From: <[email protected] <mailto:[email protected]>>
On Tuesday, June 12, 2018 at 11:03:28 PM UTC, Bruce wrote: From: <[email protected]>*Doesn't the superposition of states used in the cat problem. or indeed any quantum superposition, requires the system being measured to be isolated? AG * *As I see it, the total system represented by the wf ( (Alive, Undecayed) + (Dead, Decayed) ), leaving out Dirac symbols, must be isolated if it's regarded as a superposition. If so, this implies the cat is also isolated. AG*That is the root of your problem in understanding superpositions. There is absolutely no requirement for the system to be isolated in order for there to be a superposition. In fact, the opposite is the case -- each branch of the superposition decoheres by interacting with, and becoming entangled with, the environment. That is how quantum measurement theory proceeds. Isolation from the environment is a condition you made up, and it is not required. BruceFor reasons not worth explaining, I have had doubts whether a superposition requires isolation. But what it does require, at least in the cat paradox, is interference among the components. Otherwise, Schroedinger couldn't have concluded that the superposed wf implies the cat is simultaneously alive and dead. So the issue becomes whether a macro object like a cat has a well defined wave length, which IIUC, is the necessary condition for interference. AG
That is another misunderstanding on your part. Interference between components is not necessary for a superposition. As Brent explained, being "regarded as a superposition" is just choosing a coordinate system. For the cat, we can have the 'alive/dead' coordinate system, or an '(alive+dead)/(alive-dead)' coordinate system. In the first, the cat is either alive or dead; in the second the cat is in a superposition of the two stateswhichever basis vector you choose. There is nothing magical about this, it is just a matter of how you look at it. Superpositions of classical macro objects are always possible, just by rotating the basis vectors.
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