What is the wave function about?

bohm2

So in your version, like in Bohm's, the wave function itself is not enough to account for the existence of objects like cats, tables, etc. You also posit the existence of "particle-like entities" existing in 3-D space (or space-time) that are constrained by the wave function? So your version is unlike Everett's or GRW, where the wave function is everything since you also make use of a particle-like entity (something that lives in 3-D space/space-time)? Or am I misinterpreting you?

apeiron

Do you think that MWI or GRW are particle-less ontologies? That is not my reading at all. One assumes branching world histories for particles, the other the spontaneous collapse of wavefunctions to create fully-determinate particles. But neither does without particles.

Personally, I don't hold to some single interpretation of QM. I don't think we are there yet.

But I most like a consistent histories approach mixed with elements of decoherence and transactional interpretations. And as I say, the more general systems view of "particles" that would derive from an analogy with the solitons or quasi-particles of condensed matter physics.

So cats and tables are constructed of particles which are pretty definite objects - degrees of freedom trapped early in the big bang by the rapid cooling/expansion of spacetime. Electrons and protons don't seem likely to decay at current ambient cosmic temperatures and scales.

There is a history of constraint that locks these particles into place. But then there is still a fine-grain quantum uncertainty concerning their identity and interactions. At the level of cats and tables, this fuzziness is pretty irrelevant. But at the fine scale of observation, it is still part of reality.

So the division of particle vs wavefunction seems only to distinguish the aspects of a locale that are strongly determined by prior history and the aspects that remain faintly indeterminate. The "surprise" is that this allows in "retrocausality" (as in quantum eraser experiments) and other kinds of non-local weirdness.

This implies that spacetime and causal locality/determinism are in fact emergent features, not fundamental. But clearly, that is the ontology I have been arguing for all along.

So yes, we live in a classical 3+1D world in which a void is populated by particles. But that is the emergent view. The deeper view is the systems one which describes emergent objects (and the vacuum is also such an object) as the product of local degrees of freedom in interaction with global constraints.

bohm2

In MWI and the original version of GRW, it was claimed that anything beyond the wave function itself is kind of superfluous, unlike in Bohm's where you have both spaces (3-space and 3-N space). If one takes this view that the wave function is everything then, there's a problem:

Since the proposal is to take the wave function to represent physical objects, it seem natural to take configuration space as the true physical space. But clearly, we do not seem to live in confguration space. Rather, it seems obvious to us that we live in 3 dimensions. Therefore, a proponent of this view has to provide an account of why it seems as if we live in a 3-dimensional space even though we do not. Connected to that problem, we should explain how to "recover the appearances" of macroscopic objects in terms of the wave function.

Primitive Ontology and the Structure of Fundamental Physical Theories

http://www.niu.edu/~vallori/AlloriWfoPaper-Jul19.pdf

apeiron

Your core question seems to be about the reality of particles and wavefunctions, and hence about the reality of the two difference spaces they inhabit.

There would seem to be three general stances on the question of realism.

1) Something is real - it actually exists in the ontic sense.

2) Reality is an illusion - it is a picture we invent as a result of our instrumental models.

3) Reality is emergent - in this view, things don't "exist" in some brute a-causal fashion. Instead they are the emergent results of some causal process, so at best can be said to be "real persistent features".

Our instrumental models are mostly reductionist, so describe the emergent in terms of the actual. In terms of their limit states.
The upshot of this is that our models are "illusory", but only very slightly when a system is in a high state of development. A process is close enough to being crisply real when it is asymptotically close to its limits.

I of course have been defending (3), the process philosophy and systems science view.

When it comes to particles, I say they are real in the sense of solitons. They are knots locked into spacetime by a fabric of constraint. Which in turn throws the burden of realism onto spacetime itself. The 3D vacuum, or what Wilczek calls condensates, is what has to be explained first. The N particles are further definite degrees of freedom it is true - but ones that "exist" at a logically higher level of the hierarchy of "existence". They are not part of the fundamental degrees of freedom that define naked spacetime condensates.

When it comes to wavefunctions, these now are just instrumental descriptions (though they refer to something real about the world of course). Every so-called particle - and even point of spacetime - has an irreducible fuzziness. At least under the right "viewing conditions".

The vacuum and its trapped knots look strongly like a void populated by particles (with inertial spins and boosts) when spacetime is large and cold. The process that produces 3-space is asymptotically close to its limit. But change the scale of observation to the small/hot and both the particles inhabiting the vacuum, and even the vacuum itself, have their constraints relaxed, so gaining (or re-gaining) extra degrees of freedom. The wavefunction then measures these regained freedoms against the "fictional" metric of configuration space.

For configuration space to be real, we would have to have a world entirely without constraints. In Peircean terms, that would be a state of vagueness. And indeed, vagueness is populated by an infinity of degrees of freedom. The difference is that they would not be organised into "particles". So this would be much larger than a 3N space. And in fact a completely diffuse realm in which nothing could be described as actually located to a point in a realistic sense.

In practice then, wavefunctions seemed anchored to individual locations or paths in spacetime. They are evolving "loosenings" of emergent objects in an emergent 3-space. There is no fully realised configuration space inhabited by wavefunctions that exist in a non-collapsed way as envisaged by, say, MWI. Configuration space is just a concept of a general metric for measuring all these localised, passing, "loosening of constraints" against.

I think this paper from Lewis is a good analysis of the difficulties of treating configuration space as real.

bohm2

I read over the Lewis-Monton debate on this topic and found it pretty interesting. Monton goes as far to suggest that QT is a false theory because it can never be reconciled with general relativity. He is critical of both Albert's ultra-realist notion of configuration space and even Lewi's attempts to defend some aspects of wave function ontology (by trying to interpret "dimension" in non-spatial way). Monton is also not sympathetic to any attempts to try to get emergence of 3-D space from 3N-D space as suggested by Wallace and Timpson (2009). What's surprising is that even among Bohmians there are 3 different interpretations of Bohm's theory with respect to interpretations of the configuration and 3-D space:

1. Albert: Bohmian physical objects are represented by wave function consisting of a particle and its field evolving in 3N-D space.

2. Allori, Durr, Goldstein, Zanghi: physical objects are described by particles evolving in 3-D space while the wave function is an abstract entity that serves a nominalist function (a law of nature) that specifies how the objects in 3-D space evolve.

3. Bohm and Hiley: There are 2 different physical substances: particles in 3-D space and an abstract informational field that lives in configuration space (dualism at the primitive level).

And the Orthodox (Copenhagen) has arguably similar, if not greater problems:

It is interesting to note that even the orthodox quantum theory (OQT, the theory originally proposed by Bohr in which there are two separate worlds: a classical and a quantum one) involves such a dual structure: what might be regarded as its primitive ontology is the classical description of macroscopic objects, including in particular pointer orientations, while the wave function serves to determine the probability relations between the successive states of these objects. In this way, also in the case of OQT, the wave function governs the behavior of the primitive ontology. An important difference, however, between OQT on the one hand and the other theories on the other is that in the latter the primitive ontology is microscopic while in the former it is macroscopic. This makes OQT rather vague, even noncommittal, since the notion of 'macroscopic' is intrinsically vague: of how many atoms need an object consist in order to be macroscopic? And, what exactly constitutes a 'classical description' of a macroscopic object?

This stuff is really confusing the hell out of me.

http://www.niu.edu/~vallori/Allori-O...mMechanics.pdf

bohm2

I thought some might find this interesting. Maudlin writes:

On this topic, Monton traces Schrodinger’s attempt to try to reconcile the difficulty of mapping the 3N-dimensional space of the wave function with our experienced 3-dimensional space. He wants to treat the wave-function as physically “real” in order to explain interference effects but encounters difficulties when going beyond one-particle systems:

And Schrödinger does explicitly consider the possibility that the ontology for quantum mechanics involves a 3N-dimensional space. In fact, one might think that he is endorsing that ontology in a 1926 article, when he writes:

The true mechanical process is realised or represented in a fitting way by the wave processes in q-space [where “q-space” is Schrödinger’s terminology for “configuration-space”

But Schrödinger makes this claim in the context of a discussion of one-particle systems, where configuration space is just three-dimensional space. So what would he say about a multiparticle system? Schrödinger considers a two-particle system late in the paper, but has only one sentence about the physical representation of the six-dimensional wave function:

The direct interpretation of this wave function of six variables in three-dimensional space meets, at any rate initially, with difficulties of an abstract nature.

Schrödinger kept trying to develop an ontology for the wave function – there’s a long and interesting story here, but to present it all would be outside the scope of this paper. The short version of the story is that Schrödinger was looking for a way of having the wave function be a mathematical representation of physical processes in three-dimensional space. For example, Schrödinger wrote a letter in response to Lorentz’s, in which the first point he addresses is the issue of the multi-particle wave function. He writes:

I have been very sensitive to this difficulty for a long time but believe that I have now overcome it.

Schrödinger kept working on this project for a while, but by 1935 he had given up. He wrote:

I am long past the stage where I thought that one can consider the wave-function as somehow a direct description of reality.

For the record, it’s unclear to me to what extent Schrödinger gave up on the project of considering the wave function as a direct description of reality because of the measurement problem, and to what extent he gave up on the project because of the issues of interpreting the 3N-dimensional wave function as representing something existing in real, three-dimensional space. It’s clear though that Schrödinger was not willing to endorse the view that the space of reality is 3N-dimensional. (Monton in against 3N-Dimensional Space).

http://spot.colorado.edu/~monton/Bra.../Articles.html

apeiron

Schroedinger was certainly a good systems thinker.

On the 3-space vs q-space issue, isn't it simply that 3-space is our map of actuality (even if it is an emergent actuality) and q-space is our map of possibility (the ground from which actuality emerges)?

The ontic issue you seem to be banging your head against is the question of which is fundamental. But a systems approach says the dichotomy is what is fundamental - the fact reality is bounded by its two limits of the actual and the possible. From an emergence point of view, you need both to have anything.

And more generally, the whole QM interpretation game seems to be centred around two equally bad motivations here.

1) The urge to recover "primitive ontology". A strong belief that reality is composed of material objects and is ruled by locality, determinism, etc, leads to all sorts of contortions of thought to recover this view through an interpretation such Bohmian mechanics.

2) The urge to assume the least ontology. The other route is embrace the interpretation "with the least extra bits". Which leads to ontological idiocies like MWI. Or epistemic hairshirt positivism like Copenhagen.

The third response, as I see it, is to first accept reality is going to be radically different from the "primitive ontology" of mechanics. So quit trying to fix QM to make it look completely local, material and deterministic. And then also accept that a new ontology is going to be quite complex, with a lot of subsidiary bits (at least until it becomes so familiar that the supporting notions "go without saying").

The interpretation problem is far bigger. A new ontology of reality has to unite QM, GR and thermodynamics (and note that Schroedinger did blaze the trail here). Tackling just one arm, like QM, in isolation is a wasted effort.

I suppose the focus is on QM because that is seen as the fundamental theory. But that again is just a presumption of "primitive ontology" thinking, which likes to privilege the "smallest scale" of action in any causal discussion.

bohm2

I don't agree with your assessment of Bohm's interpretation. Non-locality plays a prominent role in Bohm's interpretation. The dichotomy you mention is also fundamental in Bohm's interpetation (although it's set out somewhat differently). Furthermore, the "wholeness" and bi-directional causality (between global and micro) also plays a prominent role in Bohm's interpretation (hence the title of their book "Undivided Universe"). As Maudlin writes, in assessing Bohm's interpretation:

But even with these inclusions difficulties arise in Bohm's scheme from my understanding of it. A kind of mind-body interaction problem at the micro level re-appears. How can an abstract information field that seems to represent hypothetical trajectories (potentialities) push around particles? The only option they argue, is to treat the wave function as some kind of "real" object but exactly what that means is unclear? Furthermore:

.

http://courses.cit.cornell.edu/north/QM_for_volume.pdf

apeiron

There are actually many critical differences here.

A key one in the systems perspective is precisely that wholeness is built on a micro~macro (or rather, local~global) divide. So the fundamental dichotomy is not the implicate realm (the as-yet undivided bit). It is what gets made crisply explicit. The holism lies in the local~global relationship that emerges as a result of a broken symmetry, not the underlying ground of potential.

The logic can sound similar, but it is very different. Bohm says the information organising the world is hidden at a more fundamental level. The systems view is that the information organising the world emerges in the form of its developing global constraints. The information is explicit (which is why there is no problem of how there is an interaction).

And then there is Bohm's desire to find "mind" at the fundamental level. Consciousness is a complexly emergent thing and has nothing at all to do with fundamental physical reality (at least IMO, though I agree there are systems scientists and many others who still want to somehow wrap the mysteries of mind into the mysteries of fundamental existence).

So a systems/semiotic approach focuses not on "information stored at a hidden implicate level" but instead on the information that is explicit in a system as a product of its developmental and evolutionary history. The information encoded by genes, words, membranes, synapses and other such biological machinery. Information that has nothing to do with QM levels of description.

bohm2

I'm having trouble understanding this. Doesn't that go against your point that "the wholeness is built on a micro~macro (or rather, local~global) divide"? Doesn't bi-directional causality imply that the QM levels of description are also important on the global level? I mean, is there no trace of the micro level at the global scale? I still don't understand how specifically the systems approach explains the results of the two-slit experiment? More generally, how does possibility become actuality in your system?

apeiron

As was discussed previously, a dichotomy is defined by being mutually exclusive, jointly exhaustive. So that is a very particular logical claim. It means there should be "no trace of the other" at the complementary poles of description.

Take any standard metaphysical dichotomy such as discrete~continuous, to be discrete is not to be continuous, and vice versa.

So the usual reductionist notion of a hierarchy is that it is composed of "more of the same". The macro is just a whole bunch of the micro glued together.

But the systems view - well, at least my view of it based on Anaximander, Hegel, Peirce, etc - is that the local and global levels have this dichotomous logic. The global scale is not more of the same, a bunch of locales glued together. Instead it is the antithesis - everything that the local is not. The wholeness then comes in the resulting synthesis of course. When the complementary interacts.

So taking discrete~continuous as an illustrative example again, reality would be a synthesis of these two opposing, but complementary, poles of possibility. And indeed, what do we find? On the micro-scale, reality becomes quantum - it breaks up into discreteness. While on the global scale, it instead smooths over to become GR-style continuous.

You have a situation that the logic of dichotomies actually predicts. A model of the local in QM. A model of the global in GR. And a big problem mashing one into the other to create a quantum field theory of gravity.

So the ontically complementary nature of the local and global - in the manner of Hegelian thesis and antithesis - is one key point here. It is a principle that there will be an absolute separation, as with for instance local degrees of freedom and global constraints when we are talking in terms of causality.

In a system, two things are going on! Both the differentiation (the dichotomous repulsion) and the integration (the holistic equilibrating) are happening together. Again, this maps to reality. The universe both expands (differentiates) and cools (integrates) at the same time. There is interaction between local and global, but it is a complex interaction with two faces itself.

Then there is another vital aspect of systems ontology. That is the development from vague potential to crisply developed hierarchical organisation. Or from raw possibility to definite actuality.

This introduces an ontic category that is entirely missing from reductionism. And possibility becomes actuality by dichotomisation. Local and global are not just labels for the way things are. It is the universal process by which things become definite.

Peirce talks about this in terms of firstness, secondness and thirdness - or synechism - if you want to read up on it.

I'll have a go at applying this to twin slit experiments - the quantum eraser version in particular - in another post.

bohm2

Here’s a very interesting suggestion of combining Bohm's and the GRW model (referred to as BM-GRW in the paper)so that one gets the benefits of both GRW and Bohm’s while removing some of the problems inherent in each model. At the least, it may give one some hints of what is required in a more elegant, "realist" interpretation of QM:

http://arxiv.org/PS_cache/arxiv/pdf/...104.1938v1.pdf

The author is the same one who has recently (with others) developed a Lorentz invariant matter density "realist" model:

http://arxiv.org/PS_cache/arxiv/pdf/...111.1425v1.pdf

bohm2

I thought this was another interesting perspective (to the scheme suggested above) by Antony Valentini (lecture from Perimeter Institute). He basically suggests that configuration space is "real" (like Albert, it seems) and argues that the quantum wave is a new type of "causal" agent that may take some time for us to understand it, in the same way scientists had difficulties accepting the concept of "fields" when they were first introduced. So he sees an evolution (see slides) from forces to fields to this non-local quantum wave (which does not vary with distance and appears to be completely unaffected by matter in between). So in his scheme, the configuration space is always there where the pilot wave (a radically new kind of causal agent that is more abstract than conventional forces or fields in 3-D space) propagates. He seems critical of treating the wave function as nomological (law of nature) as Goldstein/Durr and even Maudlin do. What is interesting is during the questioning (1:11) an audience member questions him about the action-reaction principle violated in this pilot-wave scheme. His answer doesn't appear very satisfying but he suggests that we must get used to thinking of QM as a non-mechanical theory. If you want to get to the nitty gritty in the video just check these times: (17:30, 32:00, 39:00, 1:11):


http://streamer.perimeterinstitute.c...c8/viewer.html

bohm2

I'm not sure if this can be done but I thought these quotes by Einstein regarding trying to reconcile the 2 spaces (configuration and our familiar 3-D space/4-D space-time) as some of the authors(e.g. Monton, Lewis, etc.) above seem to be trying to do is interesting:

http://arxiv.org/PS_cache/arxiv/pdf/...706.2661v1.pdf

ThomasT

bohm2, as I mentioned before, I think you might get more replies (and anyway I'm interested to see how more qm knowledgeable PFer's might respond to your queries) if you post your considerations in the quantum theory forum.

bohm2

I thought it was more philosophy than physics but, I'll try to post something on "The ontology of configuration space" in the QM forum and summarize in more organized form some of the papers that I posted here. I've been kind messed up the past few weeks (e.g more university, work, bills, etc.) and my medication seems to be less effective(no focus, anxiety, etc) so I hope I don't write stuff that makes no sense. Because I've noticed I'm pretty lost, the past few weeks.