What makes schrodinger cat quantum?

[diazona]

Well, if you prepare an ensemble of Schrödinger's cats in boxes, then measurements of the survival of each cat after a predetermined amount of time will be all over the place. (Some alive, some dead) So by that argument, it's just as valid to say that the cat is in a superposition of \vert\text{alive}\rangle and \vert\text{dead}\rangle as it is to say an electron is in a superposition of two states. (Of course, \vert\text{alive}\rangle and \vert\text{dead}\rangle are not single quantum states, which complicates the picture...)

 

[Bob_for_short]

What makes Schrödinger cat quantum?

Maybe Schrödinger himself? He was quite a quantum geek.

 

[Count Iblis]

The density matrix |p> <p| describes the ensemble of the set of identically prepared electron states in momentum |p>. In the position representation this density matrix is:

rho = Integral d^3x d^3y |x><x|p><p|y><y| =

1/V Integral d^3 d^3y exp[i p(x-y)] |x><y|

where V is the volume of the box each electron is in.

rho has off diagonal components, which means that one can observe coherence effects in the statistics of measurements. In contrast, the density matrix of a ensemble of electrons that all have some definite but random position in the box is:

rho = 1/V Integral d^3 x |x><x|

 

[meopemuk]

Well, if you prepare an ensemble of Schrödinger's cats in boxes, then measurements of the survival of each cat after a predetermined amount of time will be all over the place. (Some alive, some dead) So by that argument, it's just as valid to say that the cat is in a superposition of \vert\text{alive}\rangle and \vert\text{dead}\rangle as it is to say an electron is in a superposition of two states. (Of course, \vert\text{alive}\rangle and \vert\text{dead}\rangle are not single quantum states, which complicates the picture...)

Yes, I don't see any significant difference between superposition of cat states and superposition of electron states. Both of them are imaginary superpositions that exist only in minds of theoreticians. Each time we measure electron's position we get a definite value. Each time we look at a cat we see it either dead or alive.

 

[meopemuk]

The density matrix |p> <p| describes the ensemble of the set of identically prepared electron states in momentum |p>. In the position representation this density matrix is:

rho = Integral d^3x d^3y |x><x|p><p|y><y| =

1/V Integral d^3 d^3y exp[i p(x-y)] |x><y|

where V is the volume of the box each electron is in.

rho has off diagonal components, which means that one can observe coherence effects in the statistics of measurements. In contrast, the density matrix of a ensemble of electrons that all have some definite but random position in the box is:

rho = 1/V Integral d^3 x |x><x|

Yes, there are two sources of probabilities in the formalism of quantum mechanics (and in nature). One is the regular classical probability, which simply results from our incomplete specification of the preparation process (like when we throw a die on the table). This probability is described by "mixed states" in QM.

The other (intrinsically quantum) probability remains even when the preparation of the system's state is fully controlled. Quantum mechanics does not explain the origin of this randomness. It simply provides a mathematical tool for its description and analysis. The states in which the "classical" randomness is completely eliminated are called "pure states". I was talking only about such "pure states" in my posts.

 

[SW VandeCarr]

the cat isn't 'quantum'. it's the radioactive decay that is governed by quantum mechanics. if the geiger-counter detects radiation, then the vial is broken, killing the cat. since the radioactive decay is probabilistic, we cannot say whether the geiger-counter detects it until we open the box and observe what has happened.

this is one of the problems i have with this experiment. the cat is not physically, both alive and dead. however, we cannot deduce whether it is dead or alive until we look in the box. it's a silly thought experiment to be honest.

If you're talking about the cat being in two states until someone looks, I agree there's a certain "silliness" to that. However there is another aspect of the Schrödinger thought experiment that is overlooked: it undermines strict determinism. While QM is deterministic, our knowledge of quantum states is probabilistic. Through human agency we can introduce this indeterminism into the large scale world. The Many Worlds interpretation was introduced to counter this, but MW is by its very nature is metaphysical. Given this, the Schrödinger thought experiment (which could easily be an actual experiment) is profound.

 

[canoe]

Wasn't the basic premise behind Shrodinger's cat to highlight the measurement problem? And hasn't the measurement problem been adequately addressed by decoherence (i.e. that measurments are essentially taking place continually and everywhere)? Is not the principal argument against decoherence primarily thermodynamical (i.e. that it does not adequate address the possibility of a Poincare recurrence)?

I do not mean to be rhetorical in posting the above questions. I was intending to post something similar as this is my current understanding...and to see if this explanation dovetailed with the understanding of others.

 

[SW VandeCarr]

Wasn't the basic premise behind Shrodinger's cat to highlight the measurement problem? And hasn't the measurement problem been adequately addressed by decoherence (i.e. that measurments are essentially taking place continually and everywhere)? Is not the principal argument against decoherence primarily thermodynamical (i.e. that it does not adequate address the possibility of a Poincare recurrence)?

I do not mean to be rhetorical in posting the above questions. I was intending to post something similar as this is my current understanding...and to see if this explanation dovetailed with the understanding of others.

I don't know if you are responding to my post or not. If you are, you're missing the point I'm trying to make. The fate of the cat is not determined by an extended causal chain of events. It's determined by the random outcome of an experiment. The human actor is the agency by which the direction of contingent processes are dependent, not on extended (deterministic) causal chains, but rather dependent on random outcomes.

This probably was not the intent of Schrödinger's thought experiment. I'm not arguing against decoherence. Nevertheless there's a sense that we are bypassing decoherence by a construction that makes macroscopic processes directly contingent on random outcomes. MW offers a way out, but I don't think science should depend on metaphysical arguments to maintain the idea that the world is, in principle, deterministic.

 

[ZapperZ]

I don't know if you are responding to my post or not. If you are, you're missing the point I'm trying to make. The fate of the cat is not determined by an extended causal chain of events. It's determined by the random outcome of an experiment. The human actor is the agency by which the direction of contingent processes are dependent, not on extended (deterministic) causal chains, but rather dependent on random outcomes.

This was probably was not the intent of Schrödinger's thought experiment. Nevertheless there's a sense that we are bypassing decoherence by a construction that makes macroscopic processes directly contingent on random outcomes. MW offers a way out, but I don't think science should depend on metaphysical arguments to maintain the idea that the world is, in principle, deterministic.

I'm not so sure this is the case.

For example, if I, instead toss a coin, and heads means I kill the cat, and tails means the cat lives, would this be equivalent to the Schrödinger Cat scenario? It isn't. Even if I toss the coin in such a way that no one could see it, and I perform or not perform the dreaded act, what is the state of the cat? It will be EITHER dead OR alive, but not a combination of both!

The latter is what is so puzzling about the quantum scenario that is being illustrated by the cat, the superposition principle. Opening the box and determining the state of the cat, actually, is nothing unusual. A classical probability has that ability as well. It is what happens BEFORE. In a classical probability, there never was any case where all the possible states exists simultaneously. In QM case, they do! It is what makes the Schrödinger Cat scenario so puzzling, and it is what makes the Bell-type experiments more than just a conservation of momentum, angular momentum, spin, etc.

The existence of superposition of states is what has been verified in chemistry, in the Delft/Stony Brook experiments, etc.. etc. These are actual, real observation of the effects of superposition, i.e. it is not merely a reflection of our "ignorance" of the system as implied in classical statistics. These observed effects are absent in classical statistics.

Zz.

 

[Count Iblis]

For example, if I, instead toss a coin, and heads means I kill the cat, and tails means the cat lives, would this be equivalent to the Schrödinger Cat scenario? It isn't. Even if I toss the coin in such a way that no one could see it, and I perform or not perform the dreaded act, what is the state of the cat? It will be EITHER dead OR alive, but not a combination of both!

Why not? Let's assume that you are inside a perfectly isolated box with the cat, so that the initial state of the box comprising of you, the coin and cat can be taken to be a pure state (which makes the following argument easier to formulate but it isn't strictly necessary to assume this). The many particle wavefunction of the box then evolves according to the Schrödinger equation to something of the form:

|psi> = sum_i a_i |head_i>|dead_i> + sum_j b_j |tail_j>|alive_j>


It is entirely reasonable to assume that it is not the case that either all of the a_i are zero or that all of the b_j are zero, because the outcome of the coin throw depends on how you will throw the coin, which is regulated by very complex processes in the brain. If you don't do the experiment immediately, but wait a few days after entering the box, then the state of the box will suely have evolved into superposition of classical states that would each yield a different outcome of a coin throw (so, we are still assuming that coin throws are deterministic under normal circumstances).

Then the state of the box is not a classical state but we cannot do any experment in practice to demonstrate the non classical features of the superposition. That inability cannot be used to argue that the state is classical.


It would be different if a real physical mechanism that explains how a pure state can evolve into a mixed state is proposed. So, it should be explained how, even if you keep track of all the degrees of freedom and don't trace out any environmental degrees of freedom, the density matrix loses its off diagonal terms.

 

[canoe]

I don't know if you are responding to my post or not. If you are, you're missing the point I'm trying to make. The fate of the cat is not determined by an extended causal chain of events. It's determined by the random outcome of an experiment. The human actor is the agency by which the direction of contingent processes are dependent, not on extended (deterministic) causal chains, but rather dependent on random outcomes.

This probably was not the intent of Schrödinger's thought experiment. I'm not arguing against decoherence. Nevertheless there's a sense that we are bypassing decoherence by a construction that makes macroscopic processes directly contingent on random outcomes. MW offers a way out, but I don't think science should depend on metaphysical arguments to maintain the idea that the world is, in principle, deterministic.

Thank you for replying. I was not directly responding to your post, but rather was extending the discussion into a realm where I had a few questions. Perhaps that was not approriate. Nonetheless, it would seem to me that decoherence favorably augments the Copenhagan interpretation and that some of the more bizarre (bordering on metaphysical) interpretations of QT (i.e. many worlds (Everett) and consciousness causing the collapse of the wave function (Wigner)) might fall by the wayside. Perhaps the moderator might advise if I should start a new thread?

 

[ZapperZ]

Why not? Let's assume that you are inside a perfectly isolated box with the cat, so that the initial state of the box comprising of you, the coin and cat can be taken to be a pure state (which makes the following argument easier to formulate but it isn't strictly necessary to assume this). The many particle wavefunction of the box then evolves according to the Schrödinger equation to something of the form:

|psi> = sum_i a_i |head_i>|dead_i> + sum_j b_j |tail_j>|alive_j>

You need to justify why you are able to do this for a purely classical system. Just because you can write the 'wavefunction' of something, doesn't mean that it has any physical justification for it. For example, I can measure the bonding-antibonding bonds in chemistry, which is a direct consequence of the superposition of electrons being in many places. Can you show me what physical observation that I can measure from your wavefunction for coin-tossing that indicates that this description is valid?

If this is valid, Schrödinger would have used a simple coin-tossing as the source that triggers the poison, rather than a radioactive decay.

Zz.

 

[canoe]

Incidentally, doesn't decoherence provide an answer to the Schrödinger Cat scenario? Basically, that the wave functions of constituent particles become "all mixed up" (i.e. strong mixing). Thus the probalistic nature of quantum objects remains intact while mixed (i.e. non-quantum objects) decohere. Therefore, the cat is either alive or dead when the box is opened and not in some superposition of half-alive/half-dead states.

 

[Count Iblis]

You need to justify why you are able to do this for a purely classical system. Just because you can write the 'wavefunction' of something, doesn't mean that it has any physical justification for it. For example, I can measure the bonding-antibonding bonds in chemistry, which is a direct consequence of the superposition of electrons being in many places. Can you show me what physical observation that I can measure from your wavefunction for coin-tossing that indicates that this description is valid?

If this is valid, Schrödinger would have used a simple coin-tossing as the source that triggers the poison, rather than a radioactive decay.

Zz.

Well, we can read here that

Schrödinger and Einstein had exchanged letters about Einstein's EPR article, in the course of which Einstein had pointed out that the quantum superposition of an unstable keg of gunpowder will, after a while, contain both exploded and unexploded components.

Then why Schrödinger replaced the gunpowder by a radioactive atom has presumably to do with the fact that this makes the argument easier to argue.

Quantum mechanics itself tells you that, far all practical matters, the superposition cannot be distinguished from an unknown classical state. See e.g. this article:

http://arxiv.org/abs/0903.2258

 

[ZapperZ]

Well, we can read here that




Then why Schrödinger replaced the gunpowder by a radioactive atom has presumably to do with the fact that this makes the argument easier to argue.

Quantum mechanics itself tells you that, far all practical matters, the superposition cannot be distinguished from an unknown classical state. See e.g. this article:

http://arxiv.org/abs/0903.2258

You have not answered my question. Can you point out to me the effect of superposition on coin tossing?

If quantum effects are present in such a system, then QM phenomena should not be THAT strange. None of what you are citing has any relevance to what I stated, or asked. Why did the group at Delft and Stony Brook went to ALL that trouble to illustrate the Schrödinger Cat state using a laborious setup? They could have just tossed coins and be done with.

If you noticed in my first post in this thread, I cited several experimental observations that points to the effect of quantum superposition. I request you show me the same experimental observation of superposition from coin tossing. If you cannot show me this, then (i) your understanding of quantum superposition is faulty and (ii) all your effort in that post is moot, because you were working based on a faulty assumption.

I also strongly suggest, rather than reading Wikipedia (you should know me by now not to give me Wikipedia references - I do not consider those as valid reference source), maybe you should read Anthony Leggett's classic treatment on this very subject that lead to the SQUID experiments testing the Schrödinger Cat states:

A.J. Leggett "Testing the limits of quantum mechanics: motivation, state of play, prospects", J. Phys. Condens. Matt., v.14, p.415 (2002).

Zz.

 

[ZapperZ]

Incidentally, doesn't decoherence provide an answer to the Schrödinger Cat scenario? Basically, that the wave functions of constituent particles become "all mixed up" (i.e. strong mixing). Thus the probalistic nature of quantum objects remains intact while mixed (i.e. non-quantum objects) decohere. Therefore, the cat is either alive or dead when the box is opened and not in some superposition of half-alive/half-dead states.

Maybe, maybe not.

While decoherence may play a significant role in the quantum-to-classical transition, there are several other possible explanations. Some of them are not necessarily in competition with decoherence. For example, a recent paper has shown that our "coarse-grained" measurement of such a system can already cause an onset of classical measurements. Read my entry on this:

https://www.physicsforums.com/showthread.php?p=1520644

This issue of classical-quantum separation isn't a done deal, not by a long shot. We simply cannot make any definitive statement about how one evolve into another because, in physics, as it should be, we need to be able to empirically verify them, and verify them to our satisfaction. There's a lot still to be done before we get even close to that.

Zz.

 

[Count Iblis]

It is all explained here:

http://arxiv.org/abs/0903.2258

If you cannot show me this, then (i) your understanding of quantum superposition is faulty and (ii) all your effort in that post is moot, because you were working based on a faulty assumption.

As pointed out in the article ( http://arxiv.org/abs/0903.2258 ), this is absolutely not the case. The fact that you can demonstrate non classical effects in simple systems (even some macro systems, although the macroscopic nature of the squid experiments has been disputed), does not mean that this is demonstratable for any quantum superposition in practice.

 

[ZapperZ]

I'm sorry, but you continue to point to this PREPRINT as if it is an EXPERIMENTAL EVIDENCE! Investigating an experimental capability is NOT the same as an experimental evidence! I hate to think, and you should be worried as well, that you're putting ALL of your eggs into this basket. And I haven't even touched the fact that you are using a non-published work, which is something we require in the QM forum.

None of what I've cited are "investigating an experimental capability". They were ALL done, published, and verified!

Try again! I want to see the effect of superposition of coin tossing.

Zz.

 

[Count Iblis]

I'm sorry, but you continue to point to this PREPRINT as if it is an EXPERIMENTAL EVIDENCE!

It is not experimental evidence, it merely explains (giving refs to published articles) why, assuming unitary quantum mechanics, you cannot for all practical matters observe such superpositions.

This means that it is not a valid argument to point to coin tosses and then say that: "See, there is nothing quantum mechanical about this", because even if it were in some completely decohered macroscopic superposition, you could not detect any quantum effects anymore (See Ref. 14 of the article).

The question should be: "Where is the experimental evidence that Nature is not unitary"?

 

[ZapperZ]

It is not experimental evidence, it merely explains (giving refs to published articles) why, assuming unitary quantum mechanics, you cannot for all practical matters observe such superpositions.

This means that it is not a valid argument to point to coin tosses and then say that: "See, there is nothing quantum mechanical about this", because even if it were in some completely decohered macroscopic superposition, you could not detect any quantum effects anymore (See Ref. 14 of the article).

So in other words, you have no valid experimental evidence to point to me on the superposition effects in coin-tossing, something that I've asked in the very beginning. It also shows that you have no justification (unless you plan on tossing a coin near a black hole anytime soon) to show the validity of that wavefunction that you created out of thin air.

That renders the rest of your argument completely moot.

Just for future reference, I'm an experimentalist. Unless you can show empirical validity of what you are claiming, there's a very good chance that I won't buy it no matter how well you dress it.

Furthermore, if you truly believe that your coin tossing can be accurately described via your "wavefunction", then more power to you. But you should never provide the misinformation that (i) this is an accepted idea in standard physics and, more importantly, (ii) you have experimental evidence to back it up.

Zz.

 

[Count Iblis]

But you should never provide the misinformation that (i) this is an accepted idea in standard physics and, more importantly, (ii) you have experimental evidence to back it up.

Ok, but it is more accurate to say that the converse, i.e. that the wavefunction does "really" collapse, is not accepted either.

In my original post, I did write that:

Then the state of the box is not a classical state but we cannot do any experment in practice to demonstrate the non classical features of the superposition. That inability cannot be used to argue that the state is classical.

Apart form the last sentence, this is what the quoted article says.

 

[ZapperZ]

Ok, but it is more accurate to say that the converse, i.e. that the wavefunction does "really" collapse, is not accepted either.

Would you like to re-read what I posted originally that you responded to, and tell me where the issue of "really collapse" was brought up by me?

What you did instead is to construct a non-verified, highly speculative "wavefunction" for coin tossing. When I asked for experimental justification for that (meaning, experimental evidence), for some ODD reason, you gave me more theoretical arguments. Can't you see how silly this has been so far? This has been a very dumb game, and I'm the last person you want to try this on.

I have zero clue on what you are arguing, or what that has anything to do with what I said. I'm guessing that you are battling a different battle and somehow hooked your baggage onto this one. Don't do that!

Classical state is classical state! Until we know more about how quantum states evolve into classical world, you, the authors of that "preprint", and anyone else can't simply make such outlandish claim. It only reveals how little you pay attention to how we consider something to be valid in physics.

Zz.

 

[Count Iblis]

Well, the subject under discussion in this thread is "what makes Schrödinger's cat quantum", and I was just arguing along the lines of my first reply, i.e. from the point of view that there doesn't exist such a thing as a "classical world" to begin with. The world is fundamentally quantum mechanical and any classical physics can only arise as an approximation in the "classical limit".


This view may be controversial, but the whole point of the "Schrödinger cat" thought experiment, is to expose potential difficulties with this view, namely that the superpositions do not really go away for macroscopic systems.


I.m.o., the way to make experimental progress is to do experiments designed to measure violations of unitary time evolution like in the proposed expriment using a small mirror in a superposition.


How can it be reasonable to demand that to verify a theory one has to demostrate the non classical features of a system for which the theory itself implies that such effects cannot be detected for all practical purposes?

You were the one who brought up coin throws and stated that they were classical. You presumably meant that to be in an effective instrumental sense, but that's surely not in the spirit of this threat, because the same could be said of Schrödinger's cat itself.

 

[ZapperZ]

Well, the subject under discussion in this thread is "what makes Schrödinger's cat quantum", and I was just arguing along the lines of my first reply, i.e. from the point of view that there doesn't exist such a thing as a "classical world" to begin with. The world is fundamentally quantum mechanical and any classical physics can only arise as an approximation in the "classical limit".This view may be controversial, but the whole point of the "Schrödinger cat" thought experiment, is to expose potential difficulties with this view, namely that the superpositions do not really go away for macroscopic systems.I.m.o., the way to make experimental progress is to do experiments designed to measure violations of unitary time evolution like in the proposed expriment using a small mirror in a superposition.How can it be reasonable to demand that to verify a theory one has to demostrate the non classical features of a system for which the theory itself implies that such effects cannot be detected for all practical purposes?

You were the one who brought up coin throws and stated that they were classical. You presumably meant that to be in an effective instrumental sense, but that's surely not in the spirit of this threat, because the same could be said of Schrödinger's cat itself.

But you have never provided any means of showing that such "unitary evolution" can be carried out up to the classical limit AND actually derive such classical state!

In fact, one doesn't HAVE to go even that far to start "seeing" a destruction of the QM description. It has been shown that even ONE single interaction can do that!

https://www.physicsforums.com/showpost.php?p=1498616&postcount=55

I definitely brought up the coin throw AND insisted that they are classical. I have plenty of experimental evidence to back it up. Your assertion was the one without a single shred of experimental evidence. When I asked for it, you gave something else. That is what I find highly annoying and deceptive.

When you can show either (i) superposition in coin tossing OR (ii) a detailed derivation from QM principles that produce the classical phoenomena of coin tossing, then you will have a leg to stand on to make such argument. But not a single single second before. What you have done is to make an unsubstantiated, speculative assertion, which violates our Guidelines.

Zz.

 

[SW VandeCarr]

I'm not so sure this is the case.

For example, if I, instead toss a coin, and heads means I kill the cat, and tails means the cat lives, would this be equivalent to the Schrödinger Cat scenario? It isn't.

Zz.

I don't think a coin toss is equivalent of the Schrödinger Cat experiment (SCE) either, but for an additional reason: the result of a coin toss is, in principle, not a random outcome. It may be the case that the only true example of a random outcome is the realization of a quantum state.

We can argue forever about the mixed state of the cat in a box. It hasn't gotten us anywhere since the 1920's. I'm arguing that the real significance of the SCE is that it makes the case that strict determinism is not a true description of the world insofar as the world can be modeled by science. I've stated my reasoning in my two previous posts here (#36 and 38).

 

[Count Iblis]

But you have never provided any means of showing that such "unitary evolution" can be carried out up to the classical limit AND actually derive such classical state!

That is covered in numerous papers, e.g.:

http://arxiv.org/abs/quant-ph/0006117

http://arxiv.org/abs/quant-ph/0204129

http://arxiv.org/abs/quant-ph/0205108

http://arxiv.org/abs/quant-ph/0612118

 

[ZapperZ]

That is covered in numerous papers, e.g.:

http://arxiv.org/abs/quant-ph/0006117

http://arxiv.org/abs/quant-ph/0204129

http://arxiv.org/abs/quant-ph/0205108

http://arxiv.org/abs/quant-ph/0612118

Wonderful! Now derive the coin-tossing scenario! That shouldn't bee too difficult now, should it? After all, you have all the "tools" here that you need!

{For the final time, references to ArXiv article are NOT sufficient or recommended as a valid citation. Please find out where these preprints were published and use those as references}

Zz.

 

[ZapperZ]

I don't think a coin toss is equivalent of the Schrödinger Cat experiment (SCE) either, but for an additional reason: the result of a coin toss is, in principle, not a random outcome. It may be the case that the only true example of a random outcome is the realization of a quantum state.

We can argue forever about the mixed state of the cat in a box. It hasn't gotten us anywhere since the 1920's. I'm arguing that the real significance of the SCE is that it makes the case that strict determinism is not a true description of the world insofar as the world can be modeled by science. I've stated my reasoning in my two previous posts here (#36 and 38).

The problem here is that you're making an argument based on a matter of TASTES. I made an argument based on available empirical observations. The FACT that we have no "weird quantum-like phenomena" at the classical scale is my evidence. Despite what has been claimed about coin tossing, we have never, ever detected the effects of superposition of states of [head,tail]. We have, however, detected effects of superposition when 10^11 supercurrent flows simultaneously in two opposite directions.

Experimental evidence trumps any and all theoretical assertions.

Zz.

 

[SW VandeCarr]

The problem here is that you're making an argument based on a matter of TASTES. I made an argument based on available empirical observations. The FACT that we have no "weird quantum-like phenomena" at the classical scale is my evidence. Despite what has been claimed about coin tossing, we have never, ever detected the effects of superposition of states of [head,tail]. We have, however, detected effects of superposition when 10^11 supercurrent flows simultaneously in two opposite directions.

Experimental evidence trumps any and all theoretical assertions.

Zz.

I'm not sure I'm disagreeing with you. Perhaps you misunderstood my post. I'm simply saying that regardless of how decoherence actually operates, we obtain random outcomes in observing quantum states. Other outcomes in the classical world can be made contingent (by us) to these random outcomes such that they too cannot be predicted in principle (such as SCE). This is an argument against strict determinism even though QM is a deterministic model. I don't see how this is a matter of taste. I said the outcome of a coin toss is not, in principle, a random event (unless it could be demonstrated to be dependent on the realization of a quantum state).

 

[canoe]

Maybe, maybe not.

While decoherence may play a significant role in the quantum-to-classical transition, there are several other possible explanations. Some of them are not necessarily in competition with decoherence. For example, a recent paper has shown that our "coarse-grained" measurement of such a system can already cause an onset of classical measurements. Read my entry on this:

https://www.physicsforums.com/showthread.php?p=1520644

This issue of classical-quantum separation isn't a done deal, not by a long shot. We simply cannot make any definitive statement about how one evolve into another because, in physics, as it should be, we need to be able to empirically verify them, and verify them to our satisfaction. There's a lot still to be done before we get even close to that.

Zz.

An interesting read...

And of course you are entirely correct on the transitory nature of theories. Yet at any moment in time a particular principle or theory prevails. At this point in time I believe that the principle of decoherence has gained favor. I will initiate a new post based on my particular question.