Does Schrodinger's cat know whether it's dead?

ZapperZ

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That the system can be said to exist in both a1 and a2 states simultaneously. Interference is the result of superpositions of two or more waves(say passing through the double slit experiment). When performing a certain measurement on a quantum state, the result is described by a probability distribution, however we don't observe superpositions, objects in superpositions are not real(do not exist) until the state vector reduction that describes the evolution of the system.
Actually, the system exists in state |1> and |2>, not a1 and a2. But never mind. What is puzzling is that, how did you jump from what you view as what quantum superposition say, to this:

GeorgCantor said:
The problem with decoherence is that it doesn't say that matter(objects) are there all the time with properties in space. On the contrary, though it doesn't explain why we observe exatly what we do, it says that physical structures are not always there. If this doesn't blow one's mind, one must have rocks in his head.
?

Remember, this was my original question/objection!

I have no idea why you decide to give me a lesson in tunneling. Have YOU done any experiment in quantum tunneling? I have.

Zz.
 
No, because it was all subjectively stated with words like striking and appears

How about now:

"The MOST weird feature of quantum mechanics is the existence of superposition states, which are confirmed by multiple observations, logical inference and millions of practical applications to be evidence that an object was in different situations at the same time."
 

Pythagorean

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I don't think so. Read the wiki on indistinguishable particles. That's where superposition comes from, and particularly, it's a major difference between classical and quantum particles.

I think you're making a private interpretation about the evidence.
 
Actually, the system exists in state |1> and |2>, not a1 and a2. But never mind. What is puzzling is that, how did you jump from what you view as what quantum superposition say, to this:

GeorgCantor said:
The problem with decoherence is that it doesn't say that matter(objects) are there all the time with properties in space. On the contrary, though it doesn't explain why we observe exatly what we do, it says that physical structures are not always there. If this doesn't blow one's mind, one must have rocks in his head.
Remember, this was my original question/objection!.


Loose language, i guess. I meant to say superpositions, not decoherence(not just decoherence) but i think the point i was making was still comprehensible(or i hope so). My next posts centered around superpositions of cats, etc. That's what it was intended to have meant anyway.
 

ZapperZ

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Loose language, i guess. I meant to say superpositions, not decoherence(not just decoherence) but i think the point i was making was still comprehensible(or i hope so). My next posts centered around superpositions of cats, etc. That's what it was intended to have meant anyway.
But that makes it even contradictory. Here, you say that the object exists in all the possible orthogonal states:

GeogCantor said:
That the system can be said to exist in both a1 and a2 states simultaneously. Interference is the result of superpositions of two or more waves(say passing through the double slit experiment). When performing a certain measurement on a quantum state, the result is described by a probability distribution, however we don't observe superpositions, objects in superpositions are not real(do not exist) until the state vector reduction that describes the evolution of the system.
But in the quote that I originally objected to, you say they DON'T exists in any of the states!

GeorgCantor said:
The problem with decoherence is that it doesn't say that matter(objects) are there all the time with properties in space. On the contrary, though it doesn't explain why we observe exatly what we do, it says that physical structures are not always there. If this doesn't blow one's mind, one must have rocks in his head.
In fact, you claim that it doesn't say that it exist "all the time with properties of space"!

Look at what you wrote and see if it is not only consistent with physics, but consistent with each other.

Zz.
 
GeorgCantor said:
"The MOST weird feature of quantum mechanics is the existence of superposition states, which are confirmed by multiple observations, logical inference and millions of practical applications to be evidence that an object was in different situations at the same time."


I don't think so.Read the wiki on indistinguishable particles. That's where superposition comes from, and particularly, it's a major difference between classical and quantum particles.


I read it, still no reference where superpositions are coming from.



I think you're making a private interpretation about the evidence.

Evidence of what? Of superpositions? And what do you mean by "private" interpretation? That of Standard Quantum Mechanics? If so, then that's got to be a wholly world-wide "private" interpretation of the evidence, taught in ALL the major universities around the world.


Pythagorian said:
That's where superposition comes from, and particularly, it's a major difference between classical and quantum particles.
Very helpful insight, but can you show me specifically where it is explained where "superpositions" come from(from the wiki or other source) before you take the Nobel Prize.
 
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But in the quote that I originally objected to, you say they DON'T exists in any of the states!
Zz.

Yes, that's right. They don't exist as objects but they EXIST as probabilities. I made it clear several times that i was speaking of objects. There is no contradiction(see in the quotes you made the term 'object'),.
 

Pythagorean

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You must have not read t very thoroughly. Go back and look under "statistical Properties of bosons and fermions".

No need to be hostile. I'm not expecting a nobel prize for something I was taught in the standard coursework and can be found in an introductory text on qm.
 

ZapperZ

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Yes, that's right. They don't exist as objects but they EXIST as probabilities. I made it clear several times that i was speaking of objects. There is no contradiction(see in the quotes you made the term 'object'),.
But this is what is thoroughly wrong!

Existing as merely "probability" will not produce the coherence gap in the SQUID/Delft experiments! When I tossed a coin, the outcome exists merely as probabilities. You can't do anything with those probabilities other than wait for an actual measurement. This is not true in QM. You can, in fact, detect the superposition of those states, especially via a measurement of a non-commuting observable. The fact that there are such a thing as bonding-antibonding states, the coherence gap, etc.. etc. clearly shows that in those cases, both states EXIST and produced a physically significant outcome of a measurement that would not be there had they not exist.

Since you like to quote PhysicsWorld article, how come you didn't pay any attention to http://physicsworld.com/cws/article/news/2815" [Broken]?

Physicsworld said:
In 1935 Erwin Schrodinger proposed a famous thought experiment in which a cat was somehow both alive and dead at the same time. Schrodinger was attempting to demonstrate the limitations of quantum mechanics: quantum particles such as atoms can be in two or more different quantum states at the same time but surely, he argued, a classical object made of a large number of atoms, such as a cat, could not be in two different states. Now Jonathan Friedman and co-workers at the State University of New York (SUNY) in Stony Brook have demonstrated a macroscopic Schrodinger cat state for the first time (Nature 406 43). In their experiment a superconducting device is placed in a quantum superposition of two states: one that corresponds to a current flowing through the device in a clockwise direction, and another that corresponds to an anti-clockwise current.
Nowhere in there is there any implied scenario that it is the probability that is 'existing'. Rather, there is an explicit indication that (i) both properties are simultaneously present and (ii) they are the "object" itself. This review is the Stony Brook's SQUID experiment.

Zz.
 
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But this is what is thoroughly wrong!

Existing as merely "probability" will not produce the coherence gap in the SQUID/Delft experiments! When I tossed a coin, the outcome exists merely as probabilities. You can't do anything with those probabilities other than wait for an actual measurement. This is not true in QM. You can, in fact, detect the superposition of those states, especially via a measurement of a non-commuting observable. The fact that there are such a thing as bonding-antibonding states, the coherence gap, etc.. etc. clearly shows that in those cases, both states EXIST and produced a physically significant outcome of a measurement that would not be there had they not exist.

Since you like to quote PhysicsWorld article, how come you didn't pay any attention to http://physicsworld.com/cws/article/news/2815"?





Nowhere in there is there any implied scenario that it is the probability that is 'existing'. Rather, there is an explicit indication that (i) both properties are simultaneously present and (ii) they are the "object" itself. This review is the Stony Brook's SQUID experiment.

Zz.



Okay, this makes sense and i see the point you were trying to make from the beginning. Assuming that the experiment holds for larger objects, you are justified in saying that the cat(the object 'cat') does exist in all possible states simultaneously.

I've just learned a new definition of 'exist' that makes my bewilderment even greater. Perhaps because my brain got as fuzzy as its quantum states.
 
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You must have not read t very thoroughly. Go back and look under "statistical Properties of bosons and fermions".

No need to be hostile. I'm not expecting a nobel prize for something I was taught in the standard coursework and can be found in an introductory text on qm.



I didn't see it in my quantum physics textbook and i couldn't find mention of derivation of superpositions in Penrose "The Road to Reality".

I took your statement literally and it seemed to strongly imply that it is possible to derive superposition states from more basic principles, which would make quantum mechanics a fully deterministic theory. Of course this can't be done without a TOE, we are adjusting the formalism to what we observe, not vice versa.
 

Pythagorean

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I didn't see it in my quantum physics textbook and i couldn't find mention of derivation of superpositions in Penrose "The Road to Reality".

I took your statement literally and it seemed to strongly imply that it is possible to derive superposition states from more basic principles, which would make quantum mechanics a fully deterministic theory. Of course this can't be done without a TOE, we are adjusting the formalism to what we observe, not vice versa.
My statement was literal. If you don't want to formally confirm it for yourself form the wiki article:

David Griffith, Introduction to Quantum Mechanics, Section 5.1.1, Two Particle Systems: Bosons and Fermions.

The only reason I press the point is because for me, it was the ah-ha moment when I realized what "superposition of states" really meant. There's also some interesting insights about the uncertainty principle here:

http://en.wikipedia.org/wiki/Uncertainty_principle#Uncertainty_principle_and_observer_effect
 

apeiron

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Nowhere in there is there any implied scenario that it is the probability that is 'existing'. Rather, there is an explicit indication that (i) both properties are simultaneously present and (ii) they are the "object" itself.
To call the SQUID superposition an object would be misleading as an object is tangible, within the grasp of the senses. And of course the experiment only observes one or other direction of the current. Which is why I presume you put object in quotes. But even then, the superposition does not seem object-like in the sense you appear to mean - a persistent ring of activity.

The situation is just the same as a twin slit superposition. A condition is created in which a current is made to take both paths, resulting in a measurable self-interference, just as the twin slit creates an interference pattern. But would we call the "thing" passing through the twin slit situation a single "object"?

Superposition is a state to which neither the terms exist, nor non-existent, really apply. Georg's problem is that he wants to divide the world into these two strict categories as they are the two options that are possible under realism.

Clearly, he says, something in superposition does not fully exist in the naive realistic sense. But then he jumps to the conclusion, well, superposition must be a state of non-existence.

The SQUID example, just as much as twin slit experiments, shows that superpositions have physically-measureable consequences. So they exist in some sense. They can occupy a place and a time, as they do for nano-seconds in a super-cooled SQUID ring. But new words would be needed to describe the status of a superposition.

I have already suggested vagueness (vagueness being that to which the law contradiction does not apply - Peirce). But regardless, both existence and non-existence are too strong as descriptions of superpositions.
 

ZapperZ

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To call the SQUID superposition an object would be misleading as an object is tangible, within the grasp of the senses. And of course the experiment only observes one or other direction of the current. Which is why I presume you put object in quotes. But even then, the superposition does not seem object-like in the sense you appear to mean - a persistent ring of activity.
You are forgetting, or did not know, that a supercurrent is described by a coherent, single wavefunction, i.e. it is a macro-object. The same way that an entangled pair are considered to be "one" object.

The whole point of that experiment is to show that size doesn't matter to show quantum phenomena. If you can make the object's constituents coherent among themselves, then the whole thing is a single quantum object. Again, this is why http://www.pnas.org/content/94/12/6013.short" claims that superconductivity is the clearest manifestation of quantum phenomena at the macroscopic scale. It is the easiest means that we know of to create such "large" quantum object.

The situation is just the same as a twin slit superposition. A condition is created in which a current is made to take both paths, resulting in a measurable self-interference, just as the twin slit creates an interference pattern. But would we call the "thing" passing through the twin slit situation a single "object"?
Yes, I would. Protons and neutrons can do the same thing too. But are you disqualifying them because they are made up of quarks?

Superposition is a state to which neither the terms exist, nor non-existent, really apply. Georg's problem is that he wants to divide the world into these two strict categories as they are the two options that are possible under realism.

Clearly, he says, something in superposition does not fully exist in the naive realistic sense. But then he jumps to the conclusion, well, superposition must be a state of non-existence.

The SQUID example, just as much as twin slit experiments, shows that superpositions have physically-measureable consequences. So they exist in some sense. They can occupy a place and a time, as they do for nano-seconds in a super-cooled SQUID ring. But new words would be needed to describe the status of a superposition.

I have already suggested vagueness (vagueness being that to which the law contradiction does not apply - Peirce). But regardless, both existence and non-existence are too strong as descriptions of superpositions.
I only used the word 'exist' because that seems to be a popular phrase in this subforum. I've already cited a reference for a more useful terminology "physically significant". Still, the issue here is that, even without changing the words and phrase, people need to understand the actual physics involved before trying to describe it in words. The problem with learning and understanding physics through pop science description will not stop with redefining or coming up with a new phrase to replace "exist". I've seen way too many people going off on a tangent in here using various phrases in physics and taking them to mean something else - what I often called the bastardization of physics. There is no substitute to actually understanding the formalism. Period. Anything else is simply a translation of a translation.

Zz.
 
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Nowhere in there is there any implied scenario that it is the probability that is 'existing'. Rather, there is an explicit indication that (i) both properties are simultaneously present and (ii) they are the "object" itself. This review is the Stony Brook's SQUID experiment.

Zz.



When you transition from cat to "they", what happens to the law of conservation of energy?
 

ZapperZ

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When you transition from cat to "they", what happens to the law of conservation of energy?
The cat IS "they" in that experiment, i.e. a coherent, macroscopic object. So I don't undergo any transition in going from one thing to the same thing. Besides, why is there a "conservation of energy" issue here all of the sudden?

If you are asking about the superconducting transition, that's another topic altogether.

Zz.
 

apeiron

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You are forgetting, or did not know, that a supercurrent is described by a coherent, single wavefunction, i.e. it is a macro-object. The same way that an entangled pair are considered to be "one" object.
I agree both are object-like in ways, but also say they lack essential attributes of objects - in the ordinary realist sense. The same is true of classical things too, like solitons.

So it would still be nice if there was a way to talk about these things neutrally, rather than worrying about their failure to exist properly, or to be definite somethings.

We call them super-states (yet they seem less than real, even if they have some extraordinary properties). We call them quasi-particles (which is not too bad a term). We call them condensates (which says something directly about the mechanism that forms such states, so that is good). We call them weird (which is bad again as again QM is becoming a challenge to realism rather than the as yet undetermined base of the real).
 

ZapperZ

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I agree both are object-like in ways, but also say they lack essential attributes of objects - in the ordinary realist sense. The same is true of classical things too, like solitons.
It's hard to force Mother Nature to conform to our prejudices.

We call them super-states (yet they seem less than real, even if they have some extraordinary properties). We call them quasi-particles (which is not too bad a term). We call them condensates (which says something directly about the mechanism that forms such states, so that is good). We call them weird (which is bad again as again QM is becoming a challenge to realism rather than the as yet undetermined base of the real).
Not sure what the point in all of this is. "Quasiparticles" are very much well-defined within the Landau's Fermi Liquid Theory. If you consider the renormalized particle as an object, then I can't see why you can't accept the superfluid as one, considering the latter has a clearer coherence than the latter.

Zz.
 

apeiron

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It's hard to force Mother Nature to conform to our prejudices.
Which was why I was arguing the opposite - using a language in which the embedded prejudices conform with nature. But I see you have no interest in the topic.
 

apeiron

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When you transition from cat to "they", what happens to the law of conservation of energy?
Are you now talking about actual cats or examples of QM superpositions like SQUID rings and entangled buckyballs?

Does anyone still think that Schrodinger's cat can be in a state of superposition rather than decoherence? Clearly, what all the QM experiments spell out is how fragile and specific are the conditions for superposition to linger and persist in ways which seem quasi-object like in our classical realm. You need temperatures around absolute zero, or other special material conditions to get quantum condensates of matter.

So to get a cat into superposition, perhaps it would be possible, but only if you, for a start, super-cooled it. At which point, it would be dead for other reasons. And being an inhomogenous mix of atoms, not a collection of identical particles, even dropping a cat in liquid helium is unlikely to bring about a QM coherent state - a QM quasi-object.
 

Hurkyl

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Does anyone still think that Schrodinger's cat can be in a state of superposition rather than decoherence?
Decoherence doesn't destroy the superposition -- it just, FAPP, makes it a mixed state.
 

ZapperZ

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Which was why I was arguing the opposite - using a language in which the embedded prejudices conform with nature. But I see you have no interest in the topic.
I have no interest in the topic because the "effort" has to come from both directions. So far, we seem to want play name games, i.e. let's not call Pluto a planet, as if Pluto really cares. We can call it anything you want, but it still will not change the fact that most people barely understand what the physics is but would not hesitate to "philosophize" on them.

Zz.
 

apeiron

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Decoherence doesn't destroy the superposition -- it just, FAPP, makes it a mixed state.
I don't agree with "mixed state". In post #41 (https://www.physicsforums.com/showpost.php?p=2795251&postcount=41) I argued that it pushes the superposition issue to the margins.

Mixed state has the implication that a macro-object like a warm cat can be actually in a mixture of states. But experiments confirm that mixed states only exist in quasi-object fashion in marginal situations. The QM formalisms may not contain that clear distinction within them (in their current state of development). But FAPP, Schrodinger's cat can be expected to be a decohered object rather than a quasi-object.
 
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I've read several descriptions of the Schrodinger's cat thought experiment, but I've never heard anyone discuss whether the cat qualifies as an observer that can collapse the superposition of states. This seems like too simple a question not to have been raised before, but I've never head anyone raise it.

If it is, how is the thought experiment valid? If the cat being aware of its own death or continued life can collapse the superposition, then the cat is either alive or dead and not in a superposition of states.

If it is not, that raises the question of what qualifies as an observer that can collapse the superposition. Do you have to be human to be able to observe a superposition of states such that the superposition will collapse? That seems like an absurdity.
The whole idea of this QM interpretation that you need a conscious observer to collapse the wave function is already absurd, and feeds the philosophical position of Idealism.

And of course a dead cat doesn't know it's dead.
 

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