Schrödinger's Cat, uncertainty, and observation question

[themadquark]

First of all, from what I've read the descriptions of an observation or measurement in Quantum Mechanics have been quite vague. Since the word measurement is used alternatively I am going to assume that this includes all types of measurements, which brings me to a question. If the box Schrödinger's cat was in was not lead lined (And we assume the source is not an Alpha emitter as the box would likely block it) would one be able to use a Geiger counter to detect if decay had occurred or would this take the cat out of superposition, thus making it either dead or alive?

 

[Simon Bridge]

Yes. Any way of "looking inside the box" counts.
The idea of the thought-experiment is that the experimenter is able to choose when he looks.

 

[bhobba]

Simon is correct.

But please understand according to the standard Copenhagen interpretation QM is a theory about observations that appear in an assumed common sense classical world. In Schrodenger's Cat that observation occurs at the particle detector. Everything is common sense classical from that point on. The cat is alive or dead period. It makes no difference if its observed or not.

The purpose of Schroedinger's Cat was to illustrate a issue with Copenhagen. Since QM is a theory about observations in an assumed classical world and QM is the fundamental theory that is supposed to explain that world - well it obviously will find that a bit hard. It doesn't invalidate Copenhagen, but its a blemish. What is needed is a fully quantum theory of measurement.

A lot of progress has been made to that end:
http://www.ipod.org.uk/reality/reality_decoherence.asp

But without going into the details a few issues still remain eg the so called factoring problem.

Thanks
Bill

 

[Simon Bridge]

But yeah - a QM theory of measurement is kinda the physics form of the mind-body problem.

 

[themadquark]

I appreciate the excellent answers, but feel I must ask: What proposals are there for a specialised method of measuring quantum phenomena, if any?

 

[Simon Bridge]

bhobba gave you a good link for how measurement may be modeled in QM.

In QM experiments we just use detectors and so on normally, using the theory to make predictions about the outcome. i.e. if we want to know if the cat is dead we open the box and look.

 

[bhobba]

I appreciate the excellent answers, but feel I must ask: What proposals are there for a specialised method of measuring quantum phenomena, if any?

Its in the advanced literature eg:
https://www.amazon.com/dp/3540357734/?tag=pfamazon01-20

The key issue has to do with the difference between improper and proper mixtures:
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

Thanks
Bill