I "Single-world interpretations.... cannot be self-consistent"

[stevendaryl]

Yes, SR is still a classical theory and there is an objective reality behind it. My point was that the "mystery" in the twin "paradox" case was due to a failure of the thinker to wholly accept the relativity in the theory.

And I'm saying that QM is not analogous.

As to consensus among physicists CI is also referred to as the Orthodox interpretation. It still is the leading view: https://arxiv.org/abs/1301.1069
The "sexier" interpretations (EMW, BPW) get over-represented in discussion forums and Sci-Fi media.

I would dispute that it is an interpretation at all. Instead, it is a "recipe" for getting predictions out of QM. That's why I said that the orthodox interpretation really amounts to saying that we don't care about what's going on "under the hood". Which is fine, as far as it goes. But saying you don't care about a question does not mean that you've answered the question, nor does it mean that you've proved the question to be ill-posed.

That is exactly the type of "which twin is really older" question that begins with premises contrary to CI.

I disagree. I don't think they are analogous.

In the logic the set-inclusion lattice of subsets of states transitions to the quantum logic lattice of subspaces in Hilbert space. If you stick to only subspaces which are spans of a given orthogonal basis, you recover a classical logic lattice as a sub-lattice. You can embed classical descriptions in quantum. The thing is though, ALL the other subspaces have operational meaning. There are observables for these "states". There is more happening, more actions available, in a quantum logic lattice than can be expressed as a power set of a maximal set of primary states i.e. than can be expressed as point transitions between objective states. Quantum logic is a language of actions and it is a richer language than classical logic. This is why it is the natural place to start, the justification for actions are primary.

I can't make any sense of what you wrote. If that's the solution to the mystery, then I still would claim that it's unresolved.

 

[stevendaryl]

As to consensus among physicists CI is also referred to as the Orthodox interpretation. It still is the leading view: https://arxiv.org/abs/1301.1069

I would say that that survey perfectly captures the muddled state of quantum interpretations. For example:

Question 5. The measurement

• A pseudo-problem 27%
• Solved by decoherence 15%
• Solved/will be solved in another way 39%
• A severe difficulty threatening quantum mechanics 24%
• None of the above 27%

If there were that kind of spread of opinions about SR, I would say that your comparisons with SR are apt.

 

[jambaugh]

I would dispute that it is an interpretation at all. Instead, it is a "recipe" for getting predictions out of QM. That's why I said that the orthodox interpretation really amounts to saying that we don't care about what's going on "under the hood".

No it says more, it says it is meaningless* to refer to "what's going on 'under the hood'" (between acts of observation) because that is, by definition unobservable. It is the same as the aether of unrelativity being fundamentally unobservable and thus meaningless*.

*Anyone can give personal meaning to a concept, like aether, pilot waves, demons, and deities. They are meaningless in a scientific context because there is no access to them. You can claim pilot waves or many worlds and I can claim leprechauns or bowling balls, if we both predict the same observable behavior our theories are not empirically distinguishable. They are at best, meaningful in the same sense as Maxwell's mechanical model, they might provide a conceptual scaffolding for organizing your description of the real physics... how observable entities behave.

So it is not just a question of sour grapes... to claim one doesn't care because one cannot reach them... it is a deeper question of the meaning of the "grapes" existing at all, (replace the fox and grapes with the "emperor's new clothes"... I put these alternative interpretations in the same story book as the taylors' claims about the invisible cloth.)

 

[stevendaryl]

No it says more, it says it is meaningless* to refer to "what's going on 'under the hood'" (between acts of observation) because that is, by definition unobservable. It is the same as the aether of unrelativity being fundamentally unobservable and thus meaningless*.

I think that point of view is nonsense. An observation is a particular kind of interaction. To say that the only thing that is real are those interactions that count as observations is hopelessly solipsistic, in my opinion.

 

[stevendaryl]

So it is not just a question of sour grapes... to claim one doesn't care because one cannot reach them... it is a deeper question of the meaning of the "grapes" existing at all, (replace the fox and grapes with the "emperor's new clothes"... I put these alternative interpretations in the same story book as the taylors' claims about the invisible cloth.)

No, it's not any deeper. It's just a pretense of being deeper.

 

[jambaugh]

I think that point of view is nonsense. An observation is a particular kind of interaction. To say that the only thing that is real are those interactions that count as observations is hopelessly solipsistic, in my opinion.

The interactions need not themselves be observables, they need to be definable in terms of changes they make on observables.

If you claim interaction A is occurring and I claim no, interaction B is occurring and if no-where is there an observable that will be distinct depending on which case is true then it is meaningless in a scientific discussion to say either is truer than the other. You, for example cannot empirically disprove those fringe who believe in an aether. The claimed interaction between aether and clock and between aether and measuring rod, make that interaction meaningless in terms of distinguishable observations. If I were to go on about how the aether really really is there, and that's really what's going on under the hood of SR you'd shower me with far more derision than I'm feeling from you now. But nowhere could you disprove my claim because my claim is meaningless when it comes to actual changes in empirical behavior vs Einstein's version.

No, it's not any deeper. It's just a pretense of being deeper.

Is to, is to! (We can do that all day until the mods shut us down. How about some point beyond the claim.)

So let me ask you then, which is right, Bohm's Pilot waves, or Everett's Many Worlds? Both "explain" as you think of it, both make no further prediction about what we will see in the lab or observatory than is made by CI. If I create the Baugh's Many Worlds of Pilot Waves Through the Superluminal Aether with Supervising Pixies, interpretation, how can you distinguish my absurdity from theirs?

 

[Boing3000]

You, for example cannot empirically disprove those fringe who believe in an aether.

I am under the impression that science works the other way around. So let's keep the burden of proof where it belongs.

So let me ask you then, which is right, Bohm's Pilot waves, or Everett's Many Worlds?

All are. Copenhagen also. They don't go on to prove anything. For that they would need to make a distinguishable claim (experimentally verifiable)
And claiming the CI solve "a problem" by ignoring it is fine ... I suppose. But I think it is clearly closing the door to many paths of investigation. And I personally find it strange that wishful ignorance should enter the scientific method on no other ground that "a problem" is too tough to brake.

how can you distinguish my absurdity from theirs?

From my limited layman's knowledge, BM pilot wave is quite deterministic. So it could be possible to prepare a system where all the outcome would be identical. So I suppose there is no harm trying that ?
As for other interpretations, I suppose they have not been invented just to fill layman's literature (or forums), but also to distinguish themselves about possible experiment outcome. CI is quite different in that regard.

 

[zonde]

they [interactions] need to be definable in terms of changes they make on observables.

You are putting cart before the horse. Observations (even more, statistical properties of many similar observations) can't be primitive terms in explanation.
Scientific method works by formulating hypothesis (explanation), then deriving predictions from hypothesis and then testing predictions against observations.

 

[forcefield]

People often say that a physical quantity such as the component of a particle's spin along a particular axis simply doesn't have a value until measured. Okay, but what about after it is measured? Does it have a value then?

If you say it does, then it seems to me that you are assigning one type of physical interaction, a measurement, a role in making things "real" that is different from all other types of physical interaction. If you say it doesn't, then to me, you've got MWI, where nothing has definite values, not even measurements.

Well, if we take the analogue of flipping a coin, then I'd say that QM measurement is analogous to flipping the coin and looking at the result (value) is just trivial.

So there is no mystery why there is no result for the coin or for the "spin" before "measurement".

 

[Jilang]

Except for entangled pairs!

 

[stevendaryl]

Well, if we take the analogue of flipping a coin, then I'd say that QM measurement is analogous to flipping the coin and looking at the result (value) is just trivial.

So there is no mystery why there is no result for the coin or for the "spin" before "measurement".

That's treating measurement as fundamentally different from other interactions. But why is it different? A measuring device just relies on the same electromagnetic forces that most other interactions involve.

 

[forcefield]

That's treating measurement as fundamentally different from other interactions.

What do you mean ? I am considering the measurement to consist of the whole experimental configuration.

I think we are getting off topic here.

 

[stevendaryl]

What do you mean ? I am considering the measurement to consist of the whole experimental configuration.

I mean that if you take the approach that a system doesn't have a value for a property until that property is measured, then that seems to be giving a role to measurement that is different from the role of any other measurement.

I think we are getting off topic here.

To me, it seems exactly what the thread is about---whether single-world interpretations are consistent. The reason for thinking that maybe they aren't consistent is because if you treat a measurement process as just like other types of interactions, then measurement would not result in a single unique value any more than any other interaction does.

 

[forcefield]

I mean that if you take the approach that a system doesn't have a value for a property until that property is measured, then that seems to be giving a role to measurement that is different from the role of any other measurement.

I can't make sense of that.

To me, it seems exactly what the thread is about---whether single-world interpretations are consistent. The reason for thinking that maybe they aren't consistent is because if you treat a measurement process as just like other types of interactions, then measurement would not result in a single unique value any more than any other interaction does.

Then I would say that there is something wrong in the logic that does not lead to single unique values.

 

[stevendaryl]

I can't make sense of that.

Let me illustrate by an (oversimplified) example.

Let |u\rangle be the spin-up state of an electron, and let |d\rangle be the spin-down state (relative to the z-axis, say). Now, consider a measuring device that attempts to measure the spin of an electron. It starts off in the state |?\rangle, meaning it hasn't yet measured the spin. If the electron is spin-up, the device goes into state |U\rangle. If it is spin-down, the device goes into state |D\rangle. You can imagine that the device has two lights, one labeled "U" and one labeled "D", and one or the other lights turns on.

Then we would describe this as:

• |?\rangle \otimes |u\rangle \Longrightarrow |U\rangle \otimes |u\rangle (where \Longrightarrow means "evolves into"). In words: if the composite state is one where the device is in state |?\rangle and the electron is in state |u\rangle, then the composite system evolves into the state where the device is in state |U\rangle.

• |?\rangle \otimes |d\rangle \Longrightarrow |D\rangle \otimes |d\rangle If the composite state is one where the device is in state |?\rangle and the electron is in state |d\rangle, then the composite system evolves into the state where the device is in state |D\rangle.

If that's an accurate description, then the Rules of Quantum Mechanics would say:
|?\rangle \otimes (\alpha |u \rangle + \beta |d\rangle) \Longrightarrow \alpha |U\rangle \otimes |u\rangle + \beta |D\rangle \otimes |d\rangle: If the composite state is one where the device is in state |?\rangle and the electron is in a superposition of spin-up and spin-down, then the composite system evolves into a state that is a superposition of one where the device is in state |U\rangle and another state where the device is in state |D\rangle.

If the device were described by quantum mechanics, then you wouldn't get a definite result---either |U\rangle or |D\rangle---you would get a superposition of possibilities. That's what Many-Worlds says happens.

 

[forcefield]

If the device were described by quantum mechanics, then you wouldn't get a definite result---either |U\rangle or |D\rangle---you would get a superposition of possibilities. That's what Many-Worlds says happens.

Yeah well I don't buy that. I'm pretty sure Bohr didn't agree with that either.

 

[stevendaryl]

Yeah well I don't buy that. I'm pretty sure Bohr didn't agree with that either.

There is no buying or not buying. The issue is how to explain the appearance of single values for measurements in a way that is consistent with the Rules of Quantum Mechanics. Bohr simply said that QM applies to the microscopic world, while classical physics (objects have definite locations and velocities at all times) applies to macroscopic objects. But the question is whether that's actually consistent. If macroscopic objects are just made up of microscopic objects, then how can macroscopic objects behave differently than microscopic objects. How does the common-sensical world that we are familiar with arise from the Rules of Quantum Mechanics? Or does it?

Saying "I don't buy that" is not really an answer.

 

[zonde]

Electron is quantized (discrete) unit. It is unclear then what is the meaning of $\alpha |u \rangle + \beta |d\rangle$ after measuring apparatus when $|u \rangle$ and $|d\rangle$ components appear at spatially different outputs. If we say that $|\alpha|^2$ and $|\beta|^2$ are probabilities then there should be collapse i.e. $\alpha |u \rangle + \beta |d\rangle$ physically changes to $|u \rangle$ or $|d\rangle$ (and later detectors simply finds out in which output electron ended up).
But If we say that $|\alpha|^2$ and $|\beta|^2$ are something else than probabilities then how we can claim that electron is quantized?
I would say that MWI is just a way how to claim that electron is sort of quantized (in different worlds) and at the same time give meaning to superpositions of spatially separate components.

 

[stevendaryl]

Electron is quantized (discrete) unit. It is unclear then what is the meaning of $\alpha |u \rangle + \beta |d\rangle$ after measuring apparatus when $|u \rangle$ and $|d\rangle$ components appear at spatially different outputs. If we say that $|\alpha|^2$ and $|\beta|^2$ are probabilities then there should be collapse i.e. $\alpha |u \rangle + \beta |d\rangle$ physically changes to $|u \rangle$ or $|d\rangle$ (and later detectors simply finds out in which output electron ended up).

I'm not sure exactly what you're talking about, but there is no process in quantum mechanics by which a state \alpha |u\rangle + \beta |d\rangle changes nondeterministically into either the state |u\rangle or the state |d\rangle. If the measuring device is itself governed by the laws of quantum mechanics, you're never going to get a unique result. A way out is to say that measurement is a special kind of process that selects one possibility out of a superposition (with probabilities given by the square of the amplitudes), but that seems to be treating a measurement device in a way that doesn't actually follow from the way that electrons, protons, etc., behave.

 

[zonde]

I'm not sure exactly what you're talking about, but there is no process in quantum mechanics by which a state \alpha |u\rangle + \beta |d\rangle changes nondeterministically into either the state |u\rangle or the state |d\rangle. If the measuring device is itself governed by the laws of quantum mechanics, you're never going to get a unique result.

So you say that in quantum mechanics electron can only change it's relative phase relationship between components as a result of interaction i.e. \alpha |u \rangle + \beta |d\rangle \Longrightarrow \alpha |u\rangle \otimes \beta |d\rangle
But then measurement apparatus as well can only change it's relative phase relationship between components, right? I.e. in expression |?\rangle \Longrightarrow \alpha |U\rangle \otimes \beta |D\rangle state $|?\rangle$ just means different relative phase relationship between $\alpha |U\rangle$ and $\beta |D\rangle$ components.
I am referring to this expression of yours:

|?\rangle \otimes (\alpha |u \rangle + \beta |d\rangle) \Longrightarrow \alpha |U\rangle \otimes |u\rangle + \beta |D\rangle \otimes |d\rangle

Do I understand it right?

 

[PeterDonis]

Electron is quantized (discrete) unit.

This is not correct. A correct statement is that certain observables of an electron are quantized (i.e., have a discrete spectrum instead of a continuous spectrum) under certain conditions (for example, energy and angular momentum in bound states). That correct statement does not support the claims you are making.

 

[zonde]

This is not correct. A correct statement is that certain observables of an electron are quantized (i.e., have a discrete spectrum instead of a continuous spectrum) under certain conditions (for example, energy and angular momentum in bound states). That correct statement does not support the claims you are making.

How your statement that only certain observables under certain conditions have quantized spectrum makes the point that my statement is wrong?
It sounds like you are saying that in QM we can meaningfully talk about fractions of electrons, which is wrong of course.

 

[PeterDonis]

It sounds like you are saying that in QM we can meaningfully talk about fractions of electrons

No, I'm saying that you are making an incorrect assumption that there is a meaningful distinction between "an electron" and "a fraction of an electron", so that we can meaningfully ask whether an electron can be divided into smaller pieces. This would make sense if electrons were little billiard balls (or something equivalent), but they're not.

 

[zonde]

No, I'm saying that you are making an incorrect assumption that there is a meaningful distinction between "an electron" and "a fraction of an electron", so that we can meaningfully ask whether an electron can be divided into smaller pieces.

This is probably too philosophical for me but I will give it a try. As I see it if "an electron" is meaningful but "a fraction of an electron" is meaningless there is still meaningful distinction between "an electron" and "a fraction of an electron" (one is meaningful the other is not) even so we can't meaningfully talk about dividing electron into pieces.

 

[PeterDonis]

if "an electron" is meaningful but "a fraction of an electron" is meaningless

It depends on what you mean by "an electron". If you mean what you said in post #68, that an electron is "a quantized (discrete) unit", then no, "an electron" is not meaningful.

 

[zonde]

It depends on what you mean by "an electron". If you mean what you said in post #68, that an electron is "a quantized (discrete) unit", then no, "an electron" is not meaningful.

In first quantization "an electron" as a holder of observables is discrete unit.
In second quantization "an electron" as a basic unit in Fock states is quantized excitation of electron field.
I suppose it's meaningful enough.

 

[PeterDonis]

In first quantization "an electron" as a holder of observables is discrete unit.

I'm not sure what you mean by "a holder of observables". But in any case, first quantized theory doesn't work, so I'm not sure it counts as a valid model.

In second quantization "an electron" as a basic unit in Fock states is quantized excitation of electron field.

More precisely, the Fock states (eigenstates of the number operator) are a basis of the Hilbert space of the electron field. But that does not mean that all states of the electron field are Fock states; obviously that is false since the electron field can be in a state which is a superposition of multiple Fock states. So if "an electron" means "a Fock state", then not all states of the electron field are "electrons" in this sense, so "electron" is not a good term to use since there are lots of physical states, including states of the electron field in real materials, which are not "electrons". OTOH, if "an electron" means "a state of the electron field", then "electrons" are not quantized. Either way, saying "electrons are discrete units" doesn't, IMO, give a good description of the actual physics.

 

[jambaugh]

You are putting cart before the horse. Observations (even more, statistical properties of many similar observations) can't be primitive terms in explanation.
Scientific method works by formulating hypothesis (explanation), then deriving predictions from hypothesis and then testing predictions against observations.

Primitive term in definition, not in explanation. Your description of the scientific method is all well and good, but two hypotheses with common predictions are empirically indistinguishable.

I think another way to say what I'm trying to say is this. We should not be calling "Many Worlds" or "Bhom's Pilot Waves" interpretations. They are rather Models akin to Maxwell's mechanical model or the geometric model of Einstein's GR. CI is the underlying interpretation, what the mathematical components mean operationally. You can build any explanatory scaffolding you like but in the words of King Arthur " It's only a model!"

JB

 

[zonde]

Primitive term in definition, not in explanation.

Definitions are part of explanation.

Your description of the scientific method is all well and good, but two hypotheses with common predictions are empirically indistinguishable.

If one hypothesis has made prediction before experiment that confirms that prediction but the second hypothesis is made after experiment then the first hypothesis is confirmed while the second one is not. Chronology is important.

I think another way to say what I'm trying to say is this. We should not be calling "Many Worlds" or "Bhom's Pilot Waves" interpretations. They are rather Models akin to Maxwell's mechanical model or the geometric model of Einstein's GR. CI is the underlying interpretation, what the mathematical components mean operationally. You can build any explanatory scaffolding you like but in the words of King Arthur " It's only a model!"

You are trying to change common terminology. This can only add confusion and won't add any new arguments to discussion.
All our scientific theories are models of reality.
What the mathematical components mean operationally are correspondence rules.
Interpretations are models that make the same predictions.

What I think you are trying to say is that we should be satisfied with phenomenological model and consider fundamental models as unimportant. If that's what you are trying to say then I somewhat can understand this position but I do not agree with it.

 

[jambaugh]

Definitions are part of explanation.

Are you kidding me? Of course they're a part, they're even an essential to explanation. And hence the base root of everything is your definitional primitives. In modern axiomatic mathematics you begin with undefined terms because (pure) mathematics is a conceptual construct. These terms are the foundation and their meaning comes from their use in the structure of the axioms and subsequent definitions. However in science we begin with operational primatives by which we can assert "if you do this then that will always occur."

If one hypothesis has made prediction before experiment that confirms that prediction but the second hypothesis is made after experiment then the first hypothesis is confirmed while the second one is not. Chronology is important.

Now you're just being silly. By that argument we should stick with the aether version of Lorentz relativity rather than Einstein's SR? Or for that matter, conspiring demons and deities since they "explain" everything and came first in our theories of the world. Chronology is irrelevant to truth or whether something is irrelevant to the truth. Go back to my prior post and try again.

You are trying to change common terminology. This can only add confusion and won't add any new arguments to discussion.
All our scientific theories are models of reality.
What the mathematical components mean operationally are correspondence rules.
Interpretations are models that make the same predictions.

I'm trying to enlighten you to the need to subdivide your concepts. The change in common terminology happened before I came onto the scene because there are two meanings (in science) to the word interpretation. Let's use whatever words you like but let's both use the same words in the same way.

First concept: What I call an interpretation is...
A system by which we translate the concepts, terms and symbols on paper into actions and observations in the laboratory. The correspondence rules to which you referred. Call this praxic interpretation. (praxic as in pragmatic, as in operational, as in positivistic).

Second concept: What I think you are calling an interpretation...
An ontological model (world picture) of what is going on beyond the praxic interpretation. A hypothesized state of the reality of objects as they are with objective properties as they are. Call this the ontic intepretation. But I call it a ontological model.

[For a reference these praxic vs ontic qualifiers, I got them from David R. Finkelstein, see his book Quantum Relativity.]

Perhaps you don't like my definitions above and you would like to rephrase them. I am after all trying to make a specific point and I may in point of fact be biased in my wording. Suggest what you like but can you not agree that the Orthodox CI is fundamentally different in nature from say Bohm's Pilot waves and Everetts MW in that it is a praxic interpretation* while these others are ontic interpetations. *(praxic interpretation plus a stronger assertion that we should refrain from any ontic interpretations hence its conflict with these others.)

What I think you are trying to say is that we should be satisfied with phenomenological model and consider fundamental models as unimportant. If that's what you are trying to say then I somewhat can understand this position but I do not agree with it.

That is not quite what I am saying. What we feel or want is irrelevant. Nature is as nature is. And the nature of our questing toward understanding things is that we observe things happen and construct mental models to "explain them". As we push deeper and deeper there must always be a level of praxic interpretation below the level of ontic interpretation to give it meaning in any scientific sense. Either it is perpetual chicken and egg and we never stop delving deeper or there is some level past which we cannot resolve. Maybe our current phenomonlogical wall can be pushed deeper but for now we cannot resolve any observables below the level of those in QM. (There are no probes that get us past Heisenberg's uncertainty principle).

Just as with the literal chicken and egg question there's a natural starting point (an egg is an egg whether it's a chicken egg or not...) there is a natural starting point in Science based on the scientific method. An act of observation is an act of observation whether it is consistent with one or many ontological interpretations or not. You can say EMW or BPW models "explain" quantum phenomena but they are of the "Gods and Demons" variety of explanation in that they are not testable. It is thus scientifically meaningless to say one or the other is true. If in future they become testable then they will be testable with a new set of operations in the lab/observatory. These new operations will be there first before the tests can be performed and you can again argue over the "interpretations" beyond their pragmatic meaning...

 

[stevendaryl]

There is a nice talk by Ron Garrett, an engineer who has worked for Jet Propulsion Lab and for Google.

He explains, informally, why he believes that single-world interpretations of QM are not consistent.

 

[stevendaryl]

There is a nice talk by Ron Garrett, an engineer who has worked for Jet Propulsion Lab and for Google.

He explains, informally, why he believes that single-world interpretations of QM are not consistent.

It's a very long talk, so let me just summarize the reasoning, and what he means by a "single-world interpretation".

The single-world interpretation of QM is basically Copenhagen. It treats observations as "real" but treats quantum states between measurements as merely calculational tools. His argument is that this is inconsistent because measurement results such as "Alice measured spin-up" are themselves ultimately just quantum facts, no different in principle from facts such as "the electron had spin-up before it was measured".

 

[LeandroMdO]

Since one may prove, by construction, that there exist single world hidden variable theories (such as Aaronson's flow model), it seems hard to justify speculation that single-world interpretations may be inconsistent. Either observers are describable within the mathematics of quantum mechanics (in which case they are also describable, or at least simulatable by the flow model or some other hidden variable model), or they aren't, in which case quantum mechanics itself is wrong regardless of interpretation.

 

[stevendaryl]

Since one may prove, by construction, that there exist single world hidden variable theories (such as Aaronson's flow model), it seems hard to justify speculation that single-world interpretations may be inconsistent. Either observers are describable within the mathematics of quantum mechanics (in which case they are also describable, or at least simulatable by the flow model or some other hidden variable model), or they aren't, in which case quantum mechanics itself is wrong regardless of interpretation.

Thanks for the link to Aaronson's paper. It's interesting, but I haven't completely studied it yet.

But the issue is not whether observers are describable within pure quantum mechanics, but whether observers with definite states are. In the quantum mechanics of a small number of particles, if a small subsystem is in a superposition of two states, and it interacts with a second small subsystem, then afterward, the composite system will be in a superposition.

Letting \Longrightarrow be interpreted as "evolves into" (after some specified amount of time T), then QM tells us:

If |u\rangle \otimes |\emptyset\rangle \Longrightarrow |u\rangle \otimes |U\rangle and |d\rangle \otimes |\emptyset\rangle \Longrightarrow |u\rangle \otimes |D\rangle then

(\alpha |u\rangle + \beta |d\rangle) \otimes |\emptyset\rangle \Longrightarrow \alpha |u\rangle \otimes |U\rangle + \beta \otimes |D\rangle

Informally, you have two systems, the system being measured, and the system doing the measurement. For simplicity, I'm assuming that the state being measured is a simple system with a two-state basis |u\rangle and |d\rangle, the eigenstates of an operator with two eigenvalues, spin-up and spin-down. I'm assuming that the second system is measuring the observable corresponding to that eigenvalue. To be a measurement device, the second system should evolve into a "pointer state" (either |U\rangle or |D\rangle) to indicate which value it measured.

If the measuring device is itself describable by QM, then if the initial state of the system to be measured is a superposition of eigenstates, then the composite system will evolve into a superposition of two possibilities: (1) the first system is in state |u\rangle and the second system is in state |U\rangle, or (2) the first system is in state |d\rangle and the second system is in state |D\rangle.

The final state is a "many-worlds" state, in that the measuring device is not in a definite measurement state.

To get a "single-world" from this, it seems to me that you need a second kind of dynamics (the hidden-variables of Aaronson, or Bohm) that selects one possibility out of the two possible measurement states.

 

[jambaugh]

Just reviewed the video and his statement that CI is "scientifically untenable because there just is no [physical] collapse" is the classic gross misunderstanding of CI.
In CI the collapse of the wave function is the collapse of our description of the system. CI exactly distinguishes the wave function from the material system. CI says "if you now assume you've made a specific measurement of the system then you must incorporate that assumption into your description of the system".

You can always "find" a contradiction in CI or any theory if you inconsistently interpret.

* CI says the wave function is not modeling physical system but a record of information about system behavior...
* QM describes how the wave function evolves dynamically and relates to system observables.
* CI says upon receiving updated information you update your wave function (collapse)
* CI is scientifically untenable because collapsing wave functions (when interpreted as physical objects (in contradiction to CI)) is bad [by various easy to generate means of demonstration].

I didn't see anything new or unique in his talk w.r.t. the physics or its interpretation.

 

[stevendaryl]

Just reviewed the video and his statement that CI is "scientifically untenable because there just is no [physical] collapse" is the classic gross misunderstanding of CI.
In CI the collapse of the wave function is the collapse of our description of the system.

I don't think that is a consistent interpretation, in light of Bell's theorem. I think that the video does a pretty good job of explaining why that doesn't work.

 

[Denis]

But the issue is not whether observers are describable within pure quantum mechanics, but whether observers with definite states are. ...
To get a "single-world" from this, it seems to me that you need a second kind of dynamics (the hidden-variables of Aaronson, or Bohm) that selects one possibility out of the two possible measurement states.

Yes, or you need a collapse, modifying QT, so that you have no longer pure QT, or you get the wave function for Schrödinger's cat. And to make the wave function for Schrödinger's cat compatible with the single cat you observe in a definite state, you need some other additional dynamics, which are not quantum.

But "why ... single-world interpretations of QM are not consistent" makes no sense, if adding the hidden variables makes everything ok, thus, consistent, given that you cannot make inconsistent things consistent adding something.

In the talk, from 4:20 to 4:50 he rejects realism, and claims that one can show that realism is not true. Which is wrong, given the realistic interpretations. And one can easily see where the proof goes wrong - when he rejects (without mentioning them) all the realistic interpretations for having FTL, and claims that FTL would lead to causal paradoxes, completely ignoring the forbidden possibility that FTL happens in a hidden preferred frame.

 

[Denis]

I don't think that is a consistent interpretation, in light of Bell's theorem. I think that the video does a pretty good job of explaining why that doesn't work.

CI is consistent.

You can simply take dBB theory and cut away the parts which are unobservable. That means, what remains from the Bohmian trajectory $q(t)$ is the classical trajectory $q_{classical}(t)$ of the classical part, and what remains from the Bohmian global wave function is the effective wave function of the quantum part
$$ \psi_{quantum}(q_{quantum}) = \psi_{Bohmian}(q_{quantum}, q_{classical}(t)).$$

Then, throw away this formula too (once it contains things which should not exist together) and add positivist reasoning that what is not observable does not exist, and you have the CI.

 

[stevendaryl]

CI is consistent.

You can simply take dBB theory and cut away the parts which are unobservable. That means, what remains from the Bohmian trajectory $q(t)$ is the classical trajectory $q_{classical}(t)$ of the classical part, and what remains from the Bohmian global wave function is the effective wave function of the quantum part
$$ \psi_{quantum}(q_{quantum}) = \psi_{Bohmian}(q_{quantum}, q_{classical}(t)).$$

Then, throw away this formula too (once it contains things which should not exist together) and add positivist reasoning that what is not observable does not exist, and you have the CI.

Very nice description of the relationship between Bohmian mechanics and Copenhagen. Is that original with you?

 

[jambaugh]

I don't think that is a consistent interpretation, in light of Bell's theorem. I think that the video does a pretty good job of explaining why that doesn't work.

See other posts but the problem with Bell's theorem only exists if you mistakenly (in absolute opposition to CI) reify the wave function. Bell's theorem negates the ANTI-Copenhagen interpretation of the wave function as a model of some physical reality... it supports CI. CI again asserts that the wave function is akin to a classic probability distribution, it is knowledge about how the random variables which are the system observables will behave. It is not the physical reality that is in superposition, it is the description (of how things have/will behave\d); It is not the physical reality that is entangled, it is the description; it is not the physical reality that collapses it is the description. If you're going to disagree with CI know what it is saying.

This does not negate the fact that assertions of superposition, entanglement, and collapse, of our descriptions have meaning w.r.t. the actuality of phenomena out there, it is just a necessarily oblique and indirect qualification of the actual since we do not and, by Bell, cannot have direct classical knowledge of the state of "out there" our knowledge must be acquired through observations which is why we start and end with our descriptions of those observations e.g. the wave functions or more general density operators. We are of necessity phenomenologists if we wish to remain empiricists.

 

[LeandroMdO]

To get a "single-world" from this, it seems to me that you need a second kind of dynamics (the hidden-variables of Aaronson, or Bohm) that selects one possibility out of the two possible measurement states.

To get many worlds you also need another kind of dynamics that separates the mental states of the observers. The final state is a state in a superposition, not necessarily a state with "many worlds". It must first be proved that the many worlds interpretation is correct before making this assertion.

The main question is this: what kind of models are describable by the mathematics of quantum mechanics? It's clear that there are many-world models that satisfy that property, but it's also clear that there are models with a single world that also do. We can use the flow model, or the Schrödinger model, or any other such hidden variable model to construct either possibility. For that reason, any attempt to argue that either many-world interpretations or single-world interpretations are logically impossible is doomed to fail. More assumptions other than the pure axioms of quantum mechanics are needed to establish this.

 

[LeandroMdO]

I don't think that is a consistent interpretation, in light of Bell's theorem. I think that the video does a pretty good job of explaining why that doesn't work.

Bell's theorem says nothing one way or the other about whether it is logically possible to minimally interpret the quantum state as a generalization of a probability distribution. Certainly it says that it is not possible to do so in a local classical theory, so the correct interpretation is that if the fundamental theory of reality is local it is not classical, and if it is classical it is not local.

In fact, even in a theory with many-worlds this minimal interpretation of the quantum state as a book-keeping device would be correct! The many-worlds ontology would then be an explanation of why the rules work. Copenhagen truly is a minimal interpretation in the sense that every correct interpretation of quantum mechanics must agree with it:
1. Observers construct states (rays in Hilbert spaces), which are defined and evolve according to specific rules.
2. After a "measurement", the observer must update his description of the system to reflect the measurement outcome.

That is it -- whether there is a single world in which measurement outcomes happen, or whether there's a tree of irreversibly branching worlds is not relevant. The only difference in the latter case is that the observer makes an update that is only valid for his branch of the wavefunction. But that's okay, because his brothers will make updates reflecting the other possibilities.

 

[Denis]

Very nice description of the relationship between Bohmian mechanics and Copenhagen. Is that original with you?

Thanks. Yes. But I see it misses one difference, namely that in dBB the wave function is ontological, in CI not. But to reinterpret some really existing object as describing only knowledge about some object is also some sort of getting rid of what we cannot see.

See other posts but the problem with Bell's theorem only exists if you mistakenly (in absolute opposition to CI) reify the wave function. Bell's theorem negates the ANTI-Copenhagen interpretation of the wave function as a model of some physical reality...

No, given that an interpretation which "reifies" the wave function - dBB - has no problem with Bell's theorem.

 

[zonde]

Are you kidding me? Of course they're a part, they're even an essential to explanation. And hence the base root of everything is your definitional primitives. In modern axiomatic mathematics you begin with undefined terms because (pure) mathematics is a conceptual construct. These terms are the foundation and their meaning comes from their use in the structure of the axioms and subsequent definitions.

Your answer is inconsistent with your earlier answer:

Primitive term in definition, not in explanation.

However in science we begin with operational primatives by which we can assert "if you do this then that will always occur."

I disagree. "if you do this then that will always occur" is a prediction and in science we don't start with predictions.

Now you're just being silly. By that argument we should stick with the aether version of Lorentz relativity rather than Einstein's SR?

Do you say that predictions using Lorentz relativity where made and published before SR? I might have hole in my knowledge about historical situation at the time when SR came up, but I won't believe you without proper reference.

Or for that matter, conspiring demons and deities since they "explain" everything and came first in our theories of the world. Chronology is irrelevant to truth or whether something is irrelevant to the truth. Go back to my prior post and try again.

Now you are silly. Since when explanations based on conspiring demons and deities can make equally good predictions about reality as scientific theories?

I'm trying to enlighten you to the need to subdivide your concepts. The change in common terminology happened before I came onto the scene because there are two meanings (in science) to the word interpretation. Let's use whatever words you like but let's both use the same words in the same way.

First concept: What I call an interpretation is...
A system by which we translate the concepts, terms and symbols on paper into actions and observations in the laboratory. The correspondence rules to which you referred. Call this praxic interpretation. (praxic as in pragmatic, as in operational, as in positivistic).

Second concept: What I think you are calling an interpretation...
An ontological model (world picture) of what is going on beyond the praxic interpretation. A hypothesized state of the reality of objects as they are with objective properties as they are. Call this the ontic intepretation. But I call it a ontological model.

[For a reference these praxic vs ontic qualifiers, I got them from David R. Finkelstein, see his book Quantum Relativity.]

Perhaps you don't like my definitions above and you would like to rephrase them. I am after all trying to make a specific point and I may in point of fact be biased in my wording.

"Correspondence rules" is common term in philosophy of science:
https://plato.stanford.edu/entries/structure-scientific-theories/#IntTheStrPerSynVie

Suggest what you like but can you not agree that the Orthodox CI is fundamentally different in nature from say Bohm's Pilot waves and Everetts MW in that it is a praxic interpretation* while these others are ontic interpetations. *(praxic interpretation plus a stronger assertion that we should refrain from any ontic interpretations hence its conflict with these others.)

CI says that there is no deeper reality of individual members of quantum system ensembles than that given by wave function i.e. there are no hidden variables. I see this claim ontic enough to disagree with you. In contrast minimal statistical (ensemble) interpretation remains agnostic about existence of hidden variables so this is the one I would consider purely phenomenological ("praxic interpretation" as you call it).

That is not quite what I am saying. What we feel or want is irrelevant. Nature is as nature is. And the nature of our questing toward understanding things is that we observe things happen and construct mental models to "explain them". As we push deeper and deeper there must always be a level of praxic interpretation below the level of ontic interpretation to give it meaning in any scientific sense. Either it is perpetual chicken and egg and we never stop delving deeper or there is some level past which we cannot resolve. Maybe our current phenomonlogical wall can be pushed deeper but for now we cannot resolve any observables below the level of those in QM. (There are no probes that get us past Heisenberg's uncertainty principle).

Just as with the literal chicken and egg question there's a natural starting point (an egg is an egg whether it's a chicken egg or not...) there is a natural starting point in Science based on the scientific method. An act of observation is an act of observation whether it is consistent with one or many ontological interpretations or not. You can say EMW or BPW models "explain" quantum phenomena but they are of the "Gods and Demons" variety of explanation in that they are not testable. It is thus scientifically meaningless to say one or the other is true. If in future they become testable then they will be testable with a new set of operations in the lab/observatory. These new operations will be there first before the tests can be performed and you can again argue over the "interpretations" beyond their pragmatic meaning...

I disagree that "correspondence rules" (praxic interpretation) is deeper than ontic models. "Correspondence rules" is a bridge that connects ontic model with reality.
But I agree that current explanations that do not make any testable predictions beyond some common set of already known experimental facts does not lead to any new scientific knowledge. At best these models can be viewed as "working hypotheses" with the hope that in the future they will be modified so that they give novel testable predictions.

 

[jambaugh]

Your answer is inconsistent with your earlier answer

Because you're excerpt was my description of *mathematics* given for comparison to science...

I disagree. "if you do this then that will always occur" is a prediction and in science we don't start with predictions.

no that is our end, but to give meaning to those predictions we must define "doing this" vs "doing that", the words used to make those predictions are the primatives and their meaning is based on their use to make those predictions... and thus terms that have no empirical connection to predictions which can fail are without meaning.

Do you say that predictions using Lorentz relativity where made and published before SR? I might have hole in my knowledge about historical situation at the time when SR came up, but I won't believe you without proper reference.

Why do you think they're called Lorentz transformations and not Einstein transformations... (digging up reference here...)
Lorentz, Hendrik Antoon (1904), "[URL='https://en.wikisource.org/wiki/Electromagnetic_phenomena']Electromagnetic phenomena in a system moving with any velocity smaller than that of light", Proceedings of the Royal Netherlands Academy of Arts and Sciences, 6: 809–831[/URL]

Lorentz's famous transformations were developed to explain the MM experiment and that explanation utilized the concept of an aether which acting upon measuring rods caused them to shorten, and acting upon clocks caused them to slow according to the Lorentz's transformations in such a way as to make determination of ones motion through the aether unobservable. Einstein's contribution (in SR) was to take the unobservability of the aether as reason to excise it and take seriously the actual relativity of time. But the mathematics is identical to the Lorentz et al's aether version and the likewise the subsequent predictions had Einstein simply stuck with the Aether Model but continued with the E=mc^2 (in the rest frame) awkward as it may have been. This is why you keep seeing "Einstein was wrong" posts in the usenet forums every month or so with their rediscovery of aether models of relativity.

Now you are silly. Since when explanations based on conspiring demons and deities can make equally good predictions about reality as scientific theories?

They can if I ascribe to their personalities the desire and to their abilities the power to make systems obey e.g. Schrodinger's equation. Yes it is silly, but so to is the notion of infinite worlds being created every instant as quantum systems evolve. It is an example of hyperbole.

"Correspondence rules" is common term in philosophy of science:
https://plato.stanford.edu/entries/structure-scientific-theories/#IntTheStrPerSynVie

CI says that there is no deeper reality of individual members of quantum system ensembles than that given by wave function i.e. there are no hidden variables. I see this claim ontic enough to disagree with you. In contrast minimal statistical (ensemble) interpretation remains agnostic about existence of hidden variables so this is the one I would consider purely phenomenological ("praxic interpretation" as you call it).

Yes you are correct there. CI has an additional positivists caveat. It is by analogy the difference in saying the aether in relativity is not observable and asserting there is no aether. It is the difference in theology between being a pure agnostic or an agnostic atheist (believing there is no God but there is no means to prove or give evidence of that belief). You are welcome to reject CI in favor of Von Neuman's ensemble interpretation. I don't see a real difference. I reject the aether as a meaningful concept (in SR). I reject reality between measurements as a meaningful concept.

I disagree that "correspondence rules" (praxic interpretation) is deeper than ontic models. "Correspondence rules" is a bridge that connects ontic model with reality. But I agree that current explanations that do not make any testable predictions beyond some common set of already known experimental facts does not lead to any new scientific knowledge. At best these models can be viewed as "working hypotheses" with the hope that in the future they will be modified so that they give novel testable predictions.

Which is why I distinguish models from theories. As I've been using the terms for the past decades, Scientific Theories are systems of empirical prediction. Models are scaffolding for theories which include ontological hypotheses but as I qualify it should be taken as models and their ontology not necessarily be taken seriously. I may be deviating from some common usage of the terms but it is to my mind a natural divide. My essential point is that theories don't necessarily need models and QM is a theory for which CI chooses to actively reject the use of models.

I am find with agreeing to disagree w.r.t. one's personal beliefs. My ire is raised with CI is misrepresented and inanely "proven to be scientifically untenable" by means of its misrepresentation. (You = anybody reading this for...) If you choose to accept Jesus Christ as your Lord and Savior, then fine. If you choose to have faith in pilot waves guiding the very atoms, then fine! If you choose to believe in infinite worlds, in one of which you won the lottery, then fine. But it is an act of faith not science.

 

[jambaugh]

Thanks. Yes. But I see it misses one difference, namely that in dBB the wave function is ontological, in CI not. But to reinterpret some really existing object as describing only knowledge about some object is also some sort of getting rid of what we cannot see.No, given that an interpretation which "reifies" the wave function - dBB - has no problem with Bell's theorem.

Careful with the logic there. "Only exists if..." as in is a necessary condition for there being a problem. You're asserting it is not a sufficient condition which it is not and which was not my claim. My criticism of dBB is not that it runs afoul of Bell, it can't as it agrees with QM.

My problem with dBB is twofold. The aforementioned unobservability and also the point of its formulation is to provide a consistent reality but (as I understand dBB which may be quite wrong!) the necessity of causal propagation of pilot waves FTL and back in time undermine the very objectivity of the reality one is trying to assert. If the future may update the present then the present state of reality is contingent and hypothetical.

 

[zonde]

Which is why I distinguish models from theories. As I've been using the terms for the past decades, Scientific Theories are systems of empirical prediction. Models are scaffolding for theories which include ontological hypotheses but as I qualify it should be taken as models and their ontology not necessarily be taken seriously. I may be deviating from some common usage of the terms but it is to my mind a natural divide. My essential point is that theories don't necessarily need models and QM is a theory for which CI chooses to actively reject the use of models.

Say, do you take "atoms" seriously?

 

[jambaugh]

Say, do you take "atoms" seriously?

As phenomena? yes. As objects with objective state? Yes when I'm working at the classical level (gross position and momentum and low enough energies). But then as a contingent model for the underlying quantum phenomenology.

Note by the way, I can be perfectly serious about the meaning of "solid" vs "liquid" vs "gas" and at the same time point out that these lose meaning when talking about individual atoms. To my mind, "objective reality" is a similar emergent property which is perfectly useful in context but becomes meaningless when we resolve things beyond a certain point.

 

[Boing3000]

That is an interesting discussion (at least from my layman's perspective)

I reject the aether as a meaningful concept (in SR). I reject reality between measurements as a meaningful concept.

But yet, even if you take the minimal ensemble interpretation, because after all QM only describe probabilities on ensemble of events, you won't go so far as to say that elements composing those ensemble do not exist ?

(as I understand dBB which may be quite wrong!) the necessity of causal propagation of pilot waves FTL

My understanding is that the pilot wave only evolve in time and not in space. So I don't think it "propagate" in any classical(SR) sense. It seem to be very well in tune with what Bell's inequality allow us to guess about the underlying process/model.
I also am under the impression that some form of determinism is reintroduced by the pilot wave. Wouldn't that open the door for true new behavior/falsifiability ?

 

[zonde]

As phenomena? yes. As objects with objective state? Yes when I'm working at the classical level (gross position and momentum and low enough energies). But then as a contingent model for the underlying quantum phenomenology.

"Atom" is not a phenomena. It is unobservable ontic entity in many models. But without this unobservable ontic entity and models that are built on it many scientific theories would become unimaginably contrived.
What value your position then has?

Note by the way, I can be perfectly serious about the meaning of "solid" vs "liquid" vs "gas" and at the same time point out that these lose meaning when talking about individual atoms. To my mind, "objective reality" is a similar emergent property which is perfectly useful in context but becomes meaningless when we resolve things beyond a certain point.

Scientific approach assumes "objective reality" as given (experimental facts, their records, shared information etc. are objective). If you want to investigate possibility that it is not as objective as it is assumed you would have to develop different philosophical framework for that. So it's not science anyways.