Does the Act of Observing a Detector Influence Quantum Measurements?

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Discussion Overview

The discussion revolves around the concept of observation in quantum mechanics, particularly whether the act of observing a detector influences quantum measurements. It explores the definitions of "observer" and "observation," the implications of these definitions, and the philosophical questions surrounding them. The scope includes theoretical and conceptual aspects of quantum mechanics.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question what constitutes an observer and the meaning of "observe," noting that a detector is often described as an observer.
  • There is a suggestion that the knowledge of an observer may not influence the observation itself, paralleling the idea that a human observer's knowledge is independent of others' observations.
  • One participant raises a philosophical question about the existence of objects, like a rock, without observation, arguing this is a broader philosophical issue rather than a quantum-specific one.
  • Another participant notes the lack of a rigorous definition for "observer" or "measurement" in quantum mechanics, highlighting it as an open issue and stating that physicists often assume measurements occur based on practical applications of the projection postulate.
  • Some participants propose that treating everything in terms of quantum fields may provide a more consistent framework than relying on wave-particle duality and collapse.
  • It is mentioned that the formalism of quantum mechanics does not explicitly define observers but instead focuses on physical variables and their correlations, which are interpreted as observations or measurements.

Areas of Agreement / Disagreement

Participants express differing views on the nature of observation and measurement in quantum mechanics, indicating that multiple competing perspectives remain without a consensus on definitions or implications.

Contextual Notes

The discussion highlights limitations in the definitions of observers and measurements, as well as the dependence on interpretations of quantum mechanics. There are unresolved philosophical questions that extend beyond quantum physics itself.

sayetsu
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What counts as an observer, and what does it mean to "observe"? I've read a detector (machine) is an "observer." But how do we know it performed an observation without observing it? Is it possible our observation of the detector retroactively caused the wave function to collapse?
 
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sayetsu said:
I've read a detector (machine) is an "observer." But how do we know it performed an observation without observing it?
You can ask the same question about a human observer. Your knowing has nothing to do with someone else's observations.
 
One can also ask how do you know that a rock exists unless observed? It has nothing to do with quantum physics. It is a more general philosophical question with which philosophers struggled long before quantum physics was born and without any reference to a wf collapse.
 
sayetsu said:
What counts as an observer, and what does it mean to "observe"?

There is no rigorous definition of an "observer" or a "measurement" in QM. That is one of the main open issues with QM. For practical purposes, physicists simply assume a "measurement" has occurred and apply the projection postulate accordingly wherever it works best for making predictions and interpreting experimental data. But the QM formalism itself does not tell physicists when to do this; it just says "do it wherever it works best".
 
It's more consistent to treat everything in terms of quantum fields instead of applying wave particle duality(and collapse).

Quote
 
As others have mentioned, observers are not explicit in the formalism. Instead we have physical variables and their correlations. We try to identify the variables with enough classicality to be experienced by us, and see how they correlate with more explicitly quantum variables. This correlation is the closest the formalism gets to identifying an observation or measurement.
 
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