Debate Macroscopic Realism: Define or Disbelieve?

[alexepascual]

I define realism per Einstein's definition of elements of reality: "A sufficient condition for the
reality of a physical quantity is the possibility of predicting it with certainty, without disturbing the system. In quantum mechanics in the case of two physical quantities described by non-commuting operators, the knowledge of one precludes the knowledge of the other." Or as he also said: "I think that a particle must have a separate reality independent of the measurements. That is: an electron has spin, location and so forth even when it is not being measured."
That, as he points out, is contradicted by the Heisenberg Uncertainty Principle at the micro (quantum) level. So anywhere in which h is relevant, you are talking about that level and I would not expect to see realism. That is because I believe that there is no more "complete" description possible.
But I am not sure how I would translate that into macroscopic realism, except to say that I know it when I see it.

I think the problem is when we try to make a general definition of realism and expect it to work in all circumstances. If you make a separation between the microscopic and the macroscopic, then there isn't so much of a problem. Realism is a concept that was formed before we even knew anything about QM. And eventhough it was disputed by some philosofers, it worked quite well and it was consistent with classical physics and even the theory of relativity. Now, Einstein took it to an extreme and wanted it to also work for QM.
I think our friend Caroline Thompson also did. Too sad we can't argue with her anymore.
Any way, it is obvious that we still have a problem in explaining the transition form quantum to classical behavior, but that does not imply that we can't assume realism at the macroscopic level. At least we can postulate (based on our experience), define precisely what we mean by it, and see if we can find some experiment that will be inconsistent with it. If we can't find any inconsistencies, then we'll eventually have to find out exactly how we transition from the quantum realm, where realism does not work, to the macroscopic, where apparently it does.

 

[RUTA]

I would say that your both definitions are equivalent and useless, sorry. It is like saying that big business is different from the small one when it is big.

You see, if we use your definition the we can not discuss the classical vs quantum behavior at all. When there is a superposition then it is BY DEFINITION quantum, otherwise BY DEFINITION classical.

I didn't define behavior, I defined entities. And, the definitions are not equivalent unless you believe, among other things, that to be screened off means both that x and p commute and that they don't commute.

 

[DrChinese]

I think our friend Caroline Thompson also did. Too sad we can't argue with her anymore.

I am sad about her, and appreciated her drive... but honestly don't miss the discussions with her. She could be extremely frustrating (equally so in our private communications).

The thing about local realists (such as CT) is that they often fail to acknowledge the strengths of the Bell theorem & related experiments, and the theoretical difficulties of their own position. If they started there, it would be a lot easier to discuss rationally. Instead, as with Caroline, it becomes almost a religious issue and so ends up being about faith more than science. Not sure why the subject stirs such passions, but it certainly seems to.

 

[ConradDJ]

The thing is, you never observe a macroscopic object in a superposition of positions 1 meter apart.

alexepascual -- I sympathize with your difficulty getting this discussion pointed in the direction you chose to begin with... but I can't really help, I'm sorry. The thing is, you never observe ANY object in a superposition of anything. Anytime there's an observation of a system, no matter how microscopic, there's a definite result (within the range of precision of the measurement).

All our evidence of things "being in superpositions" is indirect -- by which I don't mean to say it's not convincing evidence. It certainly is, though of course how to interpret it is a big question. And of course, this indirect evidence (interference effects) shows up at the microscopic level.

But to me, this situation indicates that it's not micro- vs macro- that's significant... it's whether definite information about a system exists in the network of observation / measurement / communication-interactions. With big, massive objects there's a huge amount of redundant information about them flying around. At the quantum level, information about a system may well depend on a single particle-interaction.

Where interactional information is hugely redundant, our ideas about a reality-in-itself, "behind" the appearances, work really well.* Where the informational network is sparse, if we insist on there being a "real object" there behind what's observable, we have to describe the object as being in a superposition.

*this relates to Zurek's "quantum Darwinism" approach to decoherence, based on information redundancy.

 

[zonde]

Welcome to the thred Zonde. I have a question for you.
Would you consider "real" a thing (macroscopic) that is beyond your influence because it is in the past. (It can influence you but you can't influence it).

This question is in a bit different direction then the one I was trying to answer at first.
I think it needs to answer questions from different perspective - is measuring device considered "real"? Because as I see our classified experience is measuring device for our present and tool for predicting future.
But to give some answer I will say that past is real but it loose it's realness with age.


I would like to add some comment about discussion on connection between macroscopic realism and microscopic realism.
I hold to the view that property of "unreal" is reserved for whole entity (it's uniqueness). But taking it apart enforce some realism (or push it further to separate parts of original entity) as we are extending interaction network inside this entity.
And the reason for that as I see is that knowledge can not start in empty place and starting point of our knowledge is macroscopic realism. So we are bound by our starting point.

 

[Dmitry67]

1 meter apart... hm...

"Microscopic" is not about the SIZE or the MASS
In the mentioned Wheeler's experiment with the gravitational lensing around the galaxy, the quantum effect have the size of the galaxy.
Rerarding the mass, AFAIK systems of BILLIONS of particles can still be in a superposition:

http://www.enmediallc.com/products.html

 

[zonde]

"Microscopic" is not about the SIZE or the MASS
In the mentioned Wheeler's experiment with the gravitational lensing around the galaxy, the quantum effect have the size of the galaxy.

I still hold to my viewpoint that taking things apart leads to realism. So in this example I hold to my viewpoint that quantum effect can have realistic explanation.

 

[kote]

Responding to the OP, I'd like to point out that CI takes macroscopic realism as its primary and guiding attribute. Obviously QM forces some disturbing consequences when this is done, but that's another issue. Here's what Heisenberg has to say about reality when responding to Bohm:

What does it mean to call waves in configuration space “real”? This space is a very abstract space. The word “real” goes back to the Latin word “res,” which means “thing;” but things are in the ordinary three-dimensional space, not in an abstract configuration space.
...
Bohm considers himself able to assert: “We do not need to abandon the precise, rational, and objective description of individual systems in the realm of quantum theory.” This objective description, however, reveals itself as a kind of “ideological superstructure,” which has little to do with immediate physical reality.

Heisenberg, Werner. Physics and Philosophy: The Revolution in Modern Science. (NYC: Harper & Brothers Publishers, 1958). 130-132.​

Real objects are those things located in three-dimensional space for Heisenberg. His reference to "immediate physical reality" and denial of Bohm's objective description also imply that he defines reality by observables and only observables. On these points I think it is clear that he and Bohr agree.

 

[alexepascual]

I am sad about her, and appreciated her drive... but honestly don't miss the discussions with her. She could be extremely frustrating (equally so in our private communications).
The thing about local realists (such as CT) is that they often fail to acknowledge the strengths of the Bell theorem & related experiments, and the theoretical difficulties of their own position. If they started there, it would be a lot easier to discuss rationally. Instead, as with Caroline, it becomes almost a religious issue and so ends up being about faith more than science. Not sure why the subject stirs such passions, but it certainly seems to.

I actually never had a discussion with Caroline, but I had read some of her posts and knew how passionate she was about her ideas. Maybe we can learn something from her. Seing how frustrating it was to communicate with her, we could question ourselves and wonder if in some circumstances we may be acting a little the same way as her. I have cough myself some times doing the same thing. And I have seen the same behavior in other people who spouse other interpretations (maybe not to the same extreme we saw in her).
Still, even with all the negative implications of being stubborn and not wanting to consider the possibility of being wrong, I think her passion for the subject is something to admire.
With respect to our human interaction here in this forum, I have thought that that's something that would be worth discussing. But that would be the subject for a different thread.

 

[alexepascual]

alexepascual -- I sympathize with your difficulty getting this discussion pointed in the direction you chose to begin with... but I can't really help, I'm sorry. The thing is, you never observe ANY object in a superposition of anything. Anytime there's an observation of a system, no matter how microscopic, there's a definite result (within the range of precision of the measurement).

All our evidence of things "being in superpositions" is indirect -- by which I don't mean to say it's not convincing evidence. It certainly is, though of course how to interpret it is a big question. And of course, this indirect evidence (interference effects) shows up at the microscopic level.

But to me, this situation indicates that it's not micro- vs macro- that's significant... it's whether definite information about a system exists in the network of observation / measurement / communication-interactions. With big, massive objects there's a huge amount of redundant information about them flying around. At the quantum level, information about a system may well depend on a single particle-interaction.

Where interactional information is hugely redundant, our ideas about a reality-in-itself, "behind" the appearances, work really well.* Where the informational network is sparse, if we insist on there being a "real object" there behind what's observable, we have to describe the object as being in a superposition.

*this relates to Zurek's "quantum Darwinism" approach to decoherence, based on information redundancy.

I have to addmit I didn't express myself correctly. Of course we don't see superpositions at the microscopic level directly. But we do see interference effects when the microscopic system interacts with a macroscopic one. Apparently we don't see any signs of interference of positions widely sepatated of macroscopic objects. Separation of systems as microscopic or macroscopic is a matter of convenience and it seems to have worked very well for a long time. Physicists routinely use this concept. We still have physics separated between classical and quantum, with different math and paradigm for each. It is generaly accepted that classical physics works well for macroscopic systems while quantum physics works well for the microscopic ones. I have never heard of physicists arguing against this useful classification.
What I am trying to do is to see what our expectations at the classical level are. I would like to discuss how we expect big things like a cat or a billiard ball to behave in different circumstances. You may think that this is so clear that there may not be much to talk about. But there could be cases where we may contemplate possible paradoxes even at the level of large objects, specially when they have interacted with a quantum system.

Let me ask you: Would you consider the possibility of running into a case in which our experience leads to a conclusion that Schrodinger's cat is in a superposition of dead/alive?
(maybe through interference in some correlated system or other kind of calculation)

I have read papers by Zurek, but I don't remember reading about this "Darwinism" idea. I'll look into it.

 

[DrChinese]

I actually never had a discussion with Caroline, but I had read some of her posts and knew how passionate she was about her ideas. Maybe we can learn something from her. Seing how frustrating it was to communicate with her, we could question ourselves and wonder if in some circumstances we may be acting a little the same way as her. ...

I am sure I am guilty of that from time to time. Passion is generally good, but we have to be careful about becoming so enamored of an idea that we see only the good and none of the bad. In all honesty with Caroline, I think she knew she had only a short time and that fueled things. And there were times it could be an interesting discussion. I prefer to think in terms of what I learned in the process, and that I was better off for it.

 

[alexepascual]

1 meter apart... hm...

"Microscopic" is not about the SIZE or the MASS
In the mentioned Wheeler's experiment with the gravitational lensing around the galaxy, the quantum effect have the size of the galaxy.
Rerarding the mass, AFAIK systems of BILLIONS of particles can still be in a superposition:

http://www.enmediallc.com/products.html

From the website you quoted:
"Tiny disturbances from the environment tend to upset quantum superpositions and turn them into unambiguous reality that we see around us every day - a process known as decoherence."
With respect to the SQUID, it appears that these systems have less interaction with the environment and therefore slow decoherence. But a system like this is not typical.
I understand Wheeler's experiment involves inter-galactic distances. But the particles we are talking about are photons, which are microscopic.

Now, my question is (the same I asked other posters): Would you consider the possibility of running into some experiment where the results seem to point to a superposition of a dead/alive cat (a "real" cat, not a fake one). Or perhaps a superposition of two positions a few centimeters appart of a billiard ball?

 

[alexepascual]

I am sure I am guilty of that from time to time. Passion is generally good, but we have to be careful about becoming so enamored of an idea that we see only the good and none of the bad. In all honesty with Caroline, I think she knew she had only a short time and that fueled things. And there were times it could be an interesting discussion. I prefer to think in terms of what I learned in the process, and that I was better off for it.

It looks like we agree on this.

 

[ThomasT]

I see mainly two possibilities here with some people having positions in between.
If you believe in realism at the macroscopic level, how do you define it?
If you don't believe in it, could you still define it? not as a fact of nature but as a belief other people may have?. In this case, what is your picture of the world (only at the macroscopic level)?

The macroscopic level is the level of objective reality -- the level at which our sensory perceptions of the world are compared and evaluated. Our sensory faculties detect vibratory phenomena. Of course, I don't believe that that's all there is to Reality. Modern science has allowed us to make and test (at least indirectly) inferences about the deeper reality from which the macroscopic level phenomena amenable to our objective analysis emerge.

The picture I entertain is that Reality is fundamentally waves (disturbances) in a hierarachy of media. All of these media are particulate -- composed of bounded wave structures which have emerged from a fundamental nonparticulate medium. So, fundamentally, if we could view our universe from outside the limits of our sensory faculties, Reality is a seething cauldron of wave interactions. In this, fundamental, context there are no planets, or stars, or animals, or computers -- just disturbances in media, evolving according to some (or maybe just one) fundamental dynamic(s).

The cat isn't ever in a superposition of alive and dead. From our macroscopic perspective the cat is either alive or dead. In the deeper reality, the cat is a superposition of various interacting waves/media. The cat is one particular spatial configuration at any instant. That spatial configuration is interpreted as either alive or dead -- but it can't be both at the same time.

So, yes I believe that the macroscopic level is real. We're creatures of this level, so disputes about any level of reality have to be rendered in the form of, and arbitrated by, macroscopic phenomena.

But the macroscopic reality isn't the fundamental Reality.

 

[alexepascual]

Responding to the OP, I'd like to point out that CI takes macroscopic realism as its primary and guiding attribute. Obviously QM forces some disturbing consequences when this is done, but that's another issue.

I agree with your statement about macroscopic reality being a guiding principle for CI.
Probably the disturbing consequences you are referring to in the second sentence, are the implication that interaction of a microscopic system with a classical measuring apparatus would result in a superposition of pointer states of the classical apparatus. Certainly Von Neuman's approach would lead to this conclusion. Others have disputed that approach, but this is probably still an open question. Even if we considered the eigenstates of the measurement's observable to continue to exist after the measurement process was completed, it appears that we don't see any interference effects, and we only experience one of the possible eigenstates. So, one way or another, whatever the mechanism eventually turns out to be the correct one, the result looks pretty classical. If we prefer to see this process form the many-worlds point of view, still the conclusion would be that the worlds split and we don't see the "other worlds". As there seems to be no interference with the other worlds, the predicted results are still the same as in CI.

So kote, I would like to ask you: Would you consider the possibility that results of some future experiment might lead to the conclusion that some macroscopic object such as Schrodinger's cat is in a superposition of states? I think if that situation ever arised, it would imply a challenge to our idea of macroscopic realism. (At least it would be in the one-world view).

 

[kote]

So kote, I would like to ask you: Would you consider the possibility that results of some future experiment might lead to the conclusion that some macroscopic object such as Schrodinger's cat is in a superposition of states? I think if that situation ever arised, it would imply a challenge to our idea of macroscopic realism. (At least it would be in the one-world view).

I would consider it and tell you that it's not possible . How would you see a superposition of states? You would have to see certain things happening in certain unambiguous locations, but then, this is not a superposition. Any appearance of fuzziness could be explained classically. We will never accept any experiment that is supposed to tell us that a=b and a=!b. If we have the states b and !b then they are not both states of a. We know this a priori and by definition, and it is how we have and will interpret the results of experiments. If you have both alive and dead, you have 2 cats. If you have only one cat, then you can't have both alive and dead.

 

[alexepascual]

The cat isn't ever in a superposition of alive and dead. From our macroscopic perspective the cat is either alive or dead. In the deeper reality, the cat is a superposition of various interacting waves/media. The cat is one particular spatial configuration at any instant. That spatial configuration is interpreted as either alive or dead -- but it can't be both at the same time.
So, yes I believe that the macroscopic level is real. We're creatures of this level, so disputes about any level of reality have to be rendered in the form of, and arbitrated by, macroscopic phenomena.
But the macroscopic reality isn't the fundamental Reality.

I see you are interested in being able to define a fundamental reality from which both quantum and classical behaviors emerge. I think this is a worthy cause and a very difficult one. In this thread I was trying to avoid the topic of fundamental reality or reality as it may (or may not) apply to microscopic (quantum) systems.
You stated clearly that you would not expect Schrodinger's cat to be found in a dead/alive superposition. Of course as it was pointed out in a previous post, even a quantum system is not observed to be in a superposition. It is only that we have to assume it to be (or to have been) in a superposition based on the results of measurement.
So I would assume that you would not expect to be able to design any experiment in a lab where the results of one (or a collection) of measurements leads one to conclude that the cat was ever in a superposition of dead/alive.
So, large objects like cats are assumed to be in a well-difined macroscopic state. It's atoms may still be in states of superposition, but the object as a whole has a quite precise position. The answer to the question: Is the cat dead or alive? is expected to have a single answer. I would call this "macroscopic realism", but I guess it could be called something else if this terminology turns out to be controversial.
Now, in connection with the cat's experiment.
(1) Would you assume that the result has the same definite result if it was performed last week? (it is in your past light cone)
(2) Would you assume it will have a definite result (which you'll eventually be able to discover) if it has not yet been done. It'll be done next week so you know it is in your future light cone.
(3) Would you assume it to have a definite result if it being done right now in distant planet like Pluto? (The event is space-like) You'll can't get any information about it until 4 hours from now with a signal traveling at the speed of light.

 

[alexepascual]

I would consider it and tell you that it's not possible . How would you see a superposition of states? You would have to see certain things happening in certain unambiguous locations, but then, this is not a superposition. Any appearance of fuzziness could be explained classically. We will never accept any experiment that is supposed to tell us that a=b and a=!b. If we have the states b and !b then they are not both states of a. We know this a priori and by definition, and it is how we have and will interpret the results of experiments. If you have both alive and dead, you have 2 cats. If you have only one cat, then you can't have both alive and dead.

Of course you could never see it directly to be in a superposition. But I was wondering if you would consider as possible that the experiment leads to some distribution of outcomes which is incompatible with the idea that the cat is in a difinite state of dead or alive right before measurement. This was done in order to prove that Bell's inequalities don't hold for quantum systems. (Alain Aspect, etc.) but that was for quantum systems, not for something assumed to be classical like a cat.
In your last sentence you point to an apparent imposibility of a dead/alive superposition. Well, if someone came up with a thought experiment (or actuall experiment) whose results seemed to imply a superposition of macroscopic states, then that would be clearly a paradox because on one hand you don't expect something like that as being possible and on the other you have this experiment that seems to imply that behavior.

 

[ThomasT]

You stated clearly that you would not expect Schrodinger's cat to be found in a dead/alive superposition. Of course as it was pointed out in a previous post, even a quantum system is not observed to be in a superposition. It is only that we have to assume it to be (or to have been) in a superposition based on the results of measurement.

I don't think we have to assume that anything is in a mutually exclusive combination of states at any time. Quantum superpositions of the dead cat - alive cat sort are just statements regarding the possible outcomes of experiments.

So I would assume that you would not expect to be able to design any experiment in a lab where the results of one (or a collection) of measurements leads one to conclude that the cat was ever in a superposition of dead/alive.

You assume correctly.

Now, in connection with the cat's experiment.
(1) Would you assume that the result has the same definite result if it was performed last week? (it is in your past light cone).
(2) Would you assume it will have a definite result (which you'll eventually be able to discover) if it has not yet been done. It'll be done next week so you know it is in your future light cone.
(3) Would you assume it to have a definite result if it being done right now in distant planet like Pluto? (The event is space-like) You'll can't get any information about it until 4 hours from now with a signal traveling at the speed of light.

Yes to all.

 

[ThomasT]

Of course you could never see it directly to be in a superposition. But I was wondering if you would consider as possible that the experiment leads to some distribution of outcomes which is incompatible with the idea that the cat is in a difinite state of dead or alive right before measurement. This was done in order to prove that Bell's inequalities don't hold for quantum systems. (Alain Aspect, etc.) but that was for quantum systems, not for something assumed to be classical like a cat.
In your last sentence you point to an apparent imposibility of a dead/alive superposition. Well, if someone came up with a thought experiment (or actuall experiment) whose results seemed to imply a superposition of macroscopic states, then that would be clearly a paradox because on one hand you don't expect something like that as being possible and on the other you have this experiment that seems to imply that behavior.

I'm curious as to what sort of macroscopic phenomena you would consider to be incompatible with the idea that submicroscopic physical states are just as definite as macroscopic physical states.

I take superpositions of quantum states to be sort a formal expression of our ignorance regarding what's actually going on beneath the level of instrumental behavior. Bell tests don't tell us that the submicroscopic realm isn't real or doesn't exist or is in many different states at the same time. They do remind us that there's no comprehensive qualitative understanding of the submicroscopic realm, and this presents problems wrt formulating models of quantum experimental phenomena.

 

[zonde]

Would you consider the possibility that results of some future experiment might lead to the conclusion that some macroscopic object such as Schrodinger's cat is in a superposition of states? I think if that situation ever arised, it would imply a challenge to our idea of macroscopic realism. (At least it would be in the one-world view).

I would like to give answer to this question even if you addressed it to kote not me.

And my answer is yes, it happens all the time but you have to compare cases properly.
With properly I mean that realistic case must be similar to QM cases.

Consider such case:
Some cat breeding farm is breeding cats and they are dispatching cats in boxes where they have all that is needed for them like food and water. Boxes before dispatching are stored in yard from where they are taken to different general directions by transport company.
Number of boxes in this yard is constantly changing as new orders come in and new boxes are stored in yard and as boxes are hauled away.
However part of the cats die before they are hauled away. So some office worker is set to the task to investigate what can be done about it. First thing this person does is he collects some information about statistics of dead cats in the yard. So he asks the other person responsible for the yard to count all the boxes and to count boxes with dead cats inside. He does not care about individual cases he wants only totals.
After collecting some numbers he finds out curious thing - there are more dead cats on average if the counting is done in the daytime and less if counting is done during the night.

The interesting question is - what is your reaction when you hear this case?
What would be your reaction when you have tested number of hypotheses about the reasons for this difference and have found out that they don't work?

 

[alexepascual]

I would like to give answer to this question even if you addressed it to kote not me.

And my answer is yes, it happens all the time but you have to compare cases properly.
With properly I mean that realistic case must be similar to QM cases.

Consider such case:
Some cat breeding farm is breeding cats and they are dispatching cats in boxes where they have all that is needed for them like food and water. Boxes before dispatching are stored in yard from where they are taken to different general directions by transport company.
Number of boxes in this yard is constantly changing as new orders come in and new boxes are stored in yard and as boxes are hauled away.
However part of the cats die before they are hauled away. So some office worker is set to the task to investigate what can be done about it. First thing this person does is he collects some information about statistics of dead cats in the yard. So he asks the other person responsible for the yard to count all the boxes and to count boxes with dead cats inside. He does not care about individual cases he wants only totals.
After collecting some numbers he finds out curious thing - there are more dead cats on average if the counting is done in the daytime and less if counting is done during the night.

The interesting question is - what is your reaction when you hear this case?
What would be your reaction when you have tested number of hypotheses about the reasons for this difference and have found out that they don't work?

My conclusion might be that the assumption that a cat can't be considered in a definite state dead or alive before we open the boxes. But the thing is that apparently nobody has ever found strange results like this at the macroscopic level.

 

[alexepascual]

I'm curious as to what sort of macroscopic phenomena you would consider to be incompatible with the idea that submicroscopic physical states are just as definite as macroscopic physical states.
I take superpositions of quantum states to be sort a formal expression of our ignorance regarding what's actually going on beneath the level of instrumental behavior. Bell tests don't tell us that the submicroscopic realm isn't real or doesn't exist or is in many different states at the same time. They do remind us that there's no comprehensive qualitative understanding of the submicroscopic realm, and this presents problems wrt formulating models of quantum experimental phenomena.

First, I would like to thank you for your unambiguous answers in your previous post.
To answer your question:
I think most people interpret Bell's tests as a proof of the imposibility of local hidden-variables for quantum systems. They prove that if you consider that one of the states under study to have a definite value before measurement, you run into difficulties.
I was first a little disoriented when reading your question. Now, after reading everything you wrote, I get the impresion that you advocate for a realist picture even at the microscopic level such as in the style of Bell and others. Is this correct? I know that there are some threads in this forum that deny the validity of Bell tests as proof of the imposibility of local hidden variables. Do you agree with that position?.
I am asking you this out of curiosity, but if that is the case, I would not want to get into a discusion of that topic in this thread as here I am trying to focus on macroscopic stuff.
But I would like to know your position with respec to this anyway.

 

[ThomasT]

First, I would like to thank you for your unambiguous answers in your previous post.
To answer your question:
I think most people interpret Bell's tests as a proof of the imposibility of local hidden-variables for quantum systems. They prove that if you consider that one of the states under study to have a definite value before measurement, you run into difficulties.
I was first a little disoriented when reading your question. Now, after reading everything you wrote, I get the impresion that you advocate for a realist picture even at the microscopic level such as in the style of Bell and others. Is this correct? I know that there are some threads in this forum that deny the validity of Bell tests as proof of the imposibility of local hidden variables. Do you agree with that position?.
I am asking you this out of curiosity, but if that is the case, I would not want to get into a discusion of that topic in this thread as here I am trying to focus on macroscopic stuff.
But I would like to know your position with respec to this anyway.

I think that Bell and others have shown that nonseparable quantum states can't be modeled as separable quantum states. Explicitly local, realistic models of nonseparable quantum states are ruled out (at least until somebody comes up with a way of mathematically expressing locality that is compatible with the statistical requirement of nonseparability).

Regarding your original post, I still can't figure out why anybody would not believe in macroscopic realism. Maybe I don't understand what you're trying to get at.

 

[RUTA]

I think that Bell and others have shown that nonseparable quantum states can't be modeled as separable quantum states. Explicitly local, realistic models of nonseparable quantum states are ruled out (at least until somebody comes up with a way of mathematically expressing locality that is compatible with the statistical requirement of nonseparability).

Regarding your original post, I still can't figure out why anybody would not believe in macroscopic realism. Maybe I don't understand what you're trying to get at.

As I said in post #4 of this thread, it is possible to have nonseparable, but local, reality via ontological structural realism (if you want to see a mathematical instantiation of this, see arXiv 0908.4348, start with sections 5 & 6 then decide if you need/want to read more). In that case one does not obtain macroscopic realism if understood per ConradDJ:

"To my mind the question is -- does an object exist, with determinate states and properties, independently of the web of physical interactions through which it makes a difference to other objects?"

 

[kote]

As I said in post #4 of this thread, it is possible to have nonseparable, but local, reality via ontological structural realism (if you want to see a mathematical instantiation of this, see arXiv 0908.4348, start with sections 5 & 6 then decide if you need/want to read more). In that case one does not obtain macroscopic realism if understood per ConradDJ:

"To my mind the question is -- does an object exist, with determinate states and properties, independently of the web of physical interactions through which it makes a difference to other objects?"

I would argue that separability and locality have to do with our "macroscopic" 3 (or 4) dimensions, so some outside computer or whatever, even if local in its dimensions, does not meet the locality criterion as it is usually meant.

 

[zonde]

My conclusion might be that the assumption that a cat can't be considered in a definite state dead or alive before we open the boxes.

Then you will be minority. Most of the people in their right mind will not assume something like that because life is dynamical process that can not be suspended in some state (with very few exceptions that border with complete suspension and can not really provide explanation for this case). And life is irreversible process.

But the thing is that apparently nobody has ever found strange results like this at the macroscopic level.

Apparently you are wrong. But most people will drill down the information until they force reality into situation or alternatively they will give up for practical reasons. And practical limit can be reached very fast because with each level of deeper information amount of information grows exponentially.
But in case of reaching practical limit some people will not give up realistic view anyways because there is wast amount of evidence that previously mystical cases are solved as technology has provided access to deeper levels of information. Some other people will attribute this to mysticism. But hardly any person will attribute this situation to modern science.

 

[Dmitry67]

It would be interesting if high-energy experiments can produce outcomes with negative probabilities. As we discussed in a separate thread, objects with properties with negative propabilities display some stgange behaivor. It is integesting how such negative probabilities decoherence with the macroscopic objects. It could be a test for the macroscopic realism.

 

[RUTA]

I would argue that separability and locality have to do with our "macroscopic" 3 (or 4) dimensions,

In the OSR example I cited above, "macroscopic reality" is all that exists, i.e., quantum entities (screened off, x and p don't commute) and the wave function from QM, particles and fields from QFT, don't have any ontic status.

so some outside computer or whatever, even if local in its dimensions, does not meet the locality criterion as it is usually meant.

I have no idea what this means.

 

[kote]

In the OSR example I cited above, "macroscopic reality" is all that exists, i.e., quantum entities (screened off, x and p don't commute) and the wave function from QM, particles and fields from QFT, don't have any ontic status.

I have no idea what this means.

Sorry... confused my threads. I read "nonseparable, but local, reality via ontological structural realism" as "separable..." and thought you were talking about the sort of idea that we could be living in the matrix and the computer controlling the matrix is local and separable.

 

[alexepascual]

It would be interesting if high-energy experiments can produce outcomes with negative probabilities. As we discussed in a separate thread, objects with properties with negative propabilities display some stgange behavior. It is integesting how such negative probabilities decoherence with the macroscopic objects. It could be a test for the macroscopic realism.

The concept of negative probability is interesting. I have thought about this before. However, it may not contribute anything new. Have you read any articles discussing the concept?
Without having read about it, I would assume that negative probability could be associated with destructive interference. Given the fact that addding state vectors gives you the correct result, with the added separate probabilities plus an interference term (which could be negative or positive), I don't see how visualizing the interference term as a probability (which it is of course) may add anything new.
Now, from what you said it appears you have read some article which discusses decoherence of negative probabilities. Now, if negative probabilities decohere when we transition from the microscopic to the macroscopic realm, wouldn't that be the same behavior as that of interference?
It would be nice to have some new idea that challenges (classical) realism at the macroscopic level, but I doubt it negative probabilities is it. I said "classical" realism because from the MWI point of view, realism is retained but not in the one-world universe but in the meta-universe that includes all branches. I have called this "super-realism" but that is a term I made up. It is easy to interpret what it means though for anybody who is familiar with the MWI.
Now that I think about it, there was a lot of reaction in this thread to my idea of separating macroscopic reality form microscopic reality. Some of the reaction was because some posters want to have a unified concept of reality (or no reality) that is applicable to both the macroscopic and the microscopic. They have talked about reality at a "fundamental level". Well it is interesting that the kind of realism implied in the MWI would provide exactly that unifying view (the wave function itself is considered real) , even though the details of how the whole scheme works are still to be discovered.
From the point of view of single-world interpretations, if some experiment implied (even if it could not detect directly) the existence of the other branches, then this would be to the single-world person a challenge to their concept of macroscopic realism.

 

[kote]

The concept of negative probability is interesting. I have thought about this before.

Was it on this forum that we talked about negative probability? It's one of those things in there with superpositions of states (although it's more clear for negative probability) in that it's in principle impossible to observe. Probability has an axiomatic definition confining it between 0 and 1. This is true for continuous and discrete definitions and for the common sense definition etc. An experiment is as likely to show negative probability as it is to show 2+2=5. It can't happen by definition. If you get a negative probability, you're doing it wrong.

 

[alexepascual]

Was it on this forum that we talked about negative probability? It's one of those things in there with superpositions of states (although it's more clear for negative probability) in that it's in principle impossible to observe. Probability has an axiomatic definition confining it between 0 and 1. This is true for continuous and discrete definitions and for the common sense definition etc. An experiment is as likely to show negative probability as it is to show 2+2=5. It can't happen by definition. If you get a negative probability, you're doing it wrong.

Let's see what Dmitry has to say about this.

 

[Dmitry67]

Here is a topic: https://www.physicsforums.com/showthread.php?t=331299
And here is a very good example: http://blog.sigfpe.com/2008/04/negative-probabilities.html

So objects with negative probabilities manifest like some weird objects with inconsistent properties

 

[alexepascual]

Here is a topic: https://www.physicsforums.com/showthread.php?t=331299
And here is a very good example: http://blog.sigfpe.com/2008/04/negative-probabilities.html

So objects with negative probabilities manifest like some weird objects with inconsistent properties

Thanks for the information. Maybe at some point I will consider looking into this concept a little deeper.