Why does the wave function have to collapse upon measurement?

In summary, the Copenhagen interpretation motivates its claim that the wave function of a quantum system collapses when a property of the system is being measured by saying that repeated measurements indicate that the immediate repetition of a measurement gives the same result.
  • #1
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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  • #2
The idea is that in some cases, repeated measurements are possible, and these indicate that immediate repetition of a measurement gives the same result.
 
  • #3
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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  • #4
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?
 
  • #5
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
 
  • #6
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
 
  • #7
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 schrodinger equation, i.e. non linear quantum mechanics

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Related to Why does the wave function have to collapse upon measurement?

1. Why does the wave function have to collapse upon measurement?

The collapse of the wave function is a fundamental principle in quantum mechanics. It is a mathematical representation of the uncertainty principle, which states that it is impossible to know both the exact position and momentum of a particle at the same time. When we measure a quantum system, we are essentially collapsing the wave function to a single, specific state that corresponds to the measurement we make. Without this collapse, the probabilistic nature of quantum mechanics would not make sense.

2. How does the wave function collapse during measurement?

The collapse of the wave function occurs instantaneously and is a result of the interaction between the quantum system being measured and the measuring apparatus. When the measurement is made, the wave function collapses to a single state that corresponds to the outcome of the measurement. This process is known as wave function collapse or collapse of the state vector.

3. Are there any alternative interpretations of the collapse of the wave function?

There are several interpretations of the collapse of the wave function, including the Copenhagen interpretation, the many-worlds interpretation, and the pilot-wave theory. Each of these interpretations has its own way of explaining the collapse, but they all agree on the fundamental principle that the wave function collapses upon measurement.

4. Can the collapse of the wave function be observed or measured?

No, the collapse of the wave function cannot be directly observed or measured. It is a theoretical concept that is used to explain the probabilistic nature of quantum mechanics. However, the effects of the collapse can be observed in the outcomes of quantum experiments, which are consistent with the predictions of the collapse of the wave function.

5. Is the collapse of the wave function a reversible process?

The collapse of the wave function is generally considered to be an irreversible process. Once the wave function has collapsed, it cannot be undone. This is because the measurement process interacts with the quantum system, causing irreversible changes. However, in some interpretations of quantum mechanics, such as the many-worlds interpretation, the collapse can be seen as a temporary and reversible branching of reality.

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