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

[GeorgCantor]

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]

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]

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]

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.

 

[GeorgCantor]

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]

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]

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]

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]

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]

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 Schrödinger'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]

Does anyone still think that Schrödinger'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]

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]

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, Schrödinger's cat can be expected to be a decohered object rather than a quasi-object.

 

[robheus]

I've read several descriptions of the Schrödinger'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.