Is the cat alive, dead, both or unknown

[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?