Is the cat alive, dead, both or unknown

[bhobba]

A more complete explanantion would consider the collection to be a combination all all of the contingient universes for all of the particles for which there are unresolved superimposed potentials. In some more complicated thought experiments, multiple particles might involve a joint collection of superimposed potentials.)

The modern version of that view is after decoherence each part of the resultant mixed state is a separate world. You can find the full detail in David Wallaces book:
http://users.ox.ac.uk/~mert0130/books-emergent.shtml

Thanks
Bill

 

[write4u]

write4u said: ↑
Would it be correct to say that Schrodingers cat is in a state of superimposed potentials?

No. Its entirely classical. The observation occurred at the particle detector.
Thanks, Bll

Sorry, but that answer makes no sense, in context of the question. The superposition is before we make the observation. The experiment does not ask if the cat is dead or alive (or both), it asks when the cat is dead or alive. Until the uncertain trigger moment has arrived neither potential is explicate in reality and are superposed. We can only know when the trigger moment occurred (if at all), by looking at the particle detector (inside the box).
Until we look we cannot be certain which potential was expressed and for our purposes are superposed., IMHO. .

 

[carllooper]

Sorry, but that answer makes no sense, in context of the question. The superposition is before we make the observation. The experiment does not ask if the cat is dead or alive (or both), it asks when the cat is dead or alive. Until the uncertain trigger moment has arrived neither potential is explicate in reality and are superposed. We can only know when the trigger moment occurred (if at all), by looking at the particle detector (inside the box).
Until we look we cannot be certain which potential was expressed and for our purposes are superposed., IMHO. .

I think Bill is making a distinction between the system describing the atomic system and the cat. One can (pursuing silences in Copenhagen) enlarge the scope of that system to include the cat, the robot who opens the box, etc. Or one can contain it to the atomic system.

One can also (pursuing a different tack from Copenhagen) say that there is no dividing line. The atomic system, the cat, the entire universe is always in a superposition of states, regardless of observations.

Even when we look inside the box (or even the atomic system), there is no additional certainty, or decrease in uncertainty. When we look inside the box the cat (as a direct analogy of the atomic system) will be no different from if we didn't.

The cat will be alive or dead. A particle detection will be here or there.

To put it another way, in answer to the question: "is the cat alive or dead", regardless of whether the box is open or closed, the answer is yes.

C

 

[Quotidian]

'What did you do to the cat, Erwin? It looks half dead' ~ Mrs Schrodinger.

 

[Swamp Thing]

'What did you do to the cat, Erwin? It looks half dead' ~ Mrs Schrodinger.

Or maybe it was Scroedinger's Girlfriend, who famously accompanied him on that mountain hiking trip where he figured out his Equation.

Interestingly, it was the OP's GF who inpired this discussion

my girlfriend is wondering if while shroodingers cat was in the box, we should consider it as both unknown rather than both alive and dead. please shed some light on the subject.

 

[bhobba]

Sorry, but that answer makes no sense, in context of the question. The superposition is before we make the observation.

Its obvious the observation is made at the particle detector and occurs before the cat becomes involved or the box is opened.

My suspicion is you are confused by the term 'observation' thinking it involves a conscious observer. That is not its meaning in QM.

No one ever took seriously that the cat was in some weird live or dead superposition - in fact the prevailing Copenhagen interpretation said it wasn't, because it's obvious the observation occurred at the particle detector. The issue was the theory didn't force you to put the observation there - which was what the thought experiment highlighted. The other related issue is, since QM is a theory about observations that occur in a an assumed common-sense classical world, exactly how does that theory explain such a world - in reality everything is quantum. None of this invalidates the theory, or the standard interpretation - but its a blemish that's best done away with.

A lot of progress has been made in resolving it with a much better understanding of decoherence. But still a few issues remain. If you want to delve deeper into it, at the lay level here is the book to get:
https://www.amazon.com/dp/0465067867/?tag=pfamazon01-20

Also Lubos has written a rather good article on it:
http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html

Thanks
Bill

 

[Quotidian]

As a student of history, culture and ideas, I would say the significance of Schrodinger's remark is not something that can be simply papered over so that we can all go back to thinking that normalcy is restored. 'Move right along folks, nothing to see here', is what a lot of physicists seem to want to say. In actual fact, I'm with whoever said that reality is 'queerer than we can suppose'. We ought to live on the cusp of that, rather than persuading ourselves that everything simply adds up, especially in light of the enormity of the known philosophical and epistomological issues confronting physics.

(Incidentally I read Lindley's book previous work on http://amzn.com/1400079969, and whilst I thought it was a reasonable historical account, I thought it failed to grasp the depth of the philosophical issues at stake.)

 

[bhobba]

I would say the significance of Schrodinger's remark is not something that can be simply papered over so that we can all go back to thinking that normalcy is restored.

If by remark you mean the thought experiment, then I think you have to judge it by the appraisal of physicists about it. What they say, at least in modern times, is not what popularisations say, nor is it what philosophers sometimes say.

Technically its a variation of the argument I gave before in post 22 where the cat has been entangled with the atomic particle by the set-up. System A will be the cat and system B the atomic nucleus. We will take state |b1>|a1> as particle not emiited by nucleus, and cat alive, |b2>|a2> particle emitted and cat dead. We observe the cat - not the particle.

Now chugging through exactly the same math you get the mixed state 1/2|a1><a1| + 1/2|a2><a2|. This is NOT a superposition. Its a mixed state - the cat is either alive or dead. It comes about because of the set-up - we observe the cat - not the total system which is particle and cat.

Why didn't Schroedinger recognise this? Like I said decoherence wasn't as well understood in those days. And an issue still remains - its the difference between a proper and an improper mixed state - but that really requires another thread.

Thanks
Bill

 

[atyy]

Now chugging through exactly the same math you get the mixed state 1/2|a1><a1| + 1/2|a2><a2|. This is NOT a superposition. Its a mixed state - the cat is either alive or dead. It comes about because of the set-up - we observe the cat - not the total system which is detector and cat.

That is not correct. This mixed state is improper - it is not "ignorance interpretable".

 

[bhobba]

That is not correct. This mixed state is improper - it is not "ignorance interpretable".

Atty - you know as well as I do an improper mixed state is still a mixed state and is not a superposition. The reason its not a superposition is we are observing the cat and not the cat and particle emitted by the nucleus. The cat is entangled with it and observing the total setup is not the thought experiment - we observe the cat. Because of that it's a mixed state - not a superposition. The set-up precludes it.

Now if you want to discuss the difference between a proper and improper mixture we can do that - but I think it's better done in a separate thread.

Thanks
Bill

 

[atyy]

Atty - you know as well as I do an improper mixed state is still a mixed state and is not a superposition. The reason its not a superposition is we are observing the cat and not the cat and particle emitted by the nucleus. The cat is entangled with it and observing the total setup is not the thought experiment - we observe the cat. Because of that it's a mixed state - not a superposition. The set-up precludes it.

Now if you want to discuss the difference between a proper and improper mixture we can do that - but I think it's better done in a separate thread.

But that is the key point - the reason it is not ignorance interpretable is because the state is in some sense a superposition.

Also, the ignorance interpretability is the key point of this thread. Classical probability is always ignorance interpretable, which is why one never asks such bizarre questions in classical probability as whether the cat is alive or dead. In quantum mechanics (without BM or MWI), for either answer - superposition or improper mixed state - it is not ignorance interpretable, so cannot say that the cat is either alive or dead.

 

[Tristan C]

my girlfriend is wondering if while shroodingers cat was in the box, we should consider it as both unknown rather than both alive and dead. please shed some light on the subject.

The whole point of Schrodingers cat is that it is like a variable. This is obvious but if you think about it quantum Physics is about being able to figure it out without needing to see it. Algebra can teach us to solve for a variable. So is the cat dead or alive, it is uncertain but we can conclude that if it has nothing in the box with it it has died, because we can observe the y to get the x. All organisms die in time. The cat will die, but is it dead right now...that is our x.

 

[julcab12]

... In the Box experiment. It is usually 50/50. Details and summary. https://www.physicsforums.com/threads/clarifying-the-meaning-of-random-in-quantum-physics.819719/ #17.

 

[write4u]

I think Bill is making a distinction between the system describing the atomic system and the cat. One can (pursuing silences in Copenhagen) enlarge the scope of that system to include the cat, the robot who opens the box, etc. Or one can contain it to the atomic system.

One can also (pursuing a different tack from Copenhagen) say that there is no dividing line. The atomic system, the cat, the entire universe is always in a superposition of states, regardless of observations.

Even when we look inside the box (or even the atomic system), there is no additional certainty, or decrease in uncertainty. When we look inside the box the cat (as a direct analogy of the atomic system) will be no different from if we didn't.

The cat will be alive or dead. A particle detection will be here or there.

To put it another way, in answer to the question: "is the cat alive or dead", regardless of whether the box is open or closed, the answer is yes.

Yes, I was not so much looking at it through the lens of QM, but rather from that what comes before QM, Potential. The superposition of Implicates, before they are expressed in reality.

 

[bhobba]

But that is the key point - the reason it is not ignorance interpretable is because the state is in some sense a superposition..

That is the key point - you are observing one part of an entangled system so its NOT a superposition. Look at the actual superposition:
|p> = 1/√2|b1>|a1> + 1/√2|b2>|a2>

It's entangled and neither system is in an actual pure state. System A is not in superposition. System B is not in superposition. But what the argument shows is if you just observe system A then it is in a mixed state.

I often discuss decoherence and I sometimes get the feeling a key point is being missed by some. This seems to be it. In entangled systems each system is not in a pure state - in fact the concept makes no sense at all in such a situation. However if you observe one part of the combined system it is in a mixed state.

Thanks
Bill

 

[bhobba]

Yes, I was not so much looking at it through the lens of QM, but rather from that what comes before QM, Potential.

Can you explain to me what you mean by QM Potential?

I read a lot of QM books and I haven't come across that before.

Thanks
Bill

 

[Buzz Bloom]

Hi Bill:

The modern version of that view is after decoherence each part of the resultant mixed state is a separate world. You can find the full detail in David Wallaces book:
http://users.ox.ac.uk/%7Emert0130/books-emergent.shtml

I have not read Wallaces' book, but I have read a summary. If I remember correctly, Wallaces' Emergent Multiverse consists of multiple real universes. I found that idea too science-fictiony for my taste. This contrasts with the idea in my post in which the multiple universes are only contingent and at the moment of an observation those that were depended on a state that is not the one observed cease to exist as as a possible contingent universe.

That is one view, but a very very backwater view these days because of the severe problems it poses. For example imagine we did a Schroedinger's Cat with a robot opening the lid that recorded the result to computer memory. We then made billions of copies and scattered each copy across the cosmos. A million years later someone reads the contents of one of those copies - it would be a very very weird view of the world that's when it collapsed - and all of those copies collapsed. You could probably formulate a consistent view of the world along those lines - but - like solipsism - most would reject it as unnecessarily contrived.

I agree that based on extreme #2 one can invent thought experiments that result in very weird consequences. However, that kind of consequence does not seem to prevent physisists from continuing to make interpretations of QM with similar weird consequences. In my opinion, the entanglement action at a distance interpreation was generally accepted as good physics by many physisists, although I understand that more recently, an alternative interpreation based on something like Wallaces' multiverse has replaced action at a distance as an accptable interpreation of entanglement.

Do you know of any actual real experment that shows convincingly that interpretation #2 is untenable? I have in mind an experiment regarding some QM phenomenon like entanglement or a double split apparatus rather than cats.

BTW, using #2, as I interpret your thought experment with robots and computer memories, as long as no conscious mind ever experiences whether the cat is alive or dead, and no consciuosness ever becomes aware of the result of the robot's action in any computer memory, then the state of the cat remains as it was before the lid was opened by the robot. I am not sure I undestand what bothers you concerning "it would be a very very weird view of the world that's when it collapsed - and all of those copies collapsed." What exactly is collapsing?

In the multiverse view there are two real universes, one in which the cat is alive and one in which the cat is dead. Until a conscious mind looks at a computer record, no conscious mind knows which univese s/he exists in. In the contingent universes view, until a conscious mind looks at a computer record, two contingent universes remain; when a conscious mind does finally look, one of the two continues as the real univese, and the other doesn't.

 

[bhobba]

In my opinion, the entanglement action at a distance interpreation was generally accepted as good physics my many physisists, although I understand that more recently, an alternative interpreation based on something like Wallaces' multiverse has replaced action at a distance as an accptable interpreation of entanglement.

Not that sure it was generally accepted - but we understand it better now.

It doesn't require action at a distance - its simply a correlation that forbids naive reality.

Locality in QM is encoded in the so called cluster decomposition property:
https://www.physicsforums.com/threads/cluster-decomposition-in-qft.547574/

It only applies to uncorrelated system which entangled systems are not. So the very concept of locality is pretty meaningless for entangled systems.

Thanks
Bill

 

[write4u]

Can you explain to me what you mean by QM Potential?

I read a lot of QM books and I haven't come across that before.

Thanks
Bill

I was referring to the Bohm's state of pure potential from which the Implicates form, which then are expressed in reality as the Explicate

Can you explain to me what you mean by QM Potential?

I read a lot of QM books and I haven't come across that before.

Thanks
Bill

Perhaps I am using this in the wrong context, but this link came to mind, https://en.wikipedia.org/wiki/Quantum_superposition

I always use Potetial in the Bohmian context of "that which may become reality"

 

[bhobba]

I was referring to the Bohm's state of pure potential from which the Implicates form, which then are expressed in reality as the Explicate

Bohm's implicate order is more philosophical musings (that's being charitable) than actual physics:
https://www.physicsforums.com/threads/david-bohms-holographic-paradigm-of-the-cosmos.252110/

As the above thread explains he had a number of phases - unfortunately that wholeness stuff was from the mystical, bonkas, meaningless phase. That in no way demeans the work of his excellent and brilliant phases.

I now understand what you are talking about however - the quantum potential is part of Bohmian Mechanics from his brilliant phase. However the implicate order stuff is, being kind, philosophical musings, but really its mystical nonsense.

Thanks
Bill

 

[atyy]

That is the key point - you are observing one part of an entangled system so its NOT a superposition. Look at the actual superposition:
|p> = 1/√2|b1>|a1> + 1/√2|b2>|a2>

It's entangled and neither system is in an actual pure state. System A is not in superposition. System B is not in superposition. But what the argument shows is if you just observe system A then it is in a mixed state.

I often discuss decoherence and I sometimes get the feeling a key point is being missed by some. This seems to be it. In entangled systems each system is not in a pure state - in fact the concept makes no sense at all in such a situation. However if you observe one part of the combined system it is in a mixed state.

Sure, let's not get hung up on terminology. Why don't you address the key point - the improper mixed state is not ignorance interpretable - hence it is not unknown in the sense defined by Nugatory.

 

[bhobba]

Sure, let's not get hung up on terminology. Why don't you address the key point - the improper mixed state is not ignorance interpretable - hence it is not unknown in the sense defined by Nugatory.

Its an improper mixed state - its requires an extra interpretive assumption to be proper. I am in no way hiding that.

Thanks
Bill

 

[atyy]

Its an improper mixed state - its requires an extra interpretive assumption to be proper. I am in no way hiding that.

Thanks
Bill

Yes, that's really what I mean when I say it is a superposition. It is because the whole system remains in pure state that the mixture of the reduced density matrix isn't proper without an additional interpretive assumption (such as something like collapse or hidden variables).

 

[Buzz Bloom]

Hi Bill:

its simply a correlation that forbids naive reality.

I think I understand what this means, and it seems to me to be consistant with Wallace and also with the contingent universe concept in my post.

I don't at all intend this to be negative, but the language "naive reality" used in the quote above seems to me to be quite philosophical rather than scientific. My interpretation is that philosophically entanglement and locality are mutually exclusive concepts.

Thanks for your insight,
Buzz

 

[bhobba]

I don't at all intend this to be negative, but the language "naive reality" used in the quote above seems to me to be quite philosophical rather than scientific. My interpretation is that philosophically entanglement and locality are mutually exclusive concepts.

Naive realism is the standard terminology used in scientific literature to discuss this stuff:
https://en.wikipedia.org/wiki/Naïve_realism

Its also tied up with something called counterfactual definiteness:
https://en.wikipedia.org/?title=Counterfactual_definiteness

Thanks
Bill

 

[zonde]

It doesn't require action at a distance - its simply a correlation that forbids naive reality.

I have posted this link a lot of times recently but let me post it one more time here:
https://www.physicsforums.com/showthread.php?p=2817138#post2817138
If you say that you can get around action at a distance please point out how one should modify this model to get expected correlations without action at a distance.
This model is very simple so it makes very easy to spot any attempts that do not work.
I used this model a lot of times until I came to conclusion that there is really no way how to get around action at a distance if QM predictions about entanglement are fully valid even in idealized loophole free Bell test.

 

[Buzz Bloom]

Hi Bill:

Naive realism is the standard terminology used in scientific literature to discuss this stuff:
https://en.wikipedia.org/wiki/Naïve_realism

The following is a quote from the wikipedia article:

Naïve realism, also known as direct realism or common sense realism, is a philosophy of mind rooted in a theory of perception that claims that the senses provide us with direct awareness of the external world.​

Note what I underlined. This seems consistent with what I said in my post: "seems to me to be quite philosophical." I didn't mean the philosophical sounding language could/should not be used in science. All kinds of language styles are used. Artsy: e.g., beauty and charm. Literary whimsy: e.g., quark. The article as a whole is quite philisophical, but seems to be mostly about psychological phenomena rather th an physical.

Its also tied up with something called counterfactual definiteness:
https://en.wikipedia.org/?title=Counterfactual_definiteness

This article says clearly that the term is used in discussing QM.

In quantum mechanics, Counterfactual definiteness (CFD) is the ability to speak meaningfully of the definiteness of the results of measurements that have not been performed​

The Introduction begins:

The subject of counterfactual definiteness receives attention in the study of quantum mechanics because it is argued that, when challenged by the findings of quantum mechanics, classical physics must give up its claim to one of three assumptions: locality (no "spooky action at a distance"), counterfactual definiteness, and https://en.wikipedia.org/w/index.php?title=No-conspiracy_assumption&action=edit&redlink=1​

To me this discussion sounds more like metaphysics than physics.

I think this all this has clarified somewhat the interpretation of Fynman's quote I presented in Post #29.

Thanks again for your discussion,
Buzz

 

[bhobba]

I have posted this link a lot of times recently but let me post it one more time here:
https://www.physicsforums.com/showthread.php?p=2817138#post2817138
If you say that you can get around action at a distance please point out how one should modify this model to get expected correlations without action at a distance.

Do you know what local reality means - and what disproving it means? Hint - Bell showed you can't have both reality and locality - not that you can't have either. Also locality in QM is a much more subtle concept than that article assumes. To be specific if you assume that reality does not exist independent of observation then they can simply be correlations

Thanks
Bill

 

[my2cts]

I my self am in a superposition state.
A superposition of me going to find the cat dead and of me going to find the cat alive.

 

[zonde]

Do you know what local reality means - and what disproving it means?

I know two meanings for locality:
- causal influences are no faster than speed of light
- distance is fundamental concept
What means to disprove the first case is more or less clear.
Second case can't be disproved because it's fundamental to science.

Hint - Bell showed you can't have both reality and locality - not that you can't have either.

It has been discussed here number of times. And the point is that locality without realism is meaningless.

Also locality in QM is a much more subtle concept than that article assumes.

You said "It doesn't require action at a distance". So go ahead. Use the model to point out where is the catch.

 

[my2cts]

That is the key point - you are observing one part of an entangled system so its NOT a superposition. Look at the actual superposition:
|p> = 1/√2|b1>|a1> + 1/√2|b2>|a2>

This looks like a superposition of |b1>|a1> and |b2>|a2> to me.
The system observed is cat + killing device + unstable atom.

 

[bhobba]

It has been discussed here number of times. And the point is that locality without realism is meaningless.

That's not true - see the link about cluster decomposition. Basically in QFT locality is that uncorrelated experiments that are sufficiently separated in space have unrelated results. Note the keyword - uncorrelated. Entangled systems are correlated.

Standard QM is non-local to begin with because its based on the Galilean transformations.

Thanks
Bill

 

[bhobba]

This looks like a superposition of |b1>|a1> and |b2>|a2> to me.

Yes - so?

Thanks
Bill

 

[bhobba]

You said "It doesn't require action at a distance". So go ahead. Use the model to point out where is the catch.

The catch is obvious. Just what don't you get about QM can't be both local and reject naive realism?

Thanks
Bill

 

[zonde]

That's not true - see the link about cluster decomposition. Basically in QFT locality is that uncorrelated experiments that are sufficiently separated in space have unrelated results. Note the keyword - uncorrelated. Entangled systems are correlated.

Do you imply that QFT is not realistic?