Understanding the Cat in a Box Paradox

[rcgldr]

Basically, there are two schools of thoughts.
1. Until you look, the cat is neither dead nor alive.
2. It is allways either dead or alive even if you do not look. But in this case, a sort of nonlocal communication between physical objects is possible.
At the moment, nobody knows with certainty which view is the correct one.

The cat does (at least a living one), plus there's the easy way. Just wait about 50 years, and you can assume the cat is dead, without ever receiving any information about what's in the box, other that you've been told that there's a cat inside. It's a poor analogy in my opinion.

From my point of view, there's only one reality, observed or not. As I've posted before, if a man makes a statement in a forest and even if there is no woman to hear him, all women will know that the man will still be wrong.

 

[Anonym]

if a man makes a statement in a forest and even if there is no woman to hear him, all women will know that the man will still be wrong.

It is not always so. See, for example, Beyond the Standard Model, “Gross Tel Aviv perspective on string” session, post #14.

Regards, Dany.

 

[ZapperZ]

Yes. Ask Him why. Gmar Hatima Tova!

Regards, Dany.

P.S. Everyday working experience and knowledge of math is required to have instant feeling what is right and what is wrong in the physical theory. If you do not understand something, ask Demy for example or many others here. Your inability to check yourself disturbs me. Why I should believe that you don’t behave similarly in performing your measurements? In addition, we need explanations of the fine features of the experiments in order to understand their true content and neither you nor other experimentalists here do that.

P.P.S. Perhaps, the explanation is: in order the hydrogen atom to be stable. Otherwise, it will be nobody to ask questions.

I'm not quite sure what the heck this is. I could easily say the same about your attitude.

I also have not dissed "knowledge of math", so I'm not sure why you are attacking me on this, especially when it is very clear to anyone who has followed my argument on why QM is so difficult for the general public to understand.

And guess what? I really don't have to impress you on my "ability or how I've done my measurements. My publication track record is more than sufficient, and EVERY work that I've done has been verified elsewhere.

And what do you think we've been trying to do here? I HAVE been trying to explain the "features" of the experiment by invoking what the theoretical description is saying. And I've cited similar interpretation done by reputable physicist (unless you don't think people like Tony Leggett is in the same league as you). The FACT that the superposition principle has been conventionally interpreted as having ALL of the properties existing simultaneously isn't MY private invention. For some odd reason, this issue has been severely ignored here.

Read that Leggett paper and read those Delft/Stony Brook experiments. If you believe they made a mistake in interpreting what they have concluded, then put your money where your mouth is and write a rebuttal! Till then, all your claims on here ring hollow.

Zz.

 

[ZapperZ]

From my point of view, there's only one reality, observed or not. As I've posted before, if a man makes a statement in a forest and even if there is no woman to hear him, all women will know that the man will still be wrong.

The problem here is that using that view, you can't explain or describe the existence of all those phenomena that I've mentioned already: the existence of bonding and antibonding, and existence of the coherence gap in the Delft/Stony Brook experiment, etc. Remember, these experiments tried not the actually measure Observable A, but rather measure Observable B that either do not commute with A, or are not contextual with A. This allows for a detection of the effect of the superposition of observable A. If A is really one a definite value even before measurement (what you claim having only "one reality"), then you will have a tough time to explain those experiments. I haven't seen anyone tried that.

Zz.

 

[Fra]

From my point of view, there's only one reality, observed or not.

This is intuitively natural view extrapolated from our experience with the macroscopic and classical world, but that intuition is deceptive when trying to extrapolate it to more general cases.

But if we take the view that an observation is to be treated on the same footing as interactions, one may ask what determines the responses of a particular observer, or what determines particle interactions. If you think that reality determines his response, then if reality is not known, how can it impact our responses?

The poker analogy is pretty good! What determines the actions of player A? It is certainly not the (to him hidden) cards of the other players! Player A makes his decision based on his *expectations* on what cards the others has. The TRUE cards never explicitly enters the dynamics.

This is why it makes perfect sense to me to expect that a particles behaviour is ultimately determined by the particles expectations on the environment, as the environment changes, so does the particles expectations. This is the dynamics.

How will the person outside the box act until it's opened? It's fully aware of the possibilities and will thus act and respond to the factual superposition of possibilities. So in a sense this superposition is real and I think it's stored in the observer microstructure, brain, state and whatever depending on the type of observer (human or not).

But like others have commented, one can observe other things too... vibration of the box etc. And then certainly the collapse will probably be a quick change rather than a discontinuity, but that is only possible if the observer are able to make sow high resolution observations. Suppose the observer is a simple flip/flop device, which can only be in two states. Then this observer does not have the complexity to absorb all the additional information in ambient disturbances. This is why I personally don't find that an acceptable explanation in the general case, while it's certainly valid in special cases.

/Fredrik

 

[Demystifier]

From my point of view, there's only one reality, observed or not.

QM is compatible with a possibility that there is only one reality. However, it is not compatible with the assumption that this reality is not affected by measurements. You can still say that reality does not depend on observation, provided that you make a clear distinction between measurement and observation.

 

[Fra]

You can still say that reality does not depend on observation, provided that you make a clear distinction between measurement and observation.

What would you propose this distinction be?

/Fredrik

 

[Demystifier]

What would you propose this distinction be?

Observation involves conscious beings, while measurement does not. Measurement only requires a physical measuring "apparatus", which may or may not be constructed by humans.

 

[Fra]

Ok, I see your perspective.

Personally I don't make a fundamental distinction between a human and a measuring apparatous. I like to think that the difference is one of complexity, and a matter of communication likes aside.

/Fredrik

 

[OOO]

Observation involves conscious beings, while measurement does not. Measurement only requires a physical measuring "apparatus", which may or may not be constructed by humans.

I haven't followed the whole thread, so forgive me any misunderstanding. But isn't this distinction between measurement and observation the state of the art for interpreting quantum mechanics ?

I think no serious experimentalist will claim today that the result of his experiment depends on him observing the apparatus all the time. What should observation mean in this case ? Looking at a computer screen ? Looking at the shiny metal of a vakuum chamber ? Looking at the desk ? Moreover, would our poor experimentalist dare to take a coffee break and leave his apparatus unattended ?

On the other hand, if you get caught in your car for violating the speed limit, the judge will certainly believe you if you say you were in some alternate reality because you did not pay attention to your speedometer...

In my opinion it is quite obvious that quantum mechanical measurement means the physical process that takes place in the apparatus independent of any observer. Have I missed the point ?

 

[Demystifier]

OOO, I agree with you. Still, many serious physicists, including experimentalists, do not. I think A. Zeilinger would be an example.

 

[Demystifier]

Ok, I see your perspective.

Personally I don't make a fundamental distinction between a human and a measuring apparatous. I like to think that the difference is one of complexity, and a matter of communication likes aside.

Actually, I agree with that, provided that a human is also viewed as a physical object. But I make a difference between a human as a physical object and a human as a conscious being. In my opinion, the latter concept cannot be explained in physical terms, at least not yet.

 

[f95toli]

f95toli,

You seem to be using decoherence as a mechanism to remove any superposiiton, and thus collapse the cat's wavefunction. My understanding is that decoherence simply renders the alive and dead states in the superposition incoherenet, so that they no longer interact. world. What are you suggesting really happens, or are you not worried about this?

I think it depends on the description you are using. If you consider a two-level system interacting with a heat bath (which can be bososnic, i.e. ANY form of electromagnetic environment, including thermal fields; you can also easily generalize this in which case the interference terms are all terms n \neq m ) the effect of decoherence is to make the off-diagonal elements go to zero, i.e. you end up with a diagonal density matrix (strictly speaking one should also differentiate between energy relaxation and pure dephasing since this is important experimentally, but never mind).
Note that I am talking about decoherence due to the ENVIRONMENT now, NOT ordinary measurements (however, these system-bath interactions can be interpreted as indirect, ideal measurements; but these are still very different from "opening the box").

Chapter 4 in "The Theory of Open Quantum Systems" by Breuer give a very good overview of the field.

Whether or not I care depends on if I am in the lab or not. In the lab my main concern is to make sure that the system I am measuring is coherent long enough for me to get the information I want; what happens when the system collapses is irrelevant. Hence, whether the MW interpretation is correct or not has, in my opinion, nothing to do with physics UNLESS someone can come up with a way to test it in an actual experiment.
This does not mean that it is not interesting; but in my view all "interpretations" to date have more to do with philosophy than physics (unless they can be tested, at least in principle).
I guess you can say that I (like most experimentalist I know) use Poppers "definition" of a scientific theory, if can't be measured it ain't science.

 

[f95toli]

If you deny the experimental evidence of the collapse, you are simply crazy. The question is not whether it exists but when and where it occurs, when and where the space-time dispersion shrinks to the point.

I am not denying anything. The "collapse" is very real to me (although I don't really like this language) since the systems I work with are only useful BEFORE they collapse.
However, there was, for a long time a discussion about whether or not system with macroscopic degress of freedom (i.e. composed of 10^23 particles) could exhibit quantum coherence or not. This was not settled until the mid-eighthies when the first (conclusive) experiments on macroscopic quantum tunneling were done (using Nb Josephson junctions which are quite big, around 10x10 microns).
Conceptually, there is a big difference between an atom or a molecule (or a field) and an electronic component so big that you can actually see it.
Moreover, these experiments were done just after the Caldeira-Legget formalism had been published, meaning there was a theoretical framework in place that could be used to analyze the data (in the case of a MQT the dissipation can be modeled as a shunting impedance, which is nice since this means that you can make a direct connection between coherence and the quality factor of the Jospehson junction).

There is something called the Legget criterias that can be used to distinguish between macroscopic quantum coherence and classical systems, I am not sure how well known these are but they are described in one of the books I have on macroscopic quantum tunneling (the book by Takagi).

 

[nrqed]

So an electron that is in an H2 molecule is neither near one H atom, nor the other.

Where is the electron that somehow has formed the bonding or antibonding? It has formed it, but it isn't here nor there!

And you found this to be "better"?

Zz.

I personally feel that insisiting that the electron that formed the bonding has to be here or there is to insist on keeping a classical point of view. I would say that no, the electron that forms the bonding is not here or there, it is in this strange quantum superposition which is not well represented by saying "the electron is there and here". The electron is simply in this straneg quantum state which cannot be conveyed, in my opinion, in an appropriate way by simple words other than saying, as I mentioned, that the electron has the potentiality of being observed here or there. But before the observation is made, I feel that saying that the electron is "both here and there" does not convey adequately the meaning of a quantum state. The electron is neither here nor there (in the usual sense of something "being here" or "there"!).

If I would teach "the electron is both in a spin up and spind own state and then I make a measurement and I observe it in the spin up state"

and a student would ask me

"but before the measurement was made, the electron was both in a spin up an dspin down state so did it "stop" being in a spin down state?"

I would feel that the description of being both in a spin up and spin down would have incorrectly conveyed the situation.

But it's a question of semantics so there is not much point arguing. If you feel that describing the electron as being both spin up and spin down is a fair description of a quantum linear superposition, I can't say much more than I disagree. we have to agree to disagree.

Best regards

Patrick

 

[Anonym]

First of all, I want to be clear: I consider the experimental and theoretical investigations of the interconnection between the micro/meso/macrosystems most interesting development in QM today. However, your statements look to me as the decoherent mixture of facts and personal interpretations. For example:

Someone should perhaps point out that the "cat in a box" is a higly idealized gedanken experiment. A real cat would always be EITHER dead or alive inside the box, regardless if you open it or not.

The reason is that any object the size of a real cat is an open quantum system meaning it couples to the environment. Hence, it can never be in a superposition of dead/alive for very long (its "wavefunction" will decay extremely fast).

That “highly idealized gedanken experiment” was performed by famous American experimentalist at the beginning of 20 century in order to clean mass spectrometer. The second statement is correct. The third is obviously wrong. The fourth does not follow from the previous and is clearly the interpretation. And so on.

As far as I remember the cat "paradox" was orignally an attempt by Schrödinger to show how absurd QM was, i.e. he was implying that there must be something fundamentally wrong with the theory.

E. Schrödinger wrote:

” That prevents us from so naively accepting as valid a "blurred model" for representing reality. In itself it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.”

My point is that the cat "paradox" is not really a problem in physics anymore (and I don't think it ever was), in part simply because we got used to the idea; nowadays we instead use these effects to build useful devices. There are obviously quite a few philosophical issues, but these are largely irrelevant to the science…

I am not denying anything. The "collapse" is very real to me (although I don't really like this language) since the systems I work with are only useful BEFORE they collapse..

The purpose of my investigation is to make them useful after the collapse also. There is nothing in physics that interesting me more than what you are doing. I repeat: please, present clearly what you measure, how you measure and what are the obtained results. Please leave your explanations, philosophy and interpretations to others.

I guess you can say that I (like most experimentalist I know) use Poppers "definition" of a scientific theory, if can't be measured it ain't science.

I consider A.Einstein give a better advice for the physicist:

”Probably, I used the philosophy of that kind, but it nevertheless rubbish. Or, speaking more carefully, the remembering of what we are really observes and what we do not has probably some heuristic value. However, from the principal point of view, the attempt to formulate the theory based only on observable quantities is completely nonsense. Because in the reality everything that happens are just an opposite. Only the theory itself can decide what is and is not observable. You see, the observation, generally speaking, is very complicated notion…”

Regards, Dany.

 

[shaun_o_kane]

I think you guys miss the point of the "paradox". The equations of Quantum Mechanics say that the waveform describign the cat is in a state of half-alive and half dead. So the question is not what state the cat is in but what is the meaning of the waveform. Their is a problem only if you say that the half-dead / half-alive waveform => half alive / half dead cat.

 

[lightarrow]

Repeating the experiment many times, half of them we find a dead cat, half of them an alive cat. There's nothing more than this. The state of the cat is not changed by the experimenter opening the box, but by the interaction between the particle emitted from the radioactive substance and the detector. Before that event, the cat is alive; if that happens then the cat dies. No cat-superpositions.

 

[cesiumfrog]

No cat-superpositions.

On what basis do you make this claim?

 

[Fra]

Repeating the experiment many times, half of them we find a dead cat, half of them an alive cat. There's nothing more than this.

I personally don't find this definition sufficiently sophisticated.

This objections starts with the definition of probability itself in relation to reality. Repeating the experiment many times, raises at least three issues

1) To what degree of certainty can we guarantee that the experiment is indeed identical? Is the "certain enough" really satisfactory in the general case? I think not.

2) What about time? Repeating the experiment many times, gives us still an uncertainty in the measured true probability. And repeating the experiment infinitely many times is certainly impractical to the point of beeing ridicilous. This implies some kind of uncertainty relation at minimum.

3) What is the memory record utilized to store the potentially data infinite amount of data? Infinite storage capacity to store the correlations leads to the other absurdity. What happens to this description if we consider the memory records to have dynamical information capacities? Perhaps some observers can make observations at higher resolution due to higher complexity?

These issues does not have anything specifically to do with QM, but it relates more generally to probability theory coupled to reality, where we expect all notions to be induced from real interactions, and thus stored in real structures. Limited complexity can not possibly contain any infinite memory records, or infinitely resolved continuums? Or can it? If so, I would like to see a better argumentation.

This is one of the issues I see rooted in the QM interpretations.

/Fredrik

 

[Fra]

This was just my personal thinking and is in line with the reviews I'm personally doing, I'm sure many on here will strongly disagree.

These kind of questioning of QM foundations, interestingly also probably provides a fundamental connection to gravity. One unavoidably are lead to consider information capacities which gives a more or less intuitive connection to the generic concept of inertia which seems to give a first principle angle to the concepts of energy and mass. I think it has been a mistake to ignore the foundations for to long time. I don't see why a foundations historically seen to be reasonable satisfactory for major parts of particle physics (=special case), is necessarily solid enough for a unified theory for the general case, including not only gravity but also systems of arbitrary complexity.

/Fredrik

 

[Anonym]

On what basis do you make this claim?

Since the cat is the detector.

Repeating the experiment many times, raises at least three issues

1) To what degree of certainty can we guarantee that the experiment is indeed identical? Is the "certain enough" really satisfactory in the general case? I think not.

2) What about time? Repeating the experiment many times, gives us still an uncertainty in the measured true probability. And repeating the experiment infinitely many times is certainly impractical to the point of beeing ridicilous. This implies some kind of uncertainty relation at minimum.

3) What is the memory record utilized to store the potentially data infinite amount of data?

You will obtain the answers to your questions reading A. Tonomura et al, AJP, 57, 117 (1989). If you are curious enough.

Regards, Dany.

 

[Fra]

I will try to locate that article.

/Fredrik

 

[Fra]

I find nothing in arxiv, but it seems to be for sale at ajp website. Though seeing just the abstract it's not clear in what sense if might supply the answer to the above questions?

Of course there is sufficient memory in the environment to act as a record, but then the entire environment (ie the reminder of the universe) is the observer, which hardly makes sense either.

Does aynoone know if there's a preprint of this somewhere? It seems these older (pre-www) papers are usually hard to find in the free preprint archives.

/Fredrik

/Fredrik

 

[lightarrow]

On what basis do you make this claim?

According to one of the many possible interpretations, which I'm asserting now, the wavefunction collapse happens before the cat, between the radioactive substance and the detector (which then breaks the tube with poison). According to this interpretation, that interaction is the irreversible event, that is, the measure.
Of course it leave unanswered the question: what does "irreversible" mean and where this exactly happens? In my opinion irreversibility is the key point.

 

[shaun_o_kane]

Since the cat is the detector.

You will obtain the answers to your questions reading A. Tonomura et al, AJP, 57, 117 (1989). If you are curious enough.

The cat is a quantum system, not the detector. It should therefore be in a superimposition state according to QM. Is this supposed to be the paradox at the heart fo the measurement problem?

 

[cesiumfrog]

According to one of the many possible interpretations, which I'm asserting now, the wavefunction collapse happens before the cat, between the radioactive substance and the detector

Ah, yes. That was a popular take on the Copenhagen interpretation: that a collapse occurs when a microscopic quantum system interacts with a macroscopic classical system. Very pragmatic. Its main advantage seems to be that it says nothing new about the observer, but it also says very little about the collapse process it assumes.

It additionally has an obvious flaw, which is that in principle every (simple) macroscopic classical system can also be described as a (complicated) microscopic quantum system. If we were to write down a Hamiltonian for the (complicated) detector interacting with the atom, and numerically solve its Schroedinger equation, we would expect to always find the detector in a superposition state, in contradiction to your prior assertion. And indeed, experiments have demonstrated that large numbers of atoms can behave as a quantum-mechanical system. Do you reconcile this?

 

[Anonym]

Guys ... come on! We invented mathematics to make words less slippery!

Actually, I have nothing to add; perhaps, only to discuss the interconnection between the math and the physics.

The linear superposition of states is the mathematical property of the Schrödinger picture. It was not clear (1926-1935) what it means physically. However, E. Schrödinger demonstrated the mathematical equivalence of his and W. Heisenberg picture. In the Heisenberg picture it is translated into HUP and provide the clear definition what the QM system is: delta (A)*delta (B)>0. Also it provide the “clear” definition what the classical (macroscopic) system is: delta (A)*delta (B) = 0 (John von Neumann). And in CM every system is detector. Notice, however, that the notion of the dynamical variable as the self-adjoint operator is not defined in the Newtonian/Hamiltonian formulation of the classical physics.

Now, we know that the macroscopic system is the statistical ensemble of the microscopic subsystems. The transition from QM to CM (delta (A)*delta (B)>0 => delta (A)*delta (B) = 0) is called “the collapse of the wave packet”, that is, uses the Schrödinger picture. Physically it means that the system extended (“blurred”) in QM is imaged by the material points in CM (E. Schrödinger Cat).

Why the transition express itself as the collapse (A.Einstein, 5-th Solvay), whether the linear superposition property remains valid in CM and when and where it takes place (mesoscopic systems) – that is the Measurement Problem.

In my posts #51, #62 and #106 I referred to A.Einstein to demonstrate that he knew what going on precisely, he only didn’t know to say that mathematically.

Regards, Dany.

 

[lightarrow]

Ah, yes. That was a popular take on the Copenhagen interpretation: that a collapse occurs when a microscopic quantum system interacts with a macroscopic classical system. Very pragmatic. Its main advantage seems to be that it says nothing new about the observer, but it also says very little about the collapse process it assumes.

It additionally has an obvious flaw, which is that in principle every (simple) macroscopic classical system can also be described as a (complicated) microscopic quantum system. If we were to write down a Hamiltonian for the (complicated) detector interacting with the atom, and numerically solve its Schroedinger equation, we would expect to always find the detector in a superposition state, in contradiction to your prior assertion. And indeed, experiments have demonstrated that large numbers of atoms can behave as a quantum-mechanical system. Do you reconcile this?

Are you saying that QM can't describe irreversible processes?

 

[shaun_o_kane]

I'm afraid cesiumfrog is wrong. Copenhagen does not say QM waveform "collapses" as a result of the interaction with a macroscopic system. Copenhagen say that you can choose the quantum-classical boundary anyway you want, typically at the interaction with macroscopic measurement devices. Hence the paradox. Two views are possible: the cat is the measurement device (classical-quantum boundary) and the waveform "collapses" (not a Copenhagen term) at the cat, or the external observer is the measurement device (classical-quantum boundary).

Copenhagen is simply applying the equations differently but equally validly.