Interpretations of Quantum Mechanics (is there a general consensus?)

[Vectronix]

Hi :)

I recently read a book that states that most scientists believe the wave function represents a real field (i.e., one that possesses energy and momentum). I think this is part of the transactional interpretation of QM but not sure... can anyone confirm whether the book I read is right about this or not?

 

[martinbn]

I don't know what most scientists believe, but I find that statement strange. I would have thought that the one thing, about the wave function, they would agree on, is that it doesn't represent a real field.

 

[phyzguy]

From my experience, I would say there is not a general consensus on this point, and most scientists seem to take the view of SUAC - Shut Up And Calculate - which means they know how to do the calculations and just don't worry too much about the interpretation.

 

[juanrga]

Hi :)

I recently read a book that states that most scientists believe the wave function represents a real field (i.e., one that possesses energy and momentum). I think this is part of the transactional interpretation of QM but not sure... can anyone confirm whether the book I read is right about this or not?

You would fill some money refund form

 

[jtbell]

I recently read a book

Which book?

 

[Ken G]

Not only don't I think there's a consensus on that, I'm not even sure what the statement means. A field is real if it carries energy and momentum? How does one know if a field carries energy and momentum? I would say that thinking is backward-- we don't ask if it carries energy and momentum, and then decide we think it's real, we ask if we think it's real, and then decide it carries the energy and momentum. In other words, we all know we wish to associate energy and momentum with the wavefunction, whether we regard it as real or not, so we first have to ask if we regard it is real before we can decide whether or not it "carries" that energy and momentum, instead of just "associates with" that energy and momentum. So the field is not real if it carries energy and momentum, the field carries energy and momentum if it is real.

 

[Vectronix]

Yeah, what you said makes sense, Ken. I would have thought that most scientists don't believe the wave function is real, too, martin. I may have mis-stated the part about the wave function a bit, but here's a quote from the preface of the book:

"...if someone, not a theoretical physicist and not thoroughly acquainted with modern methods of analysis, were to attempt to digest a current article dealing with nuclear forces or cosmic rays, relying for help on the available books on the subject, he would discover to his dismay that modern quantum mechanics differs radically from that which he finds in the textbooks... More confusing to him is the interpretation of a field in the new mechanics. It seems evident that what is meant is a real field possessing energy and momentum. Yet the textbooks attach a purely symbolic meaning to the wave field of a particle, picturing the field concept merely as a probability function."

...and there you have it.

You would fill some money refund form

lol I got it from Borders bookstore before they went out of business, so... :P

Which book?

It's called Quantum Mechanics of Particles and Wave Fields, by Arthur March.

 

[juanrga]

lol I got it from Borders bookstore before they went out of business, so... :P

Try the Book publisher then

 

[Vectronix]

hehe... Do you seriously think I should? :)

 

[bhobba]

Hi :)I recently read a book that states that most scientists believe the wave function represents a real field (i.e., one that possesses energy and momentum). I think this is part of the transactional interpretation of QM but not sure... can anyone confirm whether the book I read is right about this or not?

Most probably believe it has a real existence like say an electric field does - not as an actual field - but as something that exists out there because they think a wave-function collapse is an issue. The interpretation that probably demands it is one based on quantum decoherence for that collapse and its variants - don't know about the transactional interpretation.

I personally don't believe it does - I think its like classical probability theory - its simply a device for calculating statistical outcomes. Check out:
http://arxiv.org/pdf/quant-ph/0111068v1.pdf

Thanks
Bill

 

[stevendaryl]

There is something about the wave function that makes a completely different kettle of fish than fields such as the electric field. That is, that unlike the electric field, the wave function is not a field in the physical world. It's a field in configuration space.

The distinction is this: In the case of an electric field, I can point to a particular spot, and ask "What is the value of the electric field right there?" You cannot ask the analogous question about the wave function, because it is not a probability amplitude on points in space. To see why not, consider a two-particle wave function. In general, It would be written as (simplifying to the case of 1 spatial dimension): ψ(x₁, x₂), the square of which gives the probability density of finding the first particle at position x₁ and the second particle at position x₂. It doesn't make any sense for me to point to a particular point and ask what the value of the wave function is at that point.

I don't know what the implications of this physical-space versus configuration space distinction is for whether the wave function is "real", but it certainly shows that the wave function cannot be considered an ordinary field like the electric field.

 

[Ken G]

Yet you can point to a box in real space and ask "what is the probability of finding a particle in that box", even for multiple-particle wave functions (if the particles are distinguishable, you can also specify which type of particle you are asking about). You can also ask about correlations like "what is the probability of finding particles in both of these two boxes", and so on. So it's a more sophisticated kind of field, but it seems to me one can still imagine it "exists" in real space if one wants to. True, it is kind of a "question answering field", but then, so are they all. Does one want to attribute independent existence to question-answering fields? No less so in quantum than classical physics, it was always something of a stretch in my view!

 

[martinbn]

@ Ken_G: The point of stevendaryl is that fields are represented by mathematical object that have domain spacetime not configuration space. I thought this was so obvious, that's why I didn't even say in my post!

 

[stevendaryl]

Yet you can point to a box in real space and ask "what is the probability of finding a particle in that box", even for multiple-particle wave functions (if the particles are distinguishable, you can also specify which type of particle you are asking about). You can also ask about correlations like "what is the probability of finding particles in both of these two boxes", and so on. So it's a more sophisticated kind of field, but it seems to me one can still imagine it "exists" in real space if one wants to. True, it is kind of a "question answering field", but then, so are they all. Does one want to attribute independent existence to question-answering fields? No less so in quantum than classical physics, it was always something of a stretch in my view!​

Well, I don't think there was ever any question about whether the wave function was useful for answering questions. It certainly provides information about the real world. My point is that it isn't something that resides in the real world. It isn't an object that exists in some location, nor is it a field that varies from location to location.

 

[bohm2]

I really like Matt Leifer's suggestion in this post:

Even disregarding the issue of whether the quantum state has to be ontic, Bell’s theorem already implies the same issue with simultaneity. It shows that the ontic state at B must depend on the choice of measurement at A and vice versa, and there are frames of reference in which the measurements occur in either order. There are only two possible responses to this:

1. Reject relativity at the fundamental level. Assume that there is a preferred frame of reference and have the nonlocal influences operate instantaneously in this frame. The frame will be hidden at the statistical level due to the averaging over ontic states, so you will still have Lorentz invariance at the operational level, but it means that you cannot use relativistic arguments to reason about what is happening at the ontic level, so the paradoxes do not arise. This is the solution adopted in Bohmian mechanics for example.

2. Reject one or more of the assumptions of Bell’s theorem (also assumed by PBR). For example, one could adopt a no-collapse interpretation like Everett/many-worlds, which denies the existence of ontic properties localized in spacetime, an assumption that Einstein called “separability” and that is crucial to the derivation of nonlocality. Alternatively, one could adopt one of the “neo-Copenhagen” approaches to quantum theory in which the need for an ontic state is denied. Finally, one could retain realism and single-valuedness of measurement outcomes by adopting ontologies that are not considered in the derivation of Bell’s theorem, e.g. retrocausality.

I already stated in the blog post that I like the retrocausal solution, or at least that I consider it worth investigating in more detail. This is because I prefer to retain realism, fundamental Lorentz invariance and psi-epistemicism, and it is one of the few options on the table that still has a chance of doing that. If the retrocausal program fails then I would have to drop one or more of these requirements and I fluctuate between preferring neo-Copenhagen approaches or Everett depending on whether my psi-epistemic or realist convictions are stronger on any given day. To be convinced to drop fundamental Lorentz invariance, I would have to see violations of it on the statistical level. Valentini argues that this is to be expected in the Bohmian approach for example, since the statistical washing out of nonlocal influence is analagous to being in a state of thermal equilibrium in statistical mechanics, so we should expect to see systems out of this state of equilibrium somewhere in the universe. I consider this to be a firm prediction of all such theories, and so I would need to see empirical violations of Lorentz invariance to be convinced of them.

Can the quantum state be interpreted statistically?
http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/

 

[ardenmann0]

Gell-Mann once wrote, ‘Bohr brainwashed a whole generation of physicists into ‘believing' the Copenhagen interpretation of quantum mechanics'.

 

[LaserMind]

So a wave function is not a wave and its not a particle, its an entity of some sort in 'superposition' that spreads out in x,y,z and t. We can only find out if its 'there' by decohering it. Otherwise it is not a physical, real entity.

It behaves as though it were a 'calculation' waiting for its result (at some x,y,z and t) on decoherence. It leaves no track of its path. It simply 'arrives'. We know where it came from but have no idea of its path to its destination.

So what entity can achieve this? Something superposition is not a 'thing' - its not an object that we cannot enclose or put in a container - unless we decohere. And even then decoherence results in 'values observed'.

 

[ardenmann0]

I don't know what most scientists believe, but I find that statement strange. I would have thought that the one thing, about the wave function, they would agree on, is that it doesn't represent a real field.

If it doesn't represent a real field, how can it interfere with itself in the double slit experiment?

We can't detect gravitational waves right now, but it does not mean they do not exist.
It just mean our instruments are not sensitive enough to detect them directly right now.

 

[Naty1]

Vectronix:
There are many interpretations...check here in Wikipedia
for background and introduction

http://en.wikipedia.org/wiki/Quantu...ble_functions_-_analytical_calculus_formalism

The wave function is absolutely central to quantum mechanics: it makes the subject what it is. Also; it is the source of the mysterious consequences and philosophical difficulties in what quantum mechanics means in nature, and even how nature itself behaves at the atomic scale and beyond - which continue in debate to this day.

It's probably the 'abstract vector space' formulation that's leads to major disagreements.

Here are a few quotes I saved from QUANTUM MECHANICS by Albert Messiah:

This first may be the most controversial:

In its mature form, the idea of quantum field theory is that quantum fields are the basic ingredients of the universe, and particles are just bundles of energy and momentum of the fields.

The major difficulty of classical theory in explaining submicroscopic phenomena stems from the appearance of discontinuities which result from quantized behavior.
In classical mechanics the evolution in time of physical systems is described by dynamic variables with well defined values at every instant. It became evident around 1900 phenomena on the atomic and sub atomic scale do not fit this framework...The first series of experiments forcing a revision of the wave theory of Maxwell-Lorentz was the photoelectric effect and Compton scattering.

So some new mathematical models became popular:

The Matrix Mechanics of Heisenberg and the Wave Mechanics of Schrodinger are equivalent quantum formulations…non relativistic theories. Wave mechanics (Schrodinger) utilizes the more familiar language of partial differential equations and tends to a simpler introduction to QM (than Heisenberg’s matrix mechanics

The matrix formulation starts from observable quantities...dynamical variables…. and associates with each a matrix; these matrices obey non commutative algebra. It is this non commutative algebra matrix mechanics differs from classical mechanics...In its mature form, the idea of quantum field theory is that quantum fields are the basic ingredients of the universe, and particles are just bundles of energy and momentum of the fields.

It is a POSTULATE that the Schrodinger wave equation [psi] of a quantum system completely defines its dynamical state. [The statistical results of the measurement of a dynamical variable can be deduced from the wave function...but not precisely accurate repeatable results*. ] The central problem of QM is knowing the wave function at some initial time to determine the equation of propagation of the wave [psi] for all later time. “It is quite clear that no deductive reasoning can lead us to that equation.

* This is a 'one liner' referring to the Heisenberg uncertainty principle.

So what we have, in my own words, are models. They provide some great insights, have been shown to offer many experimental predictions which have been verified to great precision, but which still leave remaining interpretational issues.

 

[Ken G]

Well, I don't think there was ever any question about whether the wave function was useful for answering questions. It certainly provides information about the real world. My point is that it isn't something that resides in the real world. It isn't an object that exists in some location, nor is it a field that varies from location to location.

My point is that with multiple particles, complete information in quantum mechanics refers not only to the particles themselves, but also to their correlations. The importance of correlations doesn't mean we are not dealing with things that "reside" in 3-space, it just means that correlations are more sophisticated animals. We would face an analogous issue if we were interested in purely classical correlations between density variations between two species in 3 space, like two types of gas. There our density correlation functions would be mathematically dependent on 3X2 space, not 3 space, because we'd be interested in questions like the probability of finding density increases in one gas given that we have nearby density increases in the other. Yet even so, no one would question that the density distributions themselves "reside" in 3 space. The mathematical animal needed to talk about correlations in 3 space is a higher dimensional object, but I don't see why that needs to compromise our sense of where these correlations "reside." It's like how in relativity, we think of events as residing in spacetime, but the fields in relativity are tensors, not vectors that take on values in spacetime. So they are more sophisticated mathematical objects, to maintain the correct invariances, yet we still think of relativistic fields as "residing" in spacetime.

 

[Ken G]

I really like Matt Leifer's suggestion in this post:

Yes I think that was well put, though I would personally question his adherence to realism at the cost of allowing retrocausality. The reason I think one should hold causation and drop realism is that causation is epistemic and realism is ontic, and I view physics as primarily epistemic, so we should always hold epistemic principles above ontic ones. That might be the most boiled-down way to restate Bohr's approach.

 

[bohm2]

The mathematical animal needed to talk about correlations in 3 space is a higher dimensional object, but I don't see why that needs to compromise our sense of where these correlations "reside."

If one isn't a wave function "realist" it doesn't matter, but if one assumes wave function "realism", doesn't that necessarily also lead to:

1. configuration space "realism" (e.g. if wave function is real, then the 3-D space of our ordinary experience must be an illusion). Or
2. at least a need to explain and find a way to recover 3-D space from configuration space and wave function ontology.

Some argue that there are problems with taking option 1. above (e.g. David Albert), however as noted by Maudlin and summarized here by Ney:

Unfortunately, for a view that takes the wave function to be an element of the fundamental ontology, the name ‘configuration space’ is misleading. According to wave function realism, particles in three-dimensional space are not ontologically prior to the wave function, and so the space the wave function inhabits is not fundamentally a space of configurations of particles in three-dimensional space.

So, then what is the "N" of 3-N dimensional space about if not particles?

Ontological Reduction and the Wave Function Ontology
http://www.rochester.edu/college/faculty/alyssaney/research/papers/Ney_ReductionWaveFunction.pdf

 

[bhobba]

at least a need to explain and find a way to recover 3-D space from configuration space and wave function ontology.

Come again - you don't need to recover anything - it makes probabilistic predictions about what happens in 3D space just like for example a probability vector predicts how a dice behaves in 3D space.

Thanks
Bill

 

[bohm2]

you don't need to recover anything - it makes probabilistic predictions about what happens in 3D space just like for example a probability vector predicts how a dice behaves in 3D space.

I'm only talking about one who is a wave function realist.

 

[Pollock]

The original question was Interpretation of QM;is there a general concensus? Why dosen't someone answer that question ?.
Does anyone still take the Copenhagen view as the best available?.What other interpretations are currently favoured?.

 

[bhobba]

The original question was Interpretation of QM;is there a general concensus? Why dosen't someone answer that question ?.Does anyone still take the Copenhagen view as the best available?.What other interpretations are currently favoured?.

No there isn't. And there are people who still adhere to Copenhagen as the best there is. What do you mean by currently favoured? These days with more to choose from its probably even more 'jumbled'. But a new one called Consistent Histories (some people say its Copenhagen done right) now has a lot of adherents and the Ensemble Interpretation of Einstein (also known as shut up and calculate - its my view) has come on strong.

Thanks
Bill

 

[bhobba]

I'm only talking about one who is a wave function realist.

Even then its the same thing - the quantum state resides in 3D space - but its exact nature is an open question.

Thanks
Bill

 

[bohm2]

Even then its the same thing - the quantum state resides in 3D space - but its exact nature is an open question.

The wave function cannot exist in 3-D space. Predictions of QM depend on the 3N-dimensional space that get lost in the 3-D representation (e.g. information about correlations among different parts of the system, that are experimentally observed are left out). For a philosophical discussion of this see the following thread:

The reality of configuration space
https://www.physicsforums.com/showthread.php?t=554543

 

[Ken G]

You're saying that if the wavefunction is regarded as real, then the space on which it takes on values must be the space in which it "lives." If the particles are instead regarded as real, then the wavefunction can just be thought of as a way to organize information about those particles, in which case the particles can still "reside" in 3 space while the wave function takes on values from some information space. I think that's true, I just don't really buy the idea that either the wave function or the particles are real. It's all just the spaces we use to picture the information-- the information of a wave function takes on values from configuration space, but that's nothing new, we have many ways of organizing information about particles that is accessed from configuration space. But even the particle concept, and the 3-space concept, are just more ways of organizing information. Why do we need to say which mode of information is real? All information is real, but it's still just information.

Hence I think a lot of this issue relies on what we think is "existing in" 3D space. The wavefunction of multiple particles is not a function on 3D space, we can agree there, but I don't see that it has any problem referring to other entities that "reside" in 3D space. We are interested in tracking correlations, so the correlations can't exist in 3D space, but what they are correlating can. I don't see why this issue is any different from using phase space to talk about N gas particles in a box, for example. The 6N dimensional phase space of those N particles is also not a 3 dimensional object, but it is clearly referring to particles that can be pictured as "residing" in 3 space, and moving through 3 space. It's just the mathematical treatment, like if we say F=ma we are looking at a second time derivative of a 3D position, but if we say F(x)=dp/dt and p=m*dx/dt, we are looking at two first time derivatives on a 6D space of x and p. No one thinks these two different formulations call into question the reality of whether particles "reside" in 3 space, if one is a realist in regard to particles, there is just a difference between the entities we are interested in versus what space we use to track our information about them. But I don't really see any point in being a realist in regard to either particles or wavefunctions-- physics manipulates information, get over it, is my attitude. (That isn't "shut up and calculate", it's "talk as much as you like, but what you are talking about is information.")

 

[bohm2]

But I don't really see any point in being a realist in regard to either particles or wavefunctions-- physics manipulates information, get over it, is my attitude. (That isn't "shut up and calculate", it's "talk as much as you like, but what you are talking about is information.")

Sure, but then realists are likely to ask "information about what" and "whose information"?

 

[StevieTNZ]

Sure, but then realists are likely to ask "information about what" and "whose information"?

Here is a paper by Renato Renner and co, entitled: Completeness of quantum theory implies that wave functions are physical properties

Given the wave function associated with a physical system, quantum theory allows us to compute predictions for the outcomes of any measurement. Since, within quantum theory, a wave function corresponds to an extremal state and is therefore maximally informative, one possible view is that it can be considered an (objective) physical property of the system. However, an alternative view, often motivated by the probabilistic nature of quantum predictions, is that the wave function represents incomplete (subjective) knowledge about some underlying physical properties. Recently, Pusey et al. [arXiv:1111.3328, 2011] showed that the latter, subjective interpretation would contradict certain physically plausible assumptions, in particular that it is possible to prepare multiple systems such that their (possibly hidden) physical properties are uncorrelated. Here we present a novel argument, showing that a subjective interpretation of the wave function can be ruled out as a consequence of the completeness of quantum theory. This allows us to establish that wave functions are physical properties, using only minimal assumptions. Specifically, the (necessary) assumptions are that quantum theory correctly predicts the statistics of measurement outcomes and that measurement settings can (in principle) be chosen freely.

http://arxiv.org/abs/1111.6597

 

[bhobba]

The wave function cannot exist in 3-D space. Predictions of QM depend on the 3N-dimensional space that get lost in the 3-D representation (e.g. information about correlations among different parts of the system, that are experimentally observed are left out). For a philosophical discussion of this see the following thread:

The reality of configuration space
https://www.physicsforums.com/showthread.php?t=554543

Cant follow that one. It can be considered a complex function f(x1,...,xn) - the xi are positions of n particles in ordinary 3d space - it doesn't have to emerge from anything. f gives the probability amplitudes of the particles having those positions. Such functions can be expanded in terms of a infinite but countable basis for theoretical convenience but that does not mean it literally resides in such abstract spaces. If you consider the f real then there is an issue exactly where it resides - it may reside just as a conjecture in some rolled up higher dimensional space that the xi are also in - but 3d space does not have to emerge from anything - its existence is built into the xi.

 

[martinbn]

I am with bohm2 on this one. And I am puzzled about what the meaning of 'real' is to people that say that the wave function is real! Usually it is said that it is real in the same way as the electromagnetic field is, but it is obviously not real in that way. To me real means that there is an object that is in 3D space that intereacts with other objects. Then clearly the wave function is not such a thing. So what does real mean to those poeple?

 

[bhobba]

I am with bohm2 on this one. And I am puzzled about what the meaning of 'real' is to people that say that the wave function is real! Usually it is said that it is real in the same way as the electromagnetic field is, but it is obviously not real in that way. To me real means that there is an object that is in 3D space that intereacts with other objects. Then clearly the wave function is not such a thing. So what does real mean to those poeple?

Real means it has an external existence and not just a calculational device. In saying it is real like an electromagnetic field it is meant it has an external existence. There are all sorts of possibilities of how that can be - here is an interesting one:
http://arxiv.org/pdf/1104.2822v1.pdf

You mentioned Bohm2 - Bohms pilot wave would be something that also had real existence - the theory is a bit vague about exactly what it is.

Thanks
Bill

 

[martinbn]

Real means it has an external existence and not just a calculational device. In saying it is real like an electromagnetic field it is meant it has an external existence. There are all sorts of possibilities of how that can be - here is an interesting one:
http://arxiv.org/pdf/1104.2822v1.pdf

You mentioned Bohm2 - Bohms pilot wave would be something that also had real existence - the theory is a bit vague about exactly what it is.

Thanks
Bill

Yes, the pilot wave would be an example, but my puzzlement remains. How can something have and external existence and its mathematical discription be a function defined on configuration space?! I think that is what bohm2 is saying also.

 

[bhobba]

Yes, the pilot wave would be an example, but my puzzlement remains. How can something have and external existence and its mathematical discription be a function defined on configuration space?! I think that is what bohm2 is saying also.

The same way the Bohm pilot wave, which can also be viewed the same way can:
http://www-physique.u-strasbg.fr/cours/l3/divers/meca_q_hervieux/Articles/Nine_form.pdf
'The quantum potential Q(x1,x2,t) changes instantaneously throughout configuration space whenever the wavefunction changes, and this mechanism is responsible for the nonlocal correlations that are so characteristic of quantum mechanics. A rather natural mechanism prevents human beings from tapping into this instantaneous change for the purpose of faster-than-light communications.'

Interestingly that paper discusses another equivalent formulation of Quantum mechanics, the Second Quantization Formulation, usually associated with QFT, but can also be a formulation for bog standard QM, which can be viewed as a field of creation and annihilation operators at all points of space.

Thanks
Bill

 

[Ken G]

Sure, but then realists are likely to ask "information about what" and "whose information"?

"Whose" information is easy-- ours. Information about what? That isn't something that physics ever tells us, any more than it tells us if there is a big guy with a beard above the clouds.

 

[Ken G]

Here is a paper by Renato Renner and co, entitled: Completeness of quantum theory implies that wave functions are physical properties

And look at what goes into their argument: "...a wave function corresponds to an extremal state and is therefore maximally informative" (my bold), and "Specifically, the (necessary) assumptions are that quantum theory correctly predicts the statistics of measurement outcomes and that measurement settings can (in principle) be chosen freely." All these statements about information, they prove only things about the nature of that information. Where does that add up to reality? Completeness of information means that it isn't information any more? And just what is "complete" information? Does the wavefunction tell us what an electron is, or what its charge or mass are, or why it obeys quantum mechanics? Does it even tell us the outcome of an individual trial? Whatever they mean by "complete", it is a purely information-related definition, and statistically so.

 

[bohm2]

"Whose" information is easy-- ours. Information about what? That isn't something that physics ever tells us, any more than it tells us if there is a big guy with a beard above the clouds.

So electrons and gravity are on par with the big guy with the beard above the clouds?

 

[Ken G]

So electrons and gravity are on par with the big guy with the beard above the clouds?

In regard to the aspect you mentioned, yes. The concepts of electrons and gravity are much more predictively useful, which is why they are physics and not religion. But that isn't what I was talking about, because predictive power is all about manipulating information. You asked what the information was information about, and that's the part that is perfectly on a par with the "big guy", expressly because there is no experiment that tells us anything about the answer to your question. Think of it this way. If you have a conversation with someone, you have no idea what is on the "other end" of that conversation outside of how it acts in the conversation, except that in that particular case you can put a "mini me" over there, and assume that what their mind is like is a lot like yours. That's exactly what you cannot do with electrons and gravity. I believe this is just what Wittgenstein meant when he famously quipped, "if a lion could talk we wouldn't understand it."

 

[bohm2]

You asked what the information was information about, and that's the part that is perfectly on a par with the "big guy", expressly because there is no experiment that tells us anything about the answer to your question.

I'm still confused here. I understand the difference between what some candidate model/theory posits as being "real" versus what is actually "real" (mind-independent reality). But irrespective of these issues, our theories/models/experiments must be about something? Doesn't information require something to be informed? The mathematical entities must represent something that there is in the world.

 

[Ken G]

But irrespective of these issues, our theories/models/experiments must be about something?

Presumably, but the issue is not what they are about, it is what we can say (using physics) about what they are about. But what we can say is exactly the same thing as the information we have-- there's just no distinction there. Not in physics, anyway, philosophy is more free to speculate.

Doesn't information require something to be informed?

Certainly-- us. We are the thing that is informed.

The mathematical entities must represent something that there is in the world.

Yet the representation is what we use in physics. One can say that experiments are done on the real world, but what the physicist manipulates to interpret, understand, and predict those observations is entirely information. Nothing else, certainly nothing in the real world. Indeed I would say this is the entire purpose of physics-- to replace the real world with useful representations (whether those representations be pointer readings, for the observer, or mathematical expressions, for the theorist). That is how we bring reality into our minds where we can do something with it.

 

[bohm2]

Certainly-- us. We are the thing that is informed.

Consider this example from molecular biology:

...in modern molecular biology, it is assumed that the DNA molecule constitutes a code (i.e. a language), and that the RNA molecules 'read' this code, and are thus in effect 'informed' as to what kind of proteins they are to make. The form of the DNA molecule thus enters into the general energy and activity of the cell. At any given moment, most of the form is inactive, as only certain parts of it are being 'read' by the RNA, according to the stage of growth and the circumstances of the cell. Here, we have a case in which the notion of active information does not depend on anything constructed by human beings.This shows that the idea of active information is not restricted to a human context, and suggests that such information may apply quite generally.

How would you describe this using your scheme? Why can't this scheme also apply in the case of sub-atomic entities as suggested by some like Hiley, Bohm, etc:

From the Heisenberg Picture to Bohm: a New Perspective on Active Information and its relation to Shannon Information.
http://www.bbk.ac.uk/tpru/BasilHiley/Vexjo2001W.pdf

Active Information and Teleportation.
http://www.bbk.ac.uk/tpru/BasilHiley/ActInfoTeleWein.pdf

 

[bhobba]

I'm still confused here. I understand the difference between what some candidate model/theory posits as being "real" versus what is actually "real" (mind-independent reality). But irrespective of these issues, our theories/models/experiments must be about something? Doesn't information require something to be informed? The mathematical entities must represent something that there is in the world.

Think of a possibly loaded dice. How it behaves is described by 6 non negative numbers that add up to one called a state vector. It doesn't represent something out there but rather a codification of the complex behavior of the dice.

The same with QM - its state vector may not represent something out there but may simply be the codification of experimentally observed behavior.

If you want a discussion of the issues involved here I suggest Chapter 9 of Ballentine QM - A Modern Development.

This view was the view of Einstein and the real crux of the Einstein-Bohr debates not the kiddy version the popular press portrays. Einstein did not believe QM was incorrect - merely incomplete - what he disliked about the Copenhagen interpretation was its view that QM was a complete theory. The view of the state vector of QM being like the state vector of probability theory suggests like when you toss a dice other factors are at work and the fact you have to resort to probabilities suggests there MAY be more to it than the Copenhagen interpretation would have you believe - we just don't know what they are yet. Note the use of the word MAY - nature may be like that at its fundamental level and there is nothing deeper - who knows.

Thanks
Bill

 

[bohm2]

Think of a possibly loaded dice. How it behaves is described by 6 non negative numbers that add up to one called a state vector. It doesn't represent something out there but rather a codification of the complex behavior of the dice.

I'm not suggesting anything like this or suggest that Einstein's view was correct. There are 3 major positions with respect to wave function ontology:

1. Wavefunctions are epistemic and there is some underlying ontic state. Quantum mechanics is the statistical theory of these ontic states in analogy with Liouville mechanics. (The scientific realism of Einstein, Rob Spekkens, Matt Leifer, etc.)

2. Wavefunctions are epistemic, but there is no deeper underlying reality. (Anti-realism-Bohr)

3. Wavefunctions are ontic (there may also be additional ontic degrees of freedom, which is an important distinction but not relevant to the present discussion). This includes: the scientific realism of Everett/many-worlds interpretation, de Broglie-Bohm theory, and spontaneous collapse models.

I'm really arguing for position 3. Ken G seems to be arguing for position 2.

This scheme comes from this site:

Can the quantum state be interpreted statistically?
http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/

While there is still some debate, it seems option 1. above has been recently ruled out via the PBR paper.

 

[bhobba]

You forgot one - the Ensemble interpretation, which I hold to, which Balentine in his well respected textbook adheres to, which Einstein adhered to, which a lot of other physicists like Lubos Motol adhere to (in fact he is very critical of that link you posted - I don't agree with him on that - but he knows his stuff). I do not agree the link you gave disproves the statistical interpretation - I do not agree with Lubos who thinks its a load of rubbish, but I do not agree it disproves anything.

Wavefunctions are epistemic and there is some underlying ontic state[/I]. Quantum mechanics is the statistical theory of these ontic states in analogy with Liouville mechanics. (The scientific realism of Einstein, Rob Spekkens, Matt Leifer, etc.)

Ontic (from the Greek ὄν, genitive ὄντος: "of that which is") is physical, real or factual existence.

No mate - that is most definitely not the statistical interpretation - its more along the lines of Nelsons Stochastic interpretation. The statistical interpretation doesn't ascribe any status to a quantum state any more than probability theory ascribes an 'ontic' existence to a probability vector.

Wavefunctions are epistemic, but there is no deeper underlying reality[/I]. (Anti-realism-Bohr)

I am not a philosophy type dude but I think that is the ensemble interpretation and not Copenhagen which takes the quantum state as fundamental and not merely as a useful device to calculate probabilities. Anyway here is a definition of it:
'The attempt to conceive the quantum-theoretical description as the complete description of the individual systems leads to unnatural theoretical interpretations, which become immediately unnecessary if one accepts the interpretation that the description refers to ensembles of systems and not to individual systems.'

And here is a link about it just to make sure we are on the same page:
http://www.kevinaylward.co.uk/qm/index.html

By the way previous discussions I have had with Ken makes me think he holds to something similar to the Ensemble intterpretation - but I could be wrong.

Thanks
Bill

 

[Ken G]

Consider this example from molecular biology: "... At any given moment, most of the form is inactive, as only certain parts of it are being 'read' by the RNA, according to the stage of growth and the circumstances of the cell. Here, we have a case in which the notion of active information does not depend on anything constructed by human beings. This shows that the idea of active information is not restricted to a human context, and suggests that such information may apply quite generally." How would you describe this using your scheme?

I would say they are quite mistaken. Notice how they have anthropomorphized the DNA and RNA! So of course there is a human there-- it is the human who wrote that anthropomorphism, who made sense of those words by applying the concept of information the way we do. They did just exactly what I meant about putting a "mini me" at the other end of the phone conversation to try and understand whatever is on the other end. For electrons and gravity, no one even tries to do that, for RNA molecules, apparently someone does, but it's really not much more than a useful analogy.

The point is, no RNA molecule is "reading" any information, nor "processing" it, that is things that our brain does when it tries to understand whatever the molecule is actually doing. The place where the information is being read is still in our heads-- we are reading the "code", that is how we think, and we are projecting how we think onto the molecules. It certainly has its purposes to do so, but we should not ignore that we are doing it, and make claims that human information processing is not involved when a human imagines a "mini me" looking over the shoulder of the functioning of mindless molecules!

Why can't this scheme also apply in the case of sub-atomic entities as suggested by some like Hiley, Bohm, etc:

We can certainly use that scheme, we do it all the time. We use information, all the time, and we imagine that information in some way "lives" in the physical world, independently of us. That's part of how information works, we ignore our role in it, because our role in it is just the part that we don't understand, having no useful model of ourselves to include in what information is. So we do it, and we benefit from it, but we should not pretend we aren't doing it. There's no need to ignore our role, just because we don't understand our role.

From the Heisenberg Picture to Bohm: a New Perspective on Active Information and its relation to Shannon Information.
http://www.bbk.ac.uk/tpru/BasilHiley/Vexjo2001W.pdf

Active Information and Teleportation.
http://www.bbk.ac.uk/tpru/BasilHiley/ActInfoTeleWein.pdf

I'm sure these are very nice applications of the concept of information, and I'm sure they are written by human intelligences, using information, just the way human intelligences give meaning to that concept.

 

[Ken G]

By the way previous discussions I have had with Ken makes me think he holds to something similar to the Ensemble intterpretation - but I could be wrong.

I can see the appeal in the ensemble interpretation, but my general approach is that there is not much point in holding to anyone interpretation-- interpretations are simply not things we should hold to. Instead, what we should hold to is a clear sense that interpretations are just that-- ways to picture what a theory is saying. We should be able to move between them, to use each like taking a different angle on the same animal. We should not view interpretations as world views-- that's what I object to. Even things like many-worlds I have no problem with if viewed as an interpretation, my issue is when people take that interpretation and argue for the actual existence of the many worlds. That's just not what interpretations are for.

Granted, some of the interpretations seem to go beyond quantum mechanics, or at least they suggest different directions to look for the next theory. That's all well and good, and all the more reason to have multiple interpretations-- it gives us more places to look. Each person might have a favorite interpretation that they like to use, and they might use it to motivate them to look somewhere different for the next theory (if they are into looking for new theories, that's certainly quite a challenge). But if we are talking about new theories, the only way we will adjudicate them is the usual way-- by observation, not by argumentation.

As an example of how similar I view interpretations, I would say that Bohm, ensemble, and Copenhagen are all essentially the same, because they all involve averaging over some set of possibilities when they talk about a wave function. Bohm averages over what we don't know about the initial condition, the ensemble averages over a set of final conditions (without specifying where what we don't know about those systems is entering the question), and Copenhagen averages over what is viewed as unknowable about the system. Put like that, it's clear why the three are all effectively the same, at least until we find some way to figure out where the need for averaging is entering. That's going to be some new theory that isn't quantum mechanics any more, and can only be adjudicated by observation.

 

[bohm2]

I would say they are quite mistaken. Notice how they have anthropomorphized the DNA and RNA! So of course there is a human there-- it is the human who wrote that anthropomorphism, who made sense of those words by applying the concept of information the way we do.

When biologists use the word "read", they don't literally mean "read" as in exactly the same way as we use the term "read" in human context. They mean the process of translation/transcription. A triplet code of a DNA molecule is transcribed into the triplet code of an mRNA molecule, etc. and ultimately translated into proteins. So the genetic code is the set of rules by which information encoded in genetic material (DNA or mRNA sequences) is translated into proteins (amino acid sequences) by living cells.

 

[Ken G]

When biologists use the word "read", they don't literally mean "read" as in exactly the same way as we use the term "read" in human context. They mean the process of translation/transcription.

Of course. My point is that the process of translationg/transcription is a very specific thing, it has nothing to do with "reading" any "information" until we say that it does. All those words make no sense until a human brain is involved-- molecules are just dumb molecules, there's absolutely no "information" there, active or otherwise, until our brains get into the act. This is exactly the point they are missing when they argue that molecules are reading and processing active information, which only makes sense when our brains are also in that sentence-- that is just what we do to understand, predict, characterize, and gain knowledge of, whatever is the mindless process that molecules are actually doing (which has nothing to do with information, and demonstrably so).

So the genetic code is the set of rules by which information encoded in genetic material (DNA or mRNA sequences) is translated into proteins (amino acid sequences) by living cells.

Yes, look at your own words: "code", "rules", and "information." That's all us, not the molecules. When we see order and purpose, it's what we do. That's how we understand things. That's how we use the concept of "information." We use it to great advantage, of course, and it is convenient to enter into a kind of lazy terminology that imagines the "information" is there with or without us, but of course it isn't, that's all just anthropomorphism, because information is all about how we understand things that have no need of understanding themselves. This isn't some fringe philosophy, everything I'm saying is perfectly demonstable-- just try and define information, or how it operates in the real world, without a mind to say what it is.

To claim that we are not involved, it seems perfectly obvious that anthropomorphisms must be explicitly and completely avoided. Are they? Why would someone use blanket anthropomorphisms in the very same sentence as a claim that human intelligence is not involved? Is there another way to say what they mean without the anthropomorphisms? I say no-- "information" is inherently anthropic, and what is so ironic is how totally anthropomorphic is their very argument that it isn't!