I'm happy to trade both locality and realism for contextuality. ;)

So what is causing the pattern is not physical energy but purely probability. — Wayfarer

There is plenty of "physical energy" represented in the experimental apparatus set up to make the quantum observation. So - given my contextual view of causality - the pattern is produced by a narrowing of the space of quantum possibility so that just this particular set of probabilities, as described by the system's wavefunction, remains.

So you are thinking in conventional bottom-up terms of probability spaces having to be constructed from an ensemble of "paths". And that is indeed pretty mysterious.

But I am pointing out how the apparatus represents a further localised constraint on raw quantum probability. Naked space would still have some (vanishingly remote) possibility of fluctuating in a way to produce a hot particle that has to pass through some pair of slits to get to some absorbing surface. But the apparatus exists as something some experimenter has invested time and energy to build. And so some probability space has been given an enduring physical shape, creating an ensemble of paths, as described by a wavefunction.

So my approach is contextual and top down. It fits with the view that the particle isn't "really there". It is contextual probability in the fashion of a soliton or phonon - the trapped excitations of a field, as described by condensed matter physics.

And remember that the excitations of condensed matter physics, these "topological defects", act like quantum particles. The similarity is not analogous but literal.

So your concern is based on the mystery of how probability spaces might arise out of nothing. My contextual approach instead says that probability spaces arise out of the constraint of everythingness. You get crisply "quantum behaviour" after the vague or indeterminate world has become sufficiently constrained so that what is left is the most irreducible aspect of that indeterminacy.

You eventually get down to the point where observables are no longer commutable. You can no longer ask all the definite questions that realism supposes of an event at once.

So the approach I am taking is holistic. World features only have sharp existence due to some localised context of constraints. Existence does not inhere in atoms or substances. Instead, atoms and substances are the end product of a suppression of flux or unbound possibility.

It's the "PBR" paper, and it argues exactly the opposite.

Sounds like something you say in a cult. Never mind me, I never got past understanding how one defines an 'observer' in QM. — Question

I enjoy collecting these fallacies - this one I will call the attribution of religion.

Can things get any more pathetic on a philosophy forum ... probably.

There is no 'observer' under Everettian QM. All physical interactions are treated exactly the same.

Can things get any more pathetic on a philosophy forum ... probably. — tom

I note that you failed to reply on Orzel's points.

You appear not to understand the implications for contextuality of locality.

You appear not to understand the implications for contextuality of locality. — tom

You appear not to be able get beyond chanting Deutsch and MWI in monotonous cult-like fashion.

Regarding that. Is there any distinction between local events and supra-local events in Everettian QM?

No idea what you are on about. All physical interactions are local, having no effect on space like separated regions. Everett respects relativity.

There is plenty of "physical energy" represented in the experimental apparatus set up to make the quantum observation. — Apokrisis

Of course, but what determines the pattern is not the consequence of things being arranged by physical forces, but as a consequence of the emergence of patterns in accordance with the 'probability wave'. So here, probability is acting causally - which is the problem, as probability is not physical.

So your concern is based on the mystery of how probability spaces might arise out of nothing. — Apokrisis

So what I would like to argue is that the 'probability wave' is 'real but not physical'.

In the blog post that Tom pointed to, David Wallace notes that:

And, if cats can be alive and dead at the same time, how come when we look at them we only see definitely-alive cats or definitely-dead cats? We can try to answer the second question by invoking some mysterious new dynamical process – a “collapse of the wave function” whereby the act of looking at half-alive, half-dead cats magically causes them to jump into alive-cat or dead-cat states – but a physical process which depends for its action on “observations”, “measurements”, even “consciousness”, doesn’t seem scientifically reputable. So people who accept the “state-as-physical” view are generally led either to try to make sense of quantum theory without collapses (that leads you to something like Everett’s many-worlds theory), or to modify or augment quantum theory so as to replace it with something scientifically less problematic.

It may seem a subtle point, but what I said was there was no (classically-imagined) particle. There was "an evolving wave of probability of detecting a (classically-imagined) particle that reflects the shape of the apparatus".

So I was trying to highlight the irreducible quantum contextuality of the existence of any "particle". — apokrisis

Fair enough. If you read my earlier posts, I suggested we could question the existence of the "particle", just like we can question the existence of objects in general. Andrew M took exception to this.

While of course there are philosophical issues here, the fact is that most people reasonably do think that many things exist and also think that standard scientific explanations are applicable to those things. So that really needs to be the starting point for any meaningful discussion. — Andrew M

As you describe, apokrisis, the particle exists only in the context of the apparatus. Now, we assign a larger context of "existence" in general to the apparatus, and this is supported by its relationship to other things, and in particular, the observer. So the existence of the particle is supported by the existence of the apparatus. If we remove this assumption, that the apparatus exists, then it follows that the particle no longer is assumed to exist. In order to understand the existence of the particle therefore, it is necessary to justify the "existence" of the apparatus, and this is to formulate an understanding of what it means to exist as an object.

One of the comments on the above blog posts is:

David’s point (or my understanding thereof) is that the wave function serves the same role in explaining where the photon hits the plate as dinosaurs serve in explaining where fossils come from — namely, you can’t do without it. It’s a crucial part of our best explanation, and therefore deserves to be called “real” (or “physical,” if you want to be a bit more precise) by any sensible criterion.

Now, notice there that "real" and "physical" are assumed to be equivalent. This figures, because all the authors there are "physicalist" - i.e. "what is physical, is real". But this is precisely the point at issue! In what sense are probabilities causative? They're not materially efficient, all they represent is likelihoods (or potentialities) - but in a very concise and indeed mathematically-exact manner.

Heisenberg accepted this, and said on those grounds that his view was more Platonist than materialist. So too did some of the other European quantum physicists, who weren't physicalists. But I'm saying, the current physicists literally can't think like that. Because they're operating within a physicalist paradigm, they can't accomodate the idea that there are non-physical realities. And what is happening as a consequence is the proliferation of these vastly speculative labyrinths of parallel worlds and multiple universes.

So what I would like to argue is that the 'probability wave' is 'real but not physical'. — Wayfarer

That's fine. So what is it in a "real but non-physical" sense?

I've already explained my own view of that - which tallies broadly with modern information theoretic and condensed matter influenced thinking.

I think what I'm saying is not in contradiction to what you're saying, but it's just looking at one particular aspect of it. Or I would hope, anyway. (The only flly-in-the-ointment being that you continue to describe your own position as 'physicalist'.)

As you describe, apokrisis, the particle exists only in the context of the apparatus. — Metaphysician Undercover

But I also generalise the notion of apparatus so that the Cosmos is "an apparatus". It does have a past history that acts as a constraint on quantum indeterminacy.

The result of cosmic evolution - its spreading and cooling - is primarily that it has transitioned from being a relativistically hot bath or radiation to largely a cool dust of massive particles. So you could say we now live in the era of "proper particles" - stably-persistent protons and elections and neutrinos.

The experimental set-up simply reveals the contextuality of all this - because experiments can relax the constraints in ways that systematically demonstrate their existence at the normal, thermally-decohered scale, of our being.

But I also generalise the notion of apparatus so that the Cosmos is "an apparatus". It does have a past history that acts as a constraint on quantum indeterminacy. — apokrisis

The "existence" of the particle is validated by its context, within the apparatus. The "existence" of the apparatus is validated by placing it within another context. If the "Cosmos" is the apparatus, then to validate its existence requires that it be positioned within a context. The past history of the Cosmos does not provide us with this context, because its history is actually part of the Cosmos. To put it into context is to relate it to something external to it.

1.

There is only one wavefunction. — tom

2.

All physical interactions are treated exactly the same. — tom

3.

All physical interactions are local, having no effect on space like separated regions. — tom

The first quote gives me the impression that this one wavefunction is representative of all interactions between objects in space, which seems to go against quote 3.

Now, I'm having trouble understanding how quote 2 and 3 can coexist. All physical interactions are treated exactly the same relative to what?

I appreciate your responses and apologize if my questions are rudimentary.

Yet still, you are not saying what you mean by non-physically real.

I don't particularly defend the term "probability wave" as its sounds overly concrete. And yet also you have to respect that it is only really making an epistemic claim about how quantum probabilities are observed to evolve in a fashion that is best described by the familiar equations of wave mechanics.

So where things get stretched is trying to read some hard realism into the formalism that turns out to work.

And then again, the point of dispute was about the issue of "time dependence".

The formalism describes each quantum event riding its own personal probability wave. So - as usual for any mathematically tractable theory - it builds in an atomism that allows bottom-up construction. As with MWI, you can then entangle individual histories to construct a whole spawning, eternally branching, never collapsing physical mess.

So there is not much disputing that interference is a property of individual wavefunction histories in the formalism. That is the successful presumption of the model.

And yes there is then a deep problem in that we believe that beyond the wavefunction, there must be its physical collapse. That is a view which both accords with common experience of seeing particles hit detector screens at some particular place, and with the highly successful presumptions of classical physical models.

So there are two strong states of belief in tension.

Then what best so far resolves the tension is to question the whole orientation of notions about realism. I appeal to the tradition of organic holism and hierarchical organisation - contextuality.

So it is "mechanics" - either classical or quantum (or statistical) - that is wrong in presuming that reality has locally inherent counterfactuality rather than provisional, contextual, counterfactuality.

That means I take indeterminacy - and its constraint - as the basic complementary ontic dichotomy from which crisp existence evolves as an expression of limit states.

And such an interpretation is consistent with the mathematics as the maths is taken to encode limit states, not atomistic actualities.

Once we get to the cosmic scale, then things turn mathematical. We can start looking for the inescapable truths of symmetry and symmetry breaking. That - as ontic structural realism now realises - becomes the larger context that restricts physical possibility in rather radical fashion.

Yet still, you are not saying what you mean by non-physically real. — Apokrisis

It's a hard question. If it was an easy question, why do you think the two greatest scientists of the 20th Century could never come to terms over it!

the point of dispute was about the issue of "time dependence". — Apokrisis

I think the original observation I have come up with is that if the interference pattern in the double-slit experiment is not rate-dependent, then it is not time-dependent, as rate is a function of time. This can't be the same for physical waves. Therefore, what is causing the pattern is non-physical.

Now, I don't think this is a crackpot theory. There is an article on Cosmos and Culture, by Ruth E. Kastner, on the need for a new paradigm, where she states:

Quantum physics requires that we "think outside the box," and that box turns out to be space-time itself. The message of quantum physics is that not only is there no absolute space or time, but that reality extends beyond space-time. Metaphorically speaking, space-time is just the "tip of the iceberg": Below the surface is a vast, unseen world of possibility. And it is that vast, unseen world that is described by quantum physics.

This is not a wholly new idea: Another founder of quantum theory, Werner Heisenberg, stated that a quantum object is "something standing in the middle between the idea of an event and the actual event, a strange kind of physical reality just in the middle between possibility and reality." Heisenberg called this "potentia," a concept originally introduced by the ancient Greek philosopher Aristotle.

She then goes on to outline something called the 'transactional interpretation', which I can't say that I understand. But what I am saying seems to be quite compatible with the quoted paragraph.

I think the original observation I have come up with is that if the interference pattern in the double-slit experiment is not rate-dependent, then it is not time-dependent, as rate is a function of time. This can't be the same for physical waves. Therefore, what is causing the pattern is non-physical. — Wayfarer

But again, quantum mechanics is not claiming the situation to be (classically) physical. That is why it talks about probability waves and not classical waves.

So this is an argument against something not at issue.

And part of the incompleteness of quantum mechanics is that it has to presume a backdrop classical time dimension to do its thing. The wavefunction of a particle is the evolution of its probabilities in time. And then at some point in time there is - the collapse.

So the double slit experiment does depend on a rate in the sense that it depends on an event actually happening the once - a wavefunction collapsing to create a recorded flash on a screen.

The mystery - from the quantum view - is how anything happens even the once with counterfactual definiteness. That is why we get the eternalism of MWI where nothing ever actually collapses and as many worlds as you like get added.

But others believe that QM can make no sense until time is also seen as an emergent feature of a deeper theory. And those are the kind of current approaches that interest me.

She then goes on to outline something called the 'transactional interpretation', which I can't say that I understand. — Wayfarer

Yep. The transactional approach tries to allow for contextual retrocausality. But it is clunky in being still a mechanical paradigm that relies on a classical notion of time and not an emergent one.

The first quote gives me the impression that this one wavefunction is representative of all interactions between objects in space, which seems to go against quote 3. — Question

Some people, being incapable of any deeper thought, put a lot of store by what something is called. The original name for Everettian QM was The Theory of the Universal Wavefunction. Since then, nothing has really change.

When realist claim the wavefunction is "real", what they are asserting is that the Reality has properties which are in one-to-one correspondence with the mathematical properties of the wavefunction and the configuration space upon which it exists.

So, this mathematical description must provide direct descriptions - e.g. atomic orbitals, and permit emergent quasi-classical physics. If it fails to do this, then QM fails. QM has been tested and analysed to destruction, and nothing has been found to render it problematic.

How the Universal Wavefunction manages to do this is down to a property of the (projective) Hilbert Space it inhabits - i.e. separability.

Just like real space, what happens in Andromeda does not affect what happens here at the same time. What happens in sectors of the Hilbert space don't affect each other immediately either.

Now, I'm having trouble understanding how quote 2 and 3 can coexist. All physical interactions are treated exactly the same relative to what? — Question

There is no special "observer" interaction, causing wavefunction collapse. All interactions are the same as each other.

But again, quantum mechanics is not claiming the situation to be (classically) physical.

But, at least some interpretations are claiming exactly that. What is the motivation for the Many-Worlds Interpretation? According to David Wallace, the expert blog poster that Tom referred to above:

'people who accept the “state-as-physical” view are generally led either to try to make sense of quantum theory without collapses (that leads you to something like Everett’s many-worlds theory) or to modify or augment quantum theory so as to replace it with something scientifically less problematic.'

'Less scientifically problematic' because 'not appealing to non-physical factors, such as observation.'

So please don't tell me that what I'm talking about is a 'dead issue' when it is directly connected with the OP.

part of the incompleteness of quantum mechanics is that it has to presume a backdrop classical time dimension... — Apokrisis

As any science must, as Kant pointed out. Anyway, that's it from me, there are far more knowledgeable people than myself involved in all this, I really have to concentrate on something else for a while, thanks, it has been very stimulating.

So please don't tell me that what I'm talking about is a 'dead issue' when it is directly connected with the OP. — Wayfarer

Where does MWI require the interference to happen between particle histories rather than within particle histories?

Thank you, I think I understand now. One last question that is on my mind. Does Everettian QM obey causality? And if not what determines the evolution of the wavefunction?

Werner Heisenberg, stated that a quantum object is "something standing in the middle between the idea of an event and the actual event, a strange kind of physical reality just in the middle between possibility and reality." Heisenberg called this "potentia," a concept originally introduced by the ancient Greek philosopher Aristotle.

This is the guts of it. The interpretive hang-ups arise because there is this feeling that physicalist ontology must make a sharp distinction between what is real and what is not real.

With classical physics, all the regular physicalist ontic commitments seem to be upheld and so there is not even an interpretive issue - except for stuff folk don't talk about, like where physical laws reside in the scheme of things, and how they actually affect the world causally.

But with quantum physics, we should have been shocked out of this kind of complacency. Instead we have people still trying to cling on in Bohmian or MW style desperation to something being "real" in a traditional comforting local realist sense.

The way out of this intellectual bind is give up on "physicalist reality", and thus also on the "others" that frame its particular dialectic. As Heisenberg suggests here, we should understand existence in terms of being in the middle of two complementary limits - like reality and possibility. Or classical counterfactuality vs quantum indeterminacy. We are bounded by two extremes and thus exist at neither of them.

And it is this essential "between-ness" which is the fundamental.

That is why I am a fan of decoherence but not MWI. Allying the formalisms of QM and statistical mechanics is a way of describing an in-between "critically poised" state. It allows the evolving history of the Cosmos to be separated from the local histories of its particles by sheer classical scale. Space and time make a real difference.

But then MWI is what you get when you still want to assign fundamental reality to the quantum formalism and pretend that the classical realm is some kind of epiphenomenal illusion.

Again, if you assign fundamental reality to the in-betweeness - the causal story of how things become separated in the first place - then the quantum and the classical become the complementary limits of that evolving process.

And this is the emergent view which physics is working towards with quantum gravity. It is why MWI itself has largely retreated from its more extreme claims about multiverse type realitiies. The Orzel's are more representative than the Tegmarks when it comes to ontological discussions in this field.

If the wavefunction exists as a mathematical conception existing in Hilbert space, then I am compelled to agree with Tegmark's belief that reality is mathematics manifest. I find it hard to think otherwise.

This is the guts of it. The interpretive hang-ups arise because there is this feeling that physicalist ontology must make a sharp distinction between what is real and what is not real.

That's what I thought I had been arguing all along.

If the wavefunction exists as a mathematical conception existing in Hilbert space, then I am compelled to agree with Tegmark's belief that reality is mathematics manifest. I find it hard to think otherwise — Question

Which is all well and good, but then arises the question of "manifested from what"?

Even Platonism demanded its chora so that imperfect reality could be manifested in actually substantial form and not remain confined to a real of ideas.

New Scientist on how everything arises from nothing: