Does Decoherence Von Neumann Interpretationrefute

[Dmitry67]

Frederik, I almost agree with you, but why are you saying

"ability to store information about the system is maximized"?

It must be just high enough

 

[Alfrez]

1 I mean now, in Quantum computing for example, 'devices' are so small that they literally consist of few atoms. And while in the beginning of 20th centruy, when measurement devices were always huge, there was some hope that some 'collapse agent' will be found at some point, now there is no such hope, and the fatal flaw of CI is obvious.

2 You can put a glass or a mirror in double slit experiment, and it won't break an interference pattern, because, dispite the complexity of interaction, neither mirror nor glass 'measure' the photon. At the same time, gamma ray photon would simply leave a track in the very same glass, so it will be definitely 'measured'.

Why can't the collapse agent be as small as a few atoms across? About gamma ray leaving tracks, what has this got to do with invalidating Copenhagen Interpretation??

 

[Fredrik]

Frederik, I almost agree with you, but why are you saying

"ability to store information about the system is maximized"?

It must be just high enough

I agree with that. I'm just guessing that we can find the "preferred" basis, let's call it B₀, by solving an optimization problem. This would mean that consciousness can exist in the worlds with the maximum information storage capabilities (i.e. the worlds identified by B₀), and also in the worlds that are the most similar to them. I expect that the information storing capabilities of the worlds identified by basis B will fall very rapidly when B is changed from B₀. This would ensure that almost all other worlds are irrelevant, and more importantly, that our world will be practically indistinguishable from one of the worlds identified by B₀.

 

[Dmitry67]

Thinking about it...
But very cold worlds (like Pluto) are much safer place to preserve information. But they are dead. So we need something more than just "information storage capabilities".

Also, could you clarify, what meaning do you include in the 'world' (hubble spaces, different MWI worlds, different bubble-worlds with different values of Standard Model parameters etc)

 

[Alfrez]

I was reviewing the concept of Decoherence and reading Tegmark article "100 Years of Quantum Mechanics" and a passage confused me. He stated:

"Decoherence explains why we do not routinely see quantum superpositions in the world around us. It is not becuse quantum mechanics intrinsically stops working for objects larger than some magic size. Instead macroscopic objects such as cats and cards are almost impossible to keep isolated to the extent needed to prevent decoherence. Microscopic objects, in contrast, are more easily isolated from their surroundings so that they retain their quantum behavior"

Is he right in saying that if you can isolate the cat or card in say a magnetic bubble containment field and avoid any external contact with surrounding or external heat, photons, etc. it can exist as superposition? But I thought superposition only occurs in simple simple such as double slit experiments where you can isolate the particles from the surrounding and hence maintain the interference. But the cat internal body has many separate stuff like blood flow and body heat. This would prevent the cells from having superposition. However, Tegmark mentioned that if you can somehow isolate the whole cat. It can initiate macroscopic superposition?? How do you define the boundary? Another example, if I can isolate my car in say the containment field, my car would experience macro superposition, however, inside the car the air from the aircon can decohere my body and prevent superposition in my body, so in what sense can you cause macroscopic superposition to the whole car but while inside, there is no superposition in my body??

 

[A. Neumaier]

Von Neumann wrote in a major physics book decades ago that consciousness was what collapse the wave function.. how could he stated this bizaare statement and the facts remain up to this day?

There is nothing bizarre in von Neumann's statements. So there is nothing to refute.
You only need to upgrade your understanding of what the terms mean.

To say that consciousness collapses the wave function is equivalent to say that it takes consciousness to interpret the universe and change the interpretation when new information arrives.

What is he really saying that only consciousness can collapse the wave function? In what context does he meant?

Instead of modeling the system by a superposition in the absence of information, you model it by one of the participating eigenstates if a measurement result becomes known. Clearly, modeling reality (and changing the model) is a conscious activity and requires a consciousness.

This is nothing mysterious, and happens also in classical physics once you have a stochastic dynamics, where the collapse is called conditional probability.

Moreover, it has nothing to do with superluminal changes, since once one changes a molde to describe something, everything in the model changes instantaneously, although the system modeled isn't changed at all.
This already happens when you apply a coordinate transformation in a classical system...

I wonder if it means he believed macroscopic superposition was possible since he believed consciousness can collapse the wave function, and in regions where there is no human like inside the moon, does it mean inside the moon material properties inside exist in superposition and in limbo with no definite particle positions??

What do you mean by ''in limbo''? The inside of the moon has lots of meaningful properties even in the absence of a sharp position (which it doesn't even have classically, by the way). Note that being in a superposition only means that there is no exact value of the position, not that there is no position at all. In particular, there is a mean position and a mean square deviation form this position, which together is adequate for most purposes.

how does the cat blood vessels pump blood when there is no position as it exists in pure limbo.

Blood vessels work quite well without each of their atonms having precise positions to 10^1000 decimals of accuracy.

 

[Alfrez]

I was reviewing the concept of Decoherence and reading Tegmark article "100 Years of Quantum Mechanics" and a passage confused me. He stated:

"Decoherence explains why we do not routinely see quantum superpositions in the world around us. It is not becuse quantum mechanics intrinsically stops working for objects larger than some magic size. Instead macroscopic objects such as cats and cards are almost impossible to keep isolated to the extent needed to prevent decoherence. Microscopic objects, in contrast, are more easily isolated from their surroundings so that they retain their quantum behavior"

Is he right in saying that if you can isolate the cat or card in say a magnetic bubble containment field and avoid any external contact with surrounding or external heat, photons, etc. it can exist as superposition? But I thought superposition only occurs in simple simple such as double slit experiments where you can isolate the particles from the surrounding and hence maintain the interference. But the cat internal body has many separate stuff like blood flow and body heat. This would prevent the cells from having superposition. However, Tegmark mentioned that if you can somehow isolate the whole cat. It can initiate macroscopic superposition?? How do you define the boundary? Another example, if I can isolate my car in say the containment field, my car would experience macro superposition, however, inside the car the air from the aircon can decohere my body and prevent superposition in my body, so in what sense can you cause macroscopic superposition to the whole car but while inside, there is no superposition in my body??

In the inquiry above. Let me add that say in the isolation field, the cat or car has a double slit like setting where two doors are in front. Should the cat or car pass thru both doors or slits and interfere just like a particle in double slit? Or doesn't it happen at all because there are too many microscopic degrees of freedom inside the cat and car body? Scientists now were able to use a buckyball molecule composed of 60 atoms and pass this thru a slit and the macroscopic object interfere. I think the buckyball entire contents are in phase. They also plan a virus in an actual double slit experiment. Should the virus internal part be in phase too before it can cause interference.. or is in phase not required.. meaning a cat can be used in a double slit experment and succeed if the whole setup can be isolated enough like some kind of containment field?? Or is it impossible due to the many microscopic degree of freedom inside the cat body which is not in phase??

 

[Alfrez]

In the inquiry above. Let me add that say in the isolation field, the cat or car has a double slit like setting where two doors are in front. Should the cat or car pass thru both doors or slits and interfere just like a particle in double slit? Or doesn't it happen at all because there are too many microscopic degrees of freedom inside the cat and car body? Scientists now were able to use a buckyball molecule composed of 60 atoms and pass this thru a slit and the macroscopic object interfere. I think the buckyball entire contents are in phase. They also plan a virus in an actual double slit experiment. Should the virus internal part be in phase too before it can cause interference.. or is in phase not required.. meaning a cat can be used in a double slit experment and succeed if the whole setup can be isolated enough like some kind of containment field?? Or is it impossible due to the many microscopic degree of freedom inside the cat body which is not in phase??

Oh, I think the above is another bad example, the de broglie wavelength of the cat is very small so it shouldn't interfere with the slits or doors in a double slit/door experiment supposed the whole setup can be isolated enough. Right?

I think a better example is the original one, the Schroedinger Cat experiment. When Schroedinger proposed it. They didn't know if macroscopic superposition could happen. They didn't know if collapse really occurred or not. But now we have a very sophisticated model of Decoherence and we supposed collapse never happen. So we should go back to the Schroedinger Cat Experiment. Supposed the cat and radioactive substance in the whole setup could be totally isolated in a special containtment field. Could we have superposition of live and dead cat?

As I think I understand it now. To initiate macroscopic superposition, it has to be entangled to any quantum particle or setup which can produce quantum choices.

 

[Dmitry67]

Here you are, there is even a very nice picture!
http://en.wikipedia.org/wiki/Schrödinger's_cat#Many-worlds_interpretation_.26_consistent_histories

 

[Alfrez]

Here you are, there is even a very nice picture!
http://en.wikipedia.org/wiki/Schrödinger's_cat#Many-worlds_interpretation_.26_consistent_histories

Note even such simple thing as double slit experiment can split worlds.. where in one world, the particle passes thru the right slit, in the second word, the particle passes thru the left slit. Now are you saying that after it happened, the 2 worlds continues the independent histories such that in the first world, China will be at war with US in 2020 while in the second world, the Arabs will be at war with US in 2020?? So a simple splitting of the double slit can cause a second world to exist indepedently??

If you believe it. Why not just believe that randomness is intrinsic in QM and where the particle will pass thru, left or right is just a random event without splitting of worlds? The price to pay to avoid randomness is to propose millions of worlds. Isn't this an extreme measure to take??

 

[Alfrez]

There is nothing bizarre in von Neumann's statements. So there is nothing to refute.
You only need to upgrade your understanding of what the terms mean.

To say that consciousness collapses the wave function is equivalent to say that it takes consciousness to interpret the universe and change the interpretation when new information arrives.



Instead of modeling the system by a superposition in the absence of information, you model it by one of the participating eigenstates if a measurement result becomes known. Clearly, modeling reality (and changing the model) is a conscious activity and requires a consciousness.

This is nothing mysterious, and happens also in classical physics once you have a stochastic dynamics, where the collapse is called conditional probability.

Moreover, it has nothing to do with superluminal changes, since once one changes a molde to describe something, everything in the model changes instantaneously, although the system modeled isn't changed at all.
This already happens when you apply a coordinate transformation in a classical system...



What do you mean by ''in limbo''? The inside of the moon has lots of meaningful properties even in the absence of a sharp position (which it doesn't even have classically, by the way). Note that being in a superposition only means that there is no exact value of the position, not that there is no position at all. In particular, there is a mean position and a mean square deviation form this position, which together is adequate for most purposes.



Blood vessels work quite well without each of their atonms having precise positions to 10^1000 decimals of accuracy.

Which one do you believe is the case concerning the possibilities in the components of a quantum superposition and why?

1. |u>+|v> means that the there are (at least) two copies of the system, one of which is in state |u> and the other in state |v>.

2. |u>+|v> doesn't actually represent the properties of the system, but is just a part of a mathematical formalism that can be used to calculate probabilities of possible results of experiments.

Is the latter Copenhagen? I'm not sure if Fredrik means the second is strictly Copenhagen. But the first one can also be Copenhagen, isn't it?

 

[Dmitry67]

Note even such simple thing as double slit experiment can split worlds.. where in one world, the particle passes thru the right slit, in the second word, the particle passes thru the left slit. Now are you saying that after it happened, the 2 worlds continues the independent histories such that in the first world, China will be at war with US in 2020 while in the second world, the Arabs will be at war with US in 2020?? So a simple splitting of the double slit can cause a second world to exist indepedently??

If you believe it. Why not just believe that randomness is intrinsic in QM and where the particle will pass thru, left or right is just a random event without splitting of worlds? The price to pay to avoid randomness is to propose millions of worlds. Isn't this an extreme measure to take??

1 You are still having the same mental block. You see no problem accepting the INFINITY of worlds (in infinite universe) but can't accept the aditional finite, countable number of worlds?

2 Note that no experiment split the whole universe. 'Splitting' is a physical process propagating at v<=c via interaction. Making double slit experiment here you don't split Andromeda galaxy.

3 There are much more than millions worlds, but

4 yes, use truly random (QM) event to decide if you stay at home or go to work. Then definitely 2 copies of you will behave differently. What problem do you see with it except saying that it is "absurd"?

 

[Dmitry67]

If you believe it. Why not just believe that randomness is intrinsic in QM and where the particle will pass thru, left or right is just a random event without splitting of worlds? The price to pay to avoid randomness is to propose millions of worlds. Isn't this an extreme measure to take??

1. Because God does not play dice! (c)
2. Because you can't define randomness without defining what is measurement first. And it appears that measurement is ill-defined concept.
3. I don't see anything extreme in MWI approach.

 

[A. Neumaier]

Which one do you believe is the case concerning the possibilities in the components of a quantum superposition and why?

1. |u>+|v> means that the there are (at least) two copies of the system, one of which is in state |u> and the other in state |v>.

2. |u>+|v> doesn't actually represent the properties of the system, but is just a part of a mathematical formalism that can be used to calculate probabilities of possible results of experiments.

Neither. |u>+|v> actually represents the properties
(i) of the system, according to the Copenhagen interpretation,
(ii) of an ensemble of identically prepared systems, according to the statistical interpretation.
If the uncertainty (root mean square deviation from the mean) is small enough, there is little difference between the two interpretations. This is in particular the case for macroscopic observables, such as the position of the center of mass of the moon.

Is the latter Copenhagen? I'm not sure if Fredrik means the second is strictly Copenhagen. But the first one can also be Copenhagen, isn't it?

None of 1. or 2. is Copenhagen. (i) is.

 

[Fredrik]

I prefer not to use the term "Copenhagen interpretation" if I can avoid it, because every person who uses it seems to mean something different.

 

[Alfrez]

Guys. I have an inquiry about the preferred basis problem in Decoherence which I've been studying the past 5 hours. It is one of the most important and interesting concepts in the latest quantum findings. Rather than create a new thread. I'd put it here to in this thread (so as to conclude it too). My questions are at the bottom after brief quotes to get in the mood:

http://public.lanl.gov/whz/images/decoherence.pdf

"Environment can destroy coherence between the states of a quantum system. This is decoherence. According to quantum theory, every superposition of quantum states is a legal quantum state. This egalitarian quantum principle of superposition applies in isolated systems. However, not all quantum superpositions are treated equally by decoherence. Interaction with the environment will typically single out a preferred set of states. These pointer states remain untouched in spite of the environment, while their superpositions lose phase coherence and decohere. Their name—pointer states—
originates from the context of quantum measurements, where they were originally introduced (Zurek, 1981). They are the preferred states of the pointer of the apparatus.
They are stable and, hence, retain a faithful record of and remain correlated with the outcome of the measurement in spite of decoherence."

.....

My questions.

The environment selects the pointer states or preferred basis which explains why a chair is in classical position of space. Now I'd like to know how what kind of shielding (whether magnetic, plasma, etc.) is possible that can be created such that the chair can be prevented from being Einselected.. meaning the preferred basis wouldn't be classical anymore but composed of say up and down at the same time. What sort of experiments have been proposed that can do this? This is to prove once and for all the Decoherence is real even though we don't know if Copenhagen or Many Worlds or Bohmian, etc. is the physical ontology. But this Einselection Shielding Experiment is invariant to any intepretations because you are to prevent the creation of the preferred basis. The bottom line is this. The preferred basis is chosen because of interaction with a classical environment, now if you shield the chair in a magnetic shield or plasma or other exotic shielding in such a way that it can't get contact with the classical environment, then it can initiate Schroedinger Cat like superposition where the chair can shapeshift to different shapes, something like that. We must make this experiment even on the level of the pioneering Manhattan Project to arrive at more quantum truth which we lack so intimately.

 

[A. Neumaier]

to arrive at more quantum truth which we lack so intimately.

Books on quantum physics are full of quantum truth. Lacking is only a way to make it intelligible to laymen without distorting the truth too much.

Bringing chairs into a nontrivial superposition would not change this. Zeilinger produced superpositions of buckyballs and demonstrated corresponding interference effects, but it gets harder and harder as the particle size grows. All the energy of the universe is probably not enough to do the same for a chair-sized particle.

 

[A. Neumaier]

I prefer not to use the term "Copenhagen interpretation" if I can avoid it, because every person who uses it seems to mean something different.

Still, there is a common intersection: In any of its variants, it assigns a state to each individual system rather than only to an ensemble. This is sensible since there are quantum objects like the sun that cannot be treated in an ensemble fashion but clearly has a quantum state (though we can describe it only in some coarse approximation).

 

[Alfrez]

Books on quantum physics are full of quantum truth. Lacking is only a way to make it intelligible to laymen without distorting the truth too much.

Bringing chairs into a nontrivial superposition would not change this. Zeilinger produced superpositions of buckyballs and demonstrated corresponding interference effects, but it gets harder and harder as the particle size grows. All the energy of the universe is probably not enough to do the same for a chair-sized particle.

But there is a big difference. A buckyball is a quantum object which obviously can interfere with itself. Now in the post-Copenhagen era. Wave function never collapse. Superpositions are still occurring only they are suppressed by Decoherence. However Hilbert space is big. Why is the classical state chosen or preferred. Zurek then claimed it was because the environment classical state got somehow transferred to the object. Now if we can shield this Einselection, then we can for all intent and purposes create macroscopic superposition where the chair can shapeshift into different shapes. Note again that this scenerio is not like the Buckyball where the entire molecule is in quantum coherence. Unless you are saying that the only way the chair can experience macrosuperposition is if its internal parts are in coherence. But Einselection can do the trick since everything is in superposition only we don't observe it because it is decohered. Classical state is just a very tiny bit in the hilbert space and hence classical state should not be the norm (see the pdf where the details are explained in case you are not familiar with the exotic world of Decoherence).

 

[Dmitry67]

Superpositions are still occurring only they are suppressed by Decoherence.

Decoherence does not suppress the superpositions, it just creates an illusion (for complex system A) that system B, which is communicating with system A, is in some definite state.

http://en.wikipedia.org/wiki/Wigner's_friend#Wigner.27s_friend_in_Many_Worlds

May be I am wrong, but based on language you use it appears that you interpret Decoherence as some engine of Objective collapse. But superpositions never end!

 

[Dmitry67]

Why is the classical state chosen or preferred.

based on

http://en.wikipedia.org/wiki/Wigner's_friend#Wigner.27s_friend_in_Many_Worlds

it is a purely mathematical consequence of the observer having many defreees of freedom and it can't be shielded.

Very primitive 'observers', like atoms and molecules, can 'observe' other objects directly in superposition, but they are too simple to be conscious.

 

[Alfrez]

Decoherence does not suppress the superpositions, it just creates an illusion (for complex system A) that system B, which is communicating with system A, is in some definite state.

http://en.wikipedia.org/wiki/Wigner's_friend#Wigner.27s_friend_in_Many_Worlds

May be I am wrong, but based on language you use it appears that you interpret Decoherence as some engine of Objective collapse. But superpositions never end!

What I meant is this. An actual example. My body particles are in trillions of superpositions or being entangled with the environmental particles like photons or air particles. Decoherence simply means it is not in coherence but decohered. Hence Decoherence can suppress the coherence in the superpositions of my body with the environment. Bottom line. Everything is still quantum stuff. The classical states are just a temporary states brought about by Einselection or Environment SuperSelection. If it can somehow be shield. Then we can be any state in the big Hilbert Space.

 

[Dmitry67]

An actual example. My body particles are in trillions of superpositions or being entangled with the environmental particles like photons or air particles. Decoherence simply means it is not in coherence but decohered. Hence Decoherence can suppress the coherence in the superpositions of my body with the environment. Bottom line. Everything is still quantum stuff. The classical states are just a temporary states brought about by Einselection or Environment SuperSelection. If it can somehow be shield. Then we can be any state in the big Hilbert Space.

At first, please clarify what do you mean by YOU or 'MY BODY'
Check the picture:
http://upload.wikimedia.org/wikipedia/en/b/b7/MWI_Schrodingers_cat.png
Do you mean
a. One particular history (frog's view)
b. Ensumble of all histories (the whole 'tree', birds view)

 

[Alfrez]

At first, please clarify what do you mean by YOU or 'MY BODY'
Check the picture:
http://upload.wikimedia.org/wikipedia/en/b/b7/MWI_Schrodingers_cat.png
Do you mean
a. One particular history (frog's view)
b. Ensumble of all histories (the whole 'tree', birds view)

Hmm... you are saying that in this earth, classical state is what we experienced while in other Many Worlds, they can experience a non-classical state that I won't be able to experience?

By shielding Einselection. I just want to experience a state of up-down simulataneously being up-down a legal quantum state.

Unless you are saying I can't experience both up-down state but only up or down one at a time? Hmm...

 

[Alfrez]

To be more distinct. Here's another example. By shielding Einselection in an isolated object. I can view its Ensumble of all histories such that the chair foot can be in superposition of up-down-side, etc. This is the consequence if you can shield Einselection without having to require that the entire chair should be in coherent state. This requirement only exists in pure Copenhagen collapse model. But then if Many Worlds is true, you can see the chair existing in only one state, the other states in other worlds. However, if you can view the chair in many states simultaneously. Then Many World is falsified.

 

[Dmitry67]

Hmm... you are saying that in this earth, classical state is what we experienced while in other Many Worlds, they can experience a non-classical state that I won't be able to experience?

By shielding Einselection. I just want to experience a state of up-down simulataneously being up-down a legal quantum state.

Unless you are saying I can't experience both up-down state but only up or down one at a time? Hmm...

What we are experiencing is determined by how our brains work. We remember the past, not the future, because this is how information is stored in the direction where entropy increases.

We remember the past, but we are not able to percieve the 'other' braches. Hence, in the tree of all possible branches we recall the history of our past without being aware of any splitting, which gives us an illusion that history is linear, not a tree.

As a result, what we observe is very far from what actually happens. It is not an illusion, but it is just a slice, a deformed projection of 1 thread of a multi-threaded reality...

 

[Dmitry67]

To be more distinct. Here's another example. By shielding Einselection in an isolated object. I can view its Ensumble of all histories such that the chair foot can be in superposition of up-down-side, etc. This is the consequence if you can shield Einselection without having to require that the entire chair should be in coherent state. This requirement only exists in pure Copenhagen collapse model. But then if Many Worlds is true, you can see the chair existing in only one state, the other states in other worlds. However, if you can view the chair in many states simultaneously. Then Many World is falsified.

Sorry, I don't understand the your logic, but I will try to answer.

To 'see a chair' means to 'absorb phtons from a chair'. Experiments (don't have links right now, can google it if necessary) show that after receving even 5-10 photons the decoherence becomes almost final. So you can't see chair in many states at the same time - as soon as you start receiving photons you decohere with some of the outcomes.

 

[Alfrez]

Sorry, I don't understand the your logic, but I will try to answer.

To 'see a chair' means to 'absorb phtons from a chair'. Experiments (don't have links right now, can google it if necessary) show that after receving even 5-10 photons the decoherence becomes almost final. So you can't see chair in many states at the same time - as soon as you start receiving photons you decohere with some of the outcomes.

In the double slit experiment. When we observe it, we only see one outcome. We don't see the superposition. I understand this is what you meant. However, in Decoherence and Einselection, the Einselection shielded chair is in different states being in superposition of up and down. Now if I'm also shielded from Einselection, I'm in superposition of up and down too. So I'm guessing I'd see the chair in superposition as I'm also entangled with it in complex macro superposition. Note again this is not your typical quantum coherence particle and superposition but on the more complex concept of preferred basis problem in Decoherence. You familiar with this preferred basis problem in Decoherence?

 

[Dmitry67]

What do you mean by 'shielded'? Isolated from the environment? Then how can you see it? You can't see shielded object. If it is not what you mean could you draw the experimental setup?

The preferred basis (which is in general arbitrary) you should use in order to reply questions 'what I would see' must be, of course 'YOU'

 

[Alfrez]

What do you mean by 'shielded'? Isolated from the environment? Then how can you see it? You can't see shielded object. If it is not what you mean could you draw the experimental setup?

The preferred basis (which is in general arbitrary) you should use in order to reply questions 'what I would see' must be, of course 'YOU'

I mean I'm also inside the shield. Or let's take an example the two of us. In Decoherence concept. Our body has classical states because of so called Environmental Superselection where the classical states in the environment is bestowed upon our particles. Without the environment. We can be in any state in Hilbert State. Or maybe let's use this example where only you and me are in this universe without any environment or particles. Since no classical states are being bombarded upon us. We can exist in a superposition of up and down. So we can likely see each other as states of up-down-side or halfup-halfdown-side or 1/4up-1/8down..etc. in fact any state in the superposition. Well?

 

[A. Neumaier]

But there is a big difference. A buckyball is a quantum object which obviously can interfere with itself.

A chair.is also a quantum object, only much bigger. Thus in theory it could interfere with itself just like a buckyball, if it were prepared in a superposition. But the latter is close to impossible because you cannot isolate a chair from the environment in a similar way as you can do it for a buckyball. For example, because of its size it has substantial gravitation. How would you switch it off?

Moreover, to notice the interference of buckyballs experimentally, one needs a source of many identically prepared buckyballs; this is the main difficulty in the experiment. How do you produce a source of many identically prepared chairs? Not the best factory can guarantee that the quantum state of two chairs is even close to identical. It has astronomically many degrees of freedom, but the manufacturing process controls only a small number of them, perhaps 100 or 1000...

in case you are not familiar with the exotic world of Decoherence).

I am very familiar with decoherence, but there is nothing exotic about it. Exotic is only what people interested in exotic phenomena make of it

 

[Alfrez]

A chair.is also a quantum object, only much bigger. Thus in theory it could interfere with itself just like a buckyball, if it were prepared in a superposition. But the latter is close to impossible because you cannot isolate a chair from the environment in a similar way as you can do it for a buckyball. For example, because of its size it has substantial gravitation. How would you switch it off?

Moreover, to notice the interference of buckyballs experimentally, one needs a source of many identically prepared buckyballs; this is the main difficulty in the experiment. How do you produce a source of many identically prepared chairs? Not the best factory can guarantee that the quantum state of two chairs is even close to identical. It has astronomically many degrees of freedom, but the manufacturing process controls only a small number of them, perhaps 100 or 1000...



I am very familiar with decoherence, but there is nothing exotic about it. Exotic is only what people interested in exotic phenomena make of it

You can't compare a chair to a buckyball. A buckyball 60 carbon atoms are all in coherence with one another. In a chair made of plastic, wood, and some metal. How can they be in coherence??

Anyway. In Decoherence and Einselection or Environmental Induced Superselection. The classical state of the chair is due to being influenced by the enviroment. When you place the chair in a universe without any environment, the chair won't be classical as you can have states of up-down or 1/4up-3/4down, etc. Right? And if you are in front of the chair you can see its shapeshifting because no environment is classically einselecting you and the chair. This is possible theoretically right?

 

[Alfrez]

A chair.is also a quantum object, only much bigger. Thus in theory it could interfere with itself just like a buckyball, if it were prepared in a superposition. But the latter is close to impossible because you cannot isolate a chair from the environment in a similar way as you can do it for a buckyball. For example, because of its size it has substantial gravitation. How would you switch it off?


I am very familiar with decoherence, but there is nothing exotic about it. Exotic is only what people interested in exotic phenomena make of it

Are you saying that in the new world of Decoherence, any macroscopic object such as a car can be in coherence as long as you can shield it from the environment (which practically is close to impossible as you stated due to gravity)? I thought coherence in the buckyball mean there is uniform arrangement of 60 carbon atoms. So all things must have uniform something before it can be in coherence. But you said a chair can be in coherence too. So any combination of complex macroscopic object such as car can be in superposition if the environment can be shielded? Of course this doesn't happen in Copenhagen. But then Decoherence is not really proven yet just the best model we prefer.

 

[Dmitry67]

I mean I'm also inside the shield.

Then it is a classical case of Wigner's friend experiment, explained here:
http://en.wikipedia.org/wiki/Wigner's_friend#Wigner.27s_friend_in_Many_Worlds

 

[A. Neumaier]

Are you saying that in the new world of Decoherence, any macroscopic object such as a car can be in coherence as long as you can shield it from the environment (which practically is close to impossible as you stated due to gravity)? I thought coherence in the buckyball mean there is uniform arrangement of 60 carbon atoms. So all things must have uniform something before it can be in coherence. But you said a chair can be in coherence too. So any combination of complex macroscopic object such as car can be in superposition if the environment can be shielded? Of course this doesn't happen in Copenhagen. But then Decoherence is not really proven yet just the best model we prefer.

Coherence has nothing at all to do with a symmetric arrangement of atoms.

It only means that you maintain the superposition (i.e., an approximately pure state rather than a mixture) long enough to be able to perform experiments with it. Decoherence means that the density matrix degenerates from a rank 1 matrix (corresponding to a pure state) to a diagonal matrix under the influence of noise from the environment. This degeneration is a continuous process that takes some time. If one can keep the interaction with the environment tiny, this time is very long, but it becomes smaller exponentially with the size of the system. This is a theoretically and experimentally very well established fact.

Nothing in quantum mechanics forbids an ensemble of cars to exist in a superposition. But decoherence would turn it in next to no time into a classical mixture. In practice, one cannot prepare such superpositions for large objects, because they degenerate even before they are created.