Is the cat alive, dead, both or unknown

[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?

 

[bhobba]

Do you imply that QFT is not realistic?

I make no claims one way or the other. Simply that locality in QM does not apply to correlated systems.

Thanks
Bill

 

[zonde]

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

Ok, rejecting locality leads to "action at a distance". So you say that the way out without involving "action at a distance" is to reject "naive realism", right?
Then what rejecting "naive realism" changes in that model I linked?

 

[bhobba]

Ok, rejecting locality leads to "action at a distance". So you say that the way out without involving "action at a distance" is to reject "naive realism", right? Then what rejecting "naive realism" changes in that model I linked?

See the conclusion: Reality must be non-local.

This is standard textbook stuff. All you have posted is an alternate derivation of Bells Theorem that showed you can't have both realism and locality. You can reject realism and retain locality - you can also reject both.

I am also saying that in QFT the concept of locality isn't even defined in this instance because it precludes correlated systems which EPR is. Its more subtle than the argument assumes.

Thanks
Bill

 

[zonde]

See the conclusion: Reality must be non-local.

This conclusion can't be made before loophole free Bell test has demonstrated violation of Bell inequality. So it's currently not justified.
But this is conclusion, not the model. So can you point out the catch in the model excluding conclusion?

This is standard textbook stuff. All you have posted is an alternate derivation of Bells Theorem that showed you can't have both realism and locality. You can reject realism and retain locality - you can also reject both.

Relaxing realism might be standard textbook stuff in philosophical literature but certainly not in science literature.

I am also saying that in QFT the concept of locality isn't even defined in this instance because it precludes correlated systems which EPR is. Its more subtle than the argument assumes.

You don't have to define locality in physics, you get it included with concept of distance.

 

[my2cts]

Yes - so?

Thanks
Bill

Read your own post.
Thanks

 

[bhobba]

This conclusion can't be made before loophole free Bell test has demonstrated violation of Bell inequality. So it's currently not justified.

Bells Theroem is a theorem in QM. If QM is true its true. The loophole if its not closed would disprove QM.

This is all standard textbook stuff - why you want to rehash it beats me.

Thanks
Bill

 

[bhobba]

Read your own post.

I know what I said. If you don't agree what pure state is system A in?

Thanks
Bill

 

[bhobba]

Relaxing realism might be standard textbook stuff in philosophical literature but certainly not in science literature.

You might like to read what Bell said:
https://cds.cern.ch/record/142461/files/198009299.pdf

Or even our own Dr Chinese.

Again this is standard textbook stuff eg Chapter 20 Ballentine.

EPR started it all with it's elements of reality:
http://www.drchinese.com/David/EPR.pdf

Can you please read the literature first.

Thanks
Bill

 

[my2cts]

QUOTE="bhobba, post: 5147364, member: 366323"]I know what I said. If you don't agree what pure state is system A in?

Thanks
Bill[/QUOTE]

A and B are entangled, so they are not acting like separate systems.
You ask the wrong question.

 

[bhobba]

A and B are entangled, so they are not acting like separate systems.

Exactly. And in that case what I proved in that an observation on system A shows its in a mixed state.

Thanks
Bill

 

[my2cts]

I know what I said. If you don't agree what pure state is system A in?

Thanks
Bill

I am glad you do. I also know what you said.
The cat subsystem is not in a superposition state, but the entire system is.
(Unless somebody is watching, who then becomes entangled with it).
In one of the states making up the complete state, the cat is alive. In the other it is dead.
Unless that whole/broken flask of HCN is overlooked, the observation is of the entire system.

 

[bhobba]

I am glad you do. I also know what you said.
I argue that the observation is not on a subsystem (the cat) but on the entire system.
Unless you overlooked that whole/broken flask of HCN, the observation is of the entire system.

Well I believe, and every textbook I have read on it says (its all standard textbook stuff) that if you observe system A you are not observing system A+B. It seems rather obvious. But if you don't agree - shrug.

Thanks
Bill

 

[zonde]

Can you please read the literature first.

Thanks for your concerns, but I have read the literature.

 

[my2cts]

Well I believe, and every textbook I have read on it says (its all standard textbook stuff) that if you observe system A you are not observing system A+B. It seems rather obvious. But if you don't agree - shrug.

Thanks
Bill

We probably read a disjoint set of textbooks. Mine said that if you observe A+B you do not observe A!
Try a different textbook.

 

[write4u]

I was referring to the Bohm's state of pure potential from which the Implicates form, which then are expressed in reality as the ExplicatePerhaps I am using this in the wrong context, but this link came to mind, https://en.wikipedia.org/wiki/Quantum_superposition

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

Thank you for clarifying. It's interesting that you understand and admire his physics but reject his metaphysical "musings". I have little knowledge of QM, but I identify with some of his metaphysical descriptions. I do agree that it probably has very little RW value. I just like the concept of the Pilot Wave and its inherent superposed potentials becoming expressed through a series of hierarchical steps.

I thought this might somehow apply to Schrodinger's Cat.

 

[my2cts]

if you don't agree - shrug

Not only I do not agree, it is worse.
You present a point of view that is at least incomplete if not incorrect.
But hey, shrug you too !

 

[bhobba]

Mine said that if you observe A+B you do not observe A! Try a different textbook.

It's called removing system B from control by a partial trace.

The bible on this is Schlosshauer - Decoherence - And The Quantum To Classical Transition. See section 2.4.6 on the reduced density matrix.

Of course it is entangled with system B - I am not denying that - in fact I specifically said it was. However if you just observe system A then its in a mixed state. There is no attempt to hoodwink anyone, tell an incomplete story etc etc. Its simply if you just observe system A you are not observing system A+B. In fact often, like Schroedingers cat, you don't even have access to system B.

Thanks
Bill

 

[Nick666]

I have read somewhere that Bell relies on counterfactual measurements , and these measurements somehow arent possible in nature ?

The math was something like: How can

be true at the same time as

, and still have a function that is time dependent ?

 

[bhobba]

I have read somewhere that Bell relies on counterfactual measurements

Counterfactual measurements are simply measurements you didn't take - its associated with counterfactual definiteness which a link has been given to.

Its one of the assumptions in Bell - most say it's the same as naive reality - but there is a subtle difference.

Thanks
Bill

 

[Nick666]

Allright, I see you say (?) that Bell's theorem (and QM) contradicts naive reality, but Bell(and QM) assumes CFD, so there must be some difference between CFD and naive reality, but what is that subtle difference ?

 

[rootone]

States which can only exist given that their opposite exists.
There has to be a movie in there somewhere.

 

[Nick666]

And what about the math thing I wrote ?

 

[zonde]

Allright, I see you say (?) that Bell's theorem (and QM) contradicts naive reality, but Bell(and QM) assumes CFD, so there must be some difference between CFD and naive reality, but what is that subtle difference ?

Maybe bhobba associates "naive realism" with non-contextual (hidden) variables. Say we believe that photon has objective property "polarization" and it can be determined by polarizer regardless of the state of polarizer (idependently from any hidden variables polarizer might have).
CFD I perceive as more general idea that it is meaningful to ask "what if" type questions. And these questions are meaningful even with contextual variables.

 

[atyy]

Allright, I see you say (?) that Bell's theorem (and QM) contradicts naive reality, but Bell(and QM) assumes CFD, so there must be some difference between CFD and naive reality, but what is that subtle difference ?

I don't quite understand this myself and am not sure what counterfactual definite really means nor if everyone means the same thing by it, but according to https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics MWI is not counterfactual definite. I would certainly count MWI as "naive reality" (assuming it works). So that could be a case in which naive reality and CFD differ. I find it easier to say that one assumption of a Bell inequality is that each experiment has only one outcome, whereas MWI assumes otherwise.

 

[harrylin]

[..] 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.

Also in classical physics, uncorrelated experiments that are sufficiently separated in space have unrelated results... and in any case, Galilean transformations have nothing to do with non-locality!

 

[bhobba]

Allright, I see you say (?) that Bell's theorem (and QM) contradicts naive reality, but Bell(and QM) assumes CFD, so there must be some difference between CFD and naive reality, but what is that subtle difference ?

Its not me saying it:
http://drchinese.com/David/Bell_Theorem_Easy_Math.htm

Dr Chinse spells out the two assumptions. Here the assumption that is being discussed is:
I call this assumption "Bell Reality". And... this assumption is the equivalent of assuming that the moon is there when no one looks.

This is also called naive realism. But the technical assumption is counter-factual definiteness. Its the ability to speak meaningfully of observations that haven't been done.
http://physics.stackexchange.com/qu...lism-in-locality-and-counterfactual-definiten

I personally think they are the same - but philosophy types draw a distinction and logically they are correct - but its a bit nit picky in my view.

Thanks
Bill

 

[bhobba]

II would certainly count MWI as "naive reality" (assuming it works).

So would I. It however is not counter-factual definite because you can't speak meaningfully about future measurements.

Thanks
Bill

 

[Nick666]

But if in the Bell experiment counterfactual measurements can't physically be done , why would the experiment get physical predictions or physical results?

Or at least that's what I understand, that counterfactual measurements can't physically be done.

 

[bhobba]

But if in the Bell experiment counterfactual measurements can't physically be done , why would the experiment get physical predictions or physical results?

Couterfactual definiteness doesn't say they can't be done.

Did you go through Dr Chinese's proof?

Thanks
Bill

 

[zonde]

I think that people tend to mix what is sufficient assumption for Bell inequalities and what is necessary assumption.
Sufficient assumption allows proving Bell inequalities but relaxing sufficient assumption does not necessarily invalidate Bell inequalities.
On the other hand relaxing necessary assumptions would necessarily invalidate Bell inequalities.

Say assumption that hidden variables are non-contextual is sufficient assumption of Bell inequalities but it is not necessary assumption because contextual hidden variables can't violate Bell inequlities either.