Quantum Interpretation Poll (2011)

[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.

 

[Varon]

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.

What I interepret from Nick Herbert is that those attributes don't exist in space and time at all, but more like outside it. That is. They still exist but outside spacetime. This means that during quantum superposition, position doesn't exist in principle because position requires spacetime. Since the attributes is outside spacetime, then there is nothing in spacetime to contribute to it. Maybe quantum gravity can provide more details of what is occurring.

Or let's go to HUP. When momentum is known to precise degree. Position is so smeared out. It is not because of the limitation in the instrument but because the position isn't there in principle. This is what I mean there is no position at all, akin to HUP.

 

[Varon]

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.

another thing, let me continue the Nick Herbert quote to emphasize that he meant the position doesn't exist in principle.. not because it is fuzzy. Here:

"Quantum theory was developed almost solely by Europeans. J. Robert Oppenheimer, one of the few Americans to have participated in Bohr's Copenhagen Institute, here explicitly denies the existence of the major attributes with which classical physics described in particle's external motion: "If we ask, for instance, whether the position of the electron remains the same, we must say 'no'; if we ask whether the electron's position changes with time, we must say 'no'; if we ask whether the electron is at rest, we must say 'no'; if we ask whether it is in motion, we must say 'no.'"

 

[A. Neumaier]

Note that classical system are not in superposition, but in collapsed state.

The Copenhagen interpretation makes no assumption at all about the classical environment. In particular, it doesn't associate it with collapse.

 

[A. Neumaier]

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"

And ''definite momentum'' means an infinitely precise value of the momentum. The Copenhagen interpretation never denied that a particle has an approximate momentum. If it hadn't, there were no reason to assume that a particle prepared at a source within a certain momentum range would reach the target area set up in the direction of the momentum.

 

[A. Neumaier]

Or let's go to HUP. When momentum is known to precise degree. Position is so smeared out. It is not because of the limitation in the instrument but because the position isn't there in principle. This is what I mean there is no position at all, akin to HUP.

But a real particle never has precise momentum. It is prepared at a particular place (approximate position) moving in some direction (approximate momentum), constrained by the uncertainty principle.
And from this information one can approximately predict where it will be found when, and with which momentum. Only definite (i.e., infinitely accurate) position or momentum are negated in the CI.

 

[A. Neumaier]

another thing, let me continue the Nick Herbert quote to emphasize that he meant the position doesn't exist in principle.. not because it is fuzzy. Here:

"Quantum theory was developed almost solely by Europeans. J. Robert Oppenheimer, one of the few Americans to have participated in Bohr's Copenhagen Institute, here explicitly denies the existence of the major attributes with which classical physics described in particle's external motion: "If we ask, for instance, whether the position of the electron remains the same, we must say 'no'; if we ask whether the electron's position changes with time, we must say 'no'; if we ask whether the electron is at rest, we must say 'no'; if we ask whether it is in motion, we must say 'no.'"

All but the last statement follow once position is not definite, but the last statement is simply wrong.
You shouldn't take every word of a book written for laymen as scientific gospel.

 

[harrylin]

All but the last statement follow once position is not definite, but the last statement is simply wrong.
You shouldn't take every word of a book written for laymen as scientific gospel.

That was a claim about what Oppenheimer said about his interpretation; the intended audience is irrelevant! Either that claim is true or it is false. "Scientific gospel" has nothing to do with such a citation.

 

[A. Neumaier]

That was a claim about what Oppenheimer said about his interpretation; the intended audience is irrelevant! Either that claim is true or it is false. "Scientific gospel" has nothing to do with such a citation.

Indeed; I didn't realize that it was a quote within a quote. The claim about that Oppenheimer said that might be true or wrong, what he sid is certainly wrong (though it may have been his belief).
One would also need to know the context, in which Oppenheimer said this, and whether he intended to represents the official Copenhagen interpretation (which cannot be seen from what was quoted).

 

[Rap]

What I interepret from Nick Herbert is that those attributes don't exist in space and time at all, but more like outside it. That is. They still exist but outside spacetime. This means that during quantum superposition, position doesn't exist in principle because position requires spacetime. Since the attributes is outside spacetime, then there is nothing in spacetime to contribute to it. Maybe quantum gravity can provide more details of what is occurring.

Or let's go to HUP. When momentum is known to precise degree. Position is so smeared out. It is not because of the limitation in the instrument but because the position isn't there in principle. This is what I mean there is no position at all, akin to HUP.

Shouldn't we constrain our language to avoid classical physics language when speaking of quantum phenomena? In other words, say "the position is indeterminate".

This conveys the facts and nothing more. "fuzzy" is next best, implying indeterminate. "smeared" implies multiple positions at once, which is not testable. The probability density of a measuring a position is smeared, but the position itself is indeterminate. Saying it does not exist implies existence is testable, which it is not.

 

[A. Neumaier]

Shouldn't we constrain our language to avoid classical physics language when speaking of quantum phenomena? In other words, say "the position is indeterminate".

This conveys the facts and nothing more. "fuzzy" is next best, implying indeterminate. "smeared" implies multiple positions at once, which is not testable. The probability density of a measuring a position is smeared, but the position itself is indeterminate. Saying it does not exist implies existence is testable, which it is not.

In this sense, even classical position of real objects were indeterminate. For one cannot give a position more accurately than half the diameter of an object.

 

[Rap]

In this sense, even classical position of real objects were indeterminate. For one cannot give a position more accurately than half the diameter of an object.

Yes, I should have clarified that by "position" I meant a point-like position, such as the center of mass , or center of volume, of an extended object. With this clarification, I believe the above statements apply.

 

[gpran]

I find the poll question very interesting: ‘Which Quantum Interpretation do you think is correct?’. The decision is being obtained in a democratic manner based on assumption that majority may choose the best amongst the available options. The ‘Copenhagen Interpretation’ has got maximum votes followed by the ‘some other deterministic hidden variables’ option. Does it mean that probability of finding the ‘Copenhagen Interpretation’ to be true is more than other interpretations?

Still in my opinion this is the BEST option. So I have voted for it. In any case I am trying to understand issues raised by experts in this poll and also to read material available on all such options as probability of such options being true also exists. This poll has resulted in good collections of all the available options and information about them.

 

[harrylin]

I find the poll question very interesting: ‘Which Quantum Interpretation do you think is correct?’. The decision is being obtained in a democratic manner based on assumption that majority may choose the best amongst the available options. The ‘Copenhagen Interpretation’ has got maximum votes followed by the ‘some other deterministic hidden variables’ option. Does it mean that probability of finding the ‘Copenhagen Interpretation’ to be true is more than other interpretations?

Not really: see my posts 38 and 147. The interpretations have not been grouped in a way that allows that kind of statistics, and I wonder if that is even possible. The only thing that I could conclude from this, is that there is no majority interpretation.

[..] In any case I am trying to understand issues raised by experts in this poll and also to read material available on all such options as probability of such options being true also exists. This poll has resulted in good collections of all the available options and information about them.

Yes indeed!

 

[PTM19]

My "other" interpretation is a work in progress. What i would find most appealing though would have space and time as fundamental entities and all the contents of reality captured by a locally rotated and dilated frame-field defined everywhere.

In this interpretation particles are only an approximation, wavefunctions are more fundamental but also an approximation since separability is only approximate. An electron is best described as a certain pattern of frame-field dilation and rotation extending throughout all of space and time (which describes both the electron itself and its radiation field) and superimposed on the patterns due to all the other entities in the Universe - Dirac equation specifies this pattern in an idealized case. Electron doesn't really have a well-defined position or velocity in itself (any more then a complex wave pattern on the water surface has one), those concepts only become useful in certain circumstances.

For example the pattern responsible for a measured electron when superimposed with the patterns defining fundamental constituents of measuring device (and everything else in the Universe) can be modified in such a way that concepts like velocity and position become useful in classifying behavior of the resulting pattern.

 

[ZealScience]

I find Copenhagen interpretation very wierd, and non-intuitive. Decoherece or the Multiverse can explain the problem with more logic and mathematics, though they are extremely bold and imaginative ideas. But Copenhagen's idea about conciousness is too vague and is very hard to falsify (talking about falsification here), because we can hardly know distinguish whether the observer has conciousness

 

[Rap]

I find Copenhagen interpretation very wierd, and non-intuitive.

By non-intuitive, you mean non-classical. Classical physics is intuitive, because our brains are designed to deal with classical physics problems, because that's what's necessary for our survival. We don't need to intuitively understand QM or relativity to survive, so we might ask QM to make classical sense, but we should not demand it. We should demand logical consistency, however.

Decoherece or the Multiverse can explain the problem with more logic and mathematics, though they are extremely bold and imaginative ideas.

Decoherence does not explain wave function collapse, and Multiverse makes untestable assumptions. Untestable means you can never test the theory. Like the theory that angels push the planets around in their orbits. Maybe they do, but until we can experience them, they are not part of science.

But Copenhagen's idea about conciousness is too vague and is very hard to falsify (talking about falsification here), because we can hardly know distinguish whether the observer has conciousness

I agree, there is vagueness here. However, not every Copenhagenist believes there has to be a conscious observer. Some believe (and I agree) that the wave function is a calculational tool. This means that what you need is a machine that is capable of doing quantum mechanical calculations. That "machine" can be a computer or a human scientist.

 

[ZealScience]

By non-intuitive, you mean non-classical. Classical physics is intuitive, because our brains are designed to deal with classical physics problems, because that's what's necessary for our survival. We don't need to intuitively understand QM or relativity to survive, so we might ask QM to make classical sense, but we should not demand it.

I can understand your argument, but Copenhagen Interpretate the "famous cat" mostly by conciousness. By non-intuitive, I mean we cannot understand the conciousness interaction part of the explanation. The Multiverse theory clearly described how the wave function "chooses" the result, but not that something we can't even select (which observer is consious? Maybe cat isn't, what about dogs? elephants? Gorilla?).

Decoherence does not explain wave function collapse, and Multiverse makes untestable assumptions. Untestable means you can never test the theory. Like the theory that angels push the planets around in their orbits. Maybe they do, but until we can experience them, they are not part of science.

I think here you mean Occam's Razor or the Anthropic Cosmological Principle. But Occam's Razor isjust a logic operator, by now we cannot observe the other universes by any means, and in current theories there might be no way. But something like String theory can also be "Razored", as no single string or 12 dimensional space can be never observed, but the theory is powerful because it can explain perfectly.

In my understanding, the Decoherence theory states that wave function doesn't necessarily
have to collapse, the theory is good because it says that Schrodinger is always correct, and I can see something similar to Multiverse theory.

PS:Only my personal idea, I'm just a high school student who cannot understand the theory mathematically well, please correct me!

 

[Varon]

I wonder if quantum mechanics is like general relativity in the mathematical sense.

In GR, geodesic motion can't be imagined as actually occurring in real world. In fact. We have a hard time making a one to one corresponce in it. We just accept GR as model of gravity and spacetime.

But how come there are no many interpretations of GR?

Could it be possible that QM is like GR, in that only the mathematical part makes sense and there is just no way to map it into the world one on one?

GR is a model of the world. Is QM also a model of the world?

If so. What is the equivalent of GR in the interpretation as far as this similarity in modelling is concern. Is GR closer to Copenhagen or the Statistical Interpretation. What do you think?
I may not be clear. If so. Pls. clarify this somewhat similarity between them as far as models and mathematics are concerned.

 

[Hurkyl]

In GR, geodesic motion can't be imagined as actually occurring in real world. In fact. We have a hard time making a one to one corresponce in it. We just accept GR as model of gravity and spacetime.

What do you mean by this?

 

[Varon]

What do you mean by this?

One can imagine Gravity as geodesic motion but when you are skydiving.. where is the geodesic... or how do you imagine walking inside the 4D spacetime.. something like that.
GR is a model of the world. Some say it is the world.

Could QM be similar to it. QM is the world. If so, then Many worlds, Bohmian Mechanics and others that want to let us go back to the Newtonian picture is falsified.

 

[Hurkyl]

One can imagine Gravity as geodesic motion but when you are skydiving.. where is the geodesic... or how do you imagine walking inside the 4D spacetime.. something like that.

It's somewhat common to visualize 4 dimensional geometry as a "motion picture". This maps somewhat literally onto imagining space-time.

Actually, this is often done with 3 dimensional geometry too (imagine the unit sphere as a point that expands into the unit circle, then contracts back to a point), and sometimes even in two-dimensions.

In fact, I believe this isn't even just a visualization tool -- this idea (and its generalizations) are a powerful technical device for studying geometry.

 

[Varon]

It's somewhat common to visualize 4 dimensional geometry as a "motion picture". This maps somewhat literally onto imagining space-time.

Actually, this is often done with 3 dimensional geometry too (imagine the unit sphere as a point that expands into the unit circle, then contracts back to a point), and sometimes even in two-dimensions.

In fact, I believe this isn't even just a visualization tool -- this idea (and its generalizations) are a powerful technical device for studying geometry.

I mean.. time... our concept of time... what happens in gravity is you put space and time in a graph and a little curvature here and there and bingo.. you have gravity by adding the EFE...

But then GR is just a model. No one questions how time and space so different can be united in Spacetime. We just treat it as is.. as a priori. This means Newtonian is falsified.

In QM.. maybe we don't need to have Newtonian picture like in Many Worlds and Bohmian Mechanics. Maybe somehow QM has the same weird status as GR..

 

[Fra]

Varon, I think your associations are interesting, and I for one can see several interesting connections, between QM and GR, that also includes "interpretations" of what gravity is. But the topic if shifting so much that it's to find the focus where to comment. After all we are in the QM poll thread :-)

My preferred association; that relates to previous discussions is that gravity and Einsteins equations is not a forcing fundamental law. It's more to be thought of as an equilibrium state (meaning there is also off-equilibrium possibilities). There are several lines of thinking in this direction, where gravity is seen as a kind of entropic force, where the inside view is simple a random action and from perspective you see gravitational attraction. This is interesting discussions but it's speculative and connects also to several unsolved open questions about unification of GR and QM.

About the geodesic: the inside view is that you just do a random walk, or go with the flow as per some rule of minimum resistance. This is why a free falling observer does not infer gravity. It's en external observer, seeing the first observing that infers gravitational interactions.

There is an interesting analogy with QM if you ask me. What hte inside observer "sees" is different from what an external observer sees.

So both in QM and in GR do we have the issue of different observers and how to secure that the views of different observers are "consistent". The main difference is that in GR, we do not have the issue of non-commutative information sets. All there is is classical information. This is I think why the interpretations of GR are not as common.

The interesting thing is that when you try to combine QM and GR all these interpretations of GR and of QM are blurred. Here there are different approaches, wether you think that GR must "somehow" be applied as a constraint on QM/QFT, or wether gravity is "somehow" emergent and thus is not a fixed constraint but evolving (like an equilibrium state).

You can also "interpret" that GR is about geometry, or you can try to release yourself from that abstraction and think that GR is about the relativity of inferred event indexes, in a more information theoretic view. So I think there are interpretations also here. Just like with QM, no one denies the success of GR in the tested domains. But the question is open how to understand it when considering unification of all forces in one coherent abstraction.

/Fredrik

 

[Rap]

There is an interesting analogy with QM if you ask me. What hte inside observer "sees" is different from what an external observer sees.

So both in QM and in GR do we have the issue of different observers and how to secure that the views of different observers are "consistent". The main difference is that in GR, we do not have the issue of non-commutative information sets. All there is is classical information. This is I think why the interpretations of GR are not as common.

I think there is a measurement problem, even in special relativity. Special relativity presents a bunch of particles, world lines, etc. which exist in a "frozen" spacetime, and puts constraints on the spacetime geometry of these world lines. Then comes the "observer" who is forced by his concept of "now" to create a coordinate system separating experience into space and time. To predict your or any other observer's experience, move yourself or the hypothetical observer along their world line at the speed of light. This whole measurement scenario brings in elements outside of special relativity, including the vague idea of "consciousness", similar to the situation in QM. How can there be "motion" when time has been subsumed into spacetime?

Also, what if we carry the "Wigner's friend" problem to SR? We conclude that the observer we are observing has no "choice", their development in time is determined. Do I, the outside observer, have choice then? This is "Laplace's demon" which exists in classical physics as well. Is there a counterfactual definiteness problem in SR, ignoring QM?

 

[rodolfoalvare]

I think what I call "Statistical Quantum Continuum Universe interpretation" SQCUI is more in accordance with what we see, than the many worlds interpretation, what is your opinion?
I wrote it in form of a letter to explain the interpretation to a friend.
I will appreciate any comments. If you are interested the 2 first letters are posted in: https://www.physicsforums.com/showthread.php?p=3299340

QUANTUM LETTERS TO ANAHI #2 Thursday, May 12, 2011
Statistical Quantum Continuum Universe Interpretation. (SQCUI)

Hi Anahi in this letter I will try to explain a little about my Interpretation, of quantum reality.
WHO WE ARE? WHAT WE ARE? WHERE ARE WE?...
Ever since we are little kids, we are broad up to believe that the Universe surrounds us, which is to say that we are immerse into the reality that we perceive.
One of the reasons that the concept of this Statistical Quantum Continuum Universe is so difficult to grasp is because of the misconceptions that this perceived reality give us.
To commence to explain this new approach to see the world in which we live on, we must define a few ideas that even though are common sense, they are the basis of who we are.
Every living organism of certain complexity, has two parts that are common to them; Some way of connecting to the environment (sensors); and some center were this data is use for the benefit of the organism (intelligence) This definition is very broad and you could argue that at certain levels of organization this characteristics bluer out (like in plants and bacteria).
If we think of ourselves is becomes pretty obvious that our connection to the Universe are our senses, (close your eyes, cover your ears and you’ll begin to realize that). Every single thing that you know of, it has arrived to your brain through one of these senses (there is other information that was hardwire to your brain genetically, but we will cover that latter), your brain takes this information, and makes sense (little by little) of your surroundings, in essence sees the Universe that surrounds you.
A cockroach will have the same parts (sensors and intelligence), but is very clear to us that if we see one on the floor next to us, their interpretation of the universe that surrounds it, (molecular markers, vibrations in the ground, pressure waves, etc.) will be very different than ours.
We tend to think that our interpretation of the universe is the correct one (the complete), and the cockroach is limited to their senses and intelligence. But we have to realize that our interpretation is limited by our senses (we cannot see at infrared wavelengths, etc.) and very probably by our intelligence.
Now with this bit of information let’s step back to what we know about Quantum Physics, and let’s see if we can make a little more sense of what we see around us.
Remember the tree in the forest, quantum physics says that the tree does not exist until you see it fallen or standing. In reality it says that the tree exists in the Multiverse (a fancy name for a Universe we don’t see but that it has all the possibilities in it, of all possible Universes) in a superposition of states (standing/fallen being only two of them), but when we get to the forest you only collapse one of them.
Well, to make sense of this “mambo Jambo” we will have to agree in a couple of things:

1. If what we see is one of the possible outcomes of the Multiverse (I like to call this the statistical Universe, the term Multiverse was used by Everett’s and could be misleading in my interpretation), then we are inside this “Multiverse” (Statistical Universe).

2. What we interpret as our reality is only a “slice” of this Multiverse.

3. If we take a very simplistic 2 dimensional plane to model this multiverse, imagine hills and valleys representing the statistical possibilities of an event, and “our reality” as a line that goes on one direction and angles to pass from one possibility or another, the likelihood of an event depending on the fiber of the Multiverse on this region (the laws of physics us we know them), that is to say the possibilities of an event are intrinsic to the laws of physics on this region of the multiverse (the local fiber of the Universe).

4. Our “linea de vivencia” (need a term in English) is really the collapse of the reality that we see, the “thickness” of this line is a representation of how intelligent we are (that is how much can we connect with the Statistical Quantum Continuum Universe).

Up to now you must think that this is like “you say Potato and I say Potairo” but when you start to analyze the Universe under this new interpretation, our whole conception of what this is (the Universe) changes.
Imagine for a moment that the universe is the way I listed above then:

• you are the center of the Universe you are collapsing (interpreting). Even though I see the same Universe, you are seen, is only because we are in the same statistical region of the multiverse, and we have basically the same sensors and intelligence.
• Like we mention before you have to be a superposition of Anahis, because at any given time any of you follows different statistical paths, If the structure of any Anahis in that statistical region ceases to be, (that Anahi dies) the ones that continue interpreting the universe are the only ones left, that is to say YOU WILL NEVER SEE YOUSELF DEAD! (Boggles the mind!, unfortunately this may became like a Quantum religion…)

Note: I know that this sound like total none sense but is absolutely in accordance with the physics that we see, ask any Quantum Physicist.

• Because the Universe we collapse depends of our intelligence and our sensors (or transducers for our sensors, that is to say, a thermal imaging camera permits us to see the infrared radiation translated to our eyes, therefore collapsing that reality).
This is why, when during and experiment we use a detector of spin for example to measure that characteristic of an electron, the electron in our reality (Universe) does NOT exist in any other characteristic but the Spin (in the statistical Universe that electron exists in every possible characteristic there is).
I think this interpretation successfully explains this estrange behavior that we see in quantum mechanics, that has not been satisfactory explained before.

Well Anahi I hope my explanation was good enough to transmit the message, I stop now so that I don’t give you a headache (I know I’m getting one).
In the letter that follow I will explain in detail the four point listed above, also why there is not Grandfather paradox traveling back in time (you never do), if you think you live forever when does it end? If we somehow we get better with time (the only way not to die) then entropy reverses from Chaos to Order? (Nooouu!), if not; how is it possible?
Well baby thank you for been such a patient friend, and I hope I’m a much better Physicist than writer.
Sweet dreams!