Why does the wave function have to collapse upon measurement?

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Discussion Overview

The discussion centers around the concept of wave function collapse in quantum mechanics, particularly within the framework of the Copenhagen interpretation. Participants explore the motivations behind the idea of collapse, its implications for measurements, and alternative interpretations of quantum mechanics.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants question the necessity of wave function collapse, suggesting that the Schrödinger equation could continue to describe a system without it.
  • Others note that repeated measurements yield consistent results, implying that measurement influences the quantum system, which is a point of agreement across interpretations.
  • One participant proposes that the wave function can be viewed as a mathematical tool, with various interpretations (e.g., many-worlds, de Broglie-Bohm) that do not rely on collapse.
  • There is a suggestion that measurement could be defined as an event that causes wave function collapse, raising questions about the nature of measurement itself.
  • Another viewpoint introduces the concept of decoherence, arguing that decoherence can signify a measurement without the need for a measurement apparatus.
  • A participant expresses the opinion that collapses may occur independently of measurements due to non-linear characteristics of the Schrödinger equation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the necessity or nature of wave function collapse. Multiple competing views are presented, with some advocating for the Copenhagen interpretation while others suggest alternative frameworks.

Contextual Notes

Discussions involve various interpretations of quantum mechanics, highlighting the complexity and ongoing debates surrounding the measurement problem and the role of wave function collapse.

TriKri
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How does the Copenhagen interpretation motivate its claim that the wave function of a quantum system collapses when a property of the system is being measured? I mean, was there some problem they were trying to solve by introducing the notion of wave function collapse? What would happen if the wave function would not collapse? Wouldn't it work to just continue to describe it with the Schrödinger equation like normal?
 
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The idea is that in some cases, repeated measurements are possible, and these indicate that immediate repetition of a measurement gives the same result.
 
Descriptions without collapses are possible, but then they are not called Copenhagen interpretation:
a) describe the wave-function as purely mathematical tool without physical reality (many different variants)
b) describe the measurement process itself and everything else with quantum mechanics (-> many-worlds, de-Broglie Bohm)

You cannot do "nothing", as repeated measurements (can be the same observable, but does not have to) will show that your measurement did influence the particle in those setups where Copenhagen gives a collapse (this is true for all interpretations).
 
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Is it ok to think of it the other way around? If the wavefunction collapsed then a measurement was made. Measurement is defined as that which collapses the wavefunction. Is it ok to think of it this way?
 
TriKri said:
How does the Copenhagen interpretation motivate its claim that the wave function of a quantum system collapses when a property of the system is being measured?

In that interpretation the wavefunction is like probabilities - it encodes the outcomes of observations. Its very purpose is to change when you observe it. Its like throwing a dice. Prior to throwing it each side has a 1/6th probability of coming up. Throw it and one side is a dead cert - its 'wavefunction' has collapsed.

Some other interpretations explain the 'how' - Copenhagen simply accepts it.

Thanks
Bill
 
ModusPwnd said:
Measurement is defined as that which collapses the wavefunction. Is it ok to think of it this way?

Measurement is whatever leaves a 'mark' here in he macro world.

Nowadays its usually associated with decoherence - a measurement has occurred once decoherence has happened. This means it can happen even without reference to an actual measurement apparatus. As an example, a dust particle is decohered to have a definite position by a few stray photons. One can think it has been measured.

Thanks
Bill
 
TriKri said:
How does the Copenhagen interpretation motivate its claim that the wave function of a quantum system collapses when a property of the system is being measured? I mean, was there some problem they were trying to solve by introducing the notion of wave function collapse? What would happen if the wave function would not collapse? Wouldn't it work to just continue to describe it with the Schrödinger equation like normal?


imo there are collapses without measurements, due just to a non linear character of the Schrödinger equation, i.e. non linear quantum mechanics

.
 

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