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Put a cat in a sealed box, Schrödinger said, with a gun that has a 50/50 chance of shooting the cat in response to an unpredictable, random quantum event. Because the box is built so solidly that no outside observer can get any information about what happened, then the cat is both alive and dead until someone opens the box and looks inside. Or at least, that's the dumbed-down version of the thought experiment, that's supposed to be simple enough to be comprehended by mere mortals.

The one part I've never understood, though, that seemed obvious to me even as a little kid, is how there is supposed to be any uncertainty about what happened in the first place. The cat being alive/dead is not the random event; it's an effect of the random event: the gun firing. And there's something outside of the gun that can observe it: the cat itself. So where does the uncertainty due to the event not having been observed come from?

(And yes, I realize that it's just an idea that's not meant to be taken literally, but if it's supposed to be an analogy that models a real problem, then ISTM it should be a model that doesn't have a hole in it that's so obvious a child can see it.)

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Absolutely...all the superpositions of states that the "cat" can be in have observed what the gun did. The dead cat observes that the gun has gone off, and the living cat observes that the gun has not gone off. Both "cats", each of which has observed what happened, exist at the same time as a superposition.

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  • $\begingroup$ I think that the Schrodinger's cat argument misses a very important point. For a quantum mechanical object, the act of observation interferes with the object in a way that changes it. For a classical object (the cat) the act of observing it does not change it in any way. If the cat was truly quantum-mechanical, I would expect that it could not change its "state" by observing itself, but I WOULD expect that its state would be changed if an outside observer looked at it. $\endgroup$ – David White Aug 5 '15 at 19:10
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Um, I thought it was a geiger counter, a hammer, some cyanide, and a radioactive thingy that has a 50% chance of collapsing and alerting the gieger counter to cause the hammer to fall, break the vial of cyanide and kill the cat, not a gun. Also, the cat doesn't really count as the observer in this case, even though it sees the materials. Also the cat could be blind, the steel box having absolutely no source of light, or the cat fell asleep. But the whole point of the experiment was that the cat being in two states at once is RIDICULOUS, not this is how the copenhagen interpretation works.

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