brain. But that is NOT the point here. Those atomic processes can surely be treated to sufficient accuracy by a quasi-classical model that merely adjusts atomic-scale properties that have little to do directly with our consciousness. The point of going to the pragmatic/quantum framework is to accommodate the huge macroscopic quantum effects that are directly forced upon us by the Heisenberg uncertainty principle, and that make the reduction of the wave packet of decisive importance in the determination the large-scale behaviour of the body/brain. These reductions of the wave packet are, within the pragmatic/quantum framework, projections of our knowings onto our mathematical representation of physical reality .
It is sufficient to consider a model of the brain that is mainly classical. To a good first approximation the introduction of quantum theory merely involves introducing on top of the normal classical statistical ensemble arising from our incomplete knowledge a further statistical ensembles of classical motions arising from the irreducible quantum uncertainties.
At first sight this just seems to overlay the classical statistical ensemble of brain states by another layer of statistical uncertainty that adds nothing perceptible to the uncertainties already present.
But there is a basic difference. In any single empirical instance only one member of the classical component of the statistical ensemble is actually present, but all of the members of the quantum superposition that are forced to be present by the uncertainty principle are necessarily all present simultaneously, until a reduction occurs. This presence in principle of the various superposed possibilities is the essence of quantum theory: it is entailed by the fact that the different superposed members of the quantum ensemble can interact with each other.
The presence of these superposed possibilities means that in any given empirical instance, no matter which classical element of the ensemble is actually present, the quantum ensemble spreads over all of the various possible attractors. Consequently, this quantum reduction exercises an overriding control over the choice of attractor: this choice could be the same for each of the alternative possible members of the classical ensembles, and hence independent of which of the alternative classical states (generated, for example, by the thermodynamical mixture of possibilities) is present. For the quantum principles are absolutely mute on this sort of unphysical question: What would the choice have been if the occurring situation had been other than what it actually is?
Thus the quantum choice could in principle be independent of which member of the classical statistical ensemble is present. But in that case the quantum choice would wipe out the classical uncertainties introduced by the thermal noise.
This point is raised merely to emphasize that the quantum choice is the decisive control element in cases---such as the human brain---where the irreducible quantum uncertainties are so great that essentially all of the alternative macroscopic possibilities are included within the range spanned by the quantum uncertainties.
http://www-physics.lbl.gov/~stapp/40305.tex
http://www-physics.lbl.gov/~stapp/40305.ps

... each increment in knowledge is associated with a reduction of the quantum state to one that is compatible with the new knowledge. The quantum brain is an ensemble of quasi-classical components. As just noted, this structure is similar to something that occurs in classical statistical mechanics, namely a ‘‘classical statistical ensemble.’’ But a classical statistical ensemble, though structurally similar to a quantum brain, is fundamentally a different kind of thing. It is a representation of a set of truly distinct possibilities, only one of which is real. A classical statistical ensemble is used when a person does not know which of the conceivable possibilities is real, but can assign a ‘‘probability’’ to each possibility. In contrast, ALL of the elements of the ensemble that constitute a quantum brain are equally real: no choice has yet been made among them. Consequently, and this is the key point, entire ensemble acts as a whole in the determination of the upcoming mind-brain event. Each thought is associated with the actualization of some macroscopic quasi-stable features of the brain. Thus the reduction event is a macroscopic happening. Moreover, this event involves, dynamically, the entire ensemble of quasi-classical brain states.
http://www-physics.lbl.gov/~stapp/vnr.pdf

 

[Robert Shaw]

Nobody appears to have an answer to that.
How do you define the part of the body that is the nose. Your example is absurd as is a lot of your speculation.

Macroscopic was your choice of term when you critiqued my post.

Now you're saying that nobody can define it.

Please would you clarify your previous post with language that you feel confident about yourself.

 

[Robert Shaw]

Macroscopic was your choice of term when you critiqued my post.

Now you're saying that nobody can define it.

Please would you clarify your previous post with language that you feel confident about yourself.

Here's your previous post.

"Why do you think that your macroscopic nose should have a 'quantum state' ? I cannot think of any definition of 'quantum state' that can be applied to it."

Please could you clarify it with a term other than "macroscopic" which you say is indefinable.

 

[A. Neumaier]

Some physicists consider it to be synonymous with "state preparation procedure".

This cannot be valid in a precise sense since, e.g., there are many preparation procedures preparing the same polarization state of a photon.

 

[vanhees71]

So macroscopic objects do not have a "quantum state" ?

Please tell me where is the point at which microscopic states stop being quantum states? I'm assuming you can give me an answer that's accurate to 10 decimal places.

You can't find such a "split" in a classical and a quantum world. My understanding is that the classical behavior of macroscopic matter and fields (mostly the electromagnetic field) is an emergent phenomenon, describable by many-body quantum statistics in the sense that macroscopic observables exist because of the separation of scales in spatio-temporally fast-varying fluctuating quantum observables and slow-varying macroscopic observables. The latter are often the relevant observables for macroscopic entities, and their classicality is due to the sufficiency in accuracy of appropriately coarse-grained descriptions.