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Letting the Cat Out of the Box
Can we improve on Schrodinger's famous thought experiment?

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Letting the Cat Out of the Box

Inthedark
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Posted 09/28/08 - 10:51 AM: Subject: Letting the Cat Out of the Box	#1
I am being pedantic but surely the cat counts as an observer? I'm sure it can observe itself living which means that the state of the cat is known and the is no superposition of dead and living cats. Please correct me if I am wrong and tell me why (I haven't studied physics at university an probably will have misinterpreted something). Can anyone provide a better example? I thought a vase might be a better choice as it is inanimate and not an observer but a broken/unbroken vase doesn't have the same impact as a dead/alive cat. Also If the cat is an observer what happens when it dies and can't observe anymore?
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Death Monkey
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Posted 09/28/08 - 11:12 AM:	#2
Better yet, imagine two boxes. And they each have a person and a cat in them. In each case there is a 50/50 chance that the cat will be killed, but the person is safe. After the specified time, the wall between the two boxes opens, connecting them. Now what we have is that each of the two people will either see their cat live or die. No superposition from their points of view. But each of them will say that from their point of view, the other box was in a superposition state until the wall was dropped, even though there was an observer in the other box. And an observer outside of the two boxes will say that they both were in superposition states. Kinda weird, eh? Anyway, as this should illustrate, it doesn't make any difference whether the cat is an "observer" or not. The point is that if what is happening in the box is isolated from the outside world, so that it does not become entangled (in the quantum sense) with anything on the outside, then from the point of view of anybody on the outside, it remains in a superposition state until such time as the interaction with the outside world occurs. DM
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ragus
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Posted 09/28/08 - 12:16 PM:	#3
Do you mean, DM, that a superposition state represents knowledge about the state of the physical system rather than the state of the physical system?
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Inthedark
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Posted 09/28/08 - 12:22 PM:	#4
It is very weird! I think I shall take solace in Feynman's assertion that "no-one understands quantum mechanics". What would happen if the observer on the outside could see via video cameras both of the cat and people boxes but the observers in the boxes could not see outside. If I understand what you have said the observer on the outside can observe the state of both cats and the observers in the boxes can observe the state of the cat in the box with them. However the state of the cat in the other box is still in a superposition state to the observer in the box regardless of the number of observers that have seen the other boxes state simply because the observers box is isolated. Is that right? The superposition state of the cat: Is the cat dead and alive at the same time or is it not existing in either state until it is observed?
Please remember: The aim of debate is to prove your point and not your intelligence.

Death Monkey
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Posted 09/29/08 - 11:26 AM:	#5
ragus, Do you mean, DM, that a superposition state represents knowledge about the state of the physical system rather than the state of the physical system? Not exactly. The wave-function represents the state of the physical system, but only to the extent that it can be used to make predictions of observations. Anything more than that is the result of applying some metaphysical interpretation to it. The Schroedinger's cat thought experiment is formulated from within the context of a classical metaphysical intepretation of physics, which is why it leads to seemingly contradictory results, such as the cat being "both dead and alive". If you apply one of the interpretations of QM, such as the Copenhagen interpretation, or the Many Worlds interpretation, or any other, you end up with different conclusions about the status of the cat depending on which one you choose. under Copenhagen the cat is neither dead nor alive. It's status is undetermined until the box is opened. Under the Many Worlds interpretation, the cat is both dead and alive. Both outcomes exist as different universes (branches of the wave equation). Under a (non-local) deterministic interpretation, the cat would be either dead or alive, and the apperant indeterminacy would be a result of the observable properties not uniquely specifying the deterministic hidden variables. Anyway, what I am trying to say is that my previous post discusses what we know about the boxes, because that is all we can really talk about without imposing a metaphysical interpretation onto it. But that does not mean that the superposition does not represent the physical state of the system. DM
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ragus
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Posted 09/29/08 - 01:14 PM:	#6
DM wrote what I am trying to say is that my previous post discusses what we know about the boxes, because that is all we can really talk about without imposing a metaphysical interpretation onto it. But that does not mean that the superposition does not represent the physical state of the system. I don't know what you mean by a metaphysical interpretation in this context. There seems nothing metaphysical about a cat alive or dead. Can you help me out?
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swstephe
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Posted 09/29/08 - 05:57 PM:	#7
In the thought experiment, using a cat and death was just for humorous effect. The cat couldn't be the observer, only someone outside the box. But in reality, a dead cat can't be an observer either -- unless you believe in ghosts. You would only be certain that you were alive when you were alive, so you could say the knowledge was only 50% on average.
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Posted 09/30/08 - 12:13 AM:	#8
ragus, I don't know what you mean by a metaphysical interpretation in this context. There seems nothing metaphysical about a cat alive or dead. Can you help me out? The metaphysics comes into play when specifying what you mean by saying something like "the cat is alive right now". Our intuitive notions of talking about the state of some macroscopic object like a cat, as well as concepts like simultaneity, are firmly grounded in classical mechanics. The difficulties with the cat experiment arise directly from this, because by construction it is not a classical system. It is a system where the assumptions of classical mechanics do not hold. This leaves us with a problem in specifying what we even mean when we ask "is the cat alive or dead" before opening the box. What do we mean by that question? In most cases, what the person probably means is implicitly assuming that the system is behaving in a classical way, which it isn't. So the question becomes nonsensical. One possible solution is to define what we mean in a purely instrumentalist way, such as "when I open the box, what will I observe?". In this case the answer is quite clear and unambiguous. You have a 50/50 chance of observing a live cat, and 50/50 of observing a dead one. The above is as far as you can go just using the standard model of quantum mechanics. To say anything more about the system requires you to formulate it in terms of some metaphysical interpretation. By this I mean that you have to invent some model that goes beyond being a mathematical prediction of observations, and formulate what you mean by the question in terms of that model. The Copenhagen interpretation, Many Worlds interpretation, and many others, are examples of this. They are all different models of a reality that, from the point of view of the people in them, would appear to function according to the standard model of quantum mechanics. DM
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ragus
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Posted 09/30/08 - 07:13 AM:	#9
DM wrote This leaves us with a problem in specifying what we even mean when we ask "is the cat alive or dead" before opening the box. What do we mean by that question? It seems there are three time spans. 1. Cat not in box but alive (classical description?) 2. Cat in box (quantum description) 3. Cat out of box either alive or dead. (classical description?) Are the classical descriptions acceptable?
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Death Monkey
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Posted 09/30/08 - 07:30 AM:	#10
I'm not sure what you mean by "acceptable" here. When the cat is not in the box, it is ok to consider the situation classically, if this is what you mean. DM
Pseudoscience makes Baby Jesus cry.

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