Quantum Interpretation Poll (2011)

[StevieTNZ]

Yeah, some people on here need to stop attacking others. No need to jump at each others throats. In other words, "ease up turbo".

 

[Darken-Sol]

we can guess where something is but until we look we won't know? sounds good to me

 

[Varon]

Quantum object is said to be still there even if it has no definite position. And it's not because you don't know the position, but the position doesn't exist in principle (before measurement). How can an quantum object still be there yet no position in principle? It's like the object doesn't register anymore in the spacetime continnum but still there somewhere perhaps outside spacetime?

 

[A. Neumaier]

Quantum object is said to be still there even if it has no definite position. And it's not because you don't know the position, but the position doesn't exist in principle (before measurement). How can an quantum object still be there yet no position in principle? It's like the object doesn't register anymore in the spacetime continnum but still there somewhere perhaps outside spacetime?

''has no position'' only means ''has no position to infinite precision''.

The position is just a little bit fuzzy rather than determined to infinite precision. This is the content of Heisenberg's uncertainty relation.

 

[harrylin]

I agree completely, it doesn't imply that an intuitively unlikely explanation must be true.

I would contend that relativity, like quantum mechanics, is well understood from the "shut up and calculate" point of view. But it has, like quantum mechanics, interpretational problems. Relativistic physics "exists" in a 4-D spacetime. There is no motion in this spacetime. What we perceive as motion of a particle is an unvarying 1-dimensional curve in spacetime. If you use relativity to predict what you will experience, you pretend that you are moving along your world line at the speed of light. How can we use the concept of motion when it has already been absorbed into the spacetime description? Just like the collapse of the wave function in QM, the very point at which we translate the mathematics into experience, we introduce something weird, outside of the formalism.

I agree that SR becomes a bit weird if we insist on interpreting 4D spacetime as a physical object while we still continue to use the standard concept of motion. However I do not introduce something weird like that and I don't pretend that I am moving at the speed of light: no theorem exists according to which we must interpret SR's equations that way. In contrast, Bell's theorem suggests that only implausible looking interpretations of the world can be compatible with QM.

 

[Darken-Sol]

so i can accurately say its over there but precisely miss it with my finger waving?

 

[harrylin]

See also the thread "what is the Copenhagen interpretation"!
https://www.physicsforums.com/showthread.php?t=494788

Thus it may well be that several people here who voted for "Copenhagen" in fact have opposite ideas... And perhaps that's also the case with one or two other interpretations.
I guess that's the problem with "philosophy".

 

[A. Neumaier]

See also the thread "what is the Copenhagen interpretation"!
https://www.physicsforums.com/showthread.php?t=494788

Thus it may well be that several people here who voted for "Copenhagen" in fact have opposite ideas... And perhaps that's also the case with one or two other interpretations.
I guess that's the problem with "philosophy".

No. This is just a problem with setting up this particular poll. A good poll would define its terms, by giving for each option a 1-paragraph description of the intended meaning. The early discussion in this thread revealed a number of limitations of the present poll - with poorly defined terms, missing important interpretations, etc.. To be really meaningful, the next poll of this kind should be much more carefully designed.

 

[Varon]

''has no position'' only means ''has no position to infinite precision''.

The position is just a little bit fuzzy rather than determined to infinite precision. This is the content of Heisenberg's uncertainty relation.

This is your Copenhagen version. But in original Copenhagen. The position literally doesn't exist before measurement. It's not about the position being fuzzy. It doesn't exist in principle. Hope someone can confirm if this is really the view of the original version because this is what I believed all these years.

 

[A. Neumaier]

This is your Copenhagen version.

Indeed, strictly speaking, Copenhagen is completely _silent_ about the position outside measurement.
But my interpretation makes explicit how the classical quantum interface in the Copenhagen interpretation (assumed there without any discussion) works, and hence is completely consistent with it.

If you believe that Bohr, Heisenberg, and other proponents of the Copenhagen interpretation assumed that particles with which experiments are performed are on the experimenter's desk also before it is measured, this already constitutes an approximate, macroscopic position. Without such an assumption (which belongs to the classical, macroscopic background always postulated in the Copenhagen interpretation), no meaningful experiments would be possible.

Neither would relations such as the Ehrenfest theorem make sense, which makes statements about the dynamics of the mean position.

But in original Copenhagen. The position literally doesn't exist before measurement. It's not about the position being fuzzy. It doesn't exist in principle. Hope someone can confirm if this is really the view of the original version because this is what I believed all these years.

There is no original version. The Copenhagen interpretation is essentially the view of Bohr and Heisenberg, as expressed through their (at times quite cryptic and conflicting) statements.

 

[Varon]

Indeed, strictly speaking, Copenhagen is completely _silent_ about the position outside measurement.
But my interpretation makes explicit how the classical quantum interface in the Copenhagen interpretation (assumed there without any discussion) works, and hence is completely consistent with it.

If you believe that Bohr, Heisenberg, and other proponents of the Copenhagen interpretation assumed that particles with which experiments are performed are on the experimenter's desk also before it is measured, this already constitutes an approximate, macroscopic position. Without such an assumption (which belongs to the classical, macroscopic background always postulated in the Copenhagen interpretation), no meaningful experiments would be possible.

Neither would relations such as the Ehrenfest theorem make sense, which makes statements about the dynamics of the mean position.

There is no original version. The Copenhagen interpretation is essentially the view of Bohr and Heisenberg, as expressed through their (at times quite cryptic and conflicting) statements.

This is related to Bell's Theorem. Say 2 entangled particle.. one is on earth, the other is somewhere 100 billion light years away. When you measure the spin here. Does the spin in the other side of the universe available too. If it does, it violates special relativity. Hence it shouldn't collapse yet. This means quantum properties like position doesn't even exist in principle in the other unmeasured particle. This is what is meant local realism refuted. By denying reality.. meaning reality is false. I think this is the mainstream view. Can others confirm? I want to distinguish this and Neumaier's so I'd know the difference between his and the mainstream views.

 

[SpectraCat]

This is related to Bell's Theorem. Say 2 entangled particle.. one is on earth, the other is somewhere 100 billion light years away. When you measure the spin here. Does the spin in the other side of the universe available too. If it does, it violates special relativity. Hence it shouldn't collapse yet. This means quantum properties like position doesn't even exist in principle in the other unmeasured particle. This is what is meant local realism refuted. By denying reality.. meaning reality is false. I think this is the mainstream view. Can others confirm? I want to distinguish this and Neumaier's so I'd know the difference between his and the mainstream views.

It does not violate special relativity, because no information can be transmitted in such a fashion. There is no way to passively observe one member of an entangled pair, so that you can see when it's state is determined. You must actively measure the state, and then you cannot know whether it was your measurement that collapsed the entangled state, or a measurement at the other end ... at least not without additional information about the measurements performed at the other end, which must be sent over a 'normal' channel (which must obviously obey normal relativistic restrictions on information transport.)

 

[Varon]

It does not violate special relativity, because no information can be transmitted in such a fashion. There is no way to passively observe one member of an entangled pair, so that you can see when it's state is determined. You must actively measure the state, and then you cannot know whether it was your measurement that collapsed the entangled state, or a measurement at the other end ... at least not without additional information about the measurements performed at the other end, which must be sent over a 'normal' channel (which must obviously obey normal relativistic restrictions on information transport.)

But the spirit of relativity is violated. Because without proposing local realism false and believing in non-local correlation means there is a frame in which the simulataneous collapse of the wave function between 100 billion light years away can mean something is traveling back in time. One can also say the QM non-localyl is just default where randomness rules but perhaps signal can be transferred by using extra parameter. Bottom line is. One can believe in:

1. Local Realism falsified
2. Quantum Non-locally exist

Many believe that if Local Realism is falsified. There is no need to call it non-local because there is nothing to be non-local about if realism is false. Do you follow the second case about quantum non-locality and believe realism is retained. I think this is related to Specker something theorem.

 

[SpectraCat]

This is your Copenhagen version. But in original Copenhagen. The position literally doesn't exist before measurement. It's not about the position being fuzzy. It doesn't exist in principle. Hope someone can confirm if this is really the view of the original version because this is what I believed all these years.

This simply cannot be true, because the Bohr correspondence principle shows how classical behavior emerges naturally out of quantum mechanical systems at the dimensions and masses are increased, and the quantum numbers become very large.

Now, perhaps you would say that classical systems are somehow different, because they are constantly be "measured" (for example by reflecting photons that transmit information about position to observers). That is a purely interpretative question in my view, and thus we are back to philosophy ... classical mechanics is deterministic ... we can predict with certainty where a classical particle will be at a time point in the future. We know that if we look for it at that time, it will be where it is expected to be (assuming we know about any interactions between now any the future measurement time). So, as far as classical mechanics is concerned, it behaves _as_if_ the particle has a well-defined position at all times, so that is a natural assumption to make. But as for the question, "is the moon there if no one is looking at it" ... that is a philosophical question best left for after-hours conversations over frosty beverages in my opinion.

 

[Varon]

This simply cannot be true, because the Bohr correspondence principle shows how classical behavior emerges naturally out of quantum mechanical systems at the dimensions and masses are increased, and the quantum numbers become very large.

Now, perhaps you would say that classical systems are somehow different, because they are constantly be "measured" (for example by reflecting photons that transmit information about position to observers). That is a purely interpretative question in my view, and thus we are back to philosophy ... classical mechanics is deterministic ... we can predict with certainty where a classical particle will be at a time point in the future. We know that if we look for it at that time, it will be where it is expected to be (assuming we know about any interactions between now any the future measurement time). So, as far as classical mechanics is concerned, it behaves _as_if_ the particle has a well-defined position at all times, so that is a natural assumption to make. But as for the question, "is the moon there if no one is looking at it" ... that is a philosophical question best left for after-hours conversations over frosty beverages in my opinion.

I'm talking about a quantum particle like electron. Before measurement, I believe orthodox interpretation says that the position properties doesn't even exist in principle.. meaning not because your instrument not sensitive enough to detect it, but the quantum particle doesn't have position a priori.

Remember Born proposed the wave is a wave of possibility. When Schroedinger Equation evolves deterministicly, it is all a wave of possibilities. Only when collapse happens that the position precipitates in spacetime. This is the orthodox interpretation.

 

[SpectraCat]

But the spirit of relativity is violated. Because without proposing local realism false and believing in non-local correlation means there is a frame in which the simulataneous collapse of the wave function between 100 billion light years away can mean something is traveling back in time. One can also say the QM non-localyl is just default where randomness rules but perhaps signal can be transferred by using extra parameter. Bottom line is. One can believe in:

1. Local Realism falsified
2. Quantum Non-locally exist

Many believe that if Local Realism is falsified. There is no need to call it non-local because there is nothing to be non-local about if realism is false. Do you follow the second case about quantum non-locality and believe realism is retained. I think this is related to Specker something theorem.

There is no such thing as "the spirit of relativity" ... either a system obeys relativistic causality, or it violates it .. there is no in between. Furthermore no examples of the second case have been demonstrated.

I am not an expert in interpretations, so I can't really address the second part of your question in terms of what others have said. For myself, I would say that the universe appears to obey local realism most of the time, but that if clever physicists put in a hell of a lot of effort, they can create extremely delicate quantum systems that demonstrate that exceptions to LR are *very probably* (but not certainly) allowed under certain specific circumstances. I can live with that. Perhaps that is just because I don't understand the experimental ramifications of LR being false. In other words, what significant results of physical measurements (those not related to Aspect-type tests of LR) are expected to be different if LR is false?

 

[SpectraCat]

I'm talking about a quantum particle like electron. Before measurement, I believe orthodox interpretation says that the position properties doesn't even exist in principle.. meaning not because your instrument not sensitive enough to detect it, but the quantum particle doesn't have position a priori.

Remember Born proposed the wave is a wave of possibility. When Schroedinger Equation evolves deterministicly, it is all a wave of possibilities. Only when collapse happens that the position precipitates in spacetime. This is the orthodox interpretation.

But if position doesn't exist for an electron, then it doesn't exist for a macroscopic object either, right? Any such theory would have to explain how the well-defined positions of macroscopic objects manifest out of the microscopic theory where positions don't even exist. That is why I brought up the Bohr correspondence principle.

Neumeier's point about the Ehrenfest theorem is also valid in this respect .. that theorem shows that classical mechanics is simply the dynamics of quantum mechanical expectation values (or averages). If position were completely undetermined prior to measurement, then one would not be able to make deterministic statements about the time-evolution of the average value of position ... but the Ehrenfest theorem shows precisely why such deterministic statements are possible.

 

[Varon]

There is no such thing as "the spirit of relativity" ... either a system obeys relativistic causality, or it violates it .. there is no in between. Furthermore no examples of the second case have been demonstrated.

I am not an expert in interpretations, so I can't really address the second part of your question in terms of what others have said. For myself, I would say that the universe appears to obey local realism most of the time, but that if clever physicists put in a hell of a lot of effort, they can create extremely delicate quantum systems that demonstrate that exceptions to LR are *very probably* (but not certainly) allowed under certain specific circumstances. I can live with that. Perhaps that is just because I don't understand the experimental ramifications of LR being false. In other words, what significant results of physical measurements (those not related to Aspect-type tests of LR) are expected to be different if LR is false?

Heard of the Kochen-Specker Theorem? It proves that local realism is falsified.

http://en.wikipedia.org/wiki/Kochen–Specker_theorem

"The theorem proves that there is a contradiction between two basic assumptions of the hidden variable theories intended to reproduce the results of quantum mechanics: that all hidden variables corresponding to quantum mechanical observables have definite values at any given time, and that the values of those variables are intrinsic and independent of the device used to measure them. The contradiction is caused by the fact that quantum mechanical observables need not be commutative, making it impossible to embed the algebra of these observables in a commutative algebra, assumed to represent the classical structure of the hidden variables theory."

~~~~~~~~~~~~~~~~~~~~~~~~~~~~``

So if local realism is falsified, there is nothing to be non-local about because non-locality implies there is realism. So by denying reality, non-locality is not possible. Hence position properties don't exist even in principle before measurement (contradicting Neumaier approach).

 

[A. Neumaier]

Neumeier's point about the Ehrenfest theorem is also valid in this respect .. that theorem shows that classical mechanics is simply the dynamics of quantum mechanical expectation values (or averages).

This is not quite true. The Ehrenfest theorem doesn't translate the quantum dynamics into a classical dynamics - this happens only in the limit of vanishing uncertainties (i.e., of large quantum numbers).

 

[zonde]

Heard of the Kochen-Specker Theorem? It proves that local realism is falsified.

http://en.wikipedia.org/wiki/Kochen–Specker_theorem

"The theorem proves that there is a contradiction between two basic assumptions of the hidden variable theories intended to reproduce the results of quantum mechanics: that all hidden variables corresponding to quantum mechanical observables have definite values at any given time, and that the values of those variables are intrinsic and independent of the device used to measure them. The contradiction is caused by the fact that quantum mechanical observables need not be commutative, making it impossible to embed the algebra of these observables in a commutative algebra, assumed to represent the classical structure of the hidden variables theory."

Only when outcome of measurement is predictable with certainty these two basic assumptions are true. So it proves nothing if you do not assume fair sampling in photonic experiments.

 

[Varon]

But if position doesn't exist for an electron, then it doesn't exist for a macroscopic object either, right? Any such theory would have to explain how the well-defined positions of macroscopic objects manifest out of the microscopic theory where positions don't even exist. That is why I brought up the Bohr correspondence principle.

Neumeier's point about the Ehrenfest theorem is also valid in this respect .. that theorem shows that classical mechanics is simply the dynamics of quantum mechanical expectation values (or averages). If position were completely undetermined prior to measurement, then one would not be able to make deterministic statements about the time-evolution of the average value of position ... but the Ehrenfest theorem shows precisely why such deterministic statements are possible.

macroscopic object is in collapsed state. I'm talking about quantum object in superposition.

I learned about Kochen-Specker theorem at google sci.physics. Here's the gist of it:

"http://plato.stanford.edu/entries/kochen-specker/
says that two properties we normally associate with local realism, namely
value defiteness and non conceptuality, can not both be true if QM is
correct."

**

"Did you read the kochen-specher theorem to find out what views
are in accord with QM? If you did then you would know it is perfectly ok to
deny value definiteness - indeed you can not maintain both value
definiteness and non contextuality - both usual requirements of local
reality. If you reject value definiteness then you can not say what the
spin of the other photon is because it is not being measured so there is
nothing to be non local"

 

[SpectraCat]

Heard of the Kochen-Specker Theorem? It proves that local realism is falsified.

http://en.wikipedia.org/wiki/Kochen–Specker_theorem

"The theorem proves that there is a contradiction between two basic assumptions of the hidden variable theories intended to reproduce the results of quantum mechanics: that all hidden variables corresponding to quantum mechanical observables have definite values at any given time, and that the values of those variables are intrinsic and independent of the device used to measure them. The contradiction is caused by the fact that quantum mechanical observables need not be commutative, making it impossible to embed the algebra of these observables in a commutative algebra, assumed to represent the classical structure of the hidden variables theory."

As I mentioned in my post, I am aware that local hidden variable theories have been dis-proven for quantum systems, both theoretically and (almost certainly) experimentally. However, that doesn't change the fact the local realism does a perfectly good job explaining classical systems (at least as far as I know). So it appears to me that quantum non-locality is just another example of "quantum weirdness" that goes away or is averaged out in classical systems.

Please note that I am not being dismissive of the research done in this field .. I think it is incredibly interesting on a fundamental level. However, as cool as these results are, I guess I am not sold on the earth-shattering significance that some have attached to them.

 

[SpectraCat]

This is not quite true. The Ehrenfest theorem doesn't translate the quantum dynamics into a classical dynamics - this happens only in the limit of vanishing uncertainties (i.e., of large quantum numbers).

Sure, but since I was already speaking in the context of the correspondence principle, I thought that should be clear .. sorry if it wasn't.

 

[Varon]

As I mentioned in my post, I am aware that local hidden variable theories have been dis-proven for quantum systems, both theoretically and (almost certainly) experimentally. However, that doesn't change the fact the local realism does a perfectly good job explaining classical systems (at least as far as I know). So it appears to me that quantum non-locality is just another example of "quantum weirdness" that goes away or is averaged out in classical systems.

Please note that I am not being dismissive of the research done in this field .. I think it is incredibly interesting on a fundamental level. However, as cool as these results are, I guess I am not sold on the earth-shattering significance that some have attached to them.

We were discussing if position is just fuzzy or not there in principle. Note that classical system are not in superposition, but in collapsed state. All the atoms in your body is in collapsed state, disagree?

A ray in Hilbert Space is not collapsed to the so called basis vector, so no value of position is available. In fact, Since the ray can represent momentum or spin basis. There is no position even in principle. So a quantum object in superposition doesn't have position a priori. Hope others can confirm if this is so in orthodox QM because this was what I learnt. If someone believes position is just fuzzy. At least emphasize it's your own point of view and not the mainstream to avoid confusion as I'm a qm novice myself.

 

[SpectraCat]

We were discussing if position is just fuzzy or not there in principle. Note that classical system are not in superposition, but in collapsed state. All the atoms in your body is in collapsed state, disagree?

A ray in Hilbert Space is not collapsed to the so called basis vector, so no value of position is available. In fact, Since the ray can represent momentum or spin basis. There is no position even in principle. So a quantum object in superposition doesn't have position a priori. Hope others can confirm if this is so in orthodox QM because this was what I learnt. If someone believes position is just fuzzy. At least emphasize it's your own point of view and not the mainstream to avoid confusion as I'm a qm novice myself.

You are awfully sure of yourself for an admitted novice. :) Several people have explained to you why the "fuzziness" picture is more consistent with standard QM .. you have chosen not to accept our arguments. I don't think anyone will agree that the "there is no position even in principle" point of view is consistent with standard QM or the CI. Can you give a reference for that statement (I mean a textbook or peer-reviewed article, or perhaps even a website, rather than a vague statement of "that is what I remember from years ago")?

The idea that physical observables are created by the act of measuring them is NOT standard QM as far as I am aware. Or are you only talking about observables whose operators don't commute with the Hamiltonian? If you are talking about observables in general, then how about energy? Is the energy of an eigenstate created by the act of measuring that eigenstate? Because it seems to me that you can't have it one way for superpositions and another way for eigenstates.

 

[Varon]

You are awfully sure of yourself for an admitted novice. :) Several people have explained to you why the "fuzziness" picture is more consistent with standard QM .. you have chosen not to accept our arguments. I don't think anyone will agree that the "there is no position even in principle" point of view is consistent with standard QM or the CI. Can you give a reference for that statement (I mean a textbook or peer-reviewed article, or perhaps even a website, rather than a vague statement of "that is what I remember from years ago")?

The idea that physical observables are created by the act of measuring them is NOT standard QM as far as I am aware. Or are you only talking about observables whose operators don't commute with the Hamiltonian? If you are talking about observables in general, then how about energy? Is the energy of an eigenstate created by the act of measuring that eigenstate? Because it seems to me that you can't have it one way for superpositions and another way for eigenstates.

Only you and Neumaier talks about the position being just fuzzy. Neumaier wants to wipe out the quantum world and retain the classical world (like Einstein realist program). My impression after reading countless quantum books is that position doesn't exist a priori. This is because when the wave function collapse, momentum can become the observable. So you can't treat the position as existing observable even before the wave function collapse. Hope others beside you and Neumaier can clarify this (like DrChinese, JesseM or other orthodox believers.. you know Neumaier is an exception)

 

[Rap]

Only you and Neumaier talks about the position being just fuzzy. Neumaier wants to wipe out the quantum world and retain the classical world (like Einstein realist program). My impression after reading countless quantum books is that position doesn't exist a priori. This is because when the wave function collapse, momentum can become the observable. So you can't treat the position as existing observable even before the wave function collapse. Hope others beside you and Neumaier can clarify this (like DrChinese, JesseM or other orthodox believers.. you know Neumaier is an exception)

"does the particle have a position prior to a measurement of its position?"

What does it mean, to "have a position"?

A)It means that if you attempt to measure its position prior to the measurement, you will get a definite answer. In this case, both classical and QM would answer "yes"

B) It means that if you have the identically same initial conditions, and attempt to measure the position prior to the measurement, you will get the same value every time. In this case, classical says yes, QM says no.

Are there any other definitions?

Also, what is the definition of "fuzzy"?

 

[SpectraCat]

... and attempt to measure the position prior to the measurement ...

How precisely do you propose to do that?

 

[Rap]

How precisely do you propose to do that?

By measuring it in the same way I plan to make the given measurement, but prior to the time I planned to make the given measurement.

 

[SpectraCat]

Only you and Neumaier talks about the position being just fuzzy. Neumaier wants to wipe out the quantum world and retain the classical world (like Einstein realist program). My impression after reading countless quantum books is that position doesn't exist a priori. This is because when the wave function collapse, momentum can become the observable. So you can't treat the position as existing observable even before the wave function collapse. Hope others beside you and Neumaier can clarify this (like DrChinese, JesseM or other orthodox believers.. you know Neumaier is an exception)

Ok .. so this is your impression. But can you provide a citation where it actually says that from one of the books you have read?

Anyway, this is not physics .. it is philosophy, and we are going in circles. Perhaps this will satisfy you: I am pretty sure that Bohr is on the record of saying that nothing has a reality that is independent of the context of measuring that reality. In other words, the measurement devices become entangled with the systems that they are measuring, and so nothing can ever be measured without becoming enmeshed in the context of the measurement. Is that what you are getting at when you say "position has no a priori existence"? If so, that may be the source of our misunderstanding, because to my mind at least, those are not equivalent statements ... at least I don't think that I think that they are equivalent ;).

Most of my answers have been focused on how things behave, not what they are, so that may be part of the problem as well. That is probably because I am pretty sympathetic to the Instrumentalist point of view ... not to the point of saying "shut up and calculate" like Mermin, but more along the lines of, "this interpretation stuff is illuminating, fun and possibly even worthwhile, but until someone comes up with an experimentally falsifiable hypothesis to distinguish between the various flavors, I will stick to worrying about what can be measured."

 

[Varon]

You are awfully sure of yourself for an admitted novice. :) Several people have explained to you why the "fuzziness" picture is more consistent with standard QM .. you have chosen not to accept our arguments. I don't think anyone will agree that the "there is no position even in principle" point of view is consistent with standard QM or the CI. Can you give a reference for that statement (I mean a textbook or peer-reviewed article, or perhaps even a website, rather than a vague statement of "that is what I remember from years ago")?

Ok. Here's from Nick Herbert, a physicist who wrote in Quantum Reality

"Quantum Reality #1: The Copenhagen interpretation, Part I. (There is no deep reality.) The Copenhagen interpretation, developed mainly by Bohr and Heisenberg, is the picture most physicists fall back on when you ask them what quantum theory means. Copenhagenists do not deny the existence of electrons but only the notion that these entities possesses dynamic attributes of their own. Although an electron is always measured to have a particular value of momentum, it is a mistake, according to Bohr, to imagine that before the measurement it possessed some definite momentum. The Copenhagenists believe that when an electron is not being measured, it has no definite dynamic attributes"

~~~~~~~~~~~~~~~~~~~~~~

There, Bohr believes before measurement, it has no definite dynamic attributes such as position. In other, position doesn't even exist in principle before measurement.

 

[SpectraCat]

Ok. Here's from Nick Herbert, a physicist who wrote in Quantum Reality

"Quantum Reality #1: The Copenhagen interpretation, Part I. (There is no deep reality.) The Copenhagen interpretation, developed mainly by Bohr and Heisenberg, is the picture most physicists fall back on when you ask them what quantum theory means. Copenhagenists do not deny the existence of electrons but only the notion that these entities possesses dynamic attributes of their own. Although an electron is always measured to have a particular value of momentum, it is a mistake, according to Bohr, to imagine that before the measurement it possessed some definite momentum. The Copenhagenists believe that when an electron is not being measured, it has no definite dynamic attributes"

~~~~~~~~~~~~~~~~~~~~~~

There, Bohr believes before measurement, it has no definite dynamic attributes such as position. In other, position doesn't even exist in principle before measurement.

Ok, now we are getting somewhere ... thank you for the clarifying quotation. I guess the issue with that statement is that having "no definite dynamic attributes" is different from those attributes not existing at all. The idea of "fuzziness" that Neumeier and I referred to before reflects that the electron does not have a well-defined position prior to measurement, but that the wavefunction still gives us information about where it is most likely to be found, and actually provides deterministic information about the expectation value of the position (via the Ehrenfest theorem). That seems to me to contradict the idea that the position of the electron doesn't even exist before the measurement is made.

 

[Rap]

There, Bohr believes before measurement, it has no definite dynamic attributes such as position. In other, position doesn't even exist in principle before measurement.

You slightly changed the wording. I would say the second sentence should read: "In other words, a DEFINITE position doesn't even exist in principle before measurement."

 

[SpectraCat]

By measuring it in the same way I plan to make the given measurement, but prior to the time I planned to make the given measurement.

But you of course realize that the result of the "planned" measurement cannot be guaranteed to the same in the two cases (i.e. when you make a prior measurement, and when you don't). That was the point of my comment ... that you only ever get to make one measurement on a given state .. after the measurement, it is a different state.

 

[Rap]

But you of course realize that the result of the "planned" measurement cannot be guaranteed to the same in the two cases (i.e. when you make a prior measurement, and when you don't). That was the point of my comment ... that you only ever get to make one measurement on a given state .. after the measurement, it is a different state.

Exactly. What I was doing with those statements was trying to define what "does it have a position prior to a measurement?" means, trying to show that it is an improper question. Its position prior to a measurement is described by a probability distribution, it has no measureable, definite position, by the definitions I gave.