Quantum myth 1. wave-particle duality

[Maaneli]

The wavelength of an electron is NEVER directly measured. One measures the position of several electrons and one infers the wavelength of the associated wave. I agree with Pellman that the wavefunction lives in configuration space and therefore its ontological status is not clear...

Exactly right. Surprisingly though, there are still philosophers of physics like David Albert who would insist that the wavefunction and its configuration space MUST be physically real in their own right.

The de Broglie-Bohm pilot wave theory certainly implies though that even if the wavefunction is not a physically real field, but only a mathematical representation, then it still must reflect some kind of physically real entities. The reason is that in the pilot wave theory, the wavefunction is indispensable to the empirically observed *dynamics* of the Bohmian particles that make up tables and chairs in the experimentally observed physical world. So there is still the question of what physically real fields/variables/entities are actually 'out there' in physical 3-space, to locally interact with and *cause* the Bohmian particles constituting the observed physical world, to move with a velocity dynamics that is accurately described by the pilot wave guidance equation defined in terms of the strictly mathematical wavefunction (indeed all other physical variables such as spin, helicity, charge, and mass, are properties encoded in the wavefunction, and not in the particles themselves). Otherwise, one would have to say that the Bohmian particles are the only physically real beables in the observed physical world, and that there is nothing else 'out there' in the physical world to give them their velocity dynamics; that the particles just spontaneously move with a velocity dynamics that the strictly mathematical wavefunction accurately describes via the pilot wave guidance equation. This however seems too bizarre to be true in my opinion, so I think one must ultimately look for something underlying the wavefunction, in the case that the wavefunction is not taken to be physically real.

 

[Ken G]

Why is 3-space more "real" than configuration space? Or a better question, what does physics have to do with ontology? Physics doesn't need ontology, so it seems most prudent to interpret all of physics as representational, and leave the ontology to the philosophers. What I mean by that is, philosophers can bring out the various nuances of the situation, but can never determine "which is correct", it isn't even the point of philosophy (though many seem to argue as though it were). Physics, on the other hand, does try to demonstrate what is correct, to within some practical precision target, and this is the reason to avoid ontology in physics to steer clear of what cannot be demonstrated.

 

[Demystifier]

What about QFT and so-called particle theory? Are there particles in particle theory?

This is the subject of Sec. 9.

 

[Maaneli]

Why is 3-space more "real" than configuration space? Or a better question, what does physics have to do with ontology?

3-space is regarded as more "real" for a number of reasons: electric and magnetic fields, quantum or classical, are functions on 3-space, and have amplitude and phases that can be directly and individually measured. Moreover, they are sourced fields by charge and current distributions in 3-space On the other hand, wavefunctions in configuration space have amplitude and phases that cannot be so directly measured, but only inferred by statistical ensembles of particle position measurements. Moreover, wavefunctions on configuration space are not sourced fields in any way like EM fields in 3-space. Classical Hamiltonians are also functions on even higher dimensional spaces, namely, phase space; but the phase space of a classical Hamiltonian is only a mathematical representation for the nonlocal correlations in an N-particle system, since all the corresponding classical particle trajectories are actually observed in 3-space. Another example comes from classical statistical mechanics. The Smoluchowski-diffusion equation has solutions (such as the Gibbs distribution) that, just like wavefunctions, are also functions on configuration space in phase and amplitude. Moreover, these solutions can be used to define the corresponding drift velocity for particles in the theory. However, these diffusion function solutions on configuration space do not actually represent a physically real substance diffusing in configuration space. Rather, they represent a probability measure for particles to be in a certain position or velocity configuration at a temperature T and a time t, in physical 3-space. Moreover, we know the diffusion equation and its corresponding solutions are phenomenological approximations to the Langevin equation of dynamics, which describes the microphysical degrees of freedom of particles coupled to a thermal reservoir in 3-space.

Consider also the obvious implications of a physically real configuration space, with respect to wavefunctions. If this were the case, then the dimensionality of physically real space would actually be 3N-dimensional, were N is the number of particles in the universe (~10^23). So we would actually be living in a 3*10^23 dimensional space. But then the question you must ask is how does a quantum theory (even a Bohmian quantum theory), in which the configuration space is physically real, explain how the observed physical world in 3-space arises? Consider an example from Tim Maudlin:

" It is trivial, of course, that a single mathematical point moving in a high-dimensional mathematical space can represent one or the other outcome: if there are many physical particles in a common low dimensional space moving around, then there is an evolving configuration of particles, and this can be represented (under obvious conventions) by a single point in a high-dimensional space. This abstract (non-physical) space is configuration space... But the fact that it is trivial to represent an evolving configuration of many particles by a single point (using obvious conventions) does not imply that it is comprehensible how something we thought to be an evolving configuration of many particles (such as a cat) could really be just a single particle!"

So this would be a fundamental problem for the corresponding quantum theory of measurement that would attempt to explain the emergence of our observed 3-space.

Those are some reasons.

Physics doesn't need ontology, so it seems most prudent to interpret all of physics as representational, and leave the ontology to the philosophers. What I mean by that is, philosophers can bring out the various nuances of the situation, but can never determine "which is correct", it isn't even the point of philosophy (though many seem to argue as though it were). Physics, on the other hand, does try to demonstrate what is correct, to within some practical precision target, and this is the reason to avoid ontology in physics to steer clear of what cannot be demonstrated.

Completely disagree. Physics does need (and does already have!) ontology if it is going to claim to explain anything in nature. Think of the obvious examples of physical ontologies from classical mechanics and electrodynamics. You should also learn that quantum theory without a physical ontology (such as orthodox quantum theory) suffers from the well-known measurement problems. It was only when quantum theories with ontology were developed that the measurement problems were solved. So this is an example where thinking about ontology in physics has been extremely useful and necessary. Also, you should recognize that there is no sharp distinction between physics and philosophy precisely because consistent physical theories already make ontological and metaphysical claims about the physical world. You should also recognize that the need for physical theories to make ontological claims about the physical world does not at all conflict with the fact that physics is representational, as you said. There is a difference between the ontology of a theory and the actual ontology of the real world, the latter of which can ultimately only be approximately represented by the former. Finally, I question your understanding of the word "correct", in the context that you used it.

Cheers,
Maaneli

 

[FunkyDwarf]

As far as I am (an undergraduate in his last year) concerned there is no need for wave particle duality. You can just as easily verify the same experiments by considering everything as point particles and allocating all the wavelike properties to the wavefunction which preceeds it an encodes all its information. Sure you COULD say that this separation is just nit picking and really if the wavefunction has wavelike behaviour so does the particle, but well that's just a matter of philosophy. Again physics is only concerned with things you can measure. If you create a system which is fundamentally unmeasureable, or at least a quantity in it is, then we don't care. When we're not looking at electrons through slits they could turn into a turtle to batman and back, we don't care. The only reality we have is what we can measure, and for that reason, all these things like electrons and photons are particles, not waves.

 

[Hurkyl]

Why is 3-space more "real" than configuration space? Or a better question, what does physics have to do with ontology?

One of the key parts of science is formulating hypotheses, and testing them with experiments performed in 'reality'. This requires a way to interpret the hypothesis in terms of reality -- that is an ontology.

e.g. if I don't ascribe any meaning to the word "sun" (or the other things), how could I empirically test the hypothesis "the sun will rise tomorrow"?

 

[f95toli]

Completely disagree. Physics does need (and does already have!) ontology if it is going to claim to explain anything in nature.

But the question is if we really should expect physics (and science in general) to explain anything. Ultimately, we can only judge whether or not a theory is valid by comparing its predictions with the outcome of experiments; there is no way of knowing if e.g. the assumptions made in formulating the theory or eve if its "philosophical" implications are fundamentally "correct" ; as long as the numbers coming out of the theory agrees with the number coming from our scientific instruments we will just have to accept that it is the best we got.
In principle we could have a situation where someone comes up with a theory where interactions are carried by invisible pink unicorns (IPU); if that theory turned out to be more successful in predicting numbers than or existing theories we would have to accept it. The fact that the idea of IPUs is ridiculous is irrelevant.

 

[monish]

Nevertheless, the success of molecular and solid state modeling theories and software
is that they do use single electronic/spin density fields.

http://en.wikipedia.org/wiki/Density_functional_theory#Description_of_the_theory

"The main objective of density functional theory is to replace the many-body
electronic wavefunction with the electronic density as the basic quantity"


Regards, Hans

At the risk of not having understood your point, I have to raise the following objections:

1. Is density function theory not actually an approximation method which still relies on the underlying 3n-dimensional Schroedinger wave function for its validity?

2. If this is in fact a viable, self-consistent theory, have we not at best replaced the single 3n-dimensional Schroedinger function with n 3-dimensional functions, in other words an individual wave function for each electron? Yes, each function appears to have some physical reality on its own, but its hard to picture a universe which has to keep track of so many functions all overlapping at the same point in space.

 

[Maaneli]

But the question is if we really should expect physics (and science in general) to explain anything. Ultimately, we can only judge whether or not a theory is valid by comparing its predictions with the outcome of experiments; there is no way of knowing if e.g. the assumptions made in formulating the theory or eve if its "philosophical" implications are fundamentally "correct" ; as long as the numbers coming out of the theory agrees with the number coming from our scientific instruments we will just have to accept that it is the best we got.
In principle we could have a situation where someone comes up with a theory where interactions are carried by invisible pink unicorns (IPU); if that theory turned out to be more successful in predicting numbers than or existing theories we would have to accept it. The fact that the idea of IPUs is ridiculous is irrelevant.

Tsk, tsk, this is what happens when you don't have concrete experience with foundational reformulations of physics, and how precisely they differ from the orthodox theories that you know. You actually can determine, independent of experiments, if the ontology of one physical theory is really more fundamental than another. The way is simply by seeing if one theory T1 can make the same predictions as the other theory T2, while also showing that T1 makes fewer ad-hoc postulates than T2, and can even physically derive the postulates of T2, as well as the physical ontology of T2, within some approximation limit. The concrete exemplar of this is Bohmian quantum mechanics (BQM) vs orthodox quantum mechanics (OQM), which are empirically equivalent theories. BQM and OQM share in common the assumption of the wavefunction and Schroedinger equation. But OQM has several measurement postulates (I assume you are familiar with them), as well as the Born rule postulate (I assume you know this one as well). BQM on the other hand, has no need nor any room for any of the measurement postulates, because it in fact derives all of their consequences. For example, the appearance of wavefunction collapse (which is the ontology of OQM) is derived in a crystal clear way from BQM. Moreover, BQM derives the Born rule and even suggests the possibility of deviations from the statistical predictions of OQM. For these reasons, in comparing BQM with OQM, it is clear that the latter is just a phenomenological formalism and approximation to the former. The equations of BQM have become extremely useful to condensed matter theorists and theoretical physical chemists, primarily because it computationally simplifies many problems.

Also, you should think about intertheoretic relations. QED formulated strictly in terms of the second quantized ZPE, is empirically equivalent (on the lengthscale of QED phenomena) to QED formulated strictly in terms of second quantized radiation reaction. These two completely different physical pictures however, just depend on how field operators are ordered. Now when one tries to mix QED in either formulation with the general theory of relativity (GTR), one finds that QED with only second quantized ZPE is physically inconsistent with GTR because of the infinite vacuum energy density contributed to the right hand side of the Einstein field equation. On the other hand, QED with only quantized radiation reaction effects does not predict this infinite vacuum energy density, and is thus physically consistent with the Einstein field equation of GTR; but you would never have recognized this intertheoretic consequence if you were insensitive to the differences in physical ontology between these two approaches to QED, in spite of their empirical equivalence on the lengthscales of QED phenomena. Ed Jaynes made this particular point a long time ago, but it seems to have been forgotten by many people.

So you see, thinking about physical ontology, in spite of empirical equivalence, does have value beyond beyond your foresight.

 

[Ken G]

Those are some reasons.

All interesting aspects of 3-space vs. configuration space. However, I did not see any that showed 3-space is "real" and configuration space is not. I think what is lacking here is your definition of "real". Can you provide it?

Completely disagree. Physics does need (and does already have!) ontology if it is going to claim to explain anything in nature.

On the contrary, physics needs no ontology to "explain" anything. An "explanation" is nothing but a unifying language to help us picture things that we are familiar with. If we have no familiarities, that nothing is an explanation. If you don't agree, try explaining something to a 2 year old. The absence of familiarity is a huge problem. Conversely, explaining things to people with a great many familiarities is much easier. How does that simple fact invoke ontology?

Think of the obvious examples of physical ontologies from classical mechanics and electrodynamics.

Perfect examples of what I mean. Each of them, in its day, was thought to represent an ontology, and every one of those ontologies collapsed. Now we have new ones-- I guess we should imagine we got it right this time?

You should also learn that quantum theory without a physical ontology (such as orthodox quantum theory) suffers from the well-known measurement problems.

Measurement problems stem from ontologies. Without the ontologies, there is no measurement problem. For example, I have no "problem" with measurement at all.

It was only when quantum theories with ontology were developed that the measurement problems were solved.

No, it was only when we kept track of what we were actually doing (coupling quantum systems to open classical ones) that they were solved.

So this is an example where thinking about ontology in physics has been extremely useful and necessary.

I'm sorry, how does thinking about ontology "solve" the measurement problem? I see it as being solved by leaving out ontology, by thinking of the wave function as being about information rather than requiring it to be something that must obey arbitrary "reality criteria".

Also, you should recognize that there is no sharp distinction between physics and philosophy precisely because consistent physical theories already make ontological and metaphysical claims about the physical world.

There is no sharp distinction between right and wrong either, the issue is whether or not there is value in drawing the distinction. When no value is seen in a distinction between physics and philosophy, we backtrack two thousand years and Galileo rolls over in his grave.

You should also recognize that the need for physical theories to make ontological claims about the physical world does not at all conflict with the fact that physics is representational, as you said. There is a difference between the ontology of a theory and the actual ontology of the real world, the latter of which can ultimately only be approximately represented by the former.

What is the "ontology of a theory", I would like to know. Why is it a necessary part of that theory, for example? To me, that's like saying that a theory about how fish swim has to be able to swim too.

 

[Ken G]

One of the key parts of science is formulating hypotheses, and testing them with experiments performed in 'reality'.

With that I will agree wholeheartedly.

This requires a way to interpret the hypothesis in terms of reality -- that is an ontology.

Huh? Why do I need such a concept to establish whether or not a test has succeeded? We can agree that reality exists, but we have that prior to doing any science. Science adds nothing more to that equation, it has nothing to do with ontology, because the whole point of science is to replace what exists with conceptualizations of what exists. Conceptualizations exist in that they are indeed existent conceptualizations. There is no need for anything beyond that in science. I can prove it: anyone can do science without it.

e.g. if I don't ascribe any meaning to the word "sun" (or the other things), how could I empirically test the hypothesis "the sun will rise tomorrow"?

No one said anything about meaning, we were talking about existence. Of course we need meaning, meaning is how we invoke our familiarities in order to communicate. All that must exist are those familiarities, there is no need at all for "the Sun" to exist. What is "the Sun," anyway? It is a label we have invented to conjure a set of familiarities. Those familiarities exist, and are needed to communicate science, but there is no need for science to make any statements about the existence of the Sun in order to invoke those familiarities.

Now, of course I realize we all use the shortcut of assuming there is something out there called "the Sun", but nevertheless it is important to note that that shortcut is entirely superfluous to science. Whenever you say "the Sun", any scientist is free to replace that with "whatever real phenonomena exists that manifests itself to us as a set of familiarities we conjure when we use the term the Sun". No one wants to say that every time, but the science is not one iota different. In point of fact, "the Sun" really doesn't have to mean anything more than a direction to point a telescope or a satellite, or a guide in making idealized models of reality. No existence needed, not one shred. If we're all hooked up to the Matrix but can't tell by experiment, how is science any different? Science simply doesn't care, ontology in science is just a convenience of language.

 

[reilly]

I emphatically agree that people are trigger-happy when it comes to invoking the "collapse of the wave function" when it is not necessary. This is a result of
simple ignorance of what is possible in physics with wave-on-wave interactions.
The traditional arguments against the wave theory of light, especially those invoked
in connection with the photo-electric effect and the Compton effect, are cases in point.
Both these arguments demand the collapse of the (photon's) wave function on the
grounds that e-m wave energy is too diffuse to be able to concentrate itself onto
the tiny cross-section of an electron for the observed outcome. In fact, when the
electron is treated as a wave, there are straightforward wave-on-wave pictures that
describe both effects without the need for the collapse of the wave function.

And yet the physical reality of the wave function remains so problematical in certain instances that I find it hard to believe that Hans appears willing to defend it in this thread. Because I don't think he would make such statements lightly.

So I have to ask: how are we supposed to understand the wave function of a heavy atom with many electrons? If we have s,p, and d orbitals all overlapping, then they should interfere with each other and creating oscillating charge distributions. I understand that Heisenberg more or less ridiculed the wave function on similar grounds, and that the standard theory requires us to write the wave function in multi-dimensional phase space...it's hard to reconcile this with the idea of physical reality. So is there a way out?

First allow me to say that Condon and Shortley's The Theory of Atomic Spectra pretty much touch upon your various ideas. This book was first puiblished in 1935, with more than 200 pages on multi-electron atoms. Because C&S discussed experimental data and theory, their book was a bible well into the early 60s. Also Pauling's General Chemistry discusses multi-electroan atoms as well. And even a quick read of one or the other should convince you that wave functions for, say, Uranium or deuterium are perfectly undestandable, CF the Thomas- Fermi , or Hartree-Fock approachs.

A hydrogen atom in a superpostIon of any states is possible; but it is not then , in general, an eigenstate of the Hydrogen atom. However, in reality, such a system will decay, by radiation, to the lowest hydrogen state possible.

However the electronic wave function of, say, a Lead atom, atomic weight is 207, and A=82, is very different. That is the wave function describes 82 electrons; and a description in terms of central field orbitals. A good first approximation is simply a state in which the lowest orbitals are filled -- like filling up to the Fermi-level. The closest one comes to superposition is the due to anti-symmetry imposed by the Pauli Principle. But, the state will be an eigenstate of the unperturbed Hamiltonian.

If you look up Fermi-Thomas and Hartree-Fock you'll find remarkable work that does quite well in understanding and computing ionization energies and other multi-electron atom properties. Suggests, within the Feynman constraint, these old guys did a fantastic job in atomic physics, so they must have understood and handled the multi-electron wave functions with great dispatch.As a look into the literature will show, that's exactly what they did.

Regards,
Reilly Atkinson

Question : how would you describe a gas?

 

[Ken G]

You actually can determine, independent of experiments, if the ontology of one physical theory is really more fundamental than another.

My bold shows that the razor you are applying does not establish any need for ontology in science, you have simply assumed we need it. What difference does it make to science if it uses a "more fundamental ontology", when ontology itself is not scientifically establishable? The most fundamental ontology we ever had came from the ancient Greeks, and had something to do with the Earth being the center of the universe. Now, you are saying that we should stick to the most fundamental ontology that agrees with observation, and change it as necessary. I say, why not just admit that we are not doing ontology, and not be so bothered when things we thought "existed", according to whatever is the fleetingly valid current most fundamental ontology, turn out to not exist, and just admit that isn't the purpose of the exercise in the first place? We are trying to make contact with reality, we have no need at all to specify any knowledge of what exists or doesn't exist, we just try to understand how it acts. No big deal if it acts in ways we didn't expect, no "ontological crises" needed.

Let me ask you this: which from this list exist, and which do not:
the Sun
particles
light waves
wave functions
trajectories
spacetime
If you can address this list, I'd be very curious, and if you cannot, what does your ontology really give you?

The concrete exemplar of this is Bohmian quantum mechanics (BQM) vs orthodox quantum mechanics (OQM), which are empirically equivalent theories.

And that is also the perfect example of what I'm talking about. You simply assume that certain attributes of BQM make it superior to OQM. The scientific evidence is obviously to the contrary: it isn't used much at all. That clearly shows why "ontological fundamentalism" is not important to science, which frankly doesn't surprise me.

Moreover, BQM derives the Born rule and even suggests the possibility of deviations from the statistical predictions of OQM.

By heaping on undemonstrable postulates of its own! But if there really are different predictions, then it is really science-- now go out and falsify it.

For these reasons, in comparing BQM with OQM, it is clear that the latter is just a phenomenological formalism and approximation to the former.

That you feel you can assert, without experimental evidence, which one is an "approximation" to the other, exposes crystal clearly that you really do think philosophy can be substituted for science, which is precisely what the Greeks thought two thousand years ago, and is what I am cautioning against.

The equations of BQM have become extremely useful to condensed matter theorists and theoretical physical chemists, primarily because it computationally simplifies many problems.

That is interesting, I agree, but can you argue this is anything but a niche application? There are all kinds of bizarre interpretations that become convenient in specific applications. For example, geocentrism is commonly practiced by navigators on Earth, without any ontological requirement that the Earth really be at the center of the universe.

Now when one tries to mix QED in either formulation with the general theory of relativity (GTR), one finds that QED with only second quantized ZPE is physically inconsistent with GTR because of the infinite vacuum energy density contributed to the right hand side of the Einstein field equation. On the other hand, QED with only quantized radiation reaction effects does not predict this infinite vacuum energy density, and is thus physically consistent with the Einstein field equation of GTR; but you would never have recognized this intertheoretic consequence if you were insensitive to the differences in physical ontology between these two approaches to QED, in spite of their empirical equivalence on the lengthscales of QED phenomena.

But you have not established that the key difference is ontological! In fact, the difference is the difference-- it is not ontology that makes one succeed where the other fails, but you did cite an operator ordering. There is no need to associate an ontology to an operator ordering, it's pure convenience of language! Does quantum mechanics work on atoms where classical mechanics fails because it has a different ontology, or just because it uses different models and different equations?

So you see, thinking about physical ontology, in spite of empirical equivalence, does have value beyond beyond your foresight.

I would simply say that understanding all the equivalent ways we have to think about reality has value, because you never know which one will be the best way to attack some new situation. That's exactly why you do not need ontology in science-- ontology carries with it a sense of uniqueness that one should seek to avoid.

 

[f95toli]

Tsk, tsk, this is what happens when you don't have concrete experience with foundational reformulations of physics, and how precisely they differ from the orthodox theories that you know.

So? You replace one theory with another, then what?
My point was that we can of course assume that our theories have something to do with a "reality" (which also assumes that there is a such a thing, but let's leave that aside for the moment), but that can never be more than an assumption.
What I was getting at is that testing theories always ultimately boils down to getting number that we can then compare with other numbers that we get from experiments.
We just have to very careful when we assume that the ideas/formulas that generate those numbers have anything to do with "reality". In some cases formulas are best understood as formulas. Most of the problems people have with QM comes from the interpretation; and perphaps it would sometimes be better NOT trying to interpret the mathematical models at all, but to simply accept them for what they are: A way to model the world and predict the outcome of experiments.

I use QM to plan my experiments and analyze data. In my work one of the most important tools is the Block sphere, simply because it allows me to visualize what is going on in the devices I work with. Hence, the Block sphere is a good tool, but does that neccesarily mean that it has anything to do with "reality"? Probably not. But I would argue that this is many ways besides the point, in many ways the Bloch sphere tells me just as much about the nature as microscopic theories that describe what is going on in the actual condensate or even subatomic level in the systems I work with.

 

[Ken G]

We just have to very careful when we assume that the ideas/formulas that generate those numbers have anything to do with "reality". In some cases formulas are best understood as formulas.

I agree. To me, ontology in science is a form of "verbal convenience", akin to personification of particles. How many of us have ever said "the electron experiences the electric field" or words to that effect-- personification for color and clarity of communication, nothing more. No one really thinks an electron "experiences" things, so why should we feel it has to "exist" for us to use it in our theories?

Hence, the Block sphere is a good tool, but does that neccesarily mean that it has anything to do with "reality"? Probably not.

Thank you for the concrete example, they speak volumes. Indeed, you can let the Block sphere have something to do with reality, but stop short of saying that it therefore has to be real. Perhaps I don't understand how they are using the term ontology, but it sounds like the latter usage is the intention, not the former.

 

[peter0302]

Let me ask you this: which from this list exist, and which do not:
the Sun
particles
light waves
wave functions
trajectories
spacetime
If you can address this list, I'd be very curious, and if you cannot, what does your ontology really give you?

You must agree that there are things that are more "real" than others. The number pi is a fundamental mathematical quantity but yet has no physicality to it. It merely allows us to measure and predict other observations. So there must be a fundamental difference between an abstract concept like pi that LEADS to observaitons, and the thing that actually is being observed.

The sun clearly exists because it can be observed directly through its light, heat, gravity, and magnetic field. The wave function cannot be directly observed - its properties can only be inferred based on where we see particles show up on a detector - thus it may or may not exist - it may be like pi. Same with trajectories, and spacetime. They are concepts that help us make sense of our observations but they themselves are not observed. They are like pi.

So with all that said, the universe of what is "physical" has to be limited to something that can interact with something else that is "physical." And since the wave function doens't interact with anything, but merely defines where something might show up, I have a hard time thinking that it's physical. If quantum bosons were somehow detected and BM proven, then that would be a different story.

 

[Ken G]

You must agree that there are things that are more "real" than others.

I certainly act that way, but I also recognize that this is largely a subjective distinction, that cannot be made objective via the means of science. It's a gray area, to be sure, like many in the actual application by imperfect humans of a scientific methodology that is defined in highly idealized ways. But I see more harm than benefit in thinking that science requires ontology, because I think it takes it a step toward dogma and a step away from discovery.

So there must be a fundamental difference between an abstract concept like pi that LEADS to observaitons, and the thing that actually is being observed.

I do think there is a difference between concepts and reality, I just think the former is the goal of science by observing the latter. Note that never allows us to mistake the former for the latter.

The sun clearly exists because it can be observed directly through its light, heat, gravity, and magnetic field.

Does this require that light, heat, gravity, and magnetic fields exist? We need a definition of what exists. If we take the standard approach that what exists is what we can measure, then I point out we never measure "the Sun", so that definition does not establish the existence of the Sun as anything but a unifying concept, which is exactly the only existence that I claim it has, consistent with scientific thought.

The wave function cannot be directly observed - its properties can only be inferred based on where we see particles show up on a detector - thus it may or may not exist - it may be like pi. Same with trajectories, and spacetime. They are concepts that help us make sense of our observations but they themselves are not observed.

They are unifying concepts-- like the Sun. When is our concept of something the thing itself, and isn't "thing" also a concept? Is not the existence of a concept different from what exists in reality? Does science need to make these distinctions, or can it simply accept that it lives in "concept space"?

So with all that said, the universe of what is "physical" has to be limited to something that can interact with something else that is "physical."

We don't know that everything that exists is "physical", it is just an assumption of science, required for obvious reasons. That's another reason for science to avoid ontology.

And since the wave function doens't interact with anything, but merely defines where something might show up, I have a hard time thinking that it's physical.

I certainly feel the wave function lives in "concept space", right next to electrons, spacetime, and the Sun.

 

[Maaneli]

All interesting aspects of 3-space vs. configuration space. However, I did not see any that showed 3-space is "real" and configuration space is not.

Then you didn't understand the examples. My point was to present clear and specific examples of cases where configurations space is only a mathematical representation for many body systems in 3-space, and to point out that consequently, it is quite possible and plausible, given our experiences with these well-known examples, that the configuration space of QM is probably no different.

On the contrary, physics needs no ontology to "explain" anything. An "explanation" is nothing but a unifying language to help us picture things that we are familiar with. If we have no familiarities, that nothing is an explanation. If you don't agree, try explaining something to a 2 year old. The absence of familiarity is a huge problem. Conversely, explaining things to people with a great many familiarities is much easier. How does that simple fact invoke ontology?

Any unifying language that helps you "picture" things you are familiar with, and that has ANY capacity to make predictions about how the physical world works, already has an ontology. Indeed every scientific explanation includes SOME kind of ontology. It may not though be the ontology of the real world though (recall to distinguish between ontology of a theory/explanation, and the ontology of the real world).

Perfect examples of what I mean. Each of them, in its day, was thought to represent an ontology, and every one of those ontologies collapsed. Now we have new ones-- I guess we should imagine we got it right this time?

I get the sense that you don't know what ontology means. Ontology is just what entities exists in the physical world. A physical theory always has an ontology, whether it accurately describes the world or not. Those classical ontologies did not "collapse", whatever the hell that means. They are just best regarded as approximations to the actual ontology of the world. No theory will ever have a perfectly accurate ontology, but that doesn't mean a theory doesn't have an ontology or ontology isn't useful.

Measurement problems stem from ontologies. Without the ontologies, there is no measurement problem. For example, I have no "problem" with measurement at all.

NO! the measurement problems stems from having NO ontology! The fact that you don't understand that and that you say you have no "problem" with measurement clearly tells me that you are far off from understanding what the measurement problem is, and it makes me question why I should continue having this discussion with you if you're that far behind.

No, it was only when we kept track of what we were actually doing (coupling quantum systems to open classical ones) that they were solved. I'm sorry, how does thinking about ontology "solve" the measurement problem? I see it as being solved by leaving out ontology, by thinking of the wave function as being about information rather than requiring it to be something that must obey arbitrary "reality criteria".

If you understood the measurement problem, you would understand why decoherence theory doesn't solves the problem. Not even Zurek or Zeh would claim that yet! Ontology solves the measurement problem because it tells you what your theory is fundamentally about, and how that fundamental entities of your theory behaves so as to gives rise to the appearance of of the classical world you experience. Without an ontology for quantum mechanics, you have to postulate wavefunction collapse at an arbitrary, human-specified place and time. This becomes especially problematic when you try to understand the quantum-classical limit.

There is no sharp distinction between right and wrong either, the issue is whether or not there is value in drawing the distinction. When no value is seen in a distinction between physics and philosophy, we backtrack two thousand years and Galileo rolls over in his grave.
What is the "ontology of a theory", I would like to know. Why is it a necessary part of that theory, for example? To me, that's like saying that a theory about how fish swim has to be able to swim too.

There is value in the distinction, as I have shown. A simple example of the ontology of a theory is classical mechanics: the world is made up of point particles that follow trajectories in 3-space, due to mechanical forces locally acting upon them. Or electromagnetism: the world is made up of charged point particles and electric and magnetic fields in 3-space, the latter of which induce Lorentz forces on the former and gives them their empirically observed trajectories in 3-space. It's really not a complicated idea.

 

[Maaneli]

So? You replace one theory with another, then what?
My point was that we can of course assume that our theories have something to do with a "reality" (which also assumes that there is a such a thing, but let's leave that aside for the moment), but that can never be more than an assumption.
What I was getting at is that testing theories always ultimately boils down to getting number that we can then compare with other numbers that we get from experiments.
We just have to very careful when we assume that the ideas/formulas that generate those numbers have anything to do with "reality". In some cases formulas are best understood as formulas. Most of the problems people have with QM comes from the interpretation; and perphaps it would sometimes be better NOT trying to interpret the mathematical models at all, but to simply accept them for what they are: A way to model the world and predict the outcome of experiments.

I use QM to plan my experiments and analyze data. In my work one of the most important tools is the Block sphere, simply because it allows me to visualize what is going on in the devices I work with. Hence, the Block sphere is a good tool, but does that neccesarily mean that it has anything to do with "reality"? Probably not. But I would argue that this is many ways besides the point, in many ways the Bloch sphere tells me just as much about the nature as microscopic theories that describe what is going on in the actual condensate or even subatomic level in the systems I work with.

You really should respond directly to my examples, if you expect me to reply to yours. As far as I can tell, you didn't bother to read them, which is why you entirely missed the argument.

 

[f95toli]

You really should respond directly to my examples, if you expect me to reply to yours. As far as I can tell, you didn't bother to read them, which is why you entirely missed the argument.

No, I did read what you wrote. And I did not mean to criticize what you wrote about the value of ontology. What I was addressing was the second part of this sentence:
"Physics does need (and does already have!) ontology if it is going to claim to explain anything in nature.".
This is a very good point, and I suspect many people would agree with you.
But the point of my post is that one can argue that the goal of physics is NOT necessarily to explain anything; but to just make models of the world and predict the outcome of experiments. Someone described this a while ago as the "shut up and calculate approach".
I agree that we should strive to come up with better theories, reduce the number of ad hoc assumptions, unify theories etc; but ultimately this can still never be more than an intellectually stimulating game which may or may not have something to do with "reality". It happens is a game I enjoy playing (which is one reason why I am a physicist), but one I do not neccesarly ascribe any deeper significande to anymore.

 

[Ken G]

Then you didn't understand the examples. My point was to present clear and specific examples of cases where configurations space is only a mathematical representation for many body systems in 3-space, and to point out that consequently, it is quite possible and plausible, given our experiences with these well-known examples, that the configuration space of QM is probably no different.

But I asked why that made it more real. You still haven't provided a meaning for that word, making communication around it very difficult.

Any unifying language that helps you "picture" things you are familiar with, and that has ANY capacity to make predictions about how the physical world works, already has an ontology.

You may simply assert that, but I don't see how you have established it.

Indeed every scientific explanation includes SOME kind of ontology. It may not though be the ontology of the real world though (recall to distinguish between ontology of a theory/explanation, and the ontology of the real world).

And I claim an ontology that is only in the explanation, and not intended to apply to the real world, is no ontology at all, but merely a communication device. If that is all you mean by "ontology", then I don't disagree at all-- it amounts to saying that science needs concepts. Yes, I agree, it needs concepts, I thought you were claiming it needed to imagine those concepts were real when you said it needed an ontology.

I get the sense that you don't know what ontology means. Ontology is just what entities exists in the physical world.

Well, that is just what I mean by it, but you seem to contradict it just above. "Ontology of a theory/explanation" versus "ontology of the real world" is your distinction, not mine, so which is the one about "entities that exist in the real world?"

A physical theory always has an ontology, whether it accurately describes the world or not. Those classical ontologies did not "collapse", whatever the hell that means.

It means we found that those things were not in fact "entities that exist in the real world", i.e., they represented a false ontology. I would certainly say that a false ontology "collapsed". You seem to be saying that science doesn't care about whether or not something is real, it just pretends it is, and that's what you mean by "ontology". That's actually what I've been arguing above. Perhaps we don't disagree: science pretends things are real as a kind of communication device, it needs take no stance on what is actually real. That's what I've been saying.

They are just best regarded as approximations to the actual ontology of the world.

But is the "actual ontology" crucial to science, or not? If not, I would agree, but I would also take that as why science does not need ontology. But we can amend that to saying science does not need an "actual ontology", that's all I meant. A "pretended ontology", or an "ontology of a theory/explanation", is simply what I would call a "model", and we can all agree science needs those.

No theory will ever have a perfectly accurate ontology, but that doesn't mean a theory doesn't have an ontology or ontology isn't useful.

The uselessness of an actual ontology, by which I mean the uselessness of asserting what exists in the real world, stems not from a lack of accuracy, but rather from a complete lack of need. It is simply philosophy, all science needs are models, i.e., pretend ontologies, or what you call approximate ontologies. To me an "approximate ontology" is like being "a little pregnant", but it seems the dispute is largely semantic.

NO! the measurement problems stems from having NO ontology! The fact that you don't understand that and that you say you have no "problem" with measurement clearly tells me that you are far off from understanding what the measurement problem is, and it makes me question why I should continue having this discussion with you if you're that far behind.

I believe I understand quite well what you mean by the "measurement problem", but I assert it would present no problem at all for me were I doing such experiments, just as it was no problem for a long list of physics experimenters, including Nobel prize winners. Somehow, physics has bungled along, without the ontology you claim it is useless without. Seems like a fallacious argument to me, can you cite an example of how ontology directly led to a new discovery that could not have been achieved by someone with no philosophical interests and no illusions of what entities exist in the real world?

If you understood the measurement problem, you would understand why decoherence theory doesn't solves the problem.

I understand it fine, what decoherence solves is the only part that is any problem, the part that asks physically how wavefunction collapse occurs from the scientific perspective of an open system interacting with a measurement device. It is you who wish to close that system, leaving science in the process, not I. It is your problem to solve, you invented it-- I have no problem, and can do all the same science while still sleeping fine. Unless you can make good on your claim to know that BQM will work better than OQM if it is ever put to the test. How you think you know that is the really interesting question here.

Ontology solves the measurement problem because it tells you what your theory is fundamentally about, and how that fundamental entities of your theory behaves so as to gives rise to the appearance of of the classical world you experience.

The theory tells you that, not its ontology. Will you now claim that "ontology" means nothing other than "instructions for how to apply a theory"? Again, if that is what you are saying, with no reference to "existence" at all, then we have no disagreement-- theories do indeed need instructions about how to apply them. I call that a pedagogy, not an ontology, though of course we tend to imagine that our pedagogies are ontologies just as a shortcut. I do that even when I know the ontology is false, because I recognize it as a shortcut and carry no philosphical illusions about "existence".

Without an ontology for quantum mechanics, you have to postulate wavefunction collapse at an arbitrary, human-specified place and time. This becomes especially problematic when you try to understand the quantum-classical limit.

Not arbitrary, no. The collapse happens as soon as you decide to stop tracking information and treat it as noise. We create the collapse, it is all how we treat the system, and we know exactly when we created that collapse. Why people see any mystery in that is beyond me, all the mystery is appears when we treat ourselves as part of the experiment, to which I say-- of course science creates mysteries if you relax its need for objectivity!

A simple example of the ontology of a theory is classical mechanics: the world is made up of point particles that follow trajectories in 3-space, due to mechanical forces locally acting upon them.

Thank you for concrete examples, but they perfectly illustrate my point. How is your theory one iota different if I simply don't include the "the world is made of" part? Why don't I just say "we will choose to treat the world using a model comprising of point particles..."? It's the identical theory, minus the extraneous ontology.

 

[Maaneli]

No, I did read what you wrote. And I did not mean to criticize what you wrote about the value of ontology. What I was addressing was the second part of this sentence:
"Physics does need (and does already have!) ontology if it is going to claim to explain anything in nature.".
This is a very good point, and I suspect many people would agree with you.

But the point of my post is that one can argue that the goal of physics is NOT necessarily to explain anything; but to just make models of the world and predict the outcome of experiments. Someone described this a while ago as the "shut up and calculate approach".

I'm thinking that you're not quite clearly expressing yourself. You said "one can argue that the goal of physics is NOT necessarily to explain anything; but to just make models of the world and predict the outcome of experiments." Well, making models of the world is a necessary part of coming up with ontological explanations about the physical world. Indeed it is impossible to explain anything in the world, without first making a model, which indeed is ultimately what physical theories are. It is also impossible to construct a physical model, without having also constructed an explanation! What you probably really mean to say, which would be opposed to my argument, is that the "goal" of physics is to construct formalisms strictly for the purposes of making predictions about the outcomes of experiments. I would point out though that the history of physics is actually a sharp counterexample to the shut-up and calculate way of doing physics. If you look at every major theoretical development in physics, throughout 18th-20th century, you will find evidence that they relied on thinking about ontology and treating physics as if it is trying to describe an objective reality, and not for the goal of just predicting the outcomes of experiments. This is especially true even in the era during and after the development of quantum theory.

I would like to also point out that the shut up and calculate mentality has no basis in rationality, and has more to do with psychology. I have known dozens of physicists with that mentality, who nevertheless believe that they are finding out how nature works in their approach to physics. This dualistic thinking, I would suggest, is a consequence of how they thought about the purpose of physics when they first fell in love with the subject and started out in it, and their attempts at reconciliation with their beliefs about quantum mechanics, which came from a logical positivist, orthodox point of view of the so-called "Copenhagen" interpretation.

I agree that we should strive to come up with better theories, reduce the number of ad hoc assumptions, unify theories etc; but ultimately this can still never be more than an intellectually stimulating game which may or may not have something to do with "reality". It happens is a game I enjoy playing (which is one reason why I am a physicist), but one I do not neccesarly ascribe any deeper significande to anymore.

I sharply disagree with the claim that reducing ad-hoc assumptions and unifying theories, is just an intellectual game with no deeper significance. The history of physics has also shown us that thinking about theories in the mentioned way has indeed led to empirical successes and differentiations between lesser theories. To divorce physics from ontology and physical reality, is to severely limit its scope of applicability.

 

[monish]

A hydrogen atom in a superpostIon of any states is possible; but it is not then , in general, an eigenstate of the Hydrogen atom. However, in reality, such a system will decay, by radiation, to the lowest hydrogen state possible.

And as I wrote previously, the radiation is an obvious consequence of the superposition of the states.

However the electronic wave function of, say, a Lead atom, atomic weight is 207, and A=82, is very different. That is the wave function describes 82 electrons; and a description in terms of central field orbitals. A good first approximation is simply a state in which the lowest orbitals are filled -- like filling up to the Fermi-level. The closest one comes to superposition is the due to anti-symmetry imposed by the Pauli Principle. But, the state will be an eigenstate of the unperturbed Hamiltonian.

If you look up Fermi-Thomas and Hartree-Fock you'll find remarkable work that does quite well in understanding and computing ionization energies and other multi-electron atom properties. Suggests, within the Feynman constraint, these old guys did a fantastic job in atomic physics, so they must have understood and handled the multi-electron wave functions with great dispatch.As a look into the literature will show, that's exactly what they did.

I'm understanding that these are useful computational methods to avoid an exact solution, for example, of the 246-dimensional Schroedinger equation for lead. The "picture" that goes with these methods correspond to what they tell us in first-year chemistry about how the orbitals are filled up one electron at a time. My problem arises when I ask where the electric charge is to be found. Does this not bother anybody else? In the hydrogen atom we took the square of the wave function. If the charge was spread in two wave functions, we added first, then squared. If we apply this to the lead atom...add the wave functions, then square them...we get wildly oscillating charges at every possible combination (difference, actually) of orbital frequencies.

Am I the only one bothered by this issue?

 

[Maaneli]

But I asked why that made it more real. You still haven't provided a meaning for that word, making communication around it very difficult.
You may simply assert that, but I don't see how you have established it.

You don't see how the configuration space of the classical Hamiltonian or the Gibbs distribution is not the physically real space we live in? You don't realize that we observe 3 spatial dimensions and therefore live in 3-space at the length scales of classical Hamiltonian and statistical mechanics? Something must be wrong with your senses and your detectors!

As for defining 'real', that is simply what exists in the world, independent of our sensory observations and experiences of it. Any conceptually consistent physical theory makes some statement about realism. There exists no self-consistent theory that only describes a subjective world of events. Indeed, if you really give time to think about it, it doesn't make philosophical or logical sense to say there is no physical reality. Also, I should ask you, what is your purpose for doing physics or science in general? What drives you as a so-called physicist?

And I claim an ontology that is only in the explanation, and not intended to apply to the real world, is no ontology at all, but merely a communication device. If that is all you mean by "ontology", then I don't disagree at all-- it amounts to saying that science needs concepts. Yes, I agree, it needs concepts, I thought you were claiming it needed to imagine those concepts were real when you said it needed an ontology.

Well, that is just what I mean by it, but you seem to contradict it just above. "Ontology of a theory/explanation" versus "ontology of the real world" is your distinction, not mine, so which is the one about "entities that exist in the real world?"

What are theories trying to talk about, if not an objective physical reality? You seem to think there is an inconsistency here when there isn't one at all. A clear physical theory, such as Newtonian mechanics, makes a claim about the physical ontology of the real world. Whatever that claim is, it is the ontology of Newtonian mechanics. Does that mean that this is the ACTUAL ontology of the real world - what really exists in the world? Not necessarily! A CLAIM about what actually exists in the world is not the same as what ACTUALLY exists in the world! These two things are not inconsistent, nor are they, in the context of physical theories, disconnected!

Now tell me Ken G, what is the purpose, in your mind, of a physical theory? To predict the outcomes of experiments? To "explain" the outcomes of experiments? Then ask yourself, what do you understand "explanation" to mean? For that matter, what are experiments? Where are these experiments taking place?

But is the "actual ontology" crucial to science, or not?

The belief that there is an "actual ontology" certainly is crucial to science. But that doesn't mean we can ever perfectly describe it!

I believe I understand quite well what you mean by the "measurement problem", but I assert it would present no problem at all for me were I doing such experiments, just as it was no problem for a long list of physics experimenters, including Nobel prize winners.

I don't think you understand what I mean by the measurement problem. First off, it is a problem not in experimental practice, but rather in understanding. I would challenge you also by asking you what you understand the word "measurement" to mean?

Somehow, physics has bungled along, without the ontology you claim it is useless without. Seems like a fallacious argument to me, can you cite an example of how ontology directly led to a new discovery that could not have been achieved by someone with no philosophical interests and no illusions of what entities exist in the real world?

Well I resent the word illusion, but yes I definitely can give historical examples of how ontology directly led to a new discovery. In fact, any competent student of history of physics can. Einstein's argument for Brownian motion relied on the assumption that there really are unobservable atomic particles in 3-space that bombard larger observable particles (e.g. pollen grains), and induce a random walk. This was in contradiction to Ernst Mach's belief that atoms do not exist as objectively real entities. I can also cite you the example of Schroedinger's derivation of his wave equation, which stemmed from the objective experimental observation that electrons appear have a wavelength. Schroedinger indeed derived it with the belief that he was describing what about the electron that is really 'waving'. Heisenberg, on the other hand, who had your philosophy of science, could only come up with his obscure Matrix mechanics. It was Schroedinger's wave equation derivation, by the way, that led to the discover of the Born rule. There is also Maxwell's derivation of the velocity distribution for classical particles in the kinetic theory of gases. There is also Boltzmann's discovery of his H-theorem with regard to the 2nd law of thermodynamics. None of this could likely have been possible without them thinking about what the ontology of the physical world is.

Not arbitrary, no. The collapse happens as soon as you decide to stop tracking information and treat it as noise.

As soon as "you" "decide"? Who the hell are you, and when do you decide this? To bring out the absurdity of this statement, allow me to quote John Bell:

<< It would seem that the theory [quantum mechanics] is exclusively concerned about "results of measurement", and has nothing to say about anything else. What exactly qualifies some physical systems to play the role of "measurer"? Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system ... with a Ph.D.? If the theory is to apply to anything but highly idealized laboratory operations, are we not obliged to admit that more or less "measurement-like" processes are going on more or less all the time, more or less everywhere. Do we not have jumping then all the time? >>

Also, WHAT DO YOU MEAN BY INFORMATION? INFORMATION ABOUT WHAT? By the way, decoherence theory has a perfectly natural and clearer role to play in BQM than in orthodox QM.

We create the collapse, it is all how we treat the system, and we know exactly when we created that collapse. Why people see any mystery in that is beyond me, all the mystery is appears when we treat ourselves as part of the experiment, to which I say-- of course science creates mysteries if you relax its need for objectivity!

I take it you have never read or understood John Bell or his theorem. May I recommend reading Speakable and Unspeakable in Quantum Mechanics. No opinion is worth holding onto until you put it through the ultimate, honest, challenge.

Why don't I just say "we will choose to treat the world using a model comprising of point particles..."? It's the identical theory, minus the extraneous ontology.

Um, hello, this statement you make IS a statement about ontology! Moreover, once again, it's not just a matter of arbitrary choice.

 

[reilly]

monish-I suspect you might be the only one. Study the basics of Fock space, and the description of many body systems, which are used all over the place. The absolute square of the Hg wave function gives the joint probability density of the positions of 82 electrons. You can also get the joint current density for those same electrons. That's pretty much all you need to know where the charge is.
Regards,
Reilly Atkinson

 

[xristy]

You don't see how the configuration space of the classical Hamiltonian or the Gibbs distribution is not the physically real space we live in? You don't realize that we observe 3 spatial dimensions and therefore live in 3-space at the length scales of classical Hamiltonian and statistical mechanics? Something must be wrong with your senses and your detectors!

Humans, indeed animals in general, inhabit rather complex spaces that include position, phase, velocity and so on across an array of species specific observables. Without motion and our various measurements of it we do not experience. It is an inter-subjective series of conceptual designations that are what we call living in a 3-dimensional world.

As for defining 'real', that is simply what exists in the world, independent of our sensory observations and experiences of it. Any conceptually consistent physical theory makes some statement about realism. There exists no self-consistent theory that only describes a subjective world of events. Indeed, if you really give time to think about it, it doesn't make philosophical or logical sense to say there is no physical reality.

The utter and complete relationality of what is 'real' extends to the ontologies that we establish inter-subjectively. Current physics is an excellent example of seeing 'reality' dissolve under analysis. In fact it makes excellent sense to say there is no physical reality, in the sense that you defined as that which simply exists in the world independent of our sensory observations and experiences of it. There are no quarks, or solitons or clouds or rain or stars in the sky save for our collective conceptual designations of recurring patterns of the arising of the 'real'. It is these designations that constitute the ontologies that are operational among of group of people - some of whom may self identify as scientists.

In the olden days science was an activity striving to achieve a view of that which is from a vantage point outside the 'real'. It is increasingly clear that trying to look behind the veil is not the most effective way of doing science.

That is, science as a group endeavor to establish conceptual designations of patterns of the arising of that-which-is that enable us to get out of harms way and improve our lot, which includes for some of us achieving satisfaction at seeing some patterns and ways of identifying these patterns that have some quality we call aesthetically pleasing.

It is fair to suggest that there is a way in which that-which-is arises, i.e., there is 'reality'; however, it is equally fair to understand that how it arises transcends any ontology in the sense that the complete relationality of that-which-is is without any conceptual bounds.

Schrödinger and Heisenberg had two different ontologies for the same observations that were then extended by Dirac and then Kline-Gordon, Feynman and so on. These ongoing shifts in view are not nailing down that-which-is independent of our view of that-which-is and what observations we can make and want to make for whatever purposes.

It is clear that physical theories are about the observations that we can make and ways in which we talk about them. We can not make all possible observations, and hence we can't talk in a complete sense about that-which-is, i.e., objective physical reality.

I would agree that there are always at least as many ontologies at play as there are people doing physics, if by ontology we mean conceptual frames of reference or equivalently systems of thought about how to talk about the patterns of observations that we are making.

 

[DavidWhitbeck]

You know I really think that the word "ontology" should be banned from this discussion! I am getting the impression that the frequency of that word in a post is inversely proportional to the content of the post.

 

[pellman]

This is the subject of Sec. 9.

And we'll get there even if its just you and me. But hopefully the success of this thread continues with each myth.


Ken G,

I agree that we don't necessarily require an ontological understanding of "what's really going on" underneath the wave function. But saying that really means just regarding the wave function and the equations of motion as purely an algorithm, a cookbook, a means of getting the right expectation values for our measurements and nothing more. Deliberately refusing to understand reality though doesn't quite seem in harmony with the scientific spirit to me.

However, there is a quite practical reason for going further. To formulate hypotheses scientists use mental models of the phenomenon they are studying. Once we have a working theory, like QM, it is true that we know longer need the mental models. We can just put numbers into the theory and look at the answer. But to progress ... then we have to attempt an understanding at different level, simply because that's how human brains work.

And doesn't it seem reasonable to expect that we will have a better chance at progress-- that is, developing better calculational predictions--if our models more closely match the reality?

 

[reilly]

As the great jazz artist Les McCann put it, "tryin' to make it real, compared to what?"

As a physicist, I assume the external world is real. If it's not, I really don't care, as I'll never know the truth. So far the assumption has worked for me.

As a jazz musician I think the soul and passion of music is real, I think the inner truth within many accomplished jazz- and classical -players is real. Why not? Certainly such a stance is very helpful for playing gigs.

Les McCann got it right.
Regards,
Reilly Atkinson

 

[Maaneli]

The utter and complete relationality of what is 'real' extends to the ontologies that we establish inter-subjectively. Current physics is an excellent example of seeing 'reality' dissolve under analysis. In fact it makes excellent sense to say there is no physical reality, in the sense that you defined as that which simply exists in the world independent of our sensory observations and experiences of it. There are no quarks, or solitons or clouds or rain or stars in the sky save for our collective conceptual designations of recurring patterns of the arising of the 'real'. It is these designations that constitute the ontologies that are operational among of group of people - some of whom may self identify as scientists.

Thanks for trying, but no cigar! Your philosophy is quite superficial. If you or I or anyone else goes into the same or different laboratory and measures the charge of an electron in vacuum, they will all measure the same value within experimental errors. That right there is an example of something that is objectively real. And you also seem to misunderstand what quarks, solitons, clouds, etc., are when you say none of them are 'real'. I made this point earlier that these are ontological models of physical reality, i.e., approximations (but pretty damn accurate ones) of what there really is in the world - Bell called them maybeables.

In the olden days science was an activity striving to achieve a view of that which is from a vantage point outside the 'real'.

It still is, on the average, striving towards the real, especially among the leading high energy field theorists. Haven't you ever read Weinberg's article, "Against Philosophy"? It really should be retitled "Against Positivism".

It is increasingly clear that trying to look behind the veil is not the most effective way of doing science.

Nope, wrong. You have no (nor have you even tried to give any) rational basis for making that claim.

Schrödinger and Heisenberg had two different ontologies for the same observations that were then extended by Dirac and then Kline-Gordon, Feynman and so on. These ongoing shifts in view are not nailing down that-which-is independent of our view of that-which-is and what observations we can make and want to make for whatever purposes.

This account of the relations between the various standard formulations of quantum theory is confused. In the first place, the Feynman and Schrodinger (and especially the Heisenberg matrix mechanics) formulations actually never had any clear physical ontology on their own to begin with. You know why? Because they could not account for 'measurement' processes!

I would agree that there are always at least as many ontologies at play as there are people doing physics, if by ontology we mean conceptual frames of reference or equivalently systems of thought about how to talk about the patterns of observations that we are making.

Nope, disagree. I would invite you to study Bohmian quantum mechanics vs orthodox quantum mechanics as a counter example to your belief.

 

[Maaneli]

Let me also add that I find it disappointing that you physicists who are logical positivists and refuse to try and understand how well your theories actually relate to an objective physical reality, don't seem to recognize how anti-intellectual and lazy you are with respect to your own discipline, and science in general. In fact, it is the same exact kind of anti-intellectualism and laziness exuded by high school students who are just obsessed with memorizing algorithms and formulas to get good grades on tests, and not caring about what the formulas actually mean or why the algorithms actually work. These students would say that it doesn't help them to struggle and take their time to actually *understand* the crap they need to remember for the test, because that actual hard thinking isn't likely to help them to get good grades, which is ultimately how they get scholarship awards and good college admissions. Likewise, you positivists think exactly the same way; just replace the tests with laboratory experiments, and grades with experimental predictions. Otherwise, it is pretty much the same situation. And that's not at all respectable.

 

[Ken G]

The word "ontology" is certainly causing a lot of problems. I have been using the philosophy meaning, which, from Wikipedia (http://en.wikipedia.org/wiki/Ontology), is described as:

Ontology has one basic question: "What exists?"

And other questions that may relate to science are:

What is existence?
Is existence a property?
What does it mean to say something does not exist?
What is an object?
Can one give an account of what it means to say that an object exists?
What constitutes the identity of an object?
When does an object go out of existence, as opposed to changing?
What features are essential, as opposed to merely accidental, attributes of a given object?
What are an object's properties or relations and how are they related to the object itself?

Frankly, I don't see a single question on this list that physics requires being bothered by. Indeed, the proponents in this thread don't seem to mean much by the term at all, as when it is convenient they use "ontology" to mean nothing beyond "making models", whereas at other times, they seem to chastise physics for not trying to be more than it is actually capable of (making models).

Certainly, we all believe that something exists, and we believe that we are learning about that something when we do physics, but there is zero need for physics to specify what that something is, and imagining otherwise has quite often been detrimental to the advancement of physics over its history. Physics has no need to specify or determine what is real, it only needs to successfully model it, in accord with the needs of the situation. I can't imagine why anyone would think physics is something different from that.

 

[Ken G]

Deliberately refusing to understand reality though doesn't quite seem in harmony with the scientific spirit to me.

The issue is what the word "understand" means, and what it does not mean. What it does not mean is "penetrating to the truth of existence", i.e., ontology. What it does mean is unifying whatever familiarities we have obtained by taking certain projections of reality. The projections are taken via objective observation, the unification is obtained via making models. It's just that simple, why should we pretend physics is anything different from what it is?

To formulate hypotheses scientists use mental models of the phenomenon they are studying. Once we have a working theory, like QM, it is true that we know longer need the mental models. We can just put numbers into the theory and look at the answer. But to progress ... then we have to attempt an understanding at different level, simply because that's how human brains work.

I agree with all of that, and see it as entirely consistent with my above description of what physics is.

And doesn't it seem reasonable to expect that we will have a better chance at progress-- that is, developing better calculational predictions--if our models more closely match the reality?

How does one know how "closely" our models match reality? You can come up with a series of models for an elephant, and each may come closer than the last to matching, almost exacty, the shadow an elephant makes on the ground. But even the convergent model might have very little at all do with a real elephant.

 

[Ken G]

Let me also add that I find it disappointing that you physicists who are logical positivists and refuse to try and understand how well your theories actually relate to an objective physical reality, don't seem to recognize how anti-intellectual and lazy you are with respect to your own discipline, and science in general.

What I find disappointing is how little some people have learned from the history of science. Over and over, scientists have made the mistake of thinking they were doing ontology, and determining what exists, the very makeup of the universe. They did it when they thought the universe was composed of four basic elements, but they later found that was false. They did it when they thought the heavens revolved around the Earth, but they later found that was not its structure. They did it when they thought that matter was atomistic, but they later found that fields were as important as particles. They did it when they thought reality was deterministic, and later found limited usefulness of the concept. And now they do it when they think alternate realities are spawned by the need for the "universal wave function", that untestable and unknowable entity, to evolve unitarily because the systems we objectively observe do. And they still, apparently, think they are doing ontology. Man, some people are just very slow to get the message: all we are doing is making models. We are only smart monkeys, for heaven's sake-- it's amazing how well we do at all.

As for "intellectual laziness", there is nothing more lazy than to assume that one's current understanding is what "really is". A far more challenging, insightful, and promising approach is to always look for why one's current understanding is vastly lacking, and why "existence" is actually so much more inscrutably profound than dreampt of in your philosophy. Some bard said that better.

 

[reilly]

Let me also add that I find it disappointing that you physicists who are logical positivists and refuse to try and understand how well your theories actually relate to an objective physical reality, don't seem to recognize how anti-intellectual and lazy you are with respect to your own discipline, and science in general. In fact, it is the same exact kind of anti-intellectualism and laziness exuded by high school students who are just obsessed with memorizing algorithms and formulas to get good grades on tests, and not caring about what the formulas actually mean or why the algorithms actually work. These students would say that it doesn't help them to struggle and take their time to actually *understand* the crap they need to remember for the test, because that actual hard thinking isn't likely to help them to get good grades, which is ultimately how they get scholarship awards and good college admissions. Likewise, you positivists think exactly the same way; just replace the tests with laboratory experiments, and grades with experimental predictions. Otherwise, it is pretty much the same situation. And that's not at all respectable.

Sorry, I'm more or less a logical positivist -- and I was and am a theorist and teacher, who made sure my students understood the material. Further you insult my sons, all three of whom worked very hard in high school and did well, thank you very much.

If you are into screeds, at least get your facts right.
Reilly Atkinson

 

[reilly]

What I find disappointing is how little some people have learned from the history of science. Over and over, scientists have made the mistake of thinking they were doing ontology, and determining what exists, the very makeup of the universe. They did it when they thought the universe was composed of four basic elements, but they later found that was false. They did it when they thought the heavens revolved around the Earth, but they later found that was not its structure. They did it when they thought that matter was atomistic, but they later found that fields were as important as particles. They did it when they thought reality was deterministic, and later found limited usefulness of the concept. And now they do it when they think alternate realities are spawned by the need for the "universal wave function", that untestable and unknowable entity, to evolve unitarily because the systems we objectively observe do. And they still, apparently, think they are doing ontology. Man, some people are just very slow to get the message: all we are doing is making models. We are only smart monkeys, for heaven's sake-- it's amazing how well we do at all.

As for "intellectual laziness", there is nothing more lazy than to assume that one's current understanding is what "really is". A far more challenging, insightful, and promising approach is to always look for why one's current understanding is vastly lacking, and why "existence" is actually so much more inscrutably profound than dreampt of in your philosophy. Some bard said that better.

Well said; those who neglect history are bound to repeat it.
Regards,
Reilly

 

[Ken G]

I should probably consider your specific points, as there is a lot of physics in them and I don't want to seem like I'm ducking any issues here:

You don't see how the configuration space of the classical Hamiltonian or the Gibbs distribution is not the physically real space we live in?

Correct. Indeed, string theorists have already reached that conclusion (which doesn't matter to me, I would say that anyway).

You don't realize that we observe 3 spatial dimensions and therefore live in 3-space at the length scales of classical Hamiltonian and statistical mechanics?

What do you mean "at those length scales"? Existence is now different at different length scales? That doesn't sound like existence to me, but it sure sounds like a model.

Something must be wrong with your senses and your detectors!

There is definitely something wrong with my senses and my detectors-- they are limited by my intelligence to build, apply, and interpret. Yes, they are greatly limited. Why do you think a recognition of the limitations of my detectors should convince me I should be seeing the true nature of reality? I agree that I am missing the true nature of reality, indeed that is my whole point.

As for defining 'real', that is simply what exists in the world, independent of our sensory observations and experiences of it.

If it is independent of our observations and experiences, how do we use science to find out about it? We have to interact with it to model it, and that's not an "independence", it's an interdependence. We are of course completely oblivious to anything that is real but that does not show up in any of our detectors, that's independence.

Any conceptually consistent physical theory makes some statement about realism.

No, theories make no such statement. Philosophers do, if they choose to. The theory doesn't care, it's just a model, that a philosopher may choose to hang labels like "realistic" onto.

There exists no self-consistent theory that only describes a subjective world of events.

That's just another ontology, and equally irrelevant.

Indeed, if you really give time to think about it, it doesn't make philosophical or logical sense to say there is no physical reality.

Who needs to claim there is no physical reality? I certainly don't, I'd rather make no statements about physical reality at all other than characterizing my interaction with it. There would be no point in using definitions that made there be no such thing as physical reality.

Also, I should ask you, what is your purpose for doing physics or science in general?

It's similar to why an art lover would spend time looking at a painting. No ontology there either.

What are theories trying to talk about, if not an objective physical reality?

Saying that theories are about reality is not providing them with an ontology. Paintings are about reality too. Where is the "existence" you see in a painting? The issue is, we are trying to understand about what exists, but we never need to think our models are what exists. The latter is the goal of ontology, and is unnecessary and even distracting in physics.

A clear physical theory, such as Newtonian mechanics, makes a claim about the physical ontology of the real world.

No it does not, it is a model.

A CLAIM about what actually exists in the world is not the same as what ACTUALLY exists in the world!

True, but where do you see the need to make that CLAIM at all? Why would we make claims we know are not true, especially when we don't need to?

Now tell me Ken G, what is the purpose, in your mind, of a physical theory?

A fair question, I think I answered it but to repeat: the purpose of a theory is to unify the familiarities we obtain via objective observation of reality. When we unify those familiarities, we gain power to function, and also power to make new fruitful concepts, and new tests that generate new familiarities. Existence appears nowhere in the equation, it's just hubris and we should know better by now, frankly.

Then ask yourself, what do you understand "explanation" to mean?

I presume you see that I have answered that now.

The belief that there is an "actual ontology" certainly is crucial to science.

Really? Why? I see ontology as something that lives in the head of a philosopher, why does there need to be an "actual" one?

But that doesn't mean we can ever perfectly describe it!

We are well aware that we cannot, as to assume otherwise is more preposterous than anything I can imagine, so the real issue is, do we need the concept at all? I certainly don't see why.

I don't think you understand what I mean by the measurement problem. First off, it is a problem not in experimental practice, but rather in understanding. I would challenge you also by asking you what you understand the word "measurement" to mean?

Measurement is opening a system by confronting it with a device that introduces untracked noise modes, the result of which is to produce an outcome that can only be predicted in a statistical way or within some error range. The type of decoherence that occurs is part of choosing the device, and will determine the eigenstates of the measurement. There is no scientific reason to try and include the observer in the observed system; indeed, it is the core of science (objectivity) to not do so. Now, what was the problem again?

Well I resent the word illusion, but yes I definitely can give historical examples of how ontology directly led to a new discovery. In fact, any competent student of history of physics can. Einstein's argument for Brownian motion relied on the assumption that there really are unobservable atomic particles in 3-space that bombard larger observable particles (e.g. pollen grains), and induce a random walk.

Yes, he used a model. Physicists use models, I am actually aware of this fact. I still see no ontology there-- did Einstein need to hold beliefs about pollen grains to form his testable hypothesis? Was he "taking a side" in some philosophical debate about reality, or just doing an experiment and interpreting it via a better model? And the limitations of that model would be discovered in short order. So it is in physics, no ontology needed.

This was in contradiction to Ernst Mach's belief that atoms do not exist as objectively real entities.

Physicists need "beliefs" now? That's the whole point-- they don't. Mach was silly to say he "believed" anything about matter, he could have just suggested a model for it. That's the scientific thing to do.

I can also cite you the example of Schroedinger's derivation of his wave equation, which stemmed from the objective experimental observation that electrons appear have a wavelength.

So now you are pointing out that observations lead to axiomatic structures that unify them? Yes I realize that also. I still see no ontology there.

Schroedinger indeed derived it with the belief that he was describing what about the electron that is really 'waving'.

Again the "belief" word. It just shows the error in mixing philosophy and physics. Why did he need any belief, it was just a testable hypothesis.

Heisenberg, on the other hand, who had your philosophy of science, could only come up with his obscure Matrix mechanics.

You have not shown that Heisenberg's philosophy of science was the problem here, perhaps it was just his approach. He did, after all, meet with some modest success in the field. And the Heisenberg representation of putting the time evolution in the operators instead of the wave functions is a beautiful example of the power of not thinking ontologically. That approach has great value at times, this is the point-- free your mind from ontology, and it only opens the options for how to picture the world.

There is also Maxwell's derivation of the velocity distribution for classical particles in the kinetic theory of gases. There is also Boltzmann's discovery of his H-theorem with regard to the 2nd law of thermodynamics. None of this could likely have been possible without them thinking about what the ontology of the physical world is.

No, those are all perfectly possible to think of purely as models. The proof of that is they will still be taught in school long after their ontologies are falsified.

As soon as "you" "decide"? Who the hell are you, and when do you decide this?

I am the physicist using the wave function. Who else would need a wave function? Reality itself, you think?

It would seem that the theory [quantum mechanics] is exclusively concerned about "results of measurement", and has nothing to say about anything else. [/quot]I certainly don't think that. It has a lot to say about something else: reality. But that does not require that we ignore the fact that we have chosen a particular mode for understanding reality, and that mode is what involves measurements, and we can learn nothing about reality that does not result from that choice. It is as though some physicists don't even realize there are other ways to learn about reality than doing physics!

Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system ... with a Ph.D.? If the theory is to apply to anything but highly idealized laboratory operations, are we not obliged to admit that more or less "measurement-like" processes are going on more or less all the time, more or less everywhere.

Obviously. I agree with Bell, and see no relevance at all to my remarks in this thread, or my stated views about what either science or measurement is (which are just what they are).

I take it you have never read or understood John Bell or his theorem.

Wrong.

Um, hello, this statement you make IS a statement about ontology!

This is in response to my statement "we will choose to treat the world using a model comprising of point particles." I'm sorry, but I cannot agree that that is a statement about ontology. To me, adopting a model for its predictive and explanatory value is hardly the same thing as a statement about what exists. But as I said, if you equate the word "ontology" with the phrase "making models", then there's no disagreement. However, often you appear to mean more than that, as the word itself suggests.

 

[Ken G]

Perhaps I should clarify at this point that the purpose of this exchange is to bring out certain truths, and its structure is that of a kind of point/counterpoint debate. For the record, I do not think the opposing views are those of any fool, indeed they are the views of someone knowledgeable. Furthermore, as acting physicists we all slip into imagining existence in certain ways, as a kind of mental shorthand, and it serves us well. I'm just saying that this thread is all about whether or not wave/particle duality should be viewed as a myth, and that's a very ontological issue, so we want to look carefully at the pros and cons of thinking ontologically. At the very least, we need to be able to catch ourselves when we are mistaking our chosen beliefs for what we do as scientists. I see that a lot.

 

[Maaneli]

Ken G and Reilly,

I'm sorry, but you two have misunderstood quite a number of issues here. I will explain what exactly when I get the time to.

As for your kids Reilly, you should really learn to read more carefully before getting offended. If they were the kind of students who actually cared to understand the crap they were memorizing, rather than just getting good grades, then clearly I wasn't talking about them. I was talking about kids who ONLY care about grades. And if you're a logical positivist, I'm sorry to say that I really have my doubts that you really let you're kids understand the science they were learning. I have had countless encounters with positivist scientists and science educators, and have found every one of them for the most part, antieducational and oppressive about asking deeper questions.

 

[reilly]

Ken G and Reilly,

I'm sorry, but you two have misunderstood quite a number of issues here. I will explain what exactly when I get the time to.

As for your kids Reilly, you should really learn to read more carefully before getting offended. If they were the kind of students who actually cared to understand the crap they were memorizing, rather than just getting good grades, then clearly I wasn't talking about them. I was talking about kids who ONLY care about grades. And if you're a logical positivist, I'm sorry to say that I really have my doubts that you really let you're kids understand the science they were learning. I have had countless encounters with positivist scientists and science educators, and have found every one of them for the most part, antieducational and oppressive about asking deeper questions.

You don't have a clue how I raised my kids; your inference is just plain wrong. You don't know me; you don't know my kids, nor my grandkids for that matter. So how could you deduce how I raised my kids?You are effectively doing a Joe McCarthy -- guilt by association.(Where did you get your degree?)

Tell you what: I'll read more carefully, if you write in a more measured style, which means you eschew ad-hominum attacks, and red flags, and discuss physics.

I await, with baited breath, your explanation of what I and Ken G do not understand. Ken, at least, is a pretty smart guy who does not miss much, so let 'er rip.
RA

 

[reilly]

If the wave function collapses due to a change of information available about the system (which the classical electromagnetic field does not do), then it seems that the wave function does not represent reality, but only our information about reality. Unless, of course, you are an extreme positivist who identifies information about reality with reality itself.

Could not agree more.
Regards,
Reilly Atkinson

 

[Ken G]

I await, with baited breath, your explanation of what I and Ken G do not understand. Ken, at least, is a pretty smart guy who does not miss much, so let 'er rip.

Thanks for the vote of confidence, I wouldn't claim that for myself but I'm sure I have something to learn from any exchange. Nevertheless, I am even surer that neither myself nor Reilly are "antieducation" or "hesitant to ask the deep questions". Rather, I think we are believers in education around not just what the conclusions of science are, but also, how science arrives at those conclusions and what counts as authority in science. That is often the more important form of education, both for people who will do science themselves, and for those who won't.

 

[peter0302]

Reilly, you need to chill and stop being offended because something someone says implicates you in your own mind (similar to my comment a few weeks ago). He's making very valid points about positivists and I too wonder, if you teach your students in the same fashion as you argue your points here, if they are actually doing more than memorizing equations. That's all that half of the people on this forum seem to advocate. I do not understand why we cannot find a middle ground; let the quantum cooks be cooks and let the dreamers dream.

 

[reilly]

Reilly, you need to chill and stop being offended because something someone says implicates you in your own mind (similar to my comment a few weeks ago). He's making very valid points about positivists and I too wonder, if you teach your students in the same fashion as you argue your points here, if they are actually doing more than memorizing equations. That's all that half of the people on this forum seem to advocate. I do not understand why we cannot find a middle ground; let the quantum cooks be cooks and let the dreamers dream.

This is getting funny and silly, and way off of physics -- perhaps you and manelli are telepathic, and that's how you know what I think and how I behave, with my kids and my students.

.
As in; I once knew a Peter who was a drunk; are you? After all, your name is Peter.

And, back to physics: tell me how I argue my points? I'm particularly amused by your assertion that my students may have been memory hounds; what's your basis for making your assertion?
Regards,
Reilly Atkinson

 

[peter0302]

Well, some would call me a drunk.

All I (and manelli, I think) are saying is that tunnel-vision positivism can be counterproductive and can be analogus to memorizing the equations to the exclusion of understanding them. Since you're a very vocal positivist and a teacher, I can only infer that your positivist philosophy extends to your lecutres as it does to your posts here.

Anyway, I don't think this should be personal. I just don't think anything was said here that should offend anybody (except calling me a drunk...

 

[Ken G]

All I (and manelli, I think) are saying is that tunnel-vision positivism can be counterproductive and can be analogus to memorizing the equations to the exclusion of understanding them.

I don't know what "tunnel-vision positivism" means but memorizing equations with no concept of what they mean certainly doesn't sound very good. Fortunately, no one ever gets past freshman physics by doing that, so I hardly think it could apply to anyone on this thread. I think you may be confusing the "meaning" of an equation for philosophical baggage around what is "happening in reality". What "meaning" means is, you understand how an equation culls out a successful way to analyze a problem. All philosophical baggage does is to confuse "success" for "beliefs about reality".

Physicists do need to understand, explain, and find success-- the only faith they need is that their equations will be predictive so they are not wasting their time. They certainly do not need to "believe in wave functions" to do quantum mechanics, that's ludicrous. But my question is, if I can use a wave function without "believing in it", why I am I just memorizing equations? And if I pray to the altar of MWI, why can't I just be someone who has memorized what unitarity means? Is there someone on this thread with an insight into unitariness that transcends memorizing its defining characteristics, such that you can say "I'm not memorizing any mathematical postulates or any experimental outcomes, I really see why the world has to obey the MWI?" I'm all ears.

Since you're a very vocal positivist and a teacher, I can only infer that your positivist philosophy extends to your lecutres as it does to your posts here.

What do you mean by "positivist"? Let's not have the "ontology" debacle again!