Understanding the Cat in a Box Paradox

[ZapperZ]

What does it mean? Are 8 and -1 also both there in 7? Is any number there in any other number?

Then you are missing the entire point of my original question to you if something as direct as this is "mystifying" you.

There are two separate points here that needed to be repeated:

1. Your claim that "neither x nor y" is identical to "both x and y".

2. That the mathematical equation representing the superposition of state such as $\psi = a_1|x> + a_2|y>$ can accurately be described as "neither x nor y".

What you have been trying to argue so far with these number games is #1. This is a logical fallacy. Those 2 statements are not identical, no matter what kind of "interpretation" you wish to use. Try telling someone that A is neither in that room, nor in this room. Do you think that is the same as saying A is both in this room and in that room? It is not!

As for #2, I have already pointed out the weirdness by bringing out examples using the H2 molecule and the double slit. If that equation implies "neither x nor y", then the system does NOT have the property of x and y. When we apply that to the double slit, we are then saying the particle did not pass through the left slit nor the right slit. Yet, we detect a particle on the other side of the slit. How did that happen? By magic? This scenario creates MORE problems than saying the particle passed through BOTH slits. At least there' now no question on why we would detect the particle on the other side.

Again, I asked you for sources that actually adopts your wording and interpretation. I had presented to you my sources out of respect for your knowledge in such matters, rather than just claim something without justification. I would hope that you'd reciprocate in similar manner.

Zz.

 

[cesiumfrog]

Sheesh, get a room.

It's a purely grammatical debate: Zz is saying it's in a superposition. Demy is agreeing it's state is not equal to the first eigenstate, and neither is it's state the second eigenstate. I don't think anyone needs to cite a source for that.

 

[Demystifier]

1. Your claim that "neither x nor y" is identical to "both x and y".

2. That the mathematical equation representing the superposition of state such as $\psi = a_1|x> + a_2|y>$ can accurately be described as "neither x nor y".

No, I do not claim that. In particular, I do not use words "identical" and "accurately". I agree with cesiumfrog that this discussion becomes pointless.

 

[Demystifier]

When we apply that to the double slit, we are then saying the particle did not pass through the left slit nor the right slit. Yet, we detect a particle on the other side of the slit. How did that happen? By magic?

Well, if you do not accept the existence of hidden variables, then "magic" is the best explanation that remains.

 

[lightarrow]

Well, if you do not accept the existence of hidden variables, then "magic" is the best explanation that remains.

Or that the particle doesn't exist from source to detector.

 

[reilly]

StatusX

There's a difference between classical probability "superpositions", in which we quantify our lack of complete knowledge of the system by expressing the system as being in a sort of probability weighted average of different states, and a quantum superposition. For one thing, the quantum superposition is assumed to not be due to a lack of knowledge, but is an intrinsic feature of the world. And more importantly, it is only in quantum mechanics that the different constituent states can "interfere" with each other, and affect the outcome of measurements.

For example, say we want to determine the expectation value of an observable O for a system in a superposition (A+B)/2 of two states A and B. Classically, if the values for each state are O(A) and O(B), then the expectation value for the superposition is just (O(A)+O(B))/2. However, for quantum mechanical superpositions, there is also a term of the form <A|O|B>, and this will affect the probabilities in a non-trivial way (in fact, this is essentially where the strangeness of quantum mechanics comes from).

The degree of this interference is determined roughly by the overlap (scalar product) of the different states, and in the limit of a macroscopic system, there are so many degrees of freedom that different states that are likely to come up in a superposition are almost certainly nearly orthogonal, and the expectation values computed quantum mechanically reduce to their classical values (ie, with no cross terms).

Personally, I think the only way to avoid an arbitrary distinction between big and small is to assume that macroscopic systems can be in superpositions, just ones whose consituent states don't interact (because of negligible overlap) but evolve independently, ie, a many worlds view.

Let's take a careful view of probability. First, it is part of the language of physics. Why? It's a very useful tool in many branches of physics and engineering, and has been so for at least a few hundred years. In contrast, until modern QM arrived, Hilbert Space methods were considered to be of little use, and so few people put Hilbert into their bag of tricks. My how things have changed.

Mathematicians develop probability as a branch of measure theory for a space of so-called events -- a win, drawing a certain hand in poker, measuring an electron arriving at some point in a double-slit experiment, will there be a recession in three months, and so on. Nowhere in the theory is there any restriction of application. If the shoe fits, ...

This abstract approach tells us that classical and quantum probabilities are generically the same -- they both can be described by dynamical equations for the probablity distribution-- the differences between the details, like interference phenomena, are due to the different dynamics, and to generally different initial conditions.

In fact, in at least one case the quantum and classical probability distributions are identical -- the Rutherford cross section for an electron scattering from a positive point charge at low energies(target at rest)can be derived, as Rutherford did, strictly from classical electrodynamics and mechanics. And the exact same cross section can be derived from non-rel QM. Note that scattering is defined experimentally, as events: a counter indicates yes or no, yes, an electron hit the target. The resulting set of events defines a distribution, which when properly normalized, is a probability distribution in an abstract space of scattering events. That space could care less whether the events are described by QM or classical theory. It makes no difference whether the need for a probability description is due to a lack of knowledge, or is required to make sense of a theory, or involves a highly complex system -- perhaps many components,a gas for example, or the non-linear dynamics that might describe economic phenomena

There are plenty of opportunities for interference phenomena outside of quantum physics. When I play the piano and I play middle C, I create a superposition of piano states, basically the overtone series. Changing the overtone structure, changes the sound of the note. In extreme cases, beats are produced, generally caused by two interfering vibrations. Young's experiment is nicely explained classically. Most communication transmitted by electromagnetic means involves superposition of various frequencies, like sidebands "carried" by a carrier wave. The polarization of light, a rowboat crossing a river with a downward current involve superposition The description of anything by a vector space or vector field involves superposition. We use a lot of vector concepts in physics to explain a huge range of phenomena.

Finally, don't forget that QM is weird because it was developed to describe, if not explain some very strange phenomena -- atomic spectra, electron diffraction, the Stern-Gehrlich experiment, and so on. Indeed, QM is the child of experiments.

Regards,
Reilly Atkinson







'

 

[f95toli]

StatusX


This abstract approach tells us that classical and quantum probabilities are generically the same -- they both can be described by dynamical equations for the probablity distribution-- the differences between the details, like interference phenomena, are due to the different dynamics, and to generally different initial conditions.

'

But there are some major differences. First of all the "probabilistic" nature of quantum mechanics only comes into play when we want to MEASURE something (neglecting the effect of dissipation for the moment), as long as a system is left to evolve on its own it is complettely deterministic; this is why we can use superposition to build quantum computers and in other QIP applications.
Real systems are of course always open meaning we still usually need to use statistical quantum mechanics to predict the outcome of experiments, but that is a "technical" detail which rarely changes any qualitative properties of a system; the only difference between Rabi oscillations in a closed and an open system is that they are attenuated in the latter, but there are still oscillations and the basic physics is the same.

 

[StatusX]

This abstract approach tells us that classical and quantum probabilities are generically the same -- they both can be described by dynamical equations for the probablity distribution-- the differences between the details, like interference phenomena, are due to the different dynamics, and to generally different initial conditions.

It's true that the dynamical equations could both be written in matrix form, but for a classical system the relevant matrices would all be diagonal, showing that the matrix approach is not really necessary, just a means to organize information. In a quantum system, the non-zero off-diagonal terms are completely unexpected from a classical point of view, and show that the superpositions are not merely formal devices but real physical features.

There are plenty of opportunities for interference phenomena outside of quantum physics...

This is true, and the strange thing about quantum mechanics is not really the vector space structure, but the accompanying wavefunction collapse (and more generally, with reconciling the quantum and classical descriptions of the world). Without this, quantum mechanics would just be another classical field theory, the fields being the probability distributions. But in observing, say, the position of a particle, the wavefunction collapses to a delta function, giving the appearance of a particle underlying the field. For example, in the double slit experiment, the interference fringes are not strange in themselves, what's weird is that they appear as a cummulative affect after many single particles strike specific places on the screen.

The reason I addressed your post was because it seemed you were suggesting the schrodinger cat paradox had nothing to do with quantum mechanics. It's true that before quantum mechanics, people could have imagined a similar experiment with, say, a coin flip rather than radioactive decay, and ask what the state of the cat is before we observe it. But this would just be idle philosophizing - there's no practical problem here.

The difference in the case where we have a quantum superposition is that the dynamical equations imply that a microscopic superposition, which isn't really much stranger than, say, a superposition of overtones on a piano note, should evolve into a superposition of macroscopic objects, which is something very strange, and not something we seem to observe. The cat paradox is designed to expose this problem.

 

[f95toli]

The difference in the case where we have a quantum superposition is that the dynamical equations imply that a microscopic superposition, which isn't really much stranger than, say, a superposition of overtones on a piano note, should evolve into a superposition of macroscopic objects, which is something very strange, and not something we seem to observe. The cat paradox is designed to expose this problem.

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.
Now, first of all, as I have already pointed out we now DO understand why this never happens to real cats; the theory of open quantum systems as well as measurement theory is now so well developed that there is no real mystery anymore. Hence, there is no 'paradox'.

Secondly, we DO observe superposition in macroscopic objects. E.g. superconducting qubits might not be very large but they are certainly macroscopic (a few square microns, you can easily see a flux qubit in an ordinary optical microscope). The interesting thing with modern QIP (=quantum information processing) is that it has taken many problems from the realm of philosophy to what is basically engineering: in order to observe superpositions in a real experiments on superconducting qubits we use good magnetic shields, low noise amplifiers and a lot of filtering; in order to stop the "collapse" (i.e. increase the coherence time) we design the environment of the qubit in such a way as to maximize the impedance it sees (basically microwave engineering) etc. Hence, there is nothing particulary 'esoteric' about QIP anymore. I suspect many of the things we do in the lab nowadays would have shocked Schrödinger.

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.
It is worth remembering that thermodynamics and Newtonian mechanics also got their fair share of issues but these are rarely talked about nowadays, simply because we take those theories for granted.

 

[StatusX]

Now, first of all, as I have already pointed out we now DO understand why this never happens to real cats; the theory of open quantum systems as well as measurement theory is now so well developed that there is no real mystery anymore. Hence, there is no 'paradox'.

In what sense has it been resolved? There's no dispute about the predicted observations in the Schrodinger's cat experiment: there is a certain chance we'll observe the cat to be alive and a certain chance its dead. The thought experiment is meant to address issues of interpretation, and I'm pretty sure there's nothing approaching a consensus on the correct interpretation of quantum mechanics. As I said above, I take the thought experiment to most naturally lead to a many worlds interpretation, but not everyone would agree with me (and not everyone wouldn't). And this is probably not just philosophy, as its likely we'll need to have a firm grasp of what quantum mechanics really means (not just predicts) before we can move beyond it to a unified theory.

 

[f95toli]

The thought experiment is meant to address issues of interpretation, and I'm pretty sure there's nothing approaching a consensus on the correct interpretation of quantum mechanics.

I agree. But the point I was trying to make was that originally quite a few people actually DID think that a real cat would be in a superposition of states, it wasn't merely a gedanken experiment. You can find quite a lot of older (and some newer) texts that go on about the role of a rather mysterious "observer" that apparently caused the wavefunction to collapse etc.
Dissipation, measurement theory etc are relatively new topics in QM so the concept of decoherence was rather mysterious for a long time (and is still not fully understood).

Hence, while it is true that there is no consensus about the interpretation of QM I think it is fair to say that quite a few PRACTICAL issues relating to what you can actually observe in an experiment have been sorted out during the past 20 years or so.

Moreover, I am not quite sure I agree that I believe it is all that important to understand what QM really "means", at least not from a scientific point of view. To me physics is all about predicting what I can measure in the lab (I am an experimentalist, in case you haven't guessed that already), the rest is philosophy which means that there is little hope of ever reaching a "correct" answer (but it can still be interesting).

 

[cesiumfrog]

the point I was trying to make was that originally quite a few people actually DID think that a real cat would be in a superposition of states

Quite a few still do. Do you have any evidence that they are incorrect?

 

[Anonym]

Can you cite for me any papers that actually adopted your interpretation of this scenario?

E. Schrödinger, Ann. Physik, 79, 361,(1926); 79, 489,(1926); 79, 734,(1926);80, 437, (1926); 81, 109,(1926).

Regards, Dany.

 

[Anonym]

It's no big deal to describe the Cat problem in the terms of classical probability theory, which is why I've written numerous time that the Cat problem has precious little to do with QM.

Please, provide the reference. It would be highly appreciated if you will give M&W or somebody rank 1 or 2 in Landau classification.

Regards, Dany.

 

[Anonym]

It's true that the dynamical equations could both be written in matrix form, but for a classical system the relevant matrices would all be diagonal, showing that the matrix approach is not really necessary, just a means to organize information. In a quantum system, the non-zero off-diagonal terms are completely unexpected from a classical point of view, and show that the superpositions are not merely formal devices but real physical features.
This is true, and the strange thing about quantum mechanics is not really the vector space structure, but the accompanying wavefunction collapse (and more generally, with reconciling the quantum and classical descriptions of the world). Without this, quantum mechanics would just be another classical field theory.

And without the collapse the classical field theory would just be another quantum field theory.

what's weird is that they appear as a cummulative affect after many single particles strike specific places on the screen.

Wrong. Read P.A.M.Dirac and A.Tonomura.

The reason I addressed your post was because it seemed you were suggesting the schrodinger cat paradox had nothing to do with quantum mechanics. It's true that before quantum mechanics, people could have imagined a similar experiment with, say, a coin flip rather than radioactive decay, and ask what the state of the cat is before we observe it. But this would just be idle philosophizing - there's no practical problem here.

The difference in the case where we have a quantum superposition is that the dynamical equations imply that a microscopic superposition, which isn't really much stranger than, say, a superposition of overtones on a piano note, should evolve into a superposition of macroscopic objects, which is something very strange, and not something we seem to observe. The cat paradox is designed to expose this problem.

Precisely. But then you contradict yourself. Then you will observe Rabi oscillations in the single particle macroscopic system.

Regards, Dany.

 

[Anonym]

Hence, there is nothing particulary 'esoteric' about QIP anymore. I suspect many of the things we do in the lab nowadays would have shocked Schrödinger.

I am sure the opposite. E. Schrödinger would have pleasure.

To me physics is all about predicting what I can measure in the lab (I am an experimentalist, in case you haven't guessed that already)…

The theory of open quantum systems as well as measurement theory is now so well developed that there is no real mystery anymore. Hence, there is no 'paradox'.

For your information, the Theoretical Physics is the theory of closed systems since Copernicus/Galileo Postulate of Relativity is the Principal Physical Postulate.

You completely correct in all your statements, but “unfortunately” the results of your measurements will be useless since you can’t convince anybody that they are correct. You need another lab to confirm your results. But if you claim that that lab has the same environment, nobody will believe you (it is simply wrong).

For information of all respectable contributors in the discussion, I reproduce A.Einstein notion and definition of the objective reality. I guess that A.Einstein even had no chance to read EPR paper before publication. If some stupid idiot taught and convinced you something different when you were students, you were bad students.

f95toli don’t worry, the job done. We did it (I am a math-ph, in case you haven't guessed that already)

Regards, Dany.

P.S.

in order to stop the "collapse" (i.e. increase the coherence time)…

What is the value of the experimentally measured time of the wave packet collapse? I hope you are not talking about gedanken measurements.

 

[f95toli]

Quite a few still do. Do you have any evidence that they are incorrect?

Well, if you use the same type of calculations you would use to estimate the coherence times of a qubit on a real cat (or rather an object the size of a cat) you will find that the time is extremely short; it is just too big to be insulated from the enviroment. Hence, you can't use cats to e.g. implement quantum gates. The fact that we can't KNOW if the cat is dead or alive until we open the box is to me (and I think most physicists) irrelevant from the QM point of view.
One can of course just add the condition that the cat IS insulated (using some mysterious technique) from the environment to the gedanken experiment, and then the cat would actually be in a "real" superposition. However, this could never be observed in a real experiment. Hence, the "cat paradox" is only a paradox if you add conditions that are unphysical. It is still an interesting philosophical problem, but I can't see it being very relevant to physics anymore.

As I pointed out above wa CAN observe superpositions in macroscopic objects in the lab, but only in systems that can be reasonably well decoupled from the environment; this means that we are now sure that there is no strange "transition" from QM on the microscopic level (atoms) to classical physics on at the macrosopic level (cats).

 

[Anonym]

it is just too big to be insulated from the enviroment...One can of course just add the condition that the cat IS insulated (using some mysterious technique) from the environment to the gedanken experiment.

It is quite new for me that the M.Faraday cage and A.Einstein free falling lift are mysterious experimental apparatus. And it is not clear what else your environments are.

Regards, Dany.

 

[StatusX]

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. When we observe the cat, we become entangled with its state in the following way:

|scientist before>(|alive cat> + |dead cat>)

evolves unitarily into:

|happy scientist>|alive cat>+|sad scientist>|dead cat>

Since these two wavefunctions are incoherent, they evolve independently, as if the other didn't exist. In other words, we get a many worlds interpretation, simply by denying that collapse ever occurs and acknowledging the effect of decoherence. Decoherence by itself does not cause real collapse, only an observed collapse in each world. What are you suggesting really happens, or are you not worried about this?

 

[reilly]

Reference: Private communication from Prof. R. Atkinson -- retired.
Regards,
Reilly Atkinson

Please, provide the reference. It would be highly appreciated if you will give M&W or somebody rank 1 or 2 in Landau classification.

Regards, Dany.

 

[Anonym]

Reference: Private communication from Prof. R. Atkinson -- retired.
Regards,
Reilly Atkinson

Not approved. We need you.

Regards, Dany.

 

[reilly]

I'll get back to issues of interpretation, collapse, and states in a later post. Here I will revert to my old status as a physics professor, sometimes a picky one. First, notions of dissipation in QM are hardly new. The QM fluctuation-dissipation theorem of Callen and Welton was published in 1951. Leon vanHove was writing about dissipation effects in QFT at the same time.

In fact, there is a consensus about the interpretation of QM among physicists that are involved with experiments. They all go with what might be called the pragmatic Bohr-Born interpretation. That is, the core element of that approach is the Born probability postulate. Why, Born is alive and well in EPR and "Bell" experiments -- one uses probabilities of measuring "off axis spins" in precisely the fashion that Born requires. Further, this pragmatic interpretation has been around a very long time as can be inferred from old texts -- Schiff, Kemble, Condon and Shortley, Mott and Massey, ... It's been the best game in town for a long, long time -- no one, as yet, has come up with a better alternative. Who knows what the future holds

I agree. But the point I was trying to make was that originally quite a few people actually DID think that a real cat would be in a superposition of states, it wasn't merely a gedanken experiment. You can find quite a lot of older (and some newer) texts that go on about the role of a rather mysterious "observer" that apparently caused the wavefunction to collapse etc.
Dissipation, measurement theory etc are relatively new topics in QM so the concept of decoherence was rather mysterious for a long time (and is still not fully understood).

Hence, while it is true that there is no consensus about the interpretation of QM I think it is fair to say that quite a few PRACTICAL issues relating to what you can actually observe in an experiment have been sorted out during the past 20 years or so.

Moreover, I am not quite sure I agree that I believe it is all that important to understand what QM really "means", at least not from a scientific point of view. To me physics is all about predicting what I can measure in the lab (I am an experimentalist, in case you haven't guessed that already), the rest is philosophy which means that there is little hope of ever reaching a "correct" answer (but it can still be interesting).

***********************************************************
StatusX writes:
It's true that the dynamical equations could both be written in matrix form, but for a classical system the relevant matrices would all be diagonal, showing that the matrix approach is not really necessary, just a means to organize information. In a quantum system, the non-zero off-diagonal terms are completely unexpected from a classical point of view, and show that the superpositions are not merely formal devices but real physical features.

Not so. As I indicated above, I'm talking about a classical probability system. Thus
you might check out the idea of a stochastic matrix; Kalman Filters, time series forecasting, electric current and kinetic theory of gases, correlation matrices and regression, radar tracking, and on and on.
Regards,
Reilly Atkinson

 

[Anonym]

there is no strange "transition" from QM on the microscopic level (atoms) to classical physics on at the macrosopic level (cats).

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.

The collapse is the universally valid phenomenon; therefore, the criterion must be also universally valid. What sharply distinct the Classical World from the Quantum World? Distinguishability. The correlations on the mesoscale tell us that the indistinguishability of the quantum world still maintained, only breakdown of it will define that the instant transition into the classical world took place. Mathematically it is expressed when the system state is not described anymore as the Kronecker product of the component subsystems.

The QM system has finite size when the system state is described by the hypergeometric type equations. I guess that the criterion should be the ratio v/V<<1, where V is the free volume available for that system. The absolute size of the macroscopic system doesn’t a matter. One may use that ratio as the definition of what the macroscopic means. Indeed, it is different in every specific problem. For example, in the black body box the size of the photon is the size of the box. Therefore, it is pure quantum mechanical system.

Regards, Dany.

 

[StatusX]

In fact, there is a consensus about the interpretation of QM among physicists that are involved with experiments. They all go with what might be called the pragmatic Bohr-Born interpretation.

I'm not really that shocked to hear that most experimentalists go along with the pragmatic interpretation. But as a theorist, the interpretation that's easiest to work with has no special significance to me. And it should be stressed that no interpretation has any more or less evidence than any others: they all agree perfectly well with experiment. Which one you use is, at least until we have a more complete theory, a matter of personal preference.

Not so. As I indicated above, I'm talking about a classical probability system. Thus
you might check out the idea of a stochastic matrix; Kalman Filters, time series forecasting, electric current and kinetic theory of gases, correlation matrices and regression, radar tracking, and on and on.

As far as I know, none of these go against my point that classical probability systems are approximations meant to account for incomplete knowledge of a classical system, while quantum probabilities are inherent features of the world, and states in a quantum superposition interact with each other in a way completely foreign to the states in a classical ensemble. So I'll ask, do you think that schrodinger's cat has no more relevance to quantum mechanics than it does to classical mechanics?

 

[reilly]

I'm talking theorists, who have used this pragmatic approach for many years, in thousands of papers and books -- from QM 101 to Weinberg's QFT; quantum optics, atomic and molecular and nuclear physics. Every*(virtually) paper or text discussing the S-matrix of Heisenberg, discussing cross sections and scattering uses this pragmatic approach. It's what I learned as a student, and what I taught as a professor, and what I heard and saw in lectures and seminars -- including Feynman, Oppenheimer, Vladimer Fock, GellMan, Felix Bloch, and many others. Born has been alive and well since the 1920s. Ubiquitous in a word. You might say that this pragmatic interpretation is the common practice in physics, whether in Phys. Rev. or in an undergraduate classroom.

And yes, the Schrodinger Cat issue, in my opinion, has nothing to do with either classical or quantum mechanics. Rather it's about biology and standard probability theory.

Beats are the result of interference as is Young's expt. and the systems are classical.
Regards,
Reilly Atkinson

I'm not really that shocked to hear that most experimentalists go along with the pragmatic interpretation. But as a theorist, the interpretation that's easiest to work with has no special significance to me. And it should be stressed that no interpretation has any more or less evidence than any others: they all agree perfectly well with experiment. Which one you use is, at least until we have a more complete theory, a matter of personal preference.


As far as I know, none of these go against my point that classical probability systems are approximations meant to account for incomplete knowledge of a classical system, while quantum probabilities are inherent features of the world, and states in a quantum superposition interact with each other in a way completely foreign to the states in a classical ensemble. So I'll ask, do you think that schrodinger's cat has no more relevance to quantum mechanics than it does to classical mechanics?

 

[StatusX]

I'm talking theorists, who have used this pragmatic approach for many years,

The problem with the Copenhagen approach from a theoretical point of view is that the act of "measurement" is not well-defined. There are various attempts at nailing this concept down, but none that seem obviously correct.

The difference with the many worlds view, and the reason I favor it, is that there is no collapse, and so the measurement problem disappears. In fact, that's the only real difference between it and the Copenhagen view: there are no extra assumptions, just one less. From simply denying this process and applying the idea of decoherence (which is not an assumption, but a consequence of QM common to all interpretations), the unitary schrodinger equation alone gives rise to phenonmena macroscopic beings would almost certainly interpret as wavefunction "collapse". That's too nice a fact to ignore.

And yes, the Schrodinger Cat issue, in my opinion, has nothing to do with either classical or quantum mechanics. Rather it's about biology and standard probability theory.

I'm taking it you don't consider the wavefunction to be real, but only some kind of representation of the experimenter's knowledge. If this is the case, I can understand your position.

 

[Anonym]

It's been the best game in town for a long, long time -- no one, as yet, has come up with a better alternative.

I am. And I do not need to convince anyone that it is so. It is obvious, since my roots are: Galileo, Newton, Huygens, Hamilton, Faraday, Maxwell, Einstein, Schrödinger, Dirac, Wigner, Yang and many others. It is General Theory of Fields.

The linear superposition is not violated in the classical physics, it is not observed. It is the problem of measurements when the measurement apparatus obey laws of the macroscopic physics. Therefore, it is the classical physics that must provide the natural explanation (solution) of it and not QT.

It is a serious problem; therefore, one should find a serious solution. As usual, it is invention of the previously unknown and unused mathematical framework. In that specific case, it is Real Hilbert Space. When I finished work and finished even to write paper, suddenly I remembered that I did not check whether it is not already done. The literature said that it is or trivial or not enough investigated. I entered Google and typed: Real Hilbert space. I got list of more than 3 000 000 publications. Then I typed Real Hilbert space+classical mechanics+dispersion free. Then I got zero.

If you accept that the hydrogen atom is not a physical system made out of the single electron and the single proton, I have no problem with that. If you accept that the single elementary particle may do statistic with itself, I have no problem with that either.

Regards, Dany.

 

[Demystifier]

The difference with the many worlds view, and the reason I favor it, is that there is no collapse, and so the measurement problem disappears. In fact, that's the only real difference between it and the Copenhagen view: there are no extra assumptions, just one less. From simply denying this process and applying the idea of decoherence (which is not an assumption, but a consequence of QM common to all interpretations), the unitary schrodinger equation alone gives rise to phenonmena macroscopic beings would almost certainly interpret as wavefunction "collapse". That's too nice a fact to ignore.

But this is not enough for the consistency of the many-world interpretation. Decoherence alone does not explain why only one of the possibilities is seen by the observers. See e.g.
http://xxx.lanl.gov/abs/quant-ph/0312059 (Rev. Mod. Phys. 76, 1267-1305 (2004))

 

[Fra]

I am. And I do not need to convince anyone that it is so. It is obvious, since my roots are: Galileo, Newton, Huygens, Hamilton, Faraday, Maxwell, Einstein, Schrödinger, Dirac, Wigner, Yang and many others. It is General Theory of Fields.

(Sorry for jumping into the discussion)

Dany, do you have any yet finished papers where your personal ideas are elaborated?
I'm curious.

/Fredrik

 

[ZapperZ]

But this is not enough for the consistency of the many-world interpretation. Decoherence alone does not explain why only one of the possibilities is seen by the observers. See e.g.
http://xxx.lanl.gov/abs/quant-ph/0312059 (Rev. Mod. Phys. 76, 1267-1305 (2004))

It probably just might! Read, for example, H. Ollivier et al., PRL v.93, p.220401 (2004). In it, they showed how "preferred pointer states" of the system affects what is being observed, resulting in what we see classically as an objective observation.

Zz.

 

[Demystifier]

It probably just might! Read, for example, H. Ollivier et al., PRL v.93, p.220401 (2004). In it, they showed how "preferred pointer states" of the system affects what is being observed, resulting in what we see classically as an objective observation.

I do not understand this paper. Can you explain, in simple terms, how objective observation emerges without a collapse? Or give a link where such a simple explanation is given?

 

[ZapperZ]

I do not understand this paper. Can you explain, in simple terms, how objective observation emerges without a collapse? Or give a link where such a simple explanation is given?

Er.. where does it say these things occurs without a collapse? Isn't "decoherence", by definition, implied a gazillion interactions (and thus, collapse) of the system?

I was responding to your claim that decoherence can't explain why only one outcome is seen by an observer. This paper laid out how decoherence (which, by definition, implies an interaction already with an environment) can in fact results in a "preferred" outcome, leading to a reproducible, objective observation that we see at the classical level.

Zz.

 

[Fra]

It probably just might! Read, for example, H. Ollivier et al., PRL v.93, p.220401 (2004). In it, they showed how "preferred pointer states" of the system affects what is being observed, resulting in what we see classically as an objective observation.

Quite Interesting paper. Thanks for the link! I like parts of it and, but I have doubts about some details, in particular their choice of information measures and the conditions posed, which from a quick reading seems closely related to what I'd consider to be "near information equilibrium", in the sense that they are effectively considering perturbations around an equilibrium state and may not be valid in a general case and I suspect that to make this consistent time has to be brought into the picture. It seems to have some similarities to my preferred thinking, and I think I can relate to what they are trying to do but I need to read it properly when I've got time, the page count was quite reasonable.

/Fredrik

 

[Demystifier]

Zz, as I understood, the paper you mentioned explains objective existence not simply by using decoherence, but by combining decoherence with the Zurek's existential (quantum Darwinism) interpretation of quantum mechanics. This interpretation is not the same as MWI. What I look for is a simple explanation of the existential (quantum Darwinism) interpretation of quantum mechanics.

In the meantime, I have found this:
http://www.advancedphysics.org/forum/showthread.php?t=1791
Apparently, I am not the only one who does not understand the Zurek's interpretation of QM.
Maybe we should open a separate thread.

 

[ZapperZ]

Zz, as I understood, the paper you mentioned explains objective existence not simply by using decoherence, but by combining decoherence with the Zurek's existential (quantum Darwinism) interpretation of quantum mechanics. This interpretation is not the same as MWI. What I look for is a simple explanation of the existential (quantum Darwinism) interpretation of quantum mechanics.

I didn't say that it is the same as MWI. I don't think the authors were trying to do that. However, they have tried to show that by invoking decoherence, you CAN get back the classical "certainty" that we know and love. I thought this was a very good first step, at least, in trying to figure out why our classical world has a definite objectivity, meaning you get a definite ONE outcome when you make a classical measurement. That's what they have tried to show.

Zz.