Is the cat alive, dead, both or unknown

[OCR]

Really, a very interesting thread... And, the cat is alive, however, he's getting... very pissed !

Carry on...

 

[jerromyjon]

How would we look at 3 cats in 2 boxes. We could only ever find 2 dead cats...

https://en.wikipedia.org/wiki/Bhabha_scattering
https://en.wikipedia.org/wiki/Møller_scattering

Those mean anything interesting?

 

[Buzz Bloom]

Hi JerromyJon:

The cat is alive or dead. Period.

Please read https://en.wikipedia.org/wiki/Schrödinger's_cat . It makes clear that Schrödinger's intention was to demonstrate by a paradox that the Copenhagen interpreation of QM was logically untenable. The way you have been discussing this thought experiment (TE) seems to be stuck in the paradox of the Copenhagen interpreation. Here is a quote:

Schrödinger coined the term Verschränkung (entanglement) in the course of developing the thought experiment.​

Entanglement interpretation has until recently also been caught in a similar paradox, which also has the same interpretive resolution I have recomended about the cat. You may want to look at

https://www.physicsforums.com/threads/entanglement-question.811193/​

and other threads about entaglement.

In the cat TE, the state of the particle which interacts with the detector is still unknown until the box is opened, but it has also had an unknown effect on the cat. Until the box is opened, the state of the partcle and the state of the cat are entangled.

Consider the TE elaborated a bit. Suppose the detector did not only conditionally emit a poison gas, it also set an electro-mechanical bit to 1 or 0 in a separate box. Suppose the bit is moved very far away from the cat's box. Now is is clear that the state of the cat and the state of the far away bit are entangled. If the bit box is looked at, it will instantly "predict" what will be seen when the cat box is opened, and vice versa. But there is no action at a distance faster than light message sending required.

Similarly, in the original TE, the past state of the particle is entangled with the state of the cat. The two possible states of the cat are exactly that, superimposed discrete possibilites. QM could predict the probability of each of these two possible cat states, but the reality of which of the the two states will be detected when the box is opened remains unknown until the box is opened. That is an interpretation of supersition of states that avoids paradox. The states are only contingent possibilities until a detector discovers the reality.

I hope this will be helpful,
Buzz

 

[bhobba]

It makes clear that Schrödinger's intention was to demonstrate by a paradox that the Copenhagen interpreation of QM was logically untenable.

If that was his intention (it wasn't) he failed.

Its purpose was to highlight a blemish with Copenhagen - namely where you put the classical quantum cut. The obvious place was at the particle detector - if you do that no issue arises. However the interpretation didn't force you to put it there. That's it, that's all.

In the cat TE, the state of the particle which interacts with the detector is still unknown until the box is opened, but it has also had an unknown effect on the cat. Until the box is opened, the state of the partcle and the state of the cat are entangled.

I have no idea where you are getting this from, but the the state of the cat has nothing to do with the opening or not of the box.

Thanks
Bill

 

[harrylin]

If that was his intention (it wasn't) he failed.

Its purpose was to highlight a blemish with Copenhagen - namely where you put the classical quantum cut. The obvious place was at the particle detector - if you do that no issue arises. However the interpretation didn't force you to put it there. That's it, that's all.

I have no idea where you are getting this from, but the the state of the cat has nothing to do with the opening or not of the box.

Thanks
Bill

Interesting discussion about the myth of single "Copenhagen interpretation":

"The Copenhagen interpretation is often taken to subscribe to a solution to the measurement problem that has been offered in terms of John von Neumann's projection postulate. In 1932 he suggested that the entangled state of the object and the instrument collapses to a determinate state whenever a measurement takes place. This measurement process (a type 1-process as he called it) could not be described by quantum mechanics; quantum mechanics could only described type-2 processes (i.e., the development of a quantum system in terms of Schrödinger's equation). According to von Neumann, the shift from a type 2-process to a type 1-process takes place only in the presence of the observer's consciousness. So what causes such a collapse seems to be the mind of the observer. But von Neumann never explained how it was possible for something mental to produce a material effect like the collapse of a quantum system. This led to the famous paradox of Schrödinger's cat. Although von Neumann's position is usually associated with the Copenhagen Interpretation, such a view was definitely not Bohr's [..]
[..]
The Copenhagen interpretation is not a homogenous view. This insight has begun to emerge among historians and philosophers of science over the last ten to fifteen years."
- http://plato.stanford.edu/entries/qm-copenhagen/

 

[bhobba]

The Copenhagen interpretation is not a homogenous view.

It isn't.

But it overall has a number of features discussed here, as well as its blemishes, and resolutions:
http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html

Thanks
Bill

 

[KiNGGeexD]

The cat is in a superposition of states and when you observe the cat it will collapse into the dead state, or the alive state! It's a thought experiment simply to highlight that until a measurement is made there is no way to predict the state of the cat. Determinism disappears on a quantum level and we can only calculate probabilities. Hence the power of a qubit which like a bit can have two states, 0 or 1, or a superposition of both of those states, hence more processing power. To highlight what I'm trying to say :)Regards

 

[bhobba]

The cat is in a superposition of states and when you observe the cat it will collapse into the dead state, or the alive state!

That's incorrect.

I explained carefully earlier on with the math that is exactly what is NOT going on. Because the cat is entangled with the emitted particle and you just observe the cat it is in a mixed state - not a superposition. In fact you can push it all the way back to the particle detector that is entangled with the emitted particle and is really the clearest way of looking at it. But people are so fixated with the cat its what I used.

Thanks
Bill

 

[Derek Potter]

The cat is in a superposition of states and when you observe the cat it will collapse into the dead state, or the alive state! It's a thought experiment simply to highlight that until a measurement is made there is no way to predict the state of the cat. Determinism disappears on a quantum level and we can only calculate probabilities. Hence the power of a qubit which like a bit can have two states, 0 or 1, or a superposition of both of those states, hence more processing power. To highlight what I'm trying to say :)

Your assertion about superposition, determinism and collapse is an interpretation. It also presupposes there is such a thing as "the quantum level".

 

[Buzz Bloom]

Hi Bill:

I have no idea where you are getting this from, but the the state of the cat has nothing to do with the opening or not of the box.

I hope you will excuse an small attempt at humor in my response.

I understand that there are controversies about the philosophical spectrum of possibilities for interpreting QM phenomena, in particular concerning when a particle's state changes from a superposition of possibilites to a specific single state. At one extreme, the answer is an interaction with another particle. At the other extreme, it's when a conscious mind becomes aware of a measurement. In between, there are many possible criteria that are plausible in different contexts. One such middle-of-the-road criteria is the detector. On weekends, I prefer the detector. On Monday and Tuesday I prefer the interaction, On Thursday and Friday, I prefer the mind. On Wednesday, I make up something new in the middle. Today is Thursday, so opening the box does make a difference.

A friend with a PhD in particle physics once explained a very complicated TE to me. A particle with a superposed state of discrete possibilities has a state detected, and the detection puts the particle into a different superposed state with different probabilites. If the information in the detector is destroyed before the a state of the changed particle is detected, are the probabilities of it's possible states different than if it had not been destroyed? As I vaguely remember the math of his argument, (paradoxically?) there would be a difference.

What I learned from my friend's TE (and some Zen study) is that any philosophical choice for when the superposed state changes to a discrete state can make a reasonable interpretaion of QM that works until one can find an implied paradox. One can then accept that: The true nature of reality is fundementally paradoxical, or one can choose an alternative for which a paradox has not yet been found.

Thanks for your discussion,
Buzz

 

[bhobba]

If the information in the detector is destroyed before the a state of the changed particle is detected

It will make no difference. If the detector changed state due to the detection (it could hardly not if it detected something), the thing it detected has changed state, and any further detection on that has nothing to do with what happened to the first detector.

This is tied up with what are called filtering type observations.

If your views are from discussions with someone who had advanced understanding may I suggest you start with the basics? The following is a good start:
https://www.amazon.com/dp/0465062903/?tag=pfamazon01-20

What I learned from my friend's TE (and some Zen study) is that any philosophical choice for when the superposed state changes to a discrete state can make a reasonable interpretaion of QM that works until one can find an implied paradox. One can then accept that: The true nature of reality is fundementally paradoxical, or one can choose an alternative for which a paradox has not yet been found.

I don't know too much about Zen. My background is applied math and from that perspective I have learned quite a bit of QM. What I can tell you is, while QM is counter intuitive, and somewhat weird, once you understand it, there is no paradox. Its simply a theory about observations. Schroedinger's Cat, if it didn't have a lot a guff written about it, would be seen as trivial. There is an observation at the particle detector and that's it - everything is classical from that point on.

Thanks
Bill

 

[Derek Potter]

,

Hi Bill:
I hope you will excuse an small attempt at humor in my response.

I understand that there are controversies about the philosophical spectrum of possibilities for interpreting QM phenomena, in particular concerning when a particle's state changes from a superposition of possibilites to a specific single state. At one extreme, the answer is an interaction with another particle. At the other extreme, it's when a conscious mind becomes aware of a measurement. In between, there are many possible criteria that are plausible in different contexts. One such middle-of-the-road criteria is the detector. On weekends, I prefer the detector. On Monday and Tuesday I prefer the interaction, On Thursday and Friday, I prefer the mind. On Wednesday, I make up something new in the middle. Today is Thursday, so opening the box does make a difference.

A friend with a PhD in particle physics once explained a very complicated TE to me. A particle with a superposed state of discrete possibilities has a state detected, and the detection puts the particle into a different superposed state with different probabilites. If the information in the detector is destroyed before the a state of the changed particle is detected, are the probabilities of it's possible states different than if it had not been destroyed, As I vaguely remembe the math of his argument, paradoxically there would be a difference.

What I learned from my friend's TE (and some Zen study) is that any philosophical choice for when the superposed state changes to a discrete state can make a reasonable interpretaion of QM that works until one can find an implied paradox. One can then accept that: The true nature of reality is fundementally paradoxical, or one can choose an alternative for which a paradox has not yet been found.

Thanks for your discussion,
Buzz

Well QM has nothing to do with philosophy - nothing more than the discovery that what we usually think of as reality is different from the way we usually think of it. That doesn't make it Zen, unless Zen is a lot less profound than I've been led to understand. Different from our preconceptions is not paradox.

I would agree to some extent that attempting to chase the wavefunction collapse into a corner does lead to some extraordinary claims. However this is only an issue if one insists on the state, the wavefunction, being a physical entity, or hidden property that *exists*. If one restricts discussion to things that are observable, there is no paradox, there is no collapse as such, there is just calculation of probabilities.

One may prefer to assume that the wavefunction does exist. In this case one must also saywhy observables take only their obvious (or not-so-obvious) values, such as alive or dead. Within this restricted category of interpretations (those which assume an ontic wavefunction) there is a sub-category, namely those which assume that the wavefunction jumps around when observed. It is these "actual collapse" theories which generate paradoxes. Even then, they can largely be removed if we make certain that the collapse is postponed until after all measurements have been rendered irreversible by creating macroscopic records.

edit -
But why introduce collapse at all? The appearence of collapse is explained by entanglement. The emergence of a preferred basis (the obvious values) is explained by decoherence. Why have collapse at all if it is not needed. the result may be called MWI: the system remains in a superposition of |dead> and |alive> states. The |dead> state means the state of the system - the particle (thanks, Bill), the cat, the apparatus, the observer, the environment - in which the cat is dead. Whether the observer has seen it or not makes no difference. the paradox goes away just leaving the student of QM plaintively wailing "But it's still a superposition, what happens to the other cat?" That's not a paradox it just means nature, under these suppositions (ontic wavefunctions that don't collapse) is different from what we might expect.

 

[votingmachine]

The easy way to think about it is that a measurement will collapse the wave function, and so will change the probabilities of outcomes, and can be used to send a message.

How can it be used to send a message?

 

[KiNGGeexD]

That's incorrect.

I explained carefully earlier on with the math that is exactly what is NOT going on. Because the cat is entangled with the emitted particle and you just observe the cat it is in a mixed state - not a superposition. In fact you can push it all the way back to the particle detector that is entangled with the emitted particle and is really the clearest way of looking at it. But people are so fixated with the cat its what I used.

Thanks
Bill

Apologies Bill,

I was going by what I had read in Griffiths intro to Quantum Mechanics, we live and learn, thanks for posting that link! Very interesting

 

[Buzz Bloom]

Hi Derek:

I think we agree on almost everything you said in your post #212.

Well QM has nothing to do with philosophy

I think that whether or not QM has anything to do with philosophy is a philosophical issue. Do you agree that QM consists of (1) math, (2) theory, and (3) experimental measurements, and nothing else? If not, please explain what I left out.

Is the math real? Is that a philosophical issue? As I vaguely remember Plato, he said something about ideal circles. They were either more real than the idea circle of the "real" world, or not real at all.

Is the theory real? Is that a philosophical issue? What is the nature of the realtionship between QM theory and reality? Is that a philosophical issue?

Are experimental measurements real? I think we agree that they are. Is that a philosophical issue?

That doesn't make it Zen

My readings about Zen is what first led me to think about the possibly paradoxical nature of reality. The paradoxes arising in readings about QM as well as my friend's TE made the thoughts more clear to me.

It is these "actual collapse" theories which generate paradoxes. Even then, they can largely be removed if we make certain that the collapse is postponed until after all measurements have been rendered irreversible by creating macroscopic records.

I think I agree with this completely. My post #203 was mostly an attempt to make this point by buiding a context for the conclusion:

The states are only contingent possibilities until a detector discovers the reality.

Also, my post #210 was mostly about

when a particle's state changes from a superposition of possibilites to a specific single state.

This was intended to explain that this choice was neither the math nor the theory of QM. We may still disagree, but to me the choice is philosophical.

Thanks for your discusssion,
Buzz

 

[Derek Potter]

Schrodinger's intention was stated by himself:

One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter, there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.
It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a "blurred model" for representing reality. In itself, it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.

He is quite specific. At the time there was a popular interpretation of a quantum state as being fuzzy or blurred-out. His thought experiment refutes this interpretation.

Notice too that he glosses over the OP question. The thought experiment certainly raises the question but Schrodinger was not addressing it. So when we ask "is the cat alive, dead, both or unknown?" we need to be clear which model we are using. For one thing the question does not ask "what will the observer see?", it is a question about what state the cat is in. We know that the observer will see either the cat dead or alive. That doesn't mean the cat is either one thing or the other - it could be that nature hides the real state of the cat and we just see one aspect of it.

 

[Buzz Bloom]

Hi Bill:

Thanks for the recommdation of a good primer about QM. I have been looking for one that would teach me a little knowledge about QM.

 

[Derek Potter]

This was intended to explain that this choice was neither the math nor the theory of QM. We may still disagree, but to me the choice is philosophical.
Buzz

I would not dignify it as philosophy. :) We can either accept what nature tells us or not!

 

[KiNGGeexD]

I should perhaps point out that at no point did I say the state of the cat being dead and alive was a non-zero probability scenario, I was simply stating the lack of determinism! The "slipperiness" of language

 

[votingmachine]

How can it be used to send a message?

Looking closer, I see that most places say it can't be used to send a message.

 

[Buzz Bloom]

Hi Derek:

We can either accept what nature tells us or not!

I believe (philosophically) that what nature tells us with respect to QM is the experimental results of QM measurements. I do not believe (philosophically) what QM theory tells us is the same as what nature tells us. And what QM theorists tell us, about what nature is telling us in terms of QM theory (rather than QM experiments), I believe (philosophically) is philosophy.

BTW, you also said:

Notice too that he glosses over the OP question.​

I am sorry for my denseness, but what does OP mean?

Thanks for the discussion,
Buzz

 

[OCR]

... the interpretation didn't force you to put it there.

That, (my bold) was "the blemish", Erwin Schrödinger was trying to illustrate...

It really was...

That's it, that's all.

 

[Buzz Bloom]

Hi harrylin:

http://plato.stanford.edu/entries/qm-copenhagen/

I much enjoyed your intersting post about the history of the Copenhagen Interpretation. and especially the link. I have always had a fuzzy understanding of this topic and now it has become somewhat clearer.

Thanks for you post,
Buzz

 

[StevieTNZ]

BTW, you also said:

Notice too that he glosses over the OP question.​

I am sorry for my denseness, but what does OP mean?

OP is commonly short for Original Poster (i.e. the starter of the thread).

 

[Buzz Bloom]

Hi Stevie TNZ:

Thanks for your post answering my question about OP.

Regards,
Buzz

 

[harrylin]

[..] I believe (philosophically) that what nature tells us with respect to QM is the experimental results of QM measurements. I do not believe (philosophically) what QM theory tells us is the same as what nature tells us.

Yes indeed. Nature gives us clues, and it's we who next tell ourselves things about nature based on our interpretation of what we see.

And what QM theorists tell us, about what nature is telling us in terms of QM theory (rather than QM experiments), I believe (philosophically) is philosophy.

It depends who you ask; some stay "down to earth" and stick with predictions about observations. A problem occurs when people draw metaphysical conclusions and then pretend that those are facts of nature, that nature tells us that.

 

[Derek Potter]

Hi Derek:
I believe (philosophically) that what nature tells us with respect to QM is the experimental results of QM measurements. I do not believe (philosophically) what QM theory tells us is the same as what nature tells us. And what QM theorists tell us, about what nature is telling us in terms of QM theory (rather than QM experiments), I believe (philosophically) is philosophy.

Sorry, OP = Original Post or Original Poster

Yes, I agree that nature tells us experimental results. It also tells us that QM predicts those results. That is a fact of nature too.

 

[Buzz Bloom]

Hi Derek:

Yes, I agree that nature tells us experimental results. It also tells us that QM predicts those results. That is a fact of nature too.

I accept your clarification with a minor philosophical alteration.

There is always an expermental error range. Nature tells us not only that a scientific prediction was made, but also how good. And in particular, it tells us that QED math predictions are far better (far more accurate with the smallest error ranges) than those of any other science. However, the criteria used to judge whether a prediction was "acceptably good" or not are philosophical. This is similar to the distinction between an platonic geometric ideal circle and the "real" circles we see in nature. The QED predictions are among the ideals of nature, but not exactly the same as "real" nature.

Thanks for your discussion,
Buzz

 

[Derek Potter]

i

Yes indeed. Nature gives us clues, and it's we who next tell ourselves things about nature based on our interpretation of what we see.
It depends who you ask; some stay "down to earth" and stick with predictions about observations. A problem occurs when people draw metaphysical conclusions and then pretend that those are facts of nature, that nature tells us that.

There is nothing metaphysical about asserting that the wavefunction of Schrodinger's cat is the wavefunction of a cat which is neither dead nor alive but both at once. The assertion may or may not make sense and it may or may not be a justifiable claim if it does, but it is emphatically not about introducing metaphysical postulates into QM. QM has a single metaphysical postulate: that observations occur according to its maths. That's all it needs. To explain away a single paradoxical scenario by saying it involves metaphysics is to question whether QM itself is always right. Far better to analyse what the paradoxical wavefunction actually means *within* the QM paradigm. Ironically, there is no need to stick with "observations are the only reality". One may argue that since it accurately describes what we observe, the wavefunction is, in some sense, real. Even if it's only a distillation of some underlying dynamics. In that case the redundant metaphysics actually does no harm - the superposition turns out to entail a mixed state through entanglement anyway. The paradox goes away unless you bring yet another metaphysical assumption to the matter - namely that the universe cannot support Schrodinger cat states. Why anyone should feel they can dictate what the universe can or cannot do I don't know.

 

[Derek Potter]

Hi Derek:

I accept your clarification with a minor philosophical alteration.

There is always an expermental error range. Nature tells us not only that a scientific prediction was made, but also how good. And in particular, it tells us that QED math predictions are far better (far more accurate with the smallest error ranges) than those of any other science. However, the criteria used to judge whether a prediction was "acceptably good" or not are philosophical. This is similar to the distinction between an platonic geometric ideal circle and the "real" circles we see in nature. The QED predictions are among the ideals of nature, but not exactly the same as "real" nature.

Thanks for your discussion,
Buzz

Bayesian probability would say you are wrong. If your prior assumption is that Schrodinger's cat is implausible to a googleplex of decimal places then the success of QED to a few dozen should have negligible effect on your skepticism. Mind you, you would still need to explain why it works. It's not really about ideal mathematics and practical accuracy, it's whether superposed cat states make logical sense at all.

 

[Buzz Bloom]

Hi Derek:

The assertion may or may not make sense and it may or may not be a justifiable claim if it does, but it is emphatically not about introducing metaphysical postulates into QM.

There is a distinction between (1) an philosophical assertion about a QM interpretation, and (2) an assertion that introduces metaphysical postulates into QM.
I agree (2) is a mistake. But (1) is just philosophizing about the real world based on interpreting QM theory.

Thanks for your discussion,
Buzz

 

[Buzz Bloom]

Hi Derek:

Bayesian probability would say you are wrong. If your prior assumption is that Schrodinger's cat is implausible to a googleplex of decimal places then the success of QED to a few dozen should have negligible effect on your skepticism. Mind you, you would still need to explain why it works. It's not really about ideal mathematics and practical accuracy, it's whether superposed cat states make logical sense at all.

I confess I am confused by the logic here. I don't see the connection from Baysian math to "whether superposed cat states make logical sense at all".

I think you and I agree that "superposed cat states make logical sense". I think we may (I'm not sure) disagree about what that means about nature. I do not think it means that the cat is both alive and dead. There are (at least) two possible philosophical altermatives based on when a superposition "collapses".
Before the box is opened:
(1) Collapse at the detector: Then the cat is either alive or dead depending on what was detected.
(2) Collapse when a conscious mind knows the outcome: Then the cat is still in a superposed state of two entangled contingent (not yet real) outcomes. It requires opening the box for the collapse to occur.

(1) seems more "logical" than (2). But (2) does not violate what QM is or is not able to predict.

Thanks for your discussion,
Buzz

 

[Derek Potter]

Whjat is there to philosophize about? I have never seen a cat that is alive and dead at the same time. I do not know how to build a detector of cats in the
.707(|dead> +/- |alive>) states. I have a perfectly good theory that predicts both - the inability to build a detector is not technological, it is due to decoherence and therefore something explained by the theory - and it assumes only that observations exist but (obviously) requires that the system state persists between observations. I have nothing to philosophize about, I only have questions about the physical meaning of "cat states".

Anyway, nice to talk about this stuff but we have veered a long way from the OP. I don't knoqw whether the question has been properly answered. It has made me wonder why people make such a definite statement as "the cat is both dead and alive at the same time" I have been guilty myself.

 

[Derek Potter]

Hi Derek:
I confess I am confused by the logic here. I don't see the connection from Baysian math to "whether superposed cat states make logical sense at all".

I think you and I agree that "superposed cat states make logical sense". I think we may (I'm not sure) disagree about what that means about nature, I do not think it means that the cat is both alive and dead. There are (at least) two possible philosophical altermatives based on when a superposition "collapses".
Before the box is opened:
(1) Collapse at the detector: Then the cat is either a;ive or dead depending on what was detected.
(2) Collapse when a conscious mind knows the outcome: Then the cat is still in a superimposed state of two entangled contingent (not yet real) outcomes. It requires opening the box for the collapse to occur.

(1) seems more "logical" than (2). But (2) does not violate what QM is or is not able to predict.

Thanks for your discussion,
Buzz

(3) There is no collapse.
The success of QM has confirmed a key assumption of the maths, that if a system can be in state |A> or state |B> then it can also be in a state of a|A>+b|B>. Is that odd or what? If I can be in New york and I can be in Paris then I can be partly in (interpret it how you wish) both. (NOT halfway, which would be trivial.) Collapse is a postulate that is added to QM to restore common-sense - I can't really be in two places at once. Well common-sense is not always right and reintroducing "one state at a a time" when superposition is needed anyway for the maths seems contrived.

"Consciousness causes collapse" is not testable since a typical experiment creates a superposition of data records. These would have to collapse. As they include memories, no-one would notice the collapse. Far more productive to remove collapse altogether (we have improper mixed states anyway, so why add superfluous proper ones?) and then - and only then - indulge in philosophizing about whether "all those other worlds" are acceptable.

 

[Buzz Bloom]

Hi Derek:

.707(|dead> +/- |alive>) states.

I think the issue is the "interpretation of the states: |dead> and |alive>.
(1) |dead> means he cat is dead, AND |alive> means the cat is alive.
(2) |dead> means he cat will at collapse be dead, AND |alive> means the cat will at collapse be alive.

Since today is Thursday, I find (1) OK, since I find paradoxes OK on Thursdays. If today were Monday, I would find (1) to be an unacceptable paradox. Any day of the week I think (2) is OK. (See my post #210 for an explanation about days of the week.)

Thanks for your discussion,
Buzz

 

[Derek Potter]

But why should the cat be just one thing or the other? It's not a logical necessity unless the two possibilities are mutually exclusive and you cannot prove that. You can only assume it. Which is a metaphysical assumption. To put it bluntly most of the accusations of metaphysics come from people who bring their own prejudices to the subject and are levelled at those who have suggested that maybe we should drop them!

"Electrons in two places at one? Ridiculous! Metaphysical nonsense!"

Not you, of course, but you see the point, I hope.

sigh

 

[Buzz Bloom]

Hi Derek:

But why should the cat be just one thing or the other?

In the "real" world of nature (intentrionally omitting an afterlife), that is naively and intuitively (and philosophically) understood by (most?) people, life and death are logically mutually exclusive. (I also omit such strange phenomena as completely frozen frogs reviving to active life when thawed.)

"Electrons in two places at one? Ridiculous! Metaphysical nonsense!"

As I have tried to explain, I think the "metaphysical" issue has to do with one's tollerance for paradox.

BTW, as I am sure you know, the two-split phenomenon is not the same as entanglement. The problem interpetations involve two different paradoxes.

Thanks for your discussion,
Buzz

 

[Derek Potter]

Hi Derek:
In the "real" world of nature (intentrionally omitting an afterlife), that is naively and intuitively (and philosophically) understood by (most?) people, life and death are logically mutually exclusive. (I also omit such strange phenomena as completely frozen frogs reviving to active life when thawed.)

That is an assumption which is only true if the question "is this cat alive?" has to have a yes/no answer. If alive is a derived continuous quantity then an answer like "50%" is acceptable. That is the point of my saying "if a system can be in state |A> or state |B> then it can also be in a state of a|A>+b|B>".

"No! No! No!" I hear you cry, "A cat has to be one thing or the other."

"Because?"

"BECAUSE IT DOES ! "

As I have tried to explain, I think the "metaphysical" issue has to do with one's tollerance for paradox.

I have zero tolerance for paradox. Paradoxes need to be resolved. OK, we know that a century or more has been wasted trying to find the solution to self-referential statements. As far as I know, statements about things - like cats - have no such problems.

BTW, as I am sure you know, the two-split phenomenon is not the same as entanglement. The problem interpetations involve two different paradoxes.

They have the same solution, namely superposition. And superposition is not a phenomenon, it is a property of the maths.

 

[Derek Potter]

By the way, I do not think that QM is *only* about observations. The state of the system features centrally in the maths and, since it allows us to calculate outcome probabilities it seems unreasonable to deny that the real system has a state. The existence of a state that is subject to a well-defined model means we have an understanding about the world as well as a recipe for calculation. It is this implication of some sort of realism which leads to paradoxes. There is never a paradox about what we can observe, paradoxes arise when we try to square superposition with common-sense which wants states to be all-or-nothing. As far as I know, every counter-intuitive quantum result arises this way. But I've only looked at EPR, Young's slits, Kim's DCQE, Popper's paradox, Schrodinger's Cat, Wigner's Friend. Heisenberg's Uncertainty principle and Elitzur–Vaidman bomb testers. And probably a few more that don'y come to mind right now.

 

[Swamp Thing]

How can we define an operator or a POVM that would act on the wavefunction of a live virus and spit out "1", and give us "0" for a dead virus?

Likewise for an amoeba or a cat?

 

[Buzz Bloom]

Hi Derek:

That is an assumption which is only true if the question "is this cat alive?" has to have a yes/no answer.

I disagree that it is an assumption. I see it as a philosophical world view. (Whether it is an assumption or a world view, I think we agree that the question is irrelevant to QM.) I do not believe that a person who is trying to understand the way the world works just makes up assumptions. All their life experiences, e.g., upbringing, education, and hard knocks, creates a framework for them that allows some interpretations about experience to be OK, and others not OK. Whether they would call this collection of interrelated beliefs a philosophy is a matter of the way they have learned to use vocabulary.

"No! No! No!" I hear you cry, "A cat has to be one thing or the other."

I assume we can agree that the question can be focussed on the state of the cat just before the box is opened. For some people, not requiring a yes/no answer about "Is the cat alive?" is OK, and for others it is not. For the nots, it might be neither or both. It depends on their world view.

I think you misunderstood where I am about this. I am flexible in my world view, depending on when collapse occurs. On Saturday or Sunday (interaction), OR on Monday or Tuesaday (detector), I believe state of the particle, either at the interaction or as measured by the detector, causes the cat to be either alive or dead (focussing for clarity on just before the box is opened). On Wednesday and Thursday (mind), I think neither, because the probabilistic superposition state still exists until the collapse caused by a mind seeing the state of the cat when the box is opened. On Wendesday it could be anything, including both, but knowing my inclinations I think both is unlikely.

Thanks for your discussion,
Buzz

 

[rootone]

Buzz, I am sure this has been said before but consider this:
The state of the cat gets to be 'known' by a simple apparatus, (a camera for example, which plainly does not have a mind),
however whatever the camera recorded is not revealed to any conscious observer, it is stored as a digital file.
Some thousands of years later when nobody connected with experiment is still alive, and nobody cares that much, the file is copied millions of times and then made available to millions of observers simultaneously.
Did one of those observers cause a signal to travel back in time and cause the outcome which the camera recorded?, which one?

 

[Buzz Bloom]

Hi Derek:

I have enjoyed this dialog with you very much, since exploring the philosophy of science (along with the science), has been one of my life-long hobbies. I have found the dialog helpful to my articulating to myself more clearly what my world view is. I think though we are now reaching the point of repetition.

The existence of a state that is subject to a well-defined model means we have an understanding about the world as well as a recipe for calculation.

(underlining is mine)

I almost agree with this. I differ regarding the phrase I underlined. I would replace "an understanding" with "many understandings". There are as many undestandings as their are interpretations based on world views. Some of these "understandings are (much?) better suited than others to revise models and design experiments to test the changes.

It is this implication of some sort of realism which leads to paradoxes.

I almost agree with this also. I would replace "some sort of realism" with "some of the variety of interpretations about what is implied about the real world". Some interpretations immediately lead to paradoxes. Others take a whille until the interpretation leads to a modified model which makes new predictions, and when they produce unexpected results, new intepretations and paradoxes usually arise.

paradoxes arise when we try to square superposition with common-sense which wants states to be all-or-nothing.

I almost agree with this also. " I would add the word "sometimes" or even "frequently" before "arise". I have found that some "common-sense" is much more deep and/or complex and/or logical than others. To make the statement more true, I would add "naive" after "some". I think I have some common-sense which is not naive, and I don't necessarily want states to be all-or-nothing, especially on Wednesday.

Thanks for your discussion,
Buzz

 

[Buzz Bloom]

Hi rootone:

Did one of those observers cause a signal to travel back in time and cause the outcome which the camera recorded?, which one?

The short anwser is no. Your modified thought experiment (TE) and question raises one of the trickier issues concerning the "mind" point of view (POV) about when collapse of superposition of states occurs. If you choose this POV you must do so consistantly. I think only a few (philosophers?) believe this POV is the "true" view about the way the world works. However, no reverse time causality paradox is necessary. Since this modifed TE implies the box is never opened, so no one ever knows what happened to the cat until a photograph is viewed by a suitable mind, This mind must (by other knowledge) recognize the implication about how the cat died (by poison or by starvation). (It is surely dead at the time of picture viewing. The POV simply interprets that the superposed state of the cat at the time just before the box is opened as remaining the same, way into the future of that time, and the state only collapses when a picture is viewed and properly interpreted. Using this POV, the superposition of states relates only to the probability that someone at some time will discover the fate of the cat as being by poison or starvation. Until that happens since the knowledge is absent and there is no collapse, the state remains superposed.

Now there is another wrinkle. There was an interaction regarding the cat that changed the superposed state, but it did not collapse. The picture taking modifies the reasonable range of interpretation of the probabilities and also of the two superposed states. A later interaction with the cat makes another change. That is: when the box and the cat are cremated, so that it is then impossible for a mind to know the cause of death, unless and until a picture is viewed by a suitable mind.

Another modification to the TE: No pictures are taken, and the box and cat are cremated soon after the particle is emitted. Then it beomes imposible for any mind to ever know the cause of death: by poison or by burning. Then the burnning of the box and cat also changes the superposed state without collapsing it. It never collapses.

I hope this tale helps to clarify the nature of the implications of this POV: the mind is the collapser of suprposed states.

Thanks for your post,
Buzz

 

[Derek Potter]

How can we define an operator or a POVM that would act on the wavefunction of a live virus and spit out "1", and give us "0" for a dead virus?
Likewise for an amoeba or a cat?

Define "live" classically first. Use any criterion you like. For instance, live cats run warm, dead cats go cold. Measure the temperature by detecting thermal photons in a million detectors. Cat is alive if N>100,000, dead if not. The criterion should agree with classical intuition: that N will either be <<100,000 or >>100,000.

 

[Derek Potter]

Hi Derek:
I disagree that it is an assumption. I see it as a philosophical world view. (Whether it is an assumption or a world view, I think we agree that the question is irrelevant to QM.) I do not believe that a person who is trying to understand the way the world works just makes up assumptions. All their life experiences, e.g., upbringing, education, and hard knocks, creates a framework for them that allows some interpretations about experience to be OK, and others not OK. Whether they would call this collection of interrelated beliefs a philosophy is a matter of the way they have learned to use vocabulary.
I assume we can agree that the question can be focussed on the state of the cat just before the box is opened. For some people, not requiring a yes/no answer about "Is the cat alive?" is OK, and for others it is not. For the nots, it might be neither or both. It depends on their world view.

Well it shouldn't do. QM is perfectly clear about the state. Last time I looked, everyday experience did not equip us to deal with superpositions.

I think you misunderstood where I am about this. I am flexible in my world view, depending on when collapse occurs. On Saturday or Sunday (interaction), OR on Monday or Tuesaday (detector), I believe state of the particle, either at the interaction or as measured by the detector, causes the cat to be either alive or dead (focussing for clarity on just before the box is opened). On Wednesday and Thursday (mind), I think neither, because the probabilistic superposition state still exists until the collapse caused by a mind seeing the state of the cat when the box is opened. On Wendesday it could be anything, including both, but knowing my inclinations I think both is unlikely.
Thanks for your discussion,
Buzz

QM does not need collapse of the wavefunction. Talking about the collapse of the wavefunction as if it were a physical process is doubly pernicious - it is not needed and it gets in the way.

I agree with Zeh, who is associated with "Many Minds". In Zeh's interpretation, the wavefunction does not collapse so the observer's brain ends up in a superposition of states. In one state the brain has the sensory data of seeing a dead cat, in the other a live one. Obviously, though perhaps disconcertingly to some, the observer's brain experiences both.

"I never see both!" replies life experience.

"Oh yes you do, but here I am talking to, and you are recalling from, the dead-cat state, not both states. There is, no doubt, another state in which I am talking to, and you are recalling from, the alive-cat state, not both states. As both states exist in the wavefunction I'm afraid it's an inescapable fact unless the Lizard People are messing with our minds again."

 

[Derek Potter]

Buzz, I am sure this has been said before but consider this:
The state of the cat gets to be 'known' by a simple apparatus, (a camera for example, which plainly does not have a mind),
however whatever the camera recorded is not revealed to any conscious observer, it is stored as a digital file.
Some thousands of years later when nobody connected with experiment is still alive, and nobody cares that much, the file is copied millions of times and then made available to millions of observers simultaneously.
Did one of those observers cause a signal to travel back in time and cause the outcome which the camera recorded?, which one?

No. They all did. Only the collapse didn't occur either "back in time" nor when the observers found out. There is one hyper-observer, the composite of a million separate observers. There are 2^1000000 possible outcomes. Various of them were collapsed out of existence at precise intervals according to the digits of pi - in gazillionths of a second - until there was just one left which was actualized on the 19th February 3056, some 1865 years before the observation but 2309 years after the cat died. Nobody knows why nature chose to do it this way.

By the way [hint] people do not always realize when I am being sarcastic. Or that there is (usually) a constructive point behind it.

 

[Buzz Bloom]

Hi Derek:

The discussion seems to me to becoming more and more philosophical. I enjoy it, but it might be more appropriate to move it to a philosophy forum, such as:
http://onlinephilosophyclub.com/forums/ .

QM does not need collapse of the wavefunction. Talking about the collapse of the wavefunction as if it were a physical process is doubly pernicious - it is not needed and it gets in the way.

I agree that "collapse of the wavefunction" is not physics -- it is a philosophical interpretation of QM which may or may not be useful. In this discussion I found it to be useful as a framework for talking about scenarios of a TE.

I agree with Zeh, who is associated with "Many Minds".

As haven't read Zeh, but here is a quote from https://en.wikipedia.org/wiki/Many-minds_interpretation .

The many-minds interpretation of quantum mechanics extends the many-worlds interpretation by proposing that the distinction between worlds should be made at the level of the mind of an individual observer.​

As I interpert this, it seems to require a POV that a conscious mind is necesssary for a transition to occur from a superposed state to a one specifc choice among the possible states. The underlined text is a long-winded way of avoiding saying "collapse". Is that more useful for you?

I do not think Zeh's view is any more useful to me than Everett's many worlds interpretation (MWI). I would prefer not to go into philosophical reasons for my preference, but I prefer a variation of MWI in which the "many worlds" are not "real" but contingent -- a CMWI (contingent many worlds interpretation).

This means that the total instantaneous state of a single real world at any time has a combination of "real" particles with "real" properties which are "real" measurements, together with "real" particles with contingent possible future measurements with specific probabilities that are related to both the present and future times when these measurements might take place. (Whether these contingent possible future states are "real" before they are measured, or not "real", is not relevant to the CMWI.) Each possible combination of future measurements defines a contingent future world. So at any specific time there is one "real" world and (infinitely?) many contingent worlds. When a measurement is made, (infinitely?) many contingent worlds cease to have their contingent existence, since they are no longer compatible with the measurement. When there are interactions among the particles, there are several possible scenarios in which:

(1) new "real" particles are created with possibly some specific properties and some contingent properties
(2) existing "real" particles can cease to exist
(3) the values of both "real" and contingent properties of "real" particles (including their probabilities) are changed.
​

I appologize for the long explanation, but it is the best I can do to make the CMWI POV reasonably clear with relatively few words.

Thanks for your discussion,
Buzz

.

 

[Buzz Bloom]

Hi Derek:

I get from our dialog that in your mind you have a very clear POV about interpreting QM.

I do not have a single clear POV about interpreting QM. I have many. My day-of-the-week style was intented to communicate this concept in a somewhat light-hearted way. I have preferences, but I use different POVs at different times because I find different POVs useful in different contexts. I also believe that it's usefulness is more important that it's truth. I believe this belief is very useful.

I hope you won't interpret what I am about to say as negative -- I don't intend it that way.

I believe that having a single fixed POV about anything, QM, or theology, or anything else, is more harmful than useful. The usefulness of this belief is perhaps more visisble in theology than in choosing a philosophical interpretation about QM, but I believe it applies universally.

Regards,
Buzz

 

[Derek Potter]

Hi Derek:
The discussion seems to me to becoming more and more philosophical. I enjoy it, but it might be more appropriate to move it to a philosophy forum, such as:
http://onlinephilosophyclub.com/forums/

Then I have failed completely. I'm sorry. My intention is to divide up the ideas that attach themselves to interpretation into ideas that are the realm of physics and anything left over for the philosophers to play with.

I agree that "collapse of the wavefunction" is not physics -- it is a philosophical interpretation of QM which may or may not be useful. In this discussion I found it to be useful as a framework for talking about scenarios of a TE.

I don't know who you agree with. The collapse of the wavefunction is pure physics. I do not believe it to be a necessary or useful idea but it is a theory of physics nonetheless.

As haven't read Zeh, but here is a quote from https://en.wikipedia.org/wiki/Many-minds_interpretation .

The many-minds interpretation of quantum mechanics extends the many-worlds interpretation by proposing that the distinction between worlds should be made at the level of the mind of an individual observer.​

As I interpert this, it seems to require a POV that a conscious mind is necesssary for a transition to occur from a superposed state to a one specifc choice among the possible states. The underlined text is a long-winded way of avoiding saying "collapse". Is that more useful for you?

That is almost diametrically opposite to what MW is saying. There is no collapse and there is no "specific choice" in MW. Clue - the word "many"! MM follows from MW by adding the assumption that mind supervenes on the state of the brain. This is in order to get round the Hard Problem. If mind is defined as a "mental state" without implying consciousness (e.g. "the computer thinks you have logged off") then MM is indistinguishable from MW.

I do not think Zeh's view is any more useful to me than Everett's many worlds interpretation (MWI). I would prefer not to go into philosophical reasons for my preference, but I prefer a variation of MWI in which the "many worlds" are not "real" but contingent -- a CMWI (contingent many worlds interpretation).

You can have two levels of reality if you wish but you still have to account for the superselection required to transition from contingent to actual existence.

This means that the total instantaneous state of a single real world at any time has a combination of "real" particles with "real" properties which are "real" measurements, together with "real" particles with contingent possible future measurements with specific probabilities that are related to both the present and future times when these measurements might take place. (Whether these contingent possible future states are "real" before they are measured, or not "real", is not relevant to the CMWI.) Each possible combination of future measurements defines a contingent future world. So at any specific time there is one "real" world and (infinitely?) many contingent worlds. When a measurement is made, (infinitely?) many contingent worlds cease to have their contingent existence, since they are no longer compatible with the measurement. When there are interactions among the particles, there are several possible scenarios in which:

(1) new "real" particles are created with possibly some specific properties and some contingent properties
(2) existing "real" particles can cease to exist
(3) the values of both "real" and contingent properties of "real" particles (including their probabilities) are changed.​

I appologize for the long explanation, but it is the best I can do to make the CMWI POV reasonably clear with relatively few words.

There is a vast amount of physics going on in your scenario with creation and destruction of particles. But what is the maths behind the disappearence of "particles"? QM allows the cancellation of terms in a wavefunction: we call it interference. But how do contingent possibilities interfere? You need negative probabilities! These can be used in QM, but they are a warning flag that you are NOT talking about actual probabilities. Who ever heard of a biased coin coming down heads MINUS 40% or the time and tails 140%? Whoever heard of a negative number of events? Interpreting QM is not just a matter of concocting a picture of branching possibilities and labelling some as real, others as contingent and others as defunct. The picture must be consistent with wave mechanics. Which is why Everretian MW is viable but the branching universe picture is not. It is different physics and wrong. In fact viable MWI doesn't have defined braches: whether a branch subdivides depends entirely on what basis you (the commentator, not the observer) choose. (Basis=set of states that span the state space).