Schrödinger's Cat To The Max

[PP3]

Imagine the standard Schrodinger's cat (let's call it AliceCat). It exists in a quantum superposition of both alive and dead until it is observed. But what if the observer is another Schrodinger's cat (let's call it BobCat)? A one way mirror lets BobCat observe AliceCat, but as BobCat is both alive and dead he is both observing and not observing AliceCat. What would happen? I don't think BobCat could simultaneously cause and not cause AliceCat's position to collapse into dead or alive.

 

And what if the mirror were replaced by glass so that AliceCat and BobCat were observing (and not observing) each other?

 

Am I right in thinking that only an observer that is not in a superposition can cause a superposition to collapse? If so, what would happen if a weapon big enough to destroy the universe were hooked up to a Schrodinger mechanism, putting the entire universe into a superposition (Schrodinger's universe if you will)? If there can be no observer outside the universe, presumably the whole universe and everything in it would remain in a superposition indefinitely - and no observer in the universe could cause superpositions to collapse?

 

If so, does that prove, from the fact that we can cause superpositions to collapse, that the universe is not in a superposition?

 

 

[mathematic]

My personal take. Schrodinger's cat is unrealistic. Suppose you installed a camera inside the box with the cat and continuously recroded what was happening. After opening the box the film is reviewed - I doubt very much you will a superposition of a dead cat and a live cat.

[Delta1212]

My personal take. Schrodinger's cat is unrealistic. Suppose you installed a camera inside the box with the cat and continuously recroded what was happening. After opening the box the film is reviewed - I doubt very much you will a superposition of a dead cat and a live cat.

If the camera is in the box, it would, itself, be in a superposition of having recorded a live cat and a dead cat, and collapse to one of those options upon the opening of the box.

 

An important point to keep in mind, though, is that Schrödinger's Cat is not a practical experiment. It was originally a thought experiment by Erwin Schrödinger meant to illustrate that the Copenhagen interpretation of superpositions was stupid, except that it got adopted as the go to example instead.

 

We can't properly isolate something on the scale of a cat from any interactions for it to enter a superposition state. The superposition doesn't collapse because of an observation by a person. It collapses because it interacts with something else. If that something else is completely isolated from everything else, it will enter a superposition state tied to the first superposition, but the more things you have, the harder it is to isolate them, and a cat is made of quite a lot of things.

 

As for the Schrödinger's Universe question, I suppose at that point you'd basically enter the Many World's Interpretation of QM since you'd have two different versions of the universe simultaneously? I don't know. It's a philosophical debate really, since it's not an actual, possible experiment.

[Klaynos]

The cat in the box is probably best thought of as an example of how of quantum mechanics would be of it was macroscopic.

[Delbert]

I think you are forgetting that the cat in a box is in the same state as you or me. The cat is in its (small) box universe, the same as you or me in our much larger universe. The cat is either dead or alive depending on a quantum effect of a radio active isotope. That's the same as you or me or the whole Earth being destroyed by some sequence of actions or catastrophe following a quantum effect. You me and the Earth being destroyed by such an event might be very rare, but a possibility nonetheless.

 

So when BobCat views the box by whatever method containing a dead or alive cat, it is the same situation as you or me viewing said box by the same method. It's just that the box we're in is that much bigger.

Edited August 18, 2013 by Delbert

[TrappedLight]

The cat in the box is probably best thought of as an example of how of quantum mechanics would be of it was macroscopic.

 

You mean microscopic.

 

 

We have wavefunction, but their wavelengths are too small to be detected. Because of decoherence, an object will continuously stay in a stable state. A cat is a body made up of entangled particles, the nature of the wave function isn't the same for a macroscopic body.

[pears]

My personal take. Schrodinger's cat is unrealistic. Suppose you installed a camera inside the box with the cat and continuously recroded what was happening. After opening the box the film is reviewed - I doubt very much you will a superposition of a dead cat and a live cat.

 

 

If the camera is in the box, it would, itself, be in a superposition of having recorded a live cat and a dead cat, and collapse to one of those options upon the opening of the box.

 

Wouldn't the camera be acting as observer in this case? If the camera is able to record the particles under decay light or something would have had to interfere with them and cause collapse at that point. Without the light the particles wouldn't have collapsed and the camera would have recorded nothing.

[swansont]

I think you are forgetting that the cat in a box is in the same state as you or me. The cat is in its (small) box universe, the same as you or me in our much larger universe. The cat is either dead or alive depending on a quantum effect of a radio active isotope. That's the same as you or me or the whole Earth being destroyed by some sequence of actions or catastrophe following a quantum effect. You me and the Earth being destroyed by such an event might be very rare, but a possibility nonetheless.

 

So when BobCat views the box by whatever method containing a dead or alive cat, it is the same situation as you or me viewing said box by the same method. It's just that the box we're in is that much bigger.

 

It's not the same. We are not entangled with a catastrophe, especially one that hasn't happened yet. The cat is not 50-50 entangled with the decay state until after the time has passed and the decay/poison contraption removed.

[Delbert]

 

It's not the same. We are not entangled with a catastrophe, especially one that hasn't happened yet. The cat is not 50-50 entangled with the decay state until after the time has passed and the decay/poison contraption removed.

Not quite sure that's right. We don't know what's happening inside the box, that's the conundrum. We don't know because we can't determine if a quantum event of the isotope has or hasn't taken place. Any other mechanism (i.e. non quantum) we'd have a certainty about the life or death of the cat in a closed box. But inside the box it's a different situation, if we were inside the box it maybe a quantum event but we'd know when it happened. Whereas those on the outside wouldn't.

 

The point I was making was that we on earth in this vast universe of ours, is not unlike like the cat in said box. It might be a very remote possibility but I think it is conceivable that some sort of quantum event might trigger a bigger event which might then eliminate this earth of ours. So effectively we are in a box (although a very much bigger one) like the cat. So someone outside the universe (we're getting imaginative here!) couldn't tell if we were alive or dead. But were inside the universe box, so I think it's safe to say we know what's happening.

 

In other words one of PP3s query about putting the earth into a state of superposition is that the earth is probably already in such state and we're in it and therefore know what it's like.

 

As for this looking through a one way mirror, I can't see this destroying the superposition to the outside world. It seems to me that this superposition business is lack of knowledge. We don't know what going on in the box, and the one way mirror doesn't change that. But the cat inside the box knows what going on inside and outside - which is okay.

 

I suppose there is a possibility of the one way mirror conveying information to the outside world. Whereby photons from outside hitting the cat's eye will have some consequence to the outside world which might be noticed. Those photon thingies are tricky chaps, like what happens with the double slit experiment.

[swansont]

Not quite sure that's right. We don't know what's happening inside the box, that's the conundrum. We don't know because we can't determine if a quantum event of the isotope has or hasn't taken place. Any other mechanism (i.e. non quantum) we'd have a certainty about the life or death of the cat in a closed box. But inside the box it's a different situation, if we were inside the box it maybe a quantum event but we'd know when it happened. Whereas those on the outside wouldn't.

 

That's one of the salient points about the situation: is there really a superposition after the entanglement, is the cat an observer (or should you change it t pesticide and a plant?). However, we know whether or not a catastrophe has occurred. There is no superposition.

 

The point I was making was that we on earth in this vast universe of ours, is not unlike like the cat in said box. It might be a very remote possibility but I think it is conceivable that some sort of quantum event might trigger a bigger event which might then eliminate this earth of ours. So effectively we are in a box (although a very much bigger one) like the cat. So someone outside the universe (we're getting imaginative here!) couldn't tell if we were alive or dead. But were inside the universe box, so I think it's safe to say we know what's happening.

 

In other words one of PP3s query about putting the earth into a state of superposition is that the earth is probably already in such state and we're in it and therefore know what it's like.

Or we know that we're not in a superposition, and we know what that is like.

 

As for this looking through a one way mirror, I can't see this destroying the superposition to the outside world. It seems to me that this superposition business is lack of knowledge. We don't know what going on in the box, and the one way mirror doesn't change that. But the cat inside the box knows what going on inside and outside - which is okay.

There are experiments where the information is recorded but not known to anyone, and there is no superposition/interference. Simply not knowing is not the the important thing, it's whether you can know it.

 

[mathematic]

Suppose the cat was replaced by a person. Would the person be in two quantum states until someone else opened the box, or would he be the observer himself?

[Delta1212]

 

 

 

Wouldn't the camera be acting as observer in this case? If the camera is able to record the particles under decay light or something would have had to interfere with them and cause collapse at that point. Without the light the particles wouldn't have collapsed and the camera would have recorded nothing.

No more of an observer than the cat is.

[TrappedLight]

Best not to think of macroscopic observers... There is no one observing the observer...

[pears]

But isn't the observer interfering by the very means of measurement? If the cat is in the dark it's not measuring the quantum state, but if a camera is able to see the cat then it would have been firing photons around in the box which implies something has interfered with the quantum system. Or am I misunderstanding the means by which observation affects a quantum system? I thought it was to do with measurement. Not that I'm saying the cat IS in both states. Just that I would have thought the cat being an observer would mean the cat had to measure the quantum system rather than just 'know' whether the decay had occured.

[Delta1212]

Any interaction where the state has an effect is a "measurement" of that state, regardless of whether anything "knows" about or records the state. The cat never experiences itself in a superposition because it would be immediately obvious to the cat when/whether the poison kills it. The cat is in a superposition for the rest of the universe because the very special box in this thought experiment prevents any interaction between the contents and everything else. The cat is therefore equally likely to be alive or dead until the box is opened and the cat can be interacted with. Similarly, the universe has no idea what the camera has recorded until the box is opened and the recording can be observed. The camera would be no more or less in a superposition than the cat regardless of whether it can see in the dark or not.

 

What exactly any of this "really" means physically is something of an open debate.

[pears]

Hmmm. OK thanks.