Schrödinger's Cat, uncertainty, and observation question

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Discussion Overview

The discussion centers around the implications of observation and measurement in Quantum Mechanics, particularly in the context of Schrödinger's Cat thought experiment. Participants explore the nature of measurement, its effects on superposition, and the philosophical challenges posed by quantum measurement theories.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions whether using a Geiger counter to detect decay in a non-lead lined box would collapse the superposition of Schrödinger's Cat, suggesting that any form of observation might affect the state.
  • Another participant asserts that any observation, including looking inside the box, counts as a measurement and thus collapses the superposition.
  • A third participant explains that according to the Copenhagen interpretation, the act of observation at the particle detector determines the cat's state, regardless of whether it is observed directly or not.
  • Concerns are raised about the limitations of the Copenhagen interpretation, highlighting the need for a more comprehensive quantum theory of measurement.
  • One participant draws a parallel between the challenges of quantum measurement and the mind-body problem, suggesting a deep philosophical issue remains unresolved.
  • Several participants inquire about specialized methods for measuring quantum phenomena, indicating a desire for more concrete proposals in the field.
  • References to advanced literature and links are provided to explore the modeling of measurement in Quantum Mechanics further.

Areas of Agreement / Disagreement

Participants express differing views on the implications of measurement in Quantum Mechanics, particularly regarding the effects of observation on superposition. No consensus is reached on the nature of measurement or the adequacy of existing interpretations.

Contextual Notes

Participants note the complexity of the measurement problem in Quantum Mechanics, including unresolved issues such as the factoring problem and distinctions between improper and proper mixtures. These limitations highlight the ongoing debates in the field.

themadquark
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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?
 
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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.
 
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
 
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But yeah - a QM theory of measurement is kinda the physics form of the mind-body problem.
 
I appreciate the excellent answers, but feel I must ask: What proposals are there for a specialised method of measuring quantum phenomena, if any?
 
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.
 
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