How to describe the 'real world'

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  • #1
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Just wondering,

how would one write a solution (i.e. a wavefunction, or the appropriate name given to a quantum system in such a situation) to a macroscopic object in the everyday world?
Would it be the macroscopic object is written as a superposition of states, entangled with all other superposition of states in the world (the environment)?

When you write a superposition for a macroscopic object, in the solution do you include spin up and down superpositions for the various particles that make up the object, rather than just write a superposition of macroscopic distinct states? So the final outcome would be all superposition macroscopic states as well as the microscopic superposition states of the things that make up the object?
 

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  • #2
A. Neumaier
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how would one write a solution (i.e. a wavefunction, or the appropriate name given to a quantum system in such a situation) to a macroscopic object in the everyday world?

Ignoring difficulties stemming from relativity theory, details concerning the structure of nuclei and things like colors, magnetism, or charges:

A macroscopic object would not be represented by a wave function but by a density matrix exp(-S), where S is an appropriate few-particle operator in a Fock space whose basic particle species are the different nuclei and the electrons.

The details for the choice of S depend on what sort of macroscopic object one is modeling, and at which level of detail. See, e.g., Chapter 7 of http://de.arxiv.org/abs/0810.1019
 
  • #3
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Just wondering,

how would one write a solution (i.e. a wavefunction, or the appropriate name given to a quantum system in such a situation) to a macroscopic object in the everyday world?
Would it be the macroscopic object is written as a superposition of states, entangled with all other superposition of states in the world (the environment)?

When you write a superposition for a macroscopic object, in the solution do you include spin up and down superpositions for the various particles that make up the object, rather than just write a superposition of macroscopic distinct states? So the final outcome would be all superposition macroscopic states as well as the microscopic superposition states of the things that make up the object?


newtonian physics.
 
  • #4
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A macroscopic object would not be represented by a wave function but by a density matrix exp(-S), where S is an appropriate few-particle operator in a Fock space whose basic particle species are the different nuclei and the electrons.

So the http://en.wikipedia.org/wiki/Density_matrix" [Broken] is what would describe the superpositions of the macroscopic distinct states? How would the density matrix be entangled with the environment?
 
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A. Neumaier
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So the http://en.wikipedia.org/wiki/Density_matrix" [Broken] is what would describe the superpositions of the macroscopic distinct states? How would the density matrix be entangled with the environment?

By being part of a bigger density matrix for system+ environment, which is not simply a tensor product of the density matrix of the system and that of the environment.
 
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  • #6
A. Neumaier
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newtonian physics.

Not necessarily. The macroscopic system might be a superfluid or a transistor.
These cannot be modelled in Newtonian terms.
 
  • #7
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I have one additional question.
It seems to me, that a legal interpretation of quantum mechanics is that it gives subjective and objective information. A objective information is such that already experienced wave collapse.
I think that this can answer if the moon exists if nobody never feels it?
Or how it is with this known phrase about moon?
 
  • #8
A. Neumaier
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I have one additional question.
It seems to me, that a legal interpretation of quantum mechanics is that it gives subjective and objective information. A objective information is such that already experienced wave collapse.

This has nothing to do with a collapse.

Objective information about physical systems is the part that is the subject of natural sciences; subjective information about physical systems is all the rest. The latter may be the subject of psychology, sociology or arts, however.


I
I think that this can answer if the moon exists if nobody never feels it?
Or how it is with this known phrase about moon?

If the Moon wouldn't exist when nobody sees her, she wouldn't have her common astronomical age but only the age of the oldest life forms with eyes to see the Moon. This shows that it is a very subjective, unscientific view.
 
  • #9
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I do not try here to have an alternative view on quantum mechanics. I only try to understand Brukner-Zeilinger view, and you are also co-author in some of their articles.

I were not so try to divide objective-subjective information, as you understood.

I used the word "subjective" for what they already used in their articles. (They do not use word subjective.) But when they "measured" electron spin, they is no hidden information which cannot be measured.
This information hidden from measurement is objective information. I do not speak in favour of Bohm. But it seems to me, that there is some sort of objective information in ortodox interpretation. Otherwise moon would not exist without observers and so on...

Or how it is with this "moon explanation" with this "Austrian" interpretation?

It is not easy here to ask clearly.
 
  • #11
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yeah yeah posted by you:
https://www.physicsforums.com/showthread.php?t=451342
post #11
StevieTNZ said:
There was an interesting article published by Nature earlier this year entitled 'No Moon There'. You can read it here: http://www.engr.ucr.edu/~korotkov/news/2010-NatPhys.pdf



and i say again to you:
read this one:

http://www.fqxi.org/community/articles/display/103

the superposition on macroscopic objects, not settled yet.
 
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  • #12
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Not necessarily. The macroscopic system might be a superfluid or a transistor.


to you:

I am not an expert in this, but I always thought that the current in semiconductors can be reliably calculated with usual classical methods. Actually, presently I am working in semiconductor industry where such calculations are performed routinely without any involvement of quantum mechanics or QFT.

Eugene.
 
  • #13
Fra
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Objective information about physical systems is the part that is the subject of natural sciences; subjective information about physical systems is all the rest. The latter may be the subject of psychology, sociology or arts, however.

IMHO, the objectivity in science is a negotiated consensus among the scientific community, rather than beeing eternally objective in the deeper sense. Ie. scientific knowledge is not god given truth. Therefore I think it's essential to distinguish between truth and rational opinion. Natural science is supposedly a rational inference about nature.

I personally take the essence of quantum theory as per Bohr to mean that physics is simply about rational expectations. This is the ultimate finishing off, of any forms of irrational realism.

So the subjectivity of information that is relevant to this discussion is that each observer has their own subjective information about their environment; which is RATIONALLY inferred.

The sense in which this is still objective is that the action of each such observing system reflects indirectly it's information. For example, if one observers sees two other observers iteracting with each other, then the first observer can "understand" the logic of their interacting by conjecturing that the respond to each other, based only upon what they know about each other. Here the "subjective information" is an important abstraction.

This is a generalization of the locality principle that a system is unaffected by things outside the lightcone - the rational action(seen as a decision problem) of a system is independent of information it does not posses. When you phrase it like this, I think most would agree that this is close to obvious, or at least not hard to accept as a conjecture. I even see it axiomatically, in the sense that if this is violated, it simply would not be rational decisions anymore.

I think this is the sense in which QM; containing subjective notions, is objective. The objectivity lies in the interaction of subjective notions, just like the objectivity in relativity likes in the transformations between observers.

The problem of self reference "observing observer" in QM is that coherence of reasoning suggest that the "interactions between observers" must also be subject to inference and measurement. So either you end up with an increasingly more complex superobservers, or you reach saturation - where the regular QM structure is boud to break.

The question is which makes most sense?

/Fredrik
 
  • #15
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So the authors are completely wrong in saying a macroscopic object is in a superposition? What about the other claims of MQC?

not completely wrong, i say on bigger objects.
that way the moon is safe !!! :cool:



---------------
"They say that bigger is better. Keith Schwab, Anton Zeilinger, and Markus Aspelmeyer certainly agree. They are applying the adage to both quantum devices and scientific collaborations.
Defying the standard wisdom of the nanotechnology crowd, the team wants to scale their nanotools up. They hope to create quantum effects in ever larger objects, to test how far they can push the boundary between the quantum and classical realms."


----------------

"One frontier not probed enough is in the
direction towards the real world."
- Tony Leggett.


---------------

"Because of the nonlinearity, the lifetime of two superposed states is no longer infinite. It decreases as the number of atoms in the object under study increases, going from an astronomically large value for microsystems, to extremely small values for macrosystems. Thus somewhere in between, the superposition lifetime ought to be measureable in the laboratory.
For the micro-mirror of a billion atoms, the superposition lifetime is predicted to be about ten days. If the number of atoms in the mirror is increased a thousand fold, the lifetime of superposition comes down to about a thousand seconds.
With regard to the mesoscopic region, what are usually known as nanoparticles are still too small to show any significant departures from linear quantum mechanics. One needs bigger mesoscopic objects, having about 10^{15} atoms say, to test for the new effect. And these objects must be isolated from the environment [suppession of decoherence] - this perhaps is the hardest part."
- Tejinder Singh.


-------------
read this one:

http://arxiv.org/PS_cache/arxiv/pdf/1003/1003.2774v2.pdf

"In this article we have outlined a framework for describing the evolution of relativistic quantum systems which consistently explains the behavior of both microscopic and macroscopic systems. To do this the model incorporates quantum state reduction into the standard state dynamics in a way which is not only covariant and frame independent, but also objective, naturally diferentiating between systems of diferent scale and adjusting its effect accordingly. In this way the model offers a potential unifcation of quantum and classical sectors"
-Daniel Bedingham.
 
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  • #16
A. Neumaier
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I do not try here to have an alternative view on quantum mechanics. I only try to understand Brukner-Zeilinger view, and you are also co-author in some of their articles.

Who is ''you'' (the co-author)?


I used the word "subjective" for what they already used in their articles. (They do not use word subjective.)

It would cause less misunderstanding if you wouldn't introduce your own terminology in place of theirs.

But when they "measured" electron spin, they is no hidden information which cannot be measured.

They could have measured electron momentum - they didn't, so it remained hidden. They measured spin, so it was no longer hidden. In either case, what they prepared and what they measured was objective in any meaningful sense.

it seems to me, that there is some sort of objective information in ortodox interpretation.
Indeed, there is. Everything in the orthodox interpretation is about objective information.

It is not easy here to ask clearly.

The lack of clarity comes from using fuzzy terminology.

It is nearly impossible to answer unclear questions in a clear way.
If you want to get clear answers you need to try to ask clear questions.
 
  • #17
A. Neumaier
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to you:

A transistor can be handled on very different levels. The classical treatment by engineers is still based on underlying quanutm mechanics. I'll answer in more detail in the thread you quoted.
 
  • #18
A. Neumaier
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IMHO, the objectivity in science is a negotiated consensus among the scientific community, rather than being eternally objective in the deeper sense.
The only deep sense of objective can be the consensus among the scientific community,
since whatever we communicate must be based on a consensual interpretation, in order to be unambiguously understandable. No philosophy can abstract from social conventions.

So the subjectivity of information that is relevant to this discussion is that each observer has their own subjective information about their environment; which is RATIONALLY inferred.

And only what is rational about that subjective information is subject of the natural sciences;
the irrational part is subject of psychology.
 
  • #19
Fra
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The only deep sense of objective can be the consensus among the scientific community,
since whatever we communicate must be based on a consensual interpretation, in order to be unambiguously understandable. No philosophy can abstract from social conventions.
...
And only what is rational about that subjective information is subject of the natural sciences;
the irrational part is subject of psychology.

We agree on both points.

I just wanted to point out that there is a difference between subjectivity and irrationality. Subjectivity is in physics often synonymous with relative, and does have a place.

Irrationality might possible enter in constrained form in the concext of variation and selection in the learning model. But then I do not see it as irrationality I just see it as undecidability.

/Fredrik
 

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