Is wave-function collapse a REAL incident

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In summary, there is no simple answer to the questions about wave-function collapse and its relationship to the observer and their knowledge. Different interpretations of quantum mechanics offer different explanations, and the truth may lie somewhere in between. It's important to consider definitions and the limitations of our understanding when discussing these complex topics.
  • #1
Soumya_M
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Scientists/Physicists/Truth-seekers,

I am looking for answers to some questions, which I confess are issues of gobbledygook debates. But this time I want serious and simple answers. So no debates please. My questions are as under:-
Is wave-function collapse a REAL incident or just a back-calculation to justify unexpected results of experiments on particle behaviour? Some say that we end up with absurd results while trying to LOCATE the position of a particle, because in the attempt to do so, we shine light on them which PUSHES them towards the – so called COLLAPSE. Is that the WHOLE TRUTH or is there something mysterious indeed? Does the observer’s KNOWLEDGE in any way PARTICIPATE in what results as a wave function collapse? Is there any direct EVIDENCE that the observer’s knowledge is RESPONSIBLE for the collapse? And also whether there is any precedence where the “wave-function collapse” has occurred even in the ABSENCE of an observer (simply because light was shown on the particle, although NO ONE WAS PEEPING)? I am looking for RATIONAL AND UNBIASED answers. Any help?
 
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  • #2
Good questions. Sadly, there are no simple answers. Generally, the answers depend on your definitions. So it is really all about semantics.

What we do know is that the mathematical language is a useful description. That is as far as we can say with confidence and reasonable agreement.
 
  • #3
DrChinese said:
What we do know is that the mathematical language is a useful description. That is as far as we can say with confidence and reasonable agreement.
Dear Dr. Chinese,
I also want to know if there any precedence where the “wave-function collapse” has occurred even in the ABSENCE of an observer (simply because light was shown on the particle, although NO ONE WAS PEEPING)?
 
  • #4
There are interpretations of quantum mechanics, such as the many-worlds interpretation http://en.wikipedia.org/wiki/Many-worlds_interpretation , in which observers play no special role and there is no collapse of wavefunctions. My personal take on it is that the Copenhagen interpretation clearly has foundational problems, because an observer is just a physical system like any other, and yet it is a very convenient shorthand for describing the psychological experience of working with quantum-mechanical systems in real-life experiments.

By the way, Soumya_M, if you could avoid using ALL CAPS FOR EMPHASIS, my eyeballs would thank you :-) If you want to use italics, for instance, just click on the "Go Advanced" button, select the text you want to italicize, and click on the italic I button near the left side of the bottom toolbar.
 
  • #5
bcrowell said:
an observer is just a physical system like any other, and yet it is a very convenient shorthand for describing the psychological experience of working with quantum-mechanical systems in real-life experiments.

What happens when the experiment isn't being observed, although light is shone on the particles? Does the collapse take place in absence of human observers?

And thanks for that suggestion, Bcrowell
 
  • #6
Soumya_M said:
Dear Dr. Chinese,
I also want to know if there any precedence where the “wave-function collapse” has occurred even in the ABSENCE of an observer (simply because light was shown on the particle, although NO ONE WAS PEEPING)?

Again, the answer to a certain degree depends on definitions, but I would answer that the collapse occurs even independent of a person.
 
  • #7
Soumya_M said:
What happens when the experiment isn't being observed, although light is shone on the particles? Does the collapse take place in absence of human observers?

It sounds like you're assuming that, for example, we could distinguish between the Copenhagen interpretation and the many-worlds interpretation (MWI) by doing experiments. I don't think that's the case. Your question is of the form "under condition X, will Y happen?," where X is "there's no observer" and Y is "the wavefunction collapses." But the MWI doesn't even attempt to define "observer" (which is why, to my mind, MWI makes more sense), and therefore X has no meaning outside the context of a particular interpretation of quantum mechanics.
 
  • #8
Soumya_M said:
Scientists/Physicists/Truth-seekers,

I am looking for answers to some questions, which I confess are issues of gobbledygook debates. But this time I want serious and simple answers. So no debates please. My questions are as under:-
Is wave-function collapse a REAL incident or just a back-calculation to justify unexpected results of experiments on particle behaviour? Some say that we end up with absurd results while trying to LOCATE the position of a particle, because in the attempt to do so, we shine light on them which PUSHES them towards the – so called COLLAPSE. Is that the WHOLE TRUTH or is there something mysterious indeed? Does the observer’s KNOWLEDGE in any way PARTICIPATE in what results as a wave function collapse? Is there any direct EVIDENCE that the observer’s knowledge is RESPONSIBLE for the collapse? And also whether there is any precedence where the “wave-function collapse” has occurred even in the ABSENCE of an observer (simply because light was shown on the particle, although NO ONE WAS PEEPING)? I am looking for RATIONAL AND UNBIASED answers. Any help?

If you believe in rationality, then you'd immediately consider a wave function collapse to be a false depiction of reality, but one which suffices in the mathematical framework of QM, otherwise bad things would happen. Everything pretty much rests on Heisenberg's principle, so it kind of makes sense that chaos would arise in trying to measure something subatomic from the point of view of QM.

However, the realist would argue that the wave function is not the the whole story, that there is outside information (hidden variable) inaccessible by the experimenter due to precisional limitations. Of course, in my opinion, in reality the wave function collapse is simply hogwash. Do you really think the moon is not there when no one's looking? Do you really think you can cause the death of a cat by peering into a box and seeing if it was dead or alive?
 
  • #9
DrChinese said:
Again, the answer to a certain degree depends on definitions, but I would answer that the collapse occurs even independent of a person.

Hmm...but a person is only one type of observer. How about dogs or tape recorders?
 
  • #10
CyberShot said:
Everything pretty much rests on Heisenberg's principle, so it kind of makes sense that chaos would arise in trying to measure something subatomic from the point of view of QM.

MWI has the Heisenberg principle but not wavefunction collapse.
 
  • #11
CyberShot said:
Of course, in my opinion, in reality the wave function collapse is simply hogwash. Do you really think the moon is not there when no one's looking? Do you really think you can cause the death of a cat by peering into a box and seeing if it was dead or alive?

Isn't that the whole point .. that a microscopic, or QM, phenomenon, and the logic that goes along with it, cannot be applied to a macroscopic object, like the moon. (Not too mention, it seems like Schrodinger forgot the cat is a macroscopic observer too!)

I thought Penrose had some new idea on just where and when you could really draw the line between the QM world and the macroscopic world. Seems like he also provided a possible "mechanism" behind wave-function collapse, etc.

I forget all the details though. Anybody else know?
 
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  • #12
bcrowell said:
DrChinese said:
Again, the answer to a certain degree depends on definitions, but I would answer that the collapse occurs even independent of a person.

Hmm...but a person is only one type of observer. How about dogs or tape recorders?

I was about to say this seems like it would be easy enough to prove by experiemnt, but then again, maybe it's not.

Couldn't you have a "tape recorder" that measures something and records the time at which it measures it? Then a human observer looks some time later to see the result. If the measurement time is before the human observer "observed" then clearly the wave function collapse happened indepedent of him.

I guess this isn't as easy as it sounds or the problem would already be resolved, huh?
 
  • #13
dm4b said:
Isn't that the whole point .. that a microscopic, or QM, phenomenon, and the logic that goes along with it, cannot be applied to a macroscopic object, like the moon. (Not too mention, it seems like Schrodinger forgot the cat is a macroscopic observer too!)
So are you saying that there are macroscopic experiments that falsify QM? If so, then I'm surprised they haven't been published. If not, then your statement doesn't seem to be empirically testable.

dm4b said:
I thought Penrose had some new idea on just where and when you could really draw the line between the QM world and the macroscopic world. Seems like he also provided a possible "mechanism" behind wave-function collapse, etc.
Penrose has some idiosyncratic ideas about the Copenhagen interpretation. He described them in popularized form in The Road to Reality, and I only know about them from reading at that level. They seemed silly/pointless to me, but Roger Penrose is a gazillion times smarter than me, so maybe I'm wrong, and we'll end up finding out that he's right.
 
  • #14
bcrowell said:
So are you saying that there are macroscopic experiments that falsify QM? If so, then I'm surprised they haven't been published. If not, then your statement doesn't seem to be empirically testable.

No, I wasn't saying that at all. I was mentioning what I thought was the one of the main points behind the Schrodinger's Cat story.

I do have yet to see a human being clearly exhibit wave-particle duality. I personally can only walk through one door at a time ;-)
 
  • #15
bcrowell said:
Penrose has some idiosyncratic ideas about the Copenhagen interpretation. He described them in popularized form in The Road to Reality, and I only know about them from reading at that level. They seemed silly/pointless to me, but Roger Penrose is a gazillion times smarter than me, so maybe I'm wrong, and we'll end up finding out that he's right.

Thanks Bcrowell. That's at least the 3rd time I have had that book mentioned to me. Maybe I need to read it!
 
  • #16
dm4b said:
I was about to say this seems like it would be easy enough to prove by experiemnt, but then again, maybe it's not.

Couldn't you have a "tape recorder" that measures something and records the time at which it measures it? Then a human observer looks some time later to see the result. If the measurement time is before the human observer "observed" then clearly the wave function collapse happened indepedent of him.

I guess this isn't as easy as it sounds or the problem would already be resolved, huh?

True. This has been done, and you might guess you see wave function collapse as independent. But strictly you could deny that.
 
  • #17
DrChinese said:
True. This has been done, and you might guess you see wave function collapse as independent. But strictly you could deny that.

How could you deny it? I guess I'm not making the connection. Would it be similar to Wheeler's delayed choice experiment, specifically the galactic version where we presumably cause something to come about (the path which the light took around the distant galaxy) that already happened a million years ago.
 
  • #18
dm4b said:
How could you deny it? I guess I'm not making the connection. Would it be similar to Wheeler's delayed choice experiment, specifically the galactic version where we presumably cause something to come about (the path which the light took around the distant galaxy) that already happened a million years ago.

Well, there might have existed a superposition until I observed the results. I'm just saying...
 
  • #19
DrChinese said:
Well, there might have existed a superposition until I observed the results. I'm just saying...

okay, so it is somewhat similar. Tricky stuff!
 
  • #20
Anyone knows why Objective collapse theory has to involve only spontaneous collapse or reaching a threshold. What reasoning forbids the possibility of plain measurement causing Objective collapse?

http://en.wikipedia.org/wiki/Objective_collapse_theory

"Collapse theories stand in opposition to many-world theories, in that they hold that a process of wavefunction collapse curtails the branching of the wavefunction and removes unobserved behaviour. Objective collapse theories differ from the Copenhagen interpretation in regarding both the wavefunction and the process of collapse as ontologically objective. The Copenhagen interpretation includes collapse, but it is non-committal about the objective reality of the wave function, and because of that it is possible to regard Copenhagen-style collapse as a subjective or informational phenomenon. In objective theories, there is an ontologically real wave of some sort corresponding to the mathematical wave function, and collapse occurs randomly ("spontaneous localization"), or when some physical threshold is reached, with observers having no special role."
 
  • #21
dm4b said:
I do have yet to see a human being clearly exhibit wave-particle duality. I personally can only walk through one door at a time ;-)

Probably cause there's been an observation? Therefore no superposition.
But then again, can you really consider something you know is in a definite state not being in a superposition too? Schroedinger's equation doesn't 'collapse' - the U(t) operator applied means that at the same time you know a definite state 'exists', the Schroedinger equation also applies.
 
  • #22
StevieTNZ said:
Probably cause there's been an observation? Therefore no superposition.

Are you saying if no one is around in the forest to hear, the tree is in a superposition of falling down and standing? ;-)

What constitutes an observation?

StevieTNZ said:
But then again, can you really consider something you know is in a definite state not being in a superposition too? Schroedinger's equation doesn't 'collapse' - the U(t) operator applied means that at the same time you know a definite state 'exists', the Schroedinger equation also applies.

If you mean the propagator, that evolves the state vector forward in time, but doesn't necessarily produce a definite state.

I guess I don't follow what you're saying?
 
  • #23
dm4b said:
Are you saying if no one is around in the forest to hear, the tree is in a superposition of falling down and standing? ;-)
I consider a superposition to be a quantum system in neither state A (falling down) or state B (standing).

dm4b said:
What constitutes an observation?
Dunno. But its obvious a observation has occurred when you can't walk through two doors at once. I thought it was obvious that there is a 'projection postulate' (measurement)?


dm4b said:
If you mean the propagator, that evolves the state vector forward in time, but doesn't necessarily produce a definite state.

I guess I don't follow what you're saying?

Correct. But what I'm saying is that on the surface it looks as though a quantum system is in a definite state, but it can also be considered to be in a superposition too.

e.g. an atom is definitely in box A. But it can, at the same time, be considered to be in a superposition of being in both box A and box B.
 
  • #24
StevieTNZ said:
'projection postulate' (observation/measurement)?

Right.



.
 
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  • #25
yoda jedi said:
Right.



.

Yup. :)
 
  • #26
StevieTNZ said:
I consider a superposition to be a quantum system in neither state A (falling down) or state B (standing).

Well, if you look at a simplfied wave function, say: psi = A^2*state_A + B^2*state_B, where the states are obvious and the A and Bs are the amplitudes for obtaining those states upon measurement, it sure looks like the psi IS in a superposition of both states A and B. But, of course, it may be that the wave function isn't "real" and is just a mathematical device that's good at prediciting outcomes. I think I have heard it both ways on this forum. The way I was taught was that before measurement, the particle is not physically in a superposition in the way a violin string may be amongst a set of harmonics, so from that perspective, I agree with you.

StevieTNZ said:
Dunno. But its obvious a observation has occurred when you can't walk through two doors at once. I thought it was obvious that there is a 'projection postulate' (measurement)?

Well, it does seem obvious there was an observation, agreed. What's not so obvious to me, is just how strongly quantum influences are felt or apply to the macroscopic scale in question.


StevieTNZ said:
Correct. But what I'm saying is that on the surface it looks as though a quantum system is in a definite state, but it can also be considered to be in a superposition too.

e.g. an atom is definitely in box A. But it can, at the same time, be considered to be in a superposition of being in both box A and box B.

I guess I don't really know here. If the wave function truly collapes to a single state or projection, seems to me it has to be in Box A and no longer in a superposition. Not that it couldn't go back to being in one, but upon measurement, it's not. Maybe some other folks can add more.
 
  • #27
Soumya_M said:
Is wave-function collapse a REAL incident or just a back-calculation to justify unexpected results of experiments on particle behaviour?
It is very real, at least for systems here on earth. Quantum computing would be impossible without it.
Soumya_M said:
Does the observer’s KNOWLEDGE in any way PARTICIPATE in what results as a wave function collapse? I
No. quantum mechanics is completely independent of subjective knowledge.
Some sort of collapse happens for all degrees of freedom that are coupled to an environment, no matter which properties this environment has. in particular, it need not be conscious.
Soumya_M said:
the “wave-function collapse” has occurred even in the ABSENCE of an observer (simply because light was shown on the particle, although NO ONE WAS PEEPING)?
Of courdse. We are not the center of the universe. Collapse had to happen for star formation, long before anyone was there to obsereve anything...
 
  • #28
dm4b said:
I guess I don't really know here. If the wave function truly collapes to a single state or projection, seems to me it has to be in Box A and no longer in a superposition. Not that it couldn't go back to being in one, but upon measurement, it's not. Maybe some other folks can add more.

I'll just go ahead and comment on my own post here ...

I think the double-slit experiment is an example of how you lose the superposition upon measurement. If you try and determine which slit the electron has gone through, you lose the interference pattern. You "evoke" the particle like nature of the electron, it travels through a specific slit, NOT both, and you lose your interference pattern. In other words, once you take the measurement, or make an observation, the wave function collapses and the electron chooses a specific path. And, you can no longer say it took both paths ... if it did, you'd still have the interference pattern.

Now, if you don't mess with the slits, a single electron still only makes a dot on the screen. It's only after sending many through that you see the interference pattern. The screen is another measurement that "evokes" the particle like nature of the electron. But, the interference pattern is a hint that each electron "interfered" with itself by going through both slits earlier ... where, this time around, you did not make a measurement.

I'm sure others will have more opinions on this ...
 
  • #29
DrChinese said:
True. This has been done, and you might guess you see wave function collapse as independent. But strictly you could deny that.

would the delayed choice quantum eraser be such experiment?

if so, how could you deny it? deny the functioning of the co-incidence counter? or you mean deny that a wave function ever was created to have collapsed?
 
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  • #30
dm4b said:
I'll just go ahead and comment on my own post here ...

I think the double-slit experiment is an example of how you lose the superposition upon measurement. If you try and determine which slit the electron has gone through, you lose the interference pattern. You "evoke" the particle like nature of the electron, it travels through a specific slit, NOT both, and you lose your interference pattern. In other words, once you take the measurement, or make an observation, the wave function collapses and the electron chooses a specific path. And, you can no longer say it took both paths ... if it did, you'd still have the interference pattern.

Now, if you don't mess with the slits, a single electron still only makes a dot on the screen. It's only after sending many through that you see the interference pattern. The screen is another measurement that "evokes" the particle like nature of the electron. But, the interference pattern is a hint that each electron "interfered" with itself by going through both slits earlier ... where, this time around, you did not make a measurement.

I'm sure others will have more opinions on this ...

you could recreate the superposition by erasing the which-way info...prior to the photon striking the screen...this makes it even more interesting/complicated since this means that the photon still carries the ability/information (even after we determined its path and subsequently erased it) to go back to the earlier interference/superimposed state
 
  • #31
Soumya_M said:
Scientists/Physicists/Truth-seekers,

I am looking for answers to some questions, which I confess are issues of gobbledygook debates. But this time I want serious and simple answers. So no debates please. My questions are as under:-
Is wave-function collapse a REAL incident or just a back-calculation to justify unexpected results of experiments on particle behaviour? Some say that we end up with absurd results while trying to LOCATE the position of a particle, because in the attempt to do so, we shine light on them which PUSHES them towards the – so called COLLAPSE. Is that the WHOLE TRUTH or is there something mysterious indeed? Does the observer’s KNOWLEDGE in any way PARTICIPATE in what results as a wave function collapse? Is there any direct EVIDENCE that the observer’s knowledge is RESPONSIBLE for the collapse? And also whether there is any precedence where the “wave-function collapse” has occurred even in the ABSENCE of an observer (simply because light was shown on the particle, although NO ONE WAS PEEPING)? I am looking for RATIONAL AND UNBIASED answers. Any help?

As far as I know, there is no experimental evidence for wavefunction collapse. There is no evidence for the existence of the wavefunction in space-time. It is not an observable and we do not measure any of its properties, if it has any. All we know is that the wavefunction is a mathematical construct used to calculate probabilities. It is an element of a Hilbert space. There is no known mechanism that brings about any collapse.

A quantum experiment requires a result that is a measured value of a specified observable. This gives the experiment closure. (Bohr) In the absence of a result, there is no experiment (Wheeler, Peres), and no corresponding wavefunction.

The point is this –a quantum experiment requires a result, not an observer, and not a collapsing wavefunction. Someone suggested that we throw away the word “observer” because of the confusion it engenders. I agree. Quantum events do not require a human observer. No one ever killed a cat by looking at it! There is no mysterious, lethal interaction going on between the human observer and the cat. The observer can choose what experiment to do, but his presence, or absence, does not contribute to the results. It does not matter whether he is “peeping or not”. Nor does an observer have the “power” to collapse any wavefunction. His knowledge is irrelevant.

This, of course, reflects my own bias on the matter.
Best wishes
 
  • #32
eaglelake said:
As far as I know, there is no experimental evidence for wavefunction collapse. There is no evidence for the existence of the wavefunction in space-time. It is not an observable and we do not measure any of its properties, if it has any. All we know is that the wavefunction is a mathematical construct used to calculate probabilities. It is an element of a Hilbert space. There is no known mechanism that brings about any collapse.

A quantum experiment requires a result that is a measured value of a specified observable. This gives the experiment closure. (Bohr) In the absence of a result, there is no experiment (Wheeler, Peres), and no corresponding wavefunction.

The point is this –a quantum experiment requires a result, not an observer, and not a collapsing wavefunction. Someone suggested that we throw away the word “observer” because of the confusion it engenders. I agree. Quantum events do not require a human observer. No one ever killed a cat by looking at it! There is no mysterious, lethal interaction going on between the human observer and the cat. The observer can choose what experiment to do, but his presence, or absence, does not contribute to the results. It does not matter whether he is “peeping or not”. Nor does an observer have the “power” to collapse any wavefunction. His knowledge is irrelevant.

This, of course, reflects my own bias on the matter.
Best wishes


agreed Eagle. the word "observer" should be replaced with something like "ability to know which way-path information" via instruments etc

this would reduce the number of theories going into consciousness etc
 
  • #33
San K said:
you could recreate the superposition by erasing the which-way info...prior to the photon striking the screen...this makes it even more interesting/complicated since this means that the photon still carries the ability/information (even after we determined its path and subsequently erased it) to go back to the earlier interference/superimposed state

That's what I was trying to say. The correct application, of course, is to consider the initial setup and final measurement as forming a context. Anything in between is considered "supposition".
 
  • #34
Understood, but isn't the quantum eraser thing complicating the simple point I was trying to make (in a long winded sort of way!). At the, as DrChineese called it, final measurement, the superposition is broken, and the wave function is collapsed?

Or, is this incorrect?
 
  • #35
StevieTNZ said:
Correct. But what I'm saying is that on the surface it looks as though a quantum system is in a definite state, but it can also be considered to be in a superposition too.

I was reading up on some QM interpretations and came across one I was not familar with before, relational QM.

"The essential idea behind relational quantum mechanics, following the precedent of special relativity, is that different observers may give different accounts of the same series of events: for example, to one observer at a given point in time, a system may be in a single, "collapsed" eigenstate, while to another observer at the same time, it may be in a superposition of two or more states. "


Anyhow, jives up with what you're saying to some extent, if I understood you correctly. Not sure if you are coming from the observer dependent viewpoint, such as above, though?
 
<h2>1. What is wave-function collapse?</h2><p>Wave-function collapse refers to the concept in quantum mechanics where the state of a particle, described by a wave-function, becomes a definite value upon measurement. This is also known as the "observer effect" as the act of observation causes the wave-function to collapse into a specific state.</p><h2>2. Is wave-function collapse a real phenomenon?</h2><p>Yes, wave-function collapse is a well-established phenomenon in quantum mechanics. It has been observed and confirmed through numerous experiments and is a fundamental principle in understanding the behavior of particles on a quantum level.</p><h2>3. How does wave-function collapse occur?</h2><p>Wave-function collapse occurs when a particle is observed or measured. The act of measurement causes the wave-function to collapse into a definite state, which is then observed by the observer. This is a fundamental principle in quantum mechanics and is still not fully understood.</p><h2>4. Can wave-function collapse be reversed?</h2><p>No, once a wave-function has collapsed into a definite state, it cannot be reversed. This is because the act of measurement causes irreversible changes to the particle's state. However, the wave-function can still evolve and change over time through other quantum processes.</p><h2>5. Is wave-function collapse the only explanation for quantum behavior?</h2><p>No, there are multiple interpretations and explanations for quantum behavior, including the many-worlds interpretation and the Copenhagen interpretation. Wave-function collapse is just one way to understand and explain the behavior of particles on a quantum level.</p>

1. What is wave-function collapse?

Wave-function collapse refers to the concept in quantum mechanics where the state of a particle, described by a wave-function, becomes a definite value upon measurement. This is also known as the "observer effect" as the act of observation causes the wave-function to collapse into a specific state.

2. Is wave-function collapse a real phenomenon?

Yes, wave-function collapse is a well-established phenomenon in quantum mechanics. It has been observed and confirmed through numerous experiments and is a fundamental principle in understanding the behavior of particles on a quantum level.

3. How does wave-function collapse occur?

Wave-function collapse occurs when a particle is observed or measured. The act of measurement causes the wave-function to collapse into a definite state, which is then observed by the observer. This is a fundamental principle in quantum mechanics and is still not fully understood.

4. Can wave-function collapse be reversed?

No, once a wave-function has collapsed into a definite state, it cannot be reversed. This is because the act of measurement causes irreversible changes to the particle's state. However, the wave-function can still evolve and change over time through other quantum processes.

5. Is wave-function collapse the only explanation for quantum behavior?

No, there are multiple interpretations and explanations for quantum behavior, including the many-worlds interpretation and the Copenhagen interpretation. Wave-function collapse is just one way to understand and explain the behavior of particles on a quantum level.

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