Understanding the Cat in a Box Paradox

[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.

 

[Anonym]

Dany, do you have any yet finished papers where your personal ideas are elaborated?

The paper I referred to in my post above is quant-ph/0606121 entitled “On the connection between classical and quantum mechanics”. It will be published in the HAIT JSE special issue devoted to memory of Prof. I.D.Vagner.

The related papers are:

1)physics/0504008 entitled “On the problem of Zitterbewegung of the Dirac electron”, HAIT JSE, 1 (3), 411,(2004);
2)“Quantum mechanics of non-abelian waves I”, Hadronic Journal,6, 801(1983).

The first is the corrected version of Ch. IX and the second is Ch.VIII of my Ph.D thesis entitled “Quantum Mechanics of Non-Abelian Waves”, Tel-Aviv University, 1982, unpublished.
Ch. III – Ch.VII was published as the paper written by L.P.Horwitz and L.C. Biedenharn, Ann. Phys., 157, 432 (1984).

I discuss ideas here at PF. All mentioned papers discuss mathematical results only. They use fairly advanced extensions of the functional analysis.

Not yet finished papers are:

1) On the “eigenschaften” operators in QM; finished, not written;
2) The squeezed states, the coherent states, etc.; perhaps finished, not written;
3) On relativistic QM; not finished, not written.

I understand that you are interesting in the problems of statmech. I do not believe that I will ever consider the description of more than N=3 states.

Regards, Dany.

 

[StatusX]

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))

I haven't gone through the paper ZapperZ mentioned, but my understanding is roughly as follows. Look at the state after observation:

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

If we denote the first term by |A> and the second by |B>, then decoherence says that |A> and |B> are incoherent, which roughly means that for any observable O we might measure, <A|O|B>\approx0. But as I described in post 33, this means the system is behaving essentially like a classical probabilistic ensemble, and so the results we get by continuing to apply Schrodinger's equation without collapse is the same as if we did assume collapse, ie, where we assume the cat is in a well-defined classical state, just one which we don't initially know.

In particular, |A> and |B> evolve independently: |happy scientist> evolves into |scientist picking up and hugging the cat>, while |sad scientist> independently evolves into |scientist quietly putting cat into a box>. Yes, a superposition still exists, but the two states in the superposition carry on as if it didn't, essentially because the incoherence of the states means there are no interference effects.

The question still remains: what determines which of the outcomes you experience. Evidently, you experience one, and someone else with an equal claim to be called "you" experiences the other. This is really strange, and I haven't heard any satisfying explanation that incorporates consciousness.

But for now, we can carry on noting that if you were to querry any of the different scientist-copies after he's carried out several quantum experiments, chances are very high that he'll have a memory of a world where the laws of quantum probability were closely followed, so the predictions of the theory are solid (in the probabiliistic sense which is the only sense in which QM can be verified).

 

[nrqed]

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.

I am trying to understand the next to last sentence in this paragraph. I thought that the MW interpretation and decoherence were very different beasts. Are you saying that one implies the other? I thought that MW did not make use of decoherence and vice versa.

Thanks for the interesting points.

 

[nrqed]

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 am a bit confused by the last statement. Interactions are equivalent to collapse?? I thought that interactions in the context of decogherence meant entanglement of states and that no collapse ever took place. Maybe I missed completely the point?

 

[ZapperZ]

I am a bit confused by the last statement. Interactions are equivalent to collapse?? I thought that interactions in the context of decogherence meant entanglement of states and that no collapse ever took place. Maybe I missed completely the point?

I wanted to say "loss of coherence" after so many interactions with the surrounding, but then I'm only saying what "decoherence" is. I would consider an "interaction" as a "collapse", because such interaction can in fact tell you the state of a system.

Zz.

 

[StatusX]

I am trying to understand the next to last sentence in this paragraph. I thought that the MW interpretation and decoherence were very different beasts. Are you saying that one implies the other? I thought that MW did not make use of decoherence and vice versa.

Here's a quote that explains the gist of it:

However, decoherence by itself may not give a complete solution of the measurement problem, since all components of the wave function still exist in a global superposition, which is explicitly acknowledged in the many-worlds interpretation. All decoherence explains, in this view, is why these coherences are no longer available for inspection by local observers. To present a solution to the measurement problem in most interpretations of quantum mechanics, decoherence must be supplied with some nontrivial interpretational considerations (as for example Wojciech Zurek tends to do in his Existential interpretation). However, according to Everett and DeWitt the many-worlds interpretation can be derived from the formalism alone, in which case no extra interpretational layer is required.

Basically, Everett and DeWitt reason that decoherence alone leads to what "local observers" (eg, one of the copies of the scientist) would interpret as irreversible wavefunction collapse. In other words, you could still enforce collapse, but it would be redundant (except from an ontological point of view, where it removes worlds that aren't practically accessible to us). Although decoherence is now widely accepted as a real effect, the validity of DeWitt's argument that it implies MW is still controvertial.

 

[cesiumfrog]

good post, X.

When I was first taught of MW, I was given the impression that the branching of worlds was a very random ad hoc alternative to nondeterministic collapse. Now I wonder whether historically it was first proposed with decoherence already in mind.

 

[nrqed]

a) You don't read what I say. So, let me repeat. The cat cannot be both dead and alive, it is a logical contradiction. Still, it can be in a superposition of dead and alive. In this case, it is neither dead nor alive. Sometimes we say for such a state that the cat is "both dead and alive", but it is simply an incorrect (or imprecise) language.

b) I say it is in the superposition of head and tail (recall that I am still talking within the 1. paradigm, despite the fact that I actually prefer 2.)

By the way, this is my 666th post.

as I am rereading this thread, I want to say that I agree with Demystifier.

This part of the thread was about whether a linear superposition of two states (dead or alive) should be described as "both dead and alive" or "neither dead nor alive". At thi spoint I think that everybody agrees that the most (and maybe only) accurate description is to say that the system is a linear superposition, period. But if one insists on using everyday language, it seems impossible to accurately convey what a quantum linear superposition means. Then it becomes subjective, to a point, what language is used. Still, I personally think that "both dead an alive" is misleading. It would imply that once the measurement is made, and let`s say the outcome is "alive", that the cat "ceased to be dead" since it was both dead and alive before the measurement.

I find the "neither dead nor alive" at the same better and quite unsatisfying.

I would suggest the following as the best description. A cat in the linear superposition of dead and alive is a cat which has the potential of being alive and he potential of being dead.

Just my two cents...

 

[ZapperZ]

as I am rereading this thread, I want to say that I agree with Demystifier.

This part of the thread was about whether a linear superposition of two states (dead or alive) should be described as "both dead and alive" or "neither dead nor alive". At thi spoint I think that everybody agrees that the most (and maybe only) accurate description is to say that the system is a linear superposition, period. But if one insists on using everyday language, it seems impossible to accurately convey what a quantum linear superposition means. Then it becomes subjective, to a point, what language is used. Still, I personally think that "both dead an alive" is misleading. It would imply that once the measurement is made, and let`s say the outcome is "alive", that the cat "ceased to be dead" since it was both dead and alive before the measurement.

I find the "neither dead nor alive" at the same better and quite unsatisfying.

I would suggest the following as the best description. A cat in the linear superposition of dead and alive is a cat which has the potential of being alive and he potential of being dead.

Just my two cents...

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.

 

[StatusX]

When I was first taught of MW, I was given the impression that the branching of worlds was a very random ad hoc alternative to nondeterministic collapse. Now I wonder whether historically it was first proposed with decoherence already in mind.

Yea, until a few months ago I just assumed it was someone getting carried away with their imagination and the weirdness of QM. Then I read some more about it and realized it's actually the simplest interpretation, in terms of number of assumptions, and more or less resolves the measurement problem. I'm surprised it isn't more popular than it is (I believe it's second to the Copenhagen interpretaion, depending on the kind of physicists you ask)

 

[Alan J.]

From my years of playing poker and trying to determine my opponents hand via looking for "tells" or ways to figure out if his hand is good or not based on my opponents behavior and the current environment(other information I've gathered such as the cards in my hand and other cards shown or showing). This is indeed the same problem. We can determine if the cat is alive or dead by making simple observations about it's environment whether it being atmospherical or physical. Is the box moving? Is the box shaking? Is the box warm in a particular spot? Is there air in which the cat can breathe?Is the box emitting sound? These are ways to determine if the cat is alive or not.

The same thing is, in theory, true for particle movement just we have not yet found these observations or what to look for regarding the particles environment.
And another question comes in where if 2 particles were entangled across the universe. Would the entanglements affect other traveling particles and entanglements?

 

[ueit]

Yea, until a few months ago I just assumed it was someone getting carried away with their imagination and the weirdness of QM. Then I read some more about it and realized it's actually the simplest interpretation, in terms of number of assumptions, and more or less resolves the measurement problem. I'm surprised it isn't more popular than it is (I believe it's second to the Copenhagen interpretaion, depending on the kind of physicists you ask)

Did you find out how MWI accounts for the observed probabilities (Born rule)?

 

[Fra]

Some comments.

I read that paper again last night, and while the general idea that any system will attain some level of correlation with the environment, and that there is a selective mutual pressure between environment and the system is right on...

...but like others say, I wouldn't say it solves the collapse as such, beucase OTOH the collapse isn't an issue for me becuse IMO it's simply sort of a bayesian revision due to the limited measurement resolution and finite complexity of memory - I suspect Alan who is a poker will know what I mean - I like the poker analogy too. I see no way around this. Unless you of course reformulate the problem, but the care should be taken because then we might not ask the same question.

Also, if we are consider an observer B that observes a system + observer A, then clearly we are working in two different descriptions. Observer A has not use of B:s information. Sure they can communicate, but then we add time. In my thinking (spacetime aside!) one can't transfer arbitrary amounts between two records arbitrarily. I think the information transfer is part of defining time which implies a locality in terms of information. I am eventually working on an explicit formalism for this but it a lot of things to do left.

Also, I think the assumption that there is strong correlation between the environment and the system in the first place is valid only it they are close to equilibrium - ie that the system is already "stabilized" i the environment. I figure that this is not a valid assuption in the general case. Also if one is to talk about the actual stabilisation process, this takes time, and then the argumentation gets more complicated. Information that is available in the future, is not available now. I see no sense in that argumentation.

I think the paper is interesting in a sense but it does not get rid of the collapse. The fact that C may observe the correlation between A and B the system, and sees a resolution to the collapse problem is an observation with the wrong condition. The fact that A sees a collapse, doesn't mean that everybody sees a collapse. I don't see a problem with that at all.

I think there is an intrinstic limit due to information capacity, which limits the maximum possible entanglement! and this constraint may impose collapses. I think part of the problem is that all the players have incomplete information, and it's NOT due to flawed or incompetent strategies, it's due to the limiting structures to hold correlation information and due to TIME that correlations are a dynamical thing, if you are thrown into a new environment, then you need some time to equilibrate with the environment, which is btw, mutual.

/Fredrik

 

[Alan J.]

Some comments.

I think there is an intrinstic limit due to information capacity, which limits the maximum possible entanglement! and this constraint may impose collapses. I think part of the problem is that all the players have incomplete information, and it's NOT due to flawed or incompetent strategies, it's due to the limiting structures to hold correlation information and due to TIME that correlations are a dynamical thing, if you are thrown into a new environment, then you need some time to equilibrate with the environment, which is btw, mutual.

/Fredrik

I'm going to continue with the poker analogy because it's less graphic then a dead cat.

When I sit down to a new table, I do have a set strategy and you are right. There is a time factor here. But if A has basic knowledge of environment A. And then A is thrown into environment B(or a new poker table with new people) with the knowledge of evironment A and we are observing a simular situation of a poker game. Then A would have the potential to make correct predictions on the opponents cards more so then when A started at evironment A.
Then when A is introduced to environment C and is also a simular situation of a poker game. Then A would have the knowledge of Evironments A and B. And so on and so forth until the rules or stakes of the game are changed.
There is a learning curve of player A which could potentially be humans in the future if we can learn more about environments of particles and less about their actions. This is a plausible solution because we no longer care what the particles are doing, thus we are not limited to just quantums observation problems. I.E double slot experiment.

 

[Wonderballs]

If you know the cats state, the box has been opened (even if the box remains closed). So the box will always remain closed. Unless you smell something funky which opens the closed box that is still shut.

 

[Alan J.]

If you know the cats state, the box has been opened (even if the box remains closed). So the box will always remain closed. Unless you smell something funky which opens the closed box that is still shut.

Untrue. The smell is the bi product of the box or cat. Thus making these observations is not directly interferring with the state of the cat(particle). I believe your thinking in more philosophical terms.

 

[Wonderballs]

I may not know much about this stuff, but if you do not know the cats state, the box remains closed restricting the gain of such knowledge. Like lim x --> a .

The funky smell was a joke.

 

[StatusX]

Did you find out how MWI accounts for the observed probabilities (Born rule)?

It's a good question, and I don't think there's a universally accepted answer. One idea would be that if there is a splitting for each quantum microstate of the system, how many of these go one way or the other will be determined by the magntiudes of the different results in the superposition. I don't think this has been rigorously shown though.

 

[ueit]

It's a good question, and I don't think there's a universally accepted answer. One idea would be that if there is a splitting for each quantum microstate of the system, how many of these go one way or the other will be determined by the magntiudes of the different results in the superposition. I don't think this has been rigorously shown though.

I think this is a very serious problem of MWI. It means, in fact, that it cannot explain anything. The obtained experimental results must be introduced by hand without any good reason to do so. Compare this with BM where the probabilities follow naturally. As Einstein said, "make everything as simple as possible, but not simpler."

 

[Anonym]

This part of the thread was about whether a linear superposition of two states (dead or alive) should be described as "both dead and alive" or "neither dead nor alive"... But if one insists on using everyday language, it seems impossible to accurately convey what a quantum linear superposition means.

If one insists on using everyday language, consider 2-dim plane and draw two mutually orthogonal axes on it. Then consider some line belong that plane. That line will contain one of the axes if and only if it is identical to that axis and never both. This is the fundamental property of the metric spaces; otherwise Zz may lock his lab and throw away the keys. Also that “what a quantum linear superposition means”.

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"?

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.

 

[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 ?