Is wave-function collapse a REAL incident

[Soumya_M]

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?

 

[DrChinese]

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.

 

[Soumya_M]

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)?

 

[bcrowell]

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.

 

[Soumya_M]

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

 

[DrChinese]

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.

 

[bcrowell]

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.

 

[CyberShot]

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?

 

[bcrowell]

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?

 

[bcrowell]

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.

 

[dm4b]

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 Schrödinger 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?

 

[dm4b]

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?

 

[bcrowell]

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 Schrödinger 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.

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.

 

[dm4b]

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 Schrödinger'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 ;-)

 

[dm4b]

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!

 

[DrChinese]

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.

 

[dm4b]

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.

 

[DrChinese]

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...

 

[dm4b]

Well, there might have existed a superposition until I observed the results. I'm just saying...

okay, so it is somewhat similar. Tricky stuff!

 

[rogerl]

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."

 

[StevieTNZ]

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.

 

[dm4b]

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?

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?

 

[StevieTNZ]

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).

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)?

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.

 

[yoda jedi]

'projection postulate' (observation/measurement)?

Right.



.

 

[StevieTNZ]

Right.



.

Yup. :)

 

[dm4b]

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.

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.

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.

 

[A. Neumaier]

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.

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.

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...

 

[dm4b]

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 ...

 

[San K]

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?

 

[San K]

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