What actually triggers the collapse of the wave function ?

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Discussion Overview

The discussion centers around the nature of wave function collapse in quantum mechanics, particularly in the context of the double slit experiment. Participants explore whether the collapse is triggered by observation or by environmental interactions, as well as the implications of making measurement results unobservable.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants propose that the transition from wave-like to particle-like outcomes in the double slit experiment is linked to the observation mechanism, questioning whether it is the observation itself or the interaction that causes the collapse of the wave function.
  • Others argue that the measurement problem remains unresolved, with no consensus on when or how the collapse occurs, suggesting that it may be modified by factors such as gravity.
  • A viewpoint suggests that if the observation result is made unobservable, only an apparent collapse occurs, indicating that true collapse requires retaining the measurement result.
  • Some participants assert that the current understanding is that collapse is not solely caused by observation but rather by interactions with the environment, describing this as a continuous process rather than abrupt.
  • There is mention of decoherence as a mechanism that can lead to apparent collapse, with examples provided regarding how environmental factors like air density can affect interference patterns.
  • Some participants highlight a distinction between "ancient" and "modern" views on collapse, noting that while the modern perspective incorporates decoherence, it still faces challenges regarding the nature of outcomes.
  • Questions arise about the clarity of terms like "measure and throw away," with discussions on scenarios such as destroying measurement results without observation and its implications for collapse versus decoherence.

Areas of Agreement / Disagreement

Participants express multiple competing views on the nature of wave function collapse, with no clear consensus reached. Disagreements persist regarding the roles of observation and environmental interaction in triggering collapse.

Contextual Notes

Limitations in the discussion include unresolved definitions of measurement and collapse, as well as the dependence on interpretations of quantum mechanics that may not be universally accepted.

Cobalt101
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I am wondering if there are some views on this. One of the key mysteries of the double slit experiment boils down to when the observation mechanism is placed by one of the slits - and switched on it triggers the change from wave-like outcomes to particle-like outcomes. Is it the observation or the interference of the interaction that causes the collapse of the wave function ? I am sure one could configure the experiment to be such that the observation machine is switched on, "looks" at the slit, but that its result is made unobservable. What happens ?
 
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The answer is: the measurement problem has not been solved. We don't know where collapse of the wave function occurs; or whether we modify QM to allow for collapse eg. by gravity.

The answer to your experimental question: we would see two hidden interference patterns on the back-screen. I say hidden, because if you conduct quantum eraser of which way information you correlate the data with the points and two interference patterns emerge. The combination of those interference patterns looks like the back-screen you would get if the system went through one slit or the other.
 
Cobalt101 said:
I am wondering if there are some views on this. One of the key mysteries of the double slit experiment boils down to when the observation mechanism is placed by one of the slits - and switched on it triggers the change from wave-like outcomes to particle-like outcomes. Is it the observation or the interference of the interaction that causes the collapse of the wave function ? I am sure one could configure the experiment to be such that the observation machine is switched on, "looks" at the slit, but that its result is made unobservable. What happens ?

If the result is made unobservable, then there is only apparent collapse.

Collapse occurs when one observes the result and retains the result.
 
Cobalt101 said:
I am wondering if there are some views on this. One of the key mysteries of the double slit experiment boils down to when the observation mechanism is placed by one of the slits - and switched on it triggers the change from wave-like outcomes to particle-like outcomes. Is it the observation or the interference of the interaction that causes the collapse of the wave function ? I am sure one could configure the experiment to be such that the observation machine is switched on, "looks" at the slit, but that its result is made unobservable. What happens ?
The current view is that its not caused by observation, but by interaction with the environment. Also this is not an abrupt process, but a continuous one, although it happens very very fast.
For example in the double slit experiment, it is observed that in the vacuum, the result is a interference pattern. As they increased the density of air, the interference pattern gradually disappeared.
But its not just scattering from air molecules. Even photons bouncing off the objects can cause decoherence. And even in the darkest room you can find, the thermal radiation from the walls and also the CMB is enough to induce decoherence in a very efficient way.
I suggest you read this book, of course if you have a good knowledge of QM.
At the end, I should mention that it doesn't solve the measurement problem completely, but only some parts of it.
 
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Shyan said:
The current view is that its not caused by observation, but by interaction with the environment. Also this is not an abrupt process, but a continuous one, although it happens very very fast.
For example in the double slit experiment, it is observed that in the vacuum, the result is a interference pattern. As they increased the density of air, the interference pattern gradually disappeared.
But its not just scattering from air molecules. Even photons bouncing off the objects can cause decoherence. And even in the darkest room you can find, the thermal radiation from the walls and also the CMB is enough to induce decoherence in a very efficient way.
I suggest you read this book, of course if you have a good knowledge of QM.
At the end, I should mention that it doesn't solve the measurement problem completely, but only some parts of it.

The modern point of view is the same as the ancient point of view: collapse occurs when an observation is made and the result is known. Decoherence only causes apparent collapse.
 
atyy said:
The modern point of view is the same as the ancient point of view: collapse occurs when an observation is made and the result is known. Decoherence only causes apparent collapse.
Yes, I wasn't careful. But it doesn't mean the two viewpoints are the same. In the "ancient" point of view, the collapse is a blackbox. The "modern" point of view opens up the blackbox and explains some parts of it but encounters a smaller blackbox(the problem of outcomes).
 
Shyan said:
Yes, I wasn't careful. But it doesn't mean the two viewpoints are the same. In the "ancient" point of view, the collapse is a blackbox. The "modern" point of view opens up the blackbox and explains some parts of it but encounters a smaller blackbox(the problem of outcomes).

Yes, people say that and I'm not sure whether I agree. But what is nice about the modern point of view for the ancient point of view is that decoherence is implicit in the ancient point of view, even if the ancients perhaps didn't understand it so well (though I wouldn't put it past von Neumann to have seen it and Bohm sketches it out for Bohmian Mechanics). Decoherence ensures the consistency of the ancient point of view - if we measure and throw away the results, then we can just have decoherence and apparent collapse - so collapse is really dependent on keeping the information from the measurement.
 
atyy said:
if we measure and throw away the results, then we can just have decoherence and apparent collapse - so collapse is really dependent on keeping the information from the measurement.

The exact meaning of "measure and throw away" is sometimes not clear to someone who is new to this subject. This leads to questions like, "what if I burn the printout without anyone ever looking at it"?
 
Swamp Thing said:
The exact meaning of "measure and throw away" is sometimes not clear to someone who is new to this subject. This leads to questions like, "what if I burn the printout without anyone ever looking at it"?

If you burn the printout without anyone ever looking at it, then you don't need collapse, you only need decoherence and apparent collapse. Of course if you want to say it collapsed and you threw away the results, it's fine too. But you have the option of saying it only decohered with apparent collapse, but no true collapse.

Remember, the wave function and collapse are not necessarily real, so this subjectivity is fine. We only care that we make correct predictions.
 

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