Normal

My problem with it is that even if you isolate one observer from another, say the cat from the guy outside the box, the cat can still observe the events inside the box. Self-awareness is not a necessary property of observation, as the double slit experiment considers the screen (and the device that collapses the wave function) to be an observer.

Jesse

Didn't you read my post? My whole point was that it doesn't matter whether the system in the box is an "observer" or not, as long as it is completely isolated from the outside world, then all external observers should treat it as if it's in a superposition of states. That's the point of the "Wigner's friend" though-experiment I mentioned--even if there's a person in the box, he's still in a superposition of states from the point of view of the outside world.

Kat_Somm_Faen

Well in essence eveything that interacts is "observing" a non-observer wouls be thing hanging freely in nothingness and experiencing no change or interation with any other body. It would be a single object, similar to an "atom" in a sense that it can not be fither divided at all. A quant of amtter if you will just being there. No radiation, photons - nothing else.

If you are detailed ( nitpicking, anal ) enough this analogy is incorrect since there is poison and it interacts with the cat and cat is madu up of atoms and molecules and there is air and everything else and all that stuff interacts and "observes". The "isolation" of the cat is the "thought" part of the thought experiment

Normal

OK, I guess my problem with this thought experiment is the isolation aspect of it. What constitutes isolation of states? That we can't observe the state of the cat? But if the cat observes it's own state from within the box, why is it a superposition of states for us? The cat would observe it's own state, but we would be ignorant of the state the cat observed, but the state would still be observed by the cat, no?

Calzaer

I think the question here is the same one posed in Wigner's Friend. Why does MY measurement make the wavefunction collapse, but someone else's measurement (in this case, the cat's) not make the wavefunction collapse?

Jesse

Well, basically, if any part of the isolated system is measured by another part of the system in a way that leaves a record which could be potentially examined when the "box" is opened, then that part won't behave as though it's in a superposition. If you had measuring devices at the slits in the double-slit experiment, then even if you could somehow keep them in complete isolation from the outside environment when they recorded which slit the photon when through, you still wouldn't see an interference pattern when you examined the screen. Same with anything the cat "measures" while it's in the box. But the system as a whole should be treated as though its in a single giant superposition as long as it's totally isolated (again though, such isolation is not possible in practice with current technology, you'll always get decoherence with macroscopic systems...but quantum computers require isolation to work, so perhaps we'll find clever ways to keep larger and larger systems isolated for the purposes of quantum computation).

echidna

http://atheism.about.com/library/glo..._solipsism.htm

Wyz_sub10

I think, though, that the cat's "measurement" does make the wavefunction collapse.

That's what I was getting at in my reply above.

Jesse

I don't think so--if the cat is isolated, the entire isolated system should be modeled with a single giant wavefunction until it's observed by the outside world. But as I said in my last post, there can be decoherence within that single wavefunction due to one part of the system becoming entangled with another (or one part 'observing' another), so that if you just wanted to predict the behavior of one part of the system rather than the system as a whole, you'd basically be able to use classical probabilities without having to worry about interference. Science fiction writer Greg Egan gives a short explanation of this "decoherence in one part of isolated system while system as a whole remains in superposition" here (along with a link to a longer explanation):

http://gregegan.customer.netspace.ne...coherence.html

SteveD

Schroedinger's cat example is widely misunderstood. He intended it as a counter example of why a particular interpretation of the wave function was not valid.

Here is an excerpt from his original paper.

The whole paper can be found here

Schroedinger's cat
paper

It is a very interesting read.

Steve