B Cat's point of view

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Summary
Schrondinger's Cat experiment with a different point of view
Hi,

In the Schrodinger's Cat thought experiment, we say that the cat is in a superposition of states of being either dead or alive. But isn't that opinion biased from being outside of the system? From the cat's point of view, it is either dead or alive but never both.

The same argument can be applied to macroscopic bodies as well. Before you enter a house, you can't say whether it is furnished or not. By the line of reasoning in the thought experiment, you could conclude that the house is in a superposition of states of being both furnished and unfurnished at the same time, but from the house's point of view, it is either furnished or unfurnished.

Can someone please let me know of a flaw in this line of reasoning?

Thanks,
Bhanu
 
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In the Schrodinger's Cat thought experiment, we say that the cat is in a superposition of states of being either dead or alive.
I don't know who that "we" is that you speak of (probably pop-science articles) but serious physiscists know that the cat is either alive or dead. The whole POINT that Schrödinger was making was/is that it's silly to think of the cat as being both alive and dead.
 

Mentz114

Gold Member
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Summary: Schrondinger's Cat experiment with a different point of view

Hi,

In the Schrodinger's Cat thought experiment, we say that the cat is in a superposition of states of being either dead or alive. But isn't that opinion biased from being outside of the system? From the cat's point of view, it is either dead or alive but never both.

The same argument can be applied to macroscopic bodies as well. Before you enter a house, you can't say whether it is furnished or not. By the line of reasoning in the thought experiment, you could conclude that the house is in a superposition of states of being both furnished and unfurnished at the same time, but from the house's point of view, it is either furnished or unfurnished.

Can someone please let me know of a flaw in this line of reasoning?

Thanks,
Bhanu
@phinds is correct.

Your reasoning is correct about macroscopic superposition.
According to QT, in this case it is not the cat that is or is not in a superposition - it is our information about the cat.
 
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From the cat's point of view, it is either dead or alive but never both.
This is interpretation dependent. According to the Many Worlds interpretation, the cat is both dead and alive; both the "cat dead" and the "cat alive" branches of the wave function exist. So on the MWI, "the cat's point of view" is more complicated than what you are implicitly assuming.

The whole POINT that Schrödinger was making was/is that it's silly to think of the cat as being both alive and dead.
Yes, but not everyone agrees that Schrodinger was correct.

Your reasoning is correct about macroscopic superposition.
Not if the MWI is correct; the MWI assumes that macroscopic superpositions can in fact occur.

According to QT, in this case it is not the cat that is or is not in a superposition - it is our information about the cat.
On QM interpretations in which the wave function is not real, but only describes our information about the system, yes, this is true. But not all QM interpretations are of this type.
 

Mentz114

Gold Member
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Not if the MWI is correct; the MWI assumes that macroscopic superpositions can in fact occur.


On QM interpretations in which the wave function is not real, but only describes our information about the system, yes, this is true. But not all QM interpretations are of this type.
Totally agree. But surely any interpretation that has a cat that is dead AND alive is obviously incorrect. Two different cats, perhaps ?
 
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surely any interpretation that has a cat that is dead AND alive is obviously incorrect.
No, since the MWI can be interpreted to be saying that. See below.

Two different cats, perhaps ?
It depends on what you mean by "different cats". The MWI says there is a branch of the wave function in which the cat is dead, and another branch in which it is alive, and both branches are real. Whether that counts as two different cats, or two copies of the same cat, or something else entirely for which we don't have good ordinary language words, is a matter of choice of words, not physics. The physics according to the MWI is simply that all branches of the wave function are real, and that's it.
 
Macroscopic superpositions are part of the usual quantum mechanics also. It is required for the consistency of the uncertainty relations. For instance, in a slit experiment, if we arrange a situation where we measure the momentum exchanged between the diaphragm and the particle, then the diaphragm whose momentum we measure is subject to the uncertainty relation, and has a position uncertainty ~ h/Δp. Thus a macroscopic object, the diaphragm, is in a superposition. The fact that the uncertainty relation applies to the diaphragm implies that the uncertainty in the position of the slits destroys the interference effects exactly the amount needed to protect the uncertainty relations.
 
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a macroscopic object, the diaphragm, is in a superposition.
This concept of "superposition" is basis dependent, and is not what we are talking about in the Schrodinger's cat thought experiment. The diaphragm is in a superposition of position states, but is not in a superposition of momentum states (because we just measured its momentum). And it's not entangled with anything, so there are no "multiple worlds" in the sense of the MWI. (Note that in the experiment you describe, there will be no interference.)

In the Schrodinger's cat thought experiment, the state of the cat is entangled with the state of the radioactive atom that decays inside the box, so the system of atom + cat as a whole is in a superposition of "atom decayed + cat dead" and "atom not decayed + cat alive". This kind of superposition is not basis dependent, and it is the kind that gives rise to multiple "worlds" in the MWI.
 

Mentz114

Gold Member
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It depends on what you mean by "different cats".
I knew you would say that. This topic (MWI) always becomes a discussion about what words mean.

I understand what you've said but I'll duck trying to answer.
 
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This topic (MWI) always becomes a discussion about what words mean.
Yes, because the ontology of the world according to the MWI is so different from our intuitive one that it becomes almost impossible to use ordinary words with their ordinary meanings.
 
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I don't know who that "we" is that you speak of (probably pop-science articles) but serious physiscists know that the cat is either alive or dead. The whole POINT that Schrödinger was making was/is that it's silly to think of the cat as being both alive and dead.
Hi phinds,

I am not a physicist by profession. But I do have an active interest in topics within this domain.

Could you please point me to some resources where I can learn where Schrodinger made the POINT that it's silly to think of the cat as being both alive and dead?

Thanks,
Bhanu
 
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Macroscopic superpositions are part of the usual quantum mechanics also. It is required for the consistency of the uncertainty relations. For instance, in a slit experiment, if we arrange a situation where we measure the momentum exchanged between the diaphragm and the particle, then the diaphragm whose momentum we measure is subject to the uncertainty relation, and has a position uncertainty ~ h/Δp. Thus a macroscopic object, the diaphragm, is in a superposition. The fact that the uncertainty relation applies to the diaphragm implies that the uncertainty in the position of the slits destroys the interference effects exactly the amount needed to protect the uncertainty relations.
Hi Prashant,

Could you please guide me to some material that explains better what you are talking about here?

Thanks,
Bhanu
 
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Hi phinds,

I am not a physicist by profession. But I do have an active interest in topics within this domain.

Could you please point me to some resources where I can learn where Schrodinger made the POINT that it's silly to think of the cat as being both alive and dead?

Thanks,
Bhanu
I don't have a citation for source material. You can find it pointed out in numerous posts here on PF. I realize that's not a citation, but it's been posted by several people who definitely know what they're talking about.
 
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No, since the MWI can be interpreted to be saying that. See below.



It depends on what you mean by "different cats". The MWI says there is a branch of the wave function in which the cat is dead, and another branch in which it is alive, and both branches are real. Whether that counts as two different cats, or two copies of the same cat, or something else entirely for which we don't have good ordinary language words, is a matter of choice of words, not physics. The physics according to the MWI is simply that all branches of the wave function are real, and that's it.
Hi Peter,

How can this be a choice of words? There either are alternate realities or there are not. But every quantum event generating a reality of it's own is a little bit too much to fathom. Is this interpretation in line with the Many Worlds Interpretation?

Thanks,
Bhanu
 
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There either are alternate realities or there are not.
"Alternate realities" is not a good description of what the MWI says. The MWI says that there is only one reality: the wave function. This reality is nothing like what we perceive, but that doesn't mean it isn't just one reality.

every quantum event generating a reality of it's own
I don't know what you mean by this.

Is this interpretation in line with the Many Worlds Interpretation?
What interpretation are you talking about? Can you give a reference?
 

pinball1970

Gold Member
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Hi Peter,

How can this be a choice of words? There either are alternate realities or there are not. But every quantum event generating a reality of it's own is a little bit too much to fathom. Is this interpretation in line with the Many Worlds Interpretation?

Thanks,
Bhanu
Speaking from experience of being wrong on quantum mechanics cosmology black holes and other subjects I suggest you check out the history of this. Wiki is usually ok at this, then get into the maths.

 
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"Alternate realities" is not a good description of what the MWI says. The MWI says that there is only one reality: the wave function. This reality is nothing like what we perceive, but that doesn't mean it isn't just one reality.

I don't know what you mean by this.

What interpretation are you talking about? Can you give a reference?
Yes, the one reality could be that there are an infinite number of universes. Its just that it is too hard to get my head around it.

To quote from Wikipedia:

The many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction and denies the actuality of wavefunction collapse. The existence of the other worlds makes it possible to remove randomness and action at a distance from quantum theory and thus from all physics. Many-worlds implies that all possible alternate histories and futures are real, each representing an actual "world" (or "universe"). In layman's terms, the hypothesis states there is a very large—perhaps infinite[2]—number of universes, and everything that could possibly have happened in our past, but did not, has occurred in the past of some other universe or universes. The theory is also referred to as MWI, the relative state formulation, the Everett interpretation, the theory of the universal wavefunction, many-universes interpretation, multiverse theory or just many-worlds.

That being said, when I said "every quantum event generating a reality of it's own", my understanding, is that there is a universe where all possible outcomes of an event occur. Thus, in this universe, I have started a thread on PF, but in another, I have not.

Is this reasoning correct?

Thanks
 
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the one reality could be that there are an infinite number of universes
Yes, if you define "universes" as "particular branches of the universal wave function". But nothing in the physics, if the MWI is true, picks out that definition.

all possible outcomes of an event occur
Yes, if you define "outcome" as "one particular branch of the wave function". But again, nothing in the physics, if the MWI is true, picks out that definition.
 

Nugatory

Mentor
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Could you please point me to some resources where I can learn where Schrodinger made the POINT that it's silly to think of the cat as being both alive and dead?
The cat came from a paper published in 1935. Schrödinger wrote it in German, but if you google for “Schrodinger the present situation in quantum mechanics” you will find several English-language translations. (“The present situation in quantum mechanics” is a translation of the original German title).

One translation is here: http://materias.df.uba.ar/f4Aa2012c2/files/2012/08/Schrod_cat.pdf
 
Suppose that you prepare a system of three particles and calculate its wave function far into the future. It is a very nontrivial question what in that setup constitutes a "branch" of the Many Worlds interpretation. The wave function explores all paths and interferes with itself. The hardness of defining a "branch" is a weakness of Many Worlds.

I, as a conscious subject, feel that I live in a certain "branch" of the Many Worlds. What is included in that "branch" of the wave function is not clear. The other branches continue to exist - their interference affects what I will observe in the future in my own branch.

The idea of decoherence says that we can calculate the behavior of macroscopic objects almost classically in different branches. I as a subject feel that I am such a "calculation branch" of a macroscopic object. But what exactly is included in my "calculation branch" is not clear.
 
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I, as a conscious subject, feel that I live in a certain "branch" of the Many Worlds.
But there are other branches of "you" as well; when "you" make a measurement that has multiple possible outcomes, each branch of "you" experiences a different outcome.

The other branches continue to exist - their interference affects what I will observe in the future in my own branch.
No, it doesn't. Branches in the MWI are decohered; they don't interfere with each other. If decoherence has not occurred and there is still quantum interference, then there has not been any "branching" according to the MWI.

For example, in the double slit experiment with both slits open, there is no "branching" with respect to which slit the particle goes through. There is only "branching" with respect to where on the detector screen the spot appears indicating the particle's arrival.
 
The other branches continue to exist. They are not cut off by decoherence because there is always a minuscule probability of interference.

Consider the cat in the box: when it comes out of the box (in one branch) and meows to us experimenters, we tell the cat that it existed in a superposition state in the box. The cat then understands that the other branches did exist even though the cat as a conscious subject felt that it lives in a single branch.

You cannot cut off any branch of the Many Worlds interpretation. All branches must always exist, to reproduce what we actually measure.
 
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The situation as presented reminds me of the Wigner's friend thought experiment.
 
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The other branches continue to exist.
Of course, that's the definition of the MWI.

They are not cut off by decoherence because there is always a minuscule probability of interference.
I'm not sure what you are referring to here. Experimentally such interference has never been observed.

The cat then understands that the other branches did exist
Did exist before the measurement, sure. But not that they still exist; that is interpretation dependent.
 
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Decoherence doesn't do much, really. Interference is still possible by taking into account all quantum systems involved. Maybe not practically, but in principle.
 

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