View Poll Results: Which Quantum Interpretation do you think is correct?
Copenhagen Interpretation 36 22.78%
GRW ( Spontaneous Collapse ) 2 1.27%
Consciousness induced Collapse 12 7.59%
Stochastic Mechanics 3 1.90%
Transactional Interpretation 4 2.53%
Many Worlds ( With splitting of worlds ) 13 8.23%
Everettian MWI (Decoherence) 18 11.39%
de-Broglie Bohm interpretation 18 11.39%
Some other deterministic hidden variables 16 10.13%
Ensemble interpretation 14 8.86%
Other (please specify below) 22 13.92%
Voters: 158. You may not vote on this poll

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Quantum Interpretation Poll (2011)

by Fyzix
Tags: 2011, interpretation, poll, quantum
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unusualname
#73
Apr23-11, 06:51 PM
P: 661
This poll doesn't include consistent histories, which is by far the most sensible interpretation.

I believe most of the interpretations will be at least partially consistent with the final model of reality, since you can bend an "ontological probability" into all sorts of nonsense, but if your puny evolved mind can accept an "ontological probability" then you might find the whole shebang has a surprisingly simple description.
yoda jedi
#74
Apr23-11, 07:47 PM
P: 380
Quote Quote by yoda jedi View Post

.-observer dependent.


if wave function is regarded as ontologically real, then, there is not need of observer, if the wave function is epistemic, less yet.

Quote Quote by Rap View Post



If I understand the terms "ontology" and "epistemology", I believe Copenhagen says they are neither. What is the objection?
ontological real is be independent of observer/measurement, a complete description of reality itself.
epistemic is a representation of an observer’s knowledge of reality rather than reality itself.




heisenberg:

a system is completely described by a wave function ψ, representing an observer's subjective knowledge of the system.

"The laws of nature which we formulate mathematically in quantum theory deal no longer with the particles themselves but with our knowledge of the elementary particles. ... The conception of objective reality ... evaporated into the ... mathematics that represents no longer the behavior of elementary particles but rather our knowledge of this behavior."



.
Gordon Watson
#75
Apr23-11, 07:58 PM
P: 375
Quote Quote by yoda jedi View Post
ontological real is be independent of observer/measurement, a complete description of reality itself.
epistemic is a representation of an observerís knowledge of reality rather than reality itself.




heisenberg:

a system is completely described by a wave function ψ, representing an observer's subjective knowledge of the system.

"The laws of nature which we formulate mathematically in quantum theory deal no longer with the particles themselves but with our knowledge of the elementary particles. ... The conception of objective reality ... evaporated into the ... mathematics that represents no longer the behavior of elementary particles but rather our knowledge of this behavior."

.
Dear yoda, please quote your sources. Good info is better info when sources are given.
Rap
#76
Apr23-11, 11:49 PM
P: 789
Quote Quote by rodsika View Post
You believe that a cat can never be in pure state by principle? But if one used the Heisenberg Interpretation where there is actual ontology. Can the cat exist as pure state? In Copenhagen, maybe it's not possible because they believe the wave function as just calculational tool. Without tracking the cat body down to the atoms and particles. You don't know the wave function to enter into calculation. In this sense. One can't treat the cat as in pure state when completely isolated in 100% hypothetical isolation box. But in Heisenberg Interpretation where everything actually happens. Maybe we can say that the cat is in pure state even if we didn't measure or prepare it to be in pure state from the beginning?? Or is the analysis the same in both Copenhagen and Heisenberg version where the cat can never be in pure state because beside not able to prepare it in pure state, the cat complex body parts can never in principle be in pure state? (Jesse, if you are reading this, pls comment too as we have discussed at length about pure state, mixed state but you are using Copenhagen version. What happens if we use the Heisenberg version where everything *actually* happens (like superposition, collapse) as described).
Well, I don't "believe" any scientific theory. I support the CI until I find something better. The thread you refer to is very good, but we never reached a final conclusion. Ken G. introduced the possibility that the cat is composed of entangled particles and I could never sort that out to our satisfaction. I don't think this is a problem to worry about, but I can't prove it. At this point, I think a cat could be in a pure state in principle, with the position and momenta of the particles narrowly defined, but not more than allowed by the Heisenberg uncertainty principle. This is notwithstanding the fact that to find the wave function of a cat would destroy the cat. This is true classically as well - to determine the position and momenta of every particle of the cat would destroy it. The thing that interests me is the "Wigner's friend" variation of the SC paradox. It is an excellent thought experiment concerning the "reality" of the wave function. If a scientist (Wigner's friend) is locked in a box which contains a box containing the cat, all of which is in a pure state, then Wigner's friend may use a pure wave function to describe the cat, while the scientist outside may use a pure wave function to describe Wigner's friend and the box. If Wigner's friend agrees to open the box and observe the cat at a particular time, then, to the scientist outside the box, Wigner's friend will go into a superposition state of seeing a dead cat and a live cat. The scientist outside the box opens the box, and Wigner's friend reports that the cat is alive. I am quite sure that when Wigner's friend is questioned about the experience, he will report nothing out of the ordinary, there will be no wierd experience of having been in a superposed state as described by the scientist outside the box. In other words, I am quite sure that the state of superposition that the outside scientist ascribes to Wigner's friend is not ontological reality, but rather a calculational tool. It encodes his knowledge, just as Wigner's friend's wave function encodes his. When Wigner's friend opens the box, his knowledge changes, his wave function collapses (actually it changes to a mixed state, since he cannot measure the state of the cat without destroying it). The scientist outside the box knows to a high probability that Wigner's friend has opened the box, but there will be no discontinuous change the outside scientist's wave function. When the outside scientist opens the box, his knowledge will change, and his wavefunction will change to a mixed state, for the same reason.

I never really understood all of Ken G's objections to this scenario, but every time I did come to understand what he was saying, he seemed to be correct. He is a CI supporter, so there was never any introduction of untestable assumptions, such as "ontological reality", many worlds, etc., which was a major reason why we could go as far as we did.
rodsika
#77
Apr24-11, 12:01 AM
P: 275
Quote Quote by Rap View Post
Well, I don't "believe" any scientific theory. I support the CI until I find something better. The thread you refer to is very good, but we never reached a final conclusion. Ken G. introduced the possibility that the cat is composed of entangled particles and I could never sort that out to our satisfaction. I don't think this is a problem to worry about, but I can't prove it. At this point, I think a cat could be in a pure state in principle, with the position and momenta of the particles narrowly defined, but not more than allowed by the Heisenberg uncertainty principle. This is notwithstanding the fact that to find the wave function of a cat would destroy the cat. This is true classically as well - to determine the position and momenta of every particle of the cat would destroy it. The thing that interests me is the "Wigner's friend" variation of the SC paradox. It is an excellent thought experiment concerning the "reality" of the wave function. If a scientist (Wigner's friend) is locked in a box which contains a box containing the cat, all of which is in a pure state, then Wigner's friend may use a pure wave function to describe the cat, while the scientist outside may use a pure wave function to describe Wigner's friend and the box. If Wigner's friend agrees to open the box and observe the cat at a particular time, then, to the scientist outside the box, Wigner's friend will go into a superposition state of seeing a dead cat and a live cat. The scientist outside the box opens the box, and Wigner's friend reports that the cat is alive. I am quite sure that when Wigner's friend is questioned about the experience, he will report nothing out of the ordinary, there will be no wierd experience of having been in a superposed state as described by the scientist outside the box. In other words, I am quite sure that the state of superposition that the outside scientist ascribes to Wigner's friend is not ontological reality, but rather a calculational tool. It encodes his knowledge, just as Wigner's friend's wave function encodes his. When Wigner's friend opens the box, his knowledge changes, his wave function collapses (actually it changes to a mixed state, since he cannot measure the state of the cat without destroying it). The scientist outside the box knows to a high probability that Wigner's friend has opened the box, but there will be no discontinuous change the outside scientist's wave function. When the outside scientist opens the box, his knowledge will change, and his wavefunction will change to a mixed state, for the same reason.

I never really understood all of Ken G's objections to this scenario, but every time I did come to understand what he was saying, he seemed to be correct. He is a CI supporter, so there was never any introduction of untestable assumptions, such as "ontological reality", many worlds, etc., which was a major reason why we could go as far as we did.
What Ken G was saying was simply that when the cat has other things beside him in the box such as Wigner friend or geiger counter or radioactive source, the cat becomes a subsystem, and in a subsystem, it is no longer in pure state. Hence the cat can't go into superposition.

I don't know if this is really true.

Anyway. Supposed the cat is left alone in the box and completely isolated without any thing beside him. Then he is a complete system, here I wonder if it can be in pure state.

Also what if one uses the Heisenberg Interpretation where everything *actually* happens. Here the wave function exists independently in the cat and geiger counter without the existence of the observer outside which doesn't need any encoding of knowledge or the concept of wave function as mere calculational tool. In such a case, can we say the cat is in pure state using Heisenberg ontological interpretation. Hope Jesse or Ken or other experts can assist here.
yoda jedi
#78
Apr24-11, 11:13 AM
P: 380
Quote Quote by Gordon Watson View Post
Dear yoda, please quote your sources. Good info is better info when sources are given.
Quote Quote by yoda jedi View Post
heisenberg:

a system is completely described by a wave function ψ, representing an observer's subjective knowledge of the system.



Heisenberg, W., 1958, Daedalus 87, 95
"The laws of nature which we formulate mathematically in quantum theory deal no longer with the particles themselves but with our knowledge of the elementary particles. ... The conception of objective reality ... evaporated into the ... mathematics that represents no longer the behavior of elementary particles but rather our knowledge of this behavior."



.

thanks gordon, you are welcome.

Heinsenberg, February 2, 1960 ..."The act of recording, on the other hand, which leads to the reduction of the state, is not a physical, but rather, so to say, a mathematical process. With the sudden change of our knowledge also the mathematical presentation of our knowledge undergoes of course a sudden change."...

Jammer, M., 1974,


.
Rap
#79
Apr24-11, 11:48 AM
P: 789
Quote Quote by rodsika View Post
Also what if one uses the Heisenberg Interpretation where everything *actually* happens. Here the wave function exists independently in the cat and geiger counter without the existence of the observer outside which doesn't need any encoding of knowledge or the concept of wave function as mere calculational tool. In such a case, can we say the cat is in pure state using Heisenberg ontological interpretation. Hope Jesse or Ken or other experts can assist here.
Again, you have to deal with Wigner's friend, where two different scientists have different wave functions for the same object. If the wave function is ontologically real, how do you resolve the Wigner's friend problem?

Quote Quote by yoda jedi View Post
Heinsenberg, February 2, 1960 ..."The act of recording, on the other hand, which leads to the reduction of the state, is not a physical, but rather, so to say, a mathematical process. With the sudden change of our knowledge also the mathematical presentation of our knowledge undergoes of course a sudden change."...

Jammer, M., 1974,
I agree with that, completely. The wave function collapse is a collapse in our uncertainty, not a collapse in something physical.
Einstein Mcfly
#80
Apr24-11, 03:12 PM
P: 163
Quote Quote by Matterwave View Post
Ensemble interpretation ftw!
Fyzix
#81
Apr24-11, 03:28 PM
P: 172
The ensemble interpretation doesn't really interpret anything tho.
Your still left with the same questons, why does the cat die or live?
rodsika
#82
Apr24-11, 05:16 PM
P: 275
Quote Quote by Rap View Post
Again, you have to deal with Wigner's friend, where two different scientists have different wave functions for the same object. If the wave function is ontologically real, how do you resolve the Wigner's friend problem?



I agree with that, completely. The wave function collapse is a collapse in our uncertainty, not a collapse in something physical.
But why did Heisenberg also state that the wave function (probability function) combines objective element. What does he meant by it in the following:

"The probability function combines objective and subjective elements. It contains statements about possibilities or better tendencies ('potentia' in Aristotelian philosophy), and these statements are completely objective, they do not depend on any observer; and it contains statements about our knowledge of the system, which of course are subjective in so far as they may be different for different observers."

Complete context in:

http://www.marxists.org/reference/su...e/heisenb3.htm
rodsika
#83
Apr24-11, 07:35 PM
P: 275
Quote Quote by Rap View Post
Well, I don't "believe" any scientific theory. I support the CI until I find something better. The thread you refer to is very good, but we never reached a final conclusion. Ken G. introduced the possibility that the cat is composed of entangled particles and I could never sort that out to our satisfaction. I don't think this is a problem to worry about, but I can't prove it. At this point, I think a cat could be in a pure state in principle, with the position and momenta of the particles narrowly defined, but not more than allowed by the Heisenberg uncertainty principle. This is notwithstanding the fact that to find the wave function of a cat would destroy the cat. This is true classically as well - to determine the position and momenta of every particle of the cat would destroy it. The thing that interests me is the "Wigner's friend" variation of the SC paradox. It is an excellent thought experiment concerning the "reality" of the wave function. If a scientist (Wigner's friend) is locked in a box which contains a box containing the cat, all of which is in a pure state, then Wigner's friend may use a pure wave function to describe the cat, while the scientist outside may use a pure wave function to describe Wigner's friend and the box. If Wigner's friend agrees to open the box and observe the cat at a particular time, then, to the scientist outside the box, Wigner's friend will go into a superposition state of seeing a dead cat and a live cat. The scientist outside the box opens the box, and Wigner's friend reports that the cat is alive. I am quite sure that when Wigner's friend is questioned about the experience, he will report nothing out of the ordinary, there will be no wierd experience of having been in a superposed state as described by the scientist outside the box. In other words, I am quite sure that the state of superposition that the outside scientist ascribes to Wigner's friend is not ontological reality, but rather a calculational tool. It encodes his knowledge, just as Wigner's friend's wave function encodes his. When Wigner's friend opens the box, his knowledge changes, his wave function collapses (actually it changes to a mixed state, since he cannot measure the state of the cat without destroying it). The scientist outside the box knows to a high probability that Wigner's friend has opened the box, but there will be no discontinuous change the outside scientist's wave function. When the outside scientist opens the box, his knowledge will change, and his wavefunction will change to a mixed state, for the same reason.

I never really understood all of Ken G's objections to this scenario, but every time I did come to understand what he was saying, he seemed to be correct. He is a CI supporter, so there was never any introduction of untestable assumptions, such as "ontological reality", many worlds, etc., which was a major reason why we could go as far as we did.
This interesting what you said the cat is composed of entangled particles. And you believed that a cat could be in a pure state in principle, with the position and momenta of the particles narrowly defined, but not more than allowed by the Heisenberg uncertainty principle. Well. I think a cat could only be in pure state in principle using the Many Worlds Intepretation. In Copenhagen it may not be possible if what Ken said is right. I read that thread over and over again for hours and the following statement by Ken seemed to say it all ( what he says is being scrutinized in the thread I just made "Substrates don't evolve according to Schrodinger equations?". ):

Ken wrote:

"But that's what I'm saying isn't true-- even if we start with pure states for each component of the system, when we couple them, the only pure state is now a combined system. The cat is now a substate of that system, and substates don't evolve according to the Shroedinger equation, so they don't evolve unitarily and they don't become superposition states. There is really no such thing as the state of a part of a system, but we as physicists can make correct predictions by using the concept of a mixed state to treat such substates, or in some special circumstances, we have enough information to treat a substate as a pure or superposition state. That ability is quickly lost for the cat in the box, even if it starts out in an impossible-to-know pure state."

If true, it means that Wigner friend inside the box with a box of cat is pure state as a combined system. But Wigner friend is a substate of that system and substrates don't evolve according to the Schroedinger equation. so there is no superposition of any kind state. The paradox doesn't happen.

I need confirmation if this is true. If true. Schrodinger cat can never be in superposition of dead and alive even in principle in the boring world of the Copenhagen. But it is all possible in Many worlds because here the cat and universe can be in pure state by principle.
JesseM
#84
Apr24-11, 09:13 PM
Sci Advisor
P: 8,470
Quote Quote by rodsika View Post
This interesting what you said the cat is composed of entangled particles. And you believed that a cat could be in a pure state in principle, with the position and momenta of the particles narrowly defined, but not more than allowed by the Heisenberg uncertainty principle. Well. I think a cat could only be in pure state in principle using the Many Worlds Intepretation.
If you have an isolated system like the inside of an ideal perfectly shielded box, then if immediately prior to isolating it you could perform a measurement which measured a complete set of commuting observables for the entire isolated system, this would automatically give you a pure state for the isolated system.
Quote Quote by rodsika View Post
In Copenhagen it may not be possible if what Ken said is right. I read that thread over and over again for hours and the following statement by Ken seemed to say it all ( what he says is being scrutinized in the thread I just made "Substrates don't evolve according to Schrodinger equations?". ):

Ken wrote:

"But that's what I'm saying isn't true-- even if we start with pure states for each component of the system, when we couple them, the only pure state is now a combined system. The cat is now a substate of that system, and substates don't evolve according to the Shroedinger equation, so they don't evolve unitarily and they don't become superposition states. There is really no such thing as the state of a part of a system, but we as physicists can make correct predictions by using the concept of a mixed state to treat such substates, or in some special circumstances, we have enough information to treat a substate as a pure or superposition state. That ability is quickly lost for the cat in the box, even if it starts out in an impossible-to-know pure state."
I think Ken is just saying the cat subsystem is not in a pure state, but the whole isolated system (everything inside the box, assuming the box can keep everything inside completely isolated from outside influences) can be. If you want to imagine a cat in a space suit in a perfect vacuum, then the isolated system could consist of just the cat and its suit. If the cat has external surroundings within the box, then if you divide things up into a cat subsystem plus the rest of the box as its environment, presumably there will be decoherence and the cat subsystem will be modeled as being in something close to a mixed state.
rodsika
#85
Apr24-11, 09:41 PM
P: 275
Quote Quote by JesseM View Post
If you have an isolated system like the inside of an ideal perfectly shielded box, then if immediately prior to isolating it you could perform a measurement which measured a complete set of commuting observables for the entire isolated system, this would automatically give you a pure state for the isolated system.

I think Ken is just saying the cat subsystem is not in a pure state, but the whole isolated system (everything inside the box, assuming the box can keep everything inside completely isolated from outside influences) can be. If you want to imagine a cat in a space suit in a perfect vacuum, then the isolated system could consist of just the cat and its suit. If the cat has external surroundings within the box, then if you divide things up into a cat subsystem plus the rest of the box as its environment, presumably there will be decoherence and the cat subsystem will be modeled as being in something close to a mixed state.
Do you agree with Ken that in the Copenhagen there is no way for the cat to be in superposition of being both dead and alive as when Ken stated:

"So my point is, whether we start with a putative (but impossible) pure-state cat, or if we adopt a mixture of pure states with some statistical distribution, doesn't matter for the cat paradox-- because correct quantum mechanics says that once we couple that cat to the mechanism that can kill it, there is no longer any such thing as the state of the cat in quantum mechanics. There is only a projection of the full state onto the cat degree of freedom, but that isn't a quantum mechanical state, it is a classical treatment of a quantum mechanical state. It makes no difference to the quantum mechanics if we now assert that the cat "really is" alive or dead and we have no way of knowing which, or if we assert that we have chosen to treat it that way in our mathematics-- the correct quantum mechanics is completely moot on the point, there is no cat-state wavefunction so there is no superposition of alive or dead."

So you mean decoherence is the explanation why when we couple the cat to the mechanism that can kill it, there is no longer any such thing as the state of the cat in quantum mechanics?

I'ts been 75 long years since the Schrodinger Cat. Let's settle it once and for all as far as Copenhagen interpretation is concerned. We know in many worlds, cat can be both dead and alive.. but we are just focusing on pure Copenhagen for now.
JesseM
#86
Apr24-11, 10:45 PM
Sci Advisor
P: 8,470
Quote Quote by rodsika View Post
Do you agree with Ken that in the Copenhagen there is no way for the cat to be in superposition of being both dead and alive as when Ken stated:
If he means there is no pure state for the cat I agree, but my understanding of decoherence is that you could still have a reduced density matrix for the cat subsystem, and that although decoherence would drive this reduced density matrix into something close to a mixed state, the interference terms wouldn't quite go to zero so there is still a superposition of sorts. Ken or some other knowledgeable person can correct me if I've misunderstood this stuff though...
rodsika
#87
Apr24-11, 11:43 PM
P: 275
Quote Quote by Rap View Post
Again, you have to deal with Wigner's friend, where two different scientists have different wave functions for the same object. If the wave function is ontologically real, how do you resolve the Wigner's friend problem?
 

Your Wigner friend example can be modelled with a simple illustration Supposed you have a 430 atom buckyball emitted. Since you believe superposition has no ontological reality. Then you think the buckyball will take classical trajectory to the screen? Copenhagen is pragmatic in that it doesn't want to commit to any picture of what happens. If you believe the 430 atom buckyball has classical trajectory and only after a number of trials can give you the interference patterns, then you follow the belief of ensemble or statistical interpretations where it is only meaningful after a number of runs? This is similar to Wigneg friend and the box of cat and another scientist outside the box. Only the calculations make sense and everything is classical from the beginning. Pure state then is just there is something to calculate about. So you believe in the statistic interpretation instead of pure Copenhagen (where imagining what occurs inside is outlawed) ?

I believe it is possible though that superposition is literal, so the buckyball is literally in superpositon of positions. It's like the 430 atom buckyball lost out the classical form and become an apparison or ghost in between emission and detection. Your Wigner friend example can refute this but it can't happen in the first place because of decoherence which makes the substates unable to use the Schroedinger equation and there is no quantum mechanics at all.

On the other hand, those who believe in Many Worlds believe the buckyball gets duplicated in many branches.

Bohmian believes in classical trajectory but they were "push" by the wave function and pilot wave.
Rap
#88
Apr25-11, 10:09 AM
P: 789
Quote Quote by rodsika View Post
What does Heisenberg mean by the following:

"The probability function combines objective and subjective elements. It contains statements about possibilities or better tendencies ('potentia' in Aristotelian philosophy), and these statements are completely objective, they do not depend on any observer; and it contains statements about our knowledge of the system, which of course are subjective in so far as they may be different for different observers."
I think he means that, if we agree on a wave function for a system, it encapsulates our knowledge of the system (subjective), but the probabilities that we calculate as we propagate the wave function forward in time, (using e.g. the Schroedinger equation) are objective.

Quote Quote by rodsika View Post
In Copenhagen it may not be possible if what Ken said is right.

If true, it means that Wigner friend inside the box with a box of cat is pure state as a combined system. But Wigner friend is a substate of that system and substrates don't evolve according to the Schroedinger equation.
The thing I objected to was the assumption that the cat and the device were separate systems. This seems arbitrary. I think, in principle, you can have the device and the cat as one pure state, evolving according to the Schroedinger equation. In the case of Wigner's friend, the same applies.

Quote Quote by rodsika View Post
Your Wigner friend example can be modelled with a simple illustration Supposed you have a 430 atom buckyball emitted. Since you believe superposition has no ontological reality. Then you think the buckyball will take classical trajectory to the screen?
No. QM is about measurements and the only reality is that which is revealed by those measurements. If I said the buckyball took a classical trajectory, that would mean I could measure its position and momentum to a high degree of accuracy without appreciably disturbing it, all along its trajectory. Superposition would not be an issue, the wave function would collapse at each measurement. If you say that the position and momentum is unmeasured during its travel, then QM and superposition will apply. But then, the question of whether it was following a classical trajectory is untestable, and is therefore not a proper scientific question.

Quote Quote by rodsika View Post
Your Wigner friend example can refute this but it can't happen in the first place because of decoherence which makes the substates unable to use the Schroedinger equation and there is no quantum mechanics at all.
Decoherence in this case is a mathematical approximation, not a physical occurrence. It says that you can approximately replace a pure wave function by a mixed state: an ensemble of macroscopic observations which do not yield as much information as a wavefunction collapse, and whose probabilities are additive. These observations do not collapse the wave function to an eigenstate, but rather selects one macroscopic observation out of the ensemble of observations. This is what happens when you open the box. You don't collapse the wave function, measuring the position and momenta of every particle of the cat (to within Heisenberg), such a measurement would destroy the cat. You make a much less informative measurement, noting only whether the cat is alive or dead.
A. Neumaier
#89
Apr26-11, 07:39 AM
Sci Advisor
P: 1,943
Quote Quote by tom.stoer View Post
But there is no way to describe the system "system + device + observer" unitarily, either.
Why not? The state of the whole universe, including everything, may well have a unitary evolution. It is consistent with everything I know.
rodsika
#90
Apr26-11, 08:11 AM
P: 275
Quote Quote by Rap View Post
I think he means that, if we agree on a wave function for a system, it encapsulates our knowledge of the system (subjective), but the probabilities that we calculate as we propagate the wave function forward in time, (using e.g. the Schroedinger equation) are objective.



The thing I objected to was the assumption that the cat and the device were separate systems. This seems arbitrary. I think, in principle, you can have the device and the cat as one pure state, evolving according to the Schroedinger equation. In the case of Wigner's friend, the same applies.



No. QM is about measurements and the only reality is that which is revealed by those measurements. If I said the buckyball took a classical trajectory, that would mean I could measure its position and momentum to a high degree of accuracy without appreciably disturbing it, all along its trajectory. Superposition would not be an issue, the wave function would collapse at each measurement. If you say that the position and momentum is unmeasured during its travel, then QM and superposition will apply. But then, the question of whether it was following a classical trajectory is untestable, and is therefore not a proper scientific question.



Decoherence in this case is a mathematical approximation, not a physical occurrence. It says that you can approximately replace a pure wave function by a mixed state: an ensemble of macroscopic observations which do not yield as much information as a wavefunction collapse, and whose probabilities are additive. These observations do not collapse the wave function to an eigenstate, but rather selects one macroscopic observation out of the ensemble of observations. This is what happens when you open the box. You don't collapse the wave function, measuring the position and momenta of every particle of the cat (to within Heisenberg), such a measurement would destroy the cat. You make a much less informative measurement, noting only whether the cat is alive or dead.
One can't even put a wooden chair into pure state. So how can you do it with a cat. You have to discard maybe 90% of the information so the cat would become more like a statue and it is very much dead. Lol... Also dead and alive is not like spin of a particle. Dead and alive are already classical.

But what's weird is that in Many World, the cat can be in pure state even without measuring it. Maybe you are trying to imagine a cat in Many world-like setting.

I wonder why a cat can be in pure state in Many worlds while impossible in Copenhagen. Rap or anyone?


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