Let me get this straight then, you have one mother category "vagueness", and any other category is assumed to exist as a subset of this category. — Metaphysician Undercover

Well yes and no, because vagueness would be the ground state - in being the state "beyond categorisation". And also, in the full semiotic view, categorisation is irreducibly triadic. So there is no ultimate monism - unless you want to talk about the "one thing" of the triadic semiotic relation.

In Peirce's scheme, you have the three categories of firstness, secondness and thirdness that would correspond to my "system" here of vagueness, dichotomisation and hierarchy. That is pure possibility "reacts" against itself and becomes divided towards its crisp polarities. Then having divided, the division can mix over all scales to form a hierarchically structured world.

If say discrete and continuous are the two ultimate ways things could be, then the more definite it becomes that things are categorisable as either discrete or continuous, then also you get all the various in-between states of connectedness, or disconectedness, that go along with that.

I realise that this triadic, three dimensional, approach to categorisation is difficult and unfamiliar. It allows "rotations" through an extra dimension that normal categorisation - based on strict dialectics - fails to see.

So what does that mean? It means you have to remember that the extra dimension is one of development or process that stands orthogonal to the dimension of existence or structure.

So your very words are: "...and any other category is assumed to exist as a subset of this category?". That is you are, for the moment, restricting yourself to a static structural view to the exclusion of the further possible developmental or processual view. And I would reply, yes, vagueness does kind of stand in relation to the crispness of dichotomous categories as "a mother". But then I would want to rotate the view to remind that vagueness is defined itself dichotomously as the dynamical other of crispness. And it is never left behind in the developmental trajectory as development consists of its increasing suppression.

So you are hooked on the need to make some pole of being the ground state - which then stays where it is so a (constructed) movement away from it becomes a possibility. That is how you understand prime matter, for example. You have to start with a concrete stuff that represents efficient cause.

But in my view, vagueness is itself only granted existence in terms of what develops. It is the context of any thing that happens - it is the potential. But then it is only that because something does happen. The results are the context which make vagueness "a thing".

The logic of this would be circular if it weren't in fact hierarchical or triadic. ;)

So the metaphor you want to use here is "the mother and her many possible children". That encodes a forwards in time, unidirectional, efficient causality, with an unrestricted future state. The general begets the particular. The one begets the many.

But that is a truth of a triadic metaphysics seen from just one angle. It is only one cross-section of the whole.

Switching away from the structural/static view to the developmental/dynamical view, we would say the vague begets the dichotomy of the general~particular, or the one~many, the whole~parts. And vagueness is itself - structurally - a subset of the greater relation which is the dichotomy of the vague~crisp. Vagueness is the particular child of that more general parent relationship.

The opposing terms, which describe the limits, hot and cold, big and small, for example, are always within the same category. If we describe two distinct categories with two distinct words, these are not opposing terms of co-dependency or complimentary limits, as you suggest, because those necessarily fall within the same category. — Metaphysician Undercover

You are ignoring the fact that I said the category from which complementary distinctions originate is the third category of vagueness. All categorisation has this triadic (that is, semiotic) organisation in my book ... if not yours.

So we have one category which consists of constraints and freedoms, and another category which consists of vagueness. Have you any principles whereby you establish a relationship between these two categories? — Metaphysician Undercover

I just said that a symmetry breaking must reveal that there was a symmetry to be broken.

And if the breaking produces crisp division, then the originating symmetry must be the "opposite" of that - ie: radical indeterminacy.

So the argument has been supplied.

Incompleteness certainly has something to do with it. We know from quantum uncertainty that not every physical situation is measurable. So good luck with the reality of a simulation that can't reproduce classical level detail.

MWI is such a scam in that regard. It wants you to pay attention to physical situations with the simplest binary branch structure - a particle that might freely be spin up or spin down until someone has looked. How neatly the world divides into two.

Yet most emission interactions are wildly open-ended. When a photon is absorbed at point x in spacetime, then that directly creates the vast number of spacetime locales where the event will never occur. At the very least, there is a light cone sized sphere of places - a vast surface - where the said event counterfactually didn't happen.

So rather than two worlds, the simplest (being far less environmentally constrained) emission event would spawn a truly galactic number of alternative world-lines. It is a good job that MWI now uses decoherence's thermal averaging trick to treat this raging variety as differences that don't really make a difference in the big scheme of things.

But there is a basic dishonesty in claiming both wavefunction realism and then finding ways to ignore its full consequences due to the fact that "the observer don't care" about stuff that can be epistemically averaged away as not mattering.

It doesn't matter if a particular light ray from a distant star is absorbed by your eye, or by an eye on Alpha Centauri. Your eye is going to pick up some kind of thermal event from that distant star as it produces so many of them. And yet if we are to believe MWI, every possible version of the events exists as a real superposition. There is almost infinite branching the whole time, but only a select few of these branches - like spin up vs spin down - are treated as "separable". The rest are allowed to blur into an unmentioned bulk on good old epistemic grounds - the principle of observer indifference.

I of course agree with this epistemic view - in reading it from the other side. It is the point that decoherence is about a blanding away of the quantum uncertainty to leave only classical counterfactuality standing proud. We see a world of sharp black and white because grey gets averaged away. And then ultimately - at the quantum scale - there is a limit to this counterfactuality. That is what we are seeing when we ask non-commutating questions of nature like "where exactly are you/how fast and in what direction are you heading?".

So where MWI claims global irresolvability (no collapse), I instead focus on local remnants of irresolvabilty (so all of existence is the product of a relative state of collapse, it is only absolute collapse that is impossible).

And decoherence is a statistical mechanics add-on that lets you calculate the shrinkage of quantum weirdness to it limiting minimum. Yet MWI wants to read the maths the other way round - as a tool for the endless magnification of "real possibilities in superposition".

....there is a categorical separation between physical things and mathematics. — Metaphysician Undercover

If you want to defend this particular categorical separation, go right ahead.

My point is that you can only do it via some kind of dichotomistic "othering". You will only have a metaphysically strong argument if you can describe the situation in terms of some mutually exclusive/jointly exhaustive pairing.

And so it is the kind of separation that in fact encodes a co-dependency. Each needs the other as the negation which underpins its own affirmation. And thus really any categorical separation is merely towards complementary limits. It becomes the disunity of a symmetry breaking which reveals the existence of a unitary symmetry.

So in this case, the maths stands for the eternally abstract. Which in turn means that "physical things" get reduced to the most impermanent notion of materiality - dimensionless fluctuations.

The argument is familiar to you. The proper opposition is not between substances (actual physical things) and (immaterial) ideas, It is between (physically general) potential - prime matter or Apeiron - and (mathematically general) forms.

The categorical separation I actually make - using systems jargon - is between constraints and freedoms. And then that separation in fact gets triadic or hierarchical development. That is how we end up with the hylomorphic "sandwich" of possibility, actuality and necessity.

So in the beginning there is just vagueness - the perfect symmetry of the ultimately indeterminate.

Then this gets broken. Constraints are habits or regularities - historically developed information - that break the raw symmetry and start to organise it.

But then constraints themselves encounter limits. Eventually you end up with the simplest state - like the U1 spin symmetry of electromagnetism. The symmetry of a circle. And where you get crisp symmetry emerging in that fashion, you get the baked-in freedoms of reality. You get the inertial degrees of freedom due to conservation laws as described by Noether's theorem.

Newtonian mechanics are the result of the emergent irreducibility of the freedom to move inertially in terms of translational and rotational symmetries. Relativity arises because Lorentzian symmetry is baked in for boosts or changes in energy scale.

So we have a "mathematical physics" that already tells its own story in terms of a triadic evolution. It all begins with "naked quantum chaos" - a perfectly vague symmetry of unbounded fluctuation. This symmetry is then broken by the emergence of spacetime - a Big Bang universe where dimensionality is reduced to just three global spatial directions, and filled by a cooling/expanding bath of radiation that gives everything an irreversible, symmetry-broken, direction in time.

But then as time develops, further more crisp symmetries, and thus symmetry-breakings, can manifest. The Universe gets cold and large enough for "massive particles" like protons and electrons to condense out of the radiation. We finally start to get the substantial classical things that you want to take for granted. That kind of stuff starts to pop out of the maths too.

So we already know a lot about how our notions of "maths" and "physical things" have an underlying unity, and how a disunity can evolve as further phase transitions due to cooling/expanding. Eventually things get stably broken because a particle like an electron is the mathematically simplest possible speck of matter. And then in the even longer term, all this matter will get swept up into black holes and radiated away to the coldest possible version of nothingness - the black body quantum sizzle of cosmic event horizons.

I mention all this yet again because this is modern metaphysics. It makes MWI seem the most Micky Mouse kind of philosophical contrivances. MWI nicked some of the maths of thermodynamics, but incorporates none of its deep ontology.

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.

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.

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?

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.

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.

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.

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.

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.

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.

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

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

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.

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

To say, as you did, 'there is no particle travelling through the apparatus" is to say that there is no object called "the particle" to which the complementarity principle may be applied. — Metaphysician Undercover

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".

...it shows time is not a factor in the formation of the pattern. Doesn't that strike you as being significant? — Wayfarer

Again, who is saying time is a factor in the sense that multiple events need to accumulate for there to be quantum interference?

One of the well-known problems of the double-slit experiment is that particles fired singly seem to act as though interference is happening. But how can interference occur when there's only one particle? It's one of the notorious difficulties of quantum mechanics. So I'm not saying 'they don't interfere due to superposition'; I'm saying that what appears as 'an interference pattern' isn't really interference at all - where it would be exactly that is if it really were water waves or sound waves. — Wayfarer

But again, this isn't a physical interference of the kind we imagine with classical material waves. It is the analogous "interference" of probability waves. And it is the "interference" of all the possible paths a single particle could take. And it is the "interference" which is both constructive and destructive. So it builds up probability densities as well as knocks them down.

So there is little point trying to apply some simplistic and materialistic understanding of the word "interference" here.

The 'waves', so called, really are probability distributions, not actual 'waves' at all. The equation models both them and material waves, but they're of a different nature to waves in water, because there's no medium. They're not really waves, in the same sense, and for the same reason, that electrons are not really particles. — Wayfarer

Right.

Now the reason I say that is compatible with the Copenhagen Interpretation is that there are many statements along similar lines from them: 'What we observe is not nature itself, but nature exposed to our method of questioning', said Heisenberg. Whereas, Einstein wanted to insist that there were something objectively real and (crucially), 'mind-independent', of which QM was an incomplete description. — Wayfarer

But that's ancient history. Today we know for sure that you have to give up either localism or realism. And probably have to give up both (in some sense).

However your posts here were making some kind of deal out of interference patterns not being rate-dependent. And it is not clear why you think that is relevant to the interpretation issue in any form.

If you have a wave machine making an actual wave of water in the lab, and the wave passes through twin slits, the split wave produces an interference pattern. So it is not an issue that we are talking about individual trials.

But a quantum twin slit experiment results in only a single particle like event at the detector screen. And the interference pattern disappears if the path of the particle is observed. So that's the weirdness that realism would have to explain away, and the weirdness that a CI-style pragmatism simply gives up trying to explain in terms of real world mechanism.

Not being rate dependent is not part of the weirdness. It would instead be weirder still if the particle-event was affected also by every other event both before and after it. How could we even calculate any statistics if we had to take the entire past and future of the Universe into account?

What I was told on Physics Forum, is whether the particles are fired one at at time, or whether they are fired altogether, the end result is the same. So I am saying, it can't really be a result of 'interference', can it? — Wayfarer

So are you saying the two paths of an individual quantum event don't interfere due to superposition?

And bear in mind that we are talking about the interference of probability waves. And also that interference is about the additive or cancelling effect of wave peaks and troughs arriving at a point of space and time - the detector screen.

Given that, in what sense is it not analogous to wave interference in classical mechanics?

And given that, why would you expect the rate of producing individual events to make some kind of difference to the accumulation of an interference pattern at the detector?

Do you get the complementarity principle? Is one description right and the other wrong? Or are both a reflection of some chosen measurement basis?

Rather than getting upset, show that you understand what you are talking about.

Again, in what way does the event by event accumulation of a twin slit interference pattern (or even single slit diffraction pattern) depend on the rate at which one event follows another? Where does the formalism require such a dependence?

You seem to think that the interference pattern is caused by some kind of dependency of one outcome on all the others. It is the particles that are all physically interfering with each others statistics in some kind of spooky, nonlocal, time and space defying, fashion.

But that is wrong. It is about how each event is affected by its (observational) context. So it is about a single event and the exact set-up of the apparatus for that run. And it is the human experimenters who control the state of the emission source and the apparatus, so ensuring that the interference pattern will accumulate over multiple trials replicating "the same event".

What's annoying was that this is the issue that Orzel was highlighting - the impossibility of perfect repeatability in the real thermal world. Something is always slightly different about the world. And that to me is a promising angle from which to attack the absolutism of MWI.

The pattern is dictated by the wave function. That will be so regardless of which apparatus or set-up you're using. The equation which describes the distribution is not dependent on the apparatus, although I imagine that the particulars of each set-up might produce variations because of the distances involved etc. — Wayfarer

...and you can't see how you just contradicted yourself?

In the real world, every set-up is particular, and so a particularisation of the wavefunction equation.

But the underlying determinative cause is the wave equation itself - however the wave equation is not a material cause, as it is not something which exists, it's simply a pattern of probabilities, as the name says. — Wayfarer

The equation is the useful, in the limit, generalisation or abstraction which describes no actual world until some numbers are plugged into it, just like the laws of motion.

You are making the mistake of reifying it and then treating that reification as a mysterious further concrete part of nature. Platonism redux.

So it is not simply a pattern of probabilities until some actual numbers have been plugged into the equation.

So I think the real sticking point is, how can a probability be causally efficacious. Isn't that what the whole argument is about? That's what Einstein kept saying to Bohr - 'God doesn't play dice'. He made a slogan out of it. — Wayfarer

The sticking point is that probability is irreducible. The wavefunction is the tool that limits the extent of the weirdness in useful fashion. But in the end, it can't be eliminated by just an equation. The equation - even if total information is plugged into it - can only point its finger to roughly where to expect a particle to be. So the question is how does that residual uncertainty ever get eliminated by a "real collapse".

The reason why the rate-independence is significant, is that the behaviour of individual 'particles' (not that they're actually particles) is described by the wave-function, whether they're together or separate. In other words, whatever is causing that, is independent of space/time, or, that duration and the proximity of 'particles' are not factors in determining the result. Or so it seems to me. — Wayfarer

Well you are wrong. It is an important point that the particle "goes both ways" even if it was a one-off, never to be repeated, experiment.

The problem is you can't see that just from observation of the one event.

That's not confusing super-position and entanglement, although what I'm starting to think is that the 'rate-independence' of the pattern, and the so-called 'entangled states', are actually two aspects of the same underlying cause. — Wayfarer

So with next to no demonstrable understanding of the theory, you have convinced yourself you have stumbled on the missing link which has eluded a century of physicists?

Isn't that the definition of crackpot?

So if the pattern is not rate-dependent, then by implication the cause of the pattern is not a function of time. — Wayfarer

You mean the pattern isn't the function of other particle histories. The pattern is simply a function of the fact the same maze, the same apparatus, imposes its constraints on a sequence of highly identical events.

So it is the design of the system that makes it rate-independent. You could stick the equipment in a cupboard for a thousand years, pull it out, and the quantum statistics would be unchanged.

Perhaps you are confusing entanglement and superposition in your understanding of what is going on?

...http://backreaction.blogspot.co.nz/2016/03/dear-dr-b-what-is-difference-between.html

The question seems to be: how can a particle 'interfere with itself'? — Wayfarer

The issue of course is that we have no good explanation in terms of concrete commonsense notions. So you are not going to get the kind of answer you are seeking in terms of things you think you understand.

But such caveats aside, there is no particle travelling through the apparatus. Instead there is an evolving wave of probability of detecting a particle that reflects the shape of the apparatus. If there are two slits that the wave has to pass through, then it "goes through both" and you get the resulting wave-like interference effect.

Remember that you get a wave-like defraction effect even if only a single slit is open. The slit causes particles to spray out across the detection screen. If the particles acted exactly like particles, they ought to just go straight through and burn a crisp hole in the one spot, not get smeared out across the screen.

So that is the wave~particle duality. We know that only one particle gets emitted, one particle gets detected. But on its travels, it acts like a classical wave and responds to the shape of the experimental apparatus accordingly.

It seems as if the probability distribution is itself like the so-called 'pilot wave' - in other words, it determines all the possibilities, but only in the sense of constraining the possible paths that any particle takes, whether individually or as part of beam. — Wayfarer

But don't forget the causal role being played by the apparatus here. There are some specific - classical - set of constraints being placed on the particle event. That may include experimenters making complicated delayed choice measurements with half silvered mirrors, or whatever.

So in the decoherence view, we can see this as being about the hierarchical nested constraint of quantum potential. The causality is contextual.

Start with a naked vacuum - the Universe in its most unconstrained state, without any kind of experimental apparatus. You still have some probability of an emission and absorption event. But it would be very random and patternless. The wavefunction would represent very little causal or contexual information beyond some probability of a patch of vacuum having an energetic fluctuation.

But now start to assemble an apparatus. You have a photon gun, or some other particle producing machine that heats up and is designed to produce quantum events at some controllable rate. Now you have a wavefunction that is becoming quite highly constrained by its "classical" context. It is like corralling pigs in a pen and then creating a small gate which you can open. Pigs will start to fly out in a predictable direction.

Then start adding in slits. This is like creating another pen with another gate. The pigs that happen to make a straight bee-line towards the next gate will fly through, but are then free to bend off once they are past. If there are two such gates, the pigs will form an interference pattern as they eventually smash into some distant wall set at an appropriate angle across their path of flight - a further act of constraint.

So the wavefunction itself is the product of some environmental arrangement, some set of constraints that give shape to a "process". And the collapse is then just taking that constraint a further step. It is placing an end-stop by insisting that absorption happens "right now" due to some overwhelming constraint, like a particle detector screen.

The quantum weirdness then comes in because no detector can ask every question of nature that you might expect of the one event.

In the classically-imagined world, the particle (or wave) would have some exact position and momentum at all times. But in the quantum reality, you can't answer both questions at the same time with complete certainty. So the weirdness lies in the fact that the environment can causally constrain events up to a point. But that ability to create exactness runs out before classicality believes it should.

And as I say, even a single slit results in quantum uncertainty. The narrowness makes it certain that any particle had to come through it. But at the detector, you have to pay for that certainty by losing certainty about the momentum.

There you are standing waiting for your pigs to come flying straight through your maze of gates. But while you now the pigs can only come through the gate, they are then free to veer off randomly once their path is not constrained. And so veer off they do.

In other words, whether the protons are fired singly or as a beam, makes no difference to the interference pattern. — Wayfarer

The interference is from the fact that the particle can take two possible paths through the twin slits. So it is about the particle and the apparatus, not the particle and all the other particles.

And the fact that you see a particle hitting the detector screen is the destruction of that wave function. The particle shows up at some place, and you can attach a probability to that place ranging from very low to very high.

So to "see" an interference pattern on the screen requires we collect some reasonable number of wavefunction collapses - the story of many individual particles trips through the probabilistic maze. But the point of the experiment is that even a single particle will behave like a wave - a superposition of a pair of probability waves.

Well, glad we got to the bottom of that, although it directly contradicts and answer you gave just above it. — Wayfarer

That was another Tom in another world breaking through. By his own logic, his every possible state of belief is a real macrostate. So it hardly matters if he is contradictory. That's going to be the case no matter what. :)

My apologies, I misread where Wayfarer's quote came from. It came from an article that Orzel did NOT like apparently. — tom

So I'm guessing you didn't even read that Orzel link you posted in rebuttal?

I actually asked a serious question. You might have had some worthwhile points to make about Orzel's angle.

Everett (actually bare quantum formalism) claims that any environment that interacts with the cat in superposition will itself enter a superposed state, — tom

Not sure why entering a macro superposition state is any less magical than exiting it.

The bare quantum formalism still requires its "observer", even if the tacking on of the further formalism of statistical mechanics - in the guise of the decohering environment - is certainly the way to deflate the notion of the "observer".

So collapse folk have the problem of getting rid of entanglement. No-collapse folk have the problem of initiating it. Sure the wavefunction evolves in the required fashion. But observers are then the necessary element to create the context that results in some actually specified wavefunction.

Meanwhile decoherence as a general machinery helps out both in making it clear that "observation" is not about conscious human experimenters but about the concrete existence of a thermalising environment. The Universe has the means to "observe itself" in that it has a definite past that acts as a general constraint on the indefiniteness of its future.

Nope, nowhere in MW is the claim made that measuring the spin of an electron means "you have to build an entire parallel universe around that one electron, identical in all respects except where the electron went". — tom

And how does that connect with what Orzel (or I) have argued?

The point is that even if you step back from many actual worlds - Tegmark's parallelism - MWI proponents still seem to believe in crisply real branches (and branching points). But it makes more ontological sense to treat that too as a mathematical idealisation.

So the argument is that the universe, as a whole, could never have the definiteness required to create itself as some entangled mass of matchingly definite world branches. You can get something like that occasionally - with a sufficiently isolated system. But even ordinary quantum experiments have a bit of jiggery-pokery going on in that they don't control for the fact that actual environmental isolation is physically impossible.

And physical reality ought to trump mathematical idealisation in this regard.

Orzel is also wrong. by the way. — tom

So it is clear Orzel indeed has you stumped because you can offer no analysis at all. But just saying "nope" is not going to get you out of the hole here. ;)

But insofar as physics is purported to be about what is real, then dorm-room bull is inevitable, as far as I am concerned. — Wayfarer

But physics can't claim to talk directly about what is real. All it can claim is to talk in a fashion that is systematically constrained by "the evidence". So it is ultimately a social practice. And its philosophy accepts that. But what a physicist can rightfully say is that s/he is better constrained by the evidence than most of the people who want to waffle on about metaphysical reality, employing half-baked traditional belief systems.

So the real issue here - as I believe Orzel illustrates - is that people take hardline positions on quantum interpretations because they are locked into either/or binary thinking. It must be the case either that wavefunctions are ontic or epistemic - a definite fact of the world, or a useful fiction of the mind. The same with wavefunction collapse. Or in a more general way, either classicality or quantumness is the illusion, the other the truth. Either everything is secretly hard and definite behind the scenes, or it is fuzzy and probabilistic - an eternal spawning confusion.

So there are two familiar alternatives when it comes to existence - actuality vs potentiality, being vs becoming. And a quantum interpretation must settle ultimately into one or other general category.

But why not instead see those two choices as the complementary limits on the notion of existing? Reality is never fully definite, nor fully probabilistic, always somewhere inbetween the static hardness of actuality and the soft fluidity of uncertainty.

So there are two ways of looking at quantum weirdness. Either you can take an internalist perspective - as I do - and see the classical world as a system that confines it and dissipates it. Or you can take an externalist view where quantum weirdness is essentially unconfined and spills out to take over everything. You get people saying the entirety of existence is not just a single giant superposition, but one that branches in unrestrained fashion, growing forever more byzantine.

Now the mathematics of quantum theory doesn't provide any machinery to collapse the wavefunction. So there is nothing in the bare formalism to constrain all the world branching, all the ever-expanding weirdness.

But as Orzel argues, properly speaking, this weirdness applies strictly only to isolated systems - parts of the world that are essentially disconnected from the thermal bulk. To get entanglement and quantum coherence, you have to be dealing with the very small and the very cold. And that takes special equipment. Generally the world is too hot and messy for quantum effects to manifest. The weirdness is always there, but classicality is about it becoming heavily suppressed.

So as I say, actual quantum weirdness can exist only at the very limit of the classical. The wavefunction defines that boundary where hot messy contexuality eventually peters out and all that is left - trapped inside a small and isolated spatiotemporal region - is your fundamental-level indeterminacy.

So yes, indeterminacy exists. We've manufactured it by very careful control over experimental set-ups that produce the level of thermal isolation that permit it to be the case. But to then do the MWI trick of claiming "unconfined isolation" would turn the whole universe into a giant unbroken and coherent superposition is to ignore how the world really is - so hot and messy that indeterminacy is always and everywhere in practice highly confined.

And the corollary is that the same applies to classical reality, the hot and messy bit. It doesn't have hard solid existence in the way that conventional materialist metaphysics imagines. It is everywhere and always that tiny bit quantum and indeterminate.

And the whole shebang has evolved. At the Big Bang, the Universe was basically in a generalised quantum state. It was 99.999% quantum, only fractionally classical. And now that the Universe is so cool and large, it has become 99.999% classical - at least at the scale we care about, the interactions between big and still warm lumps of mass. This is the era of the hot and messy.

Roll forward to the Heat Death and the balance shifts back to the quantum pole of existence. The contents of the Universe will only be describable in terms of a black-body quantum fizzle of ultra-cold photons being emitted by the cosmic information horizons.

From a MWI point of view, calling the Heat Death a multiplicity of worlds in superposition would be like comparing scrambled bags of sand. Technically you might claim every back to represent some unique possible state or arrangement of sand grains/quantum events. But in fact every bag is just another bag in a way that makes no useful difference. Every bag of sand world is unexcitingly similar due to the thermal inevitabilty imposed by the second law.

So my view is that this is the best metaphysical basis for interpretation - the real and possible are not two categories, one of which must be made to stick, but instead they represent the complementary bounds that form existence. The classical and the quantum mark the two ends of a spectrum. That means neither reality nor possibility are going to be 100% pure states.

And yet all interpretations try to force the issue and give an absolute categorisation in terms of various binaries. That is why all of the interpretations seem to be saying something right, yet none of them could ever get it all right because of the way they go about striving after a single definite metaphysical categorisation.

But now that quantum theory is being married to thermodynamics and information theory, now that it is importing a proper systems ontology in which you can model the kind of contextuality and scale effects that I'm talking about, things seem to be getting somewhere.

That is why I am a fan of decoherence even if I don't go along with the fanatical MWI view which wants to treat actual decoherence as a 100% illusion (resulting in completely unconfined superpositions), whereas I say that in our hot and messy classical reality, decoherence is pretty real in being only 0.0001% - or some sensible fraction - an ontic illusion.

So I would be an effective realist about both the collapse and wavefunction issue. Determinacy can approach 100% at one end of the scale, indeterminacy can approach 100% at the other. And neither in fact every completely rules. If we are going to construct a metaphysics of existence, then the fact that everything is always a messy mix, some balance on a spectrum, becomes the new foundation for interpretations.

Orzel's understanding of Many Worlds has improved over the years: — tom

Glad you think so. But I note you are avoiding saying whether you agree with his essential point. Whereas many MWI proponents get quite fundamentalist about universal wavefunction realism, Orzel is treating it more as a matter of pragmatic limits. It is pretty much impossible in practice to repeat measurements in the exact fashion that would give you a single crystaline mass of sharply branched world-lines. That version of MWI - which is pretty widespread - is a misunderstanding.

How do you measure an interference effect? Well, you look for some oscillation in the probability distribution. But that’s not a task you can accomplish with a single measurement of a single system– you can only measure probability from repeated measurements of identically prepared systems.

If you’re talking about a simple system, like a single electron or a single photon in a carefully controlled apparatus, this is easy. Everything will behave the same way from one experiment to the next, and with a bit of care, you can pick out the interference pattern. As your system gets bigger, though, “repeated measurements of identically prepared systems” become much harder to achieve. If you’re talking about a big molecule, there are lots more states it could start in, and lots more ways for it to interact with the rest of the universe. And those extra states and interactions mess up the interference effects you need to see to detect the presence of a superposition state. At some point, you can no longer confidently say that the particle of interest is in both states at once; instead, it looks like it was in a single state the whole time.

And that’s it. You appear to have picked out a single possibility at the point where your system becomes too big for you to reliably detect the fact that it’s really in a superposition.

http://scienceblogs.com/principles/2015/02/20/the-philosophical-incoherence-of-too-many-worlds/

And note how he ends for good measure....

(Finally, the above probably sounds more strongly in favor of Many-Worlds than my actual position, which shades toward agnosticism. But nothing makes me incline more toward believing in Many-Worlds than the gibberish that people write when they try to oppose it.)

So he is trying to challenge the more conventional MWI interpretations.

Now, I've realised what I think is wrong about this view. This is that science views reality through theories and hypotheses. And what I think Einstein is forgetting (and, hey, he's Einstein, so I know I'm saying a lot!) is that the kinds of purported facts that he is arguing about are only disclosed by a rational intelligence who is capable of interpreting the facts. So 'the facts' - and by extension, even the moon - don't exist irrespective of whether one is looking or not. 'Looking' is inextricably intertwined with what is being observed. That has always been the case, but it took 'the observer problem' for it to more or less come up and punch us in the nose! — Wayfarer

I think you are agreeing with me on pragmatism. And as I say, that is what comes through from Heisenberg. But also Einstein got it in that he said (in a co-authored book) that scientific concepts are free creations of the human mind. So his issue was more one of metaphysical principle. He was loathe to sacrifice a concept that had worked as well as the principle of locality.

We went along with collapse was real, and it was the "observation" which made it real. — Moliere

But what does it mean for the collapse to be real (and the wavefunction not real) in Heisenberg's Kantian view? He talks about an epistemic collapse - a change in your state of knowledge. So the emphasis is on pragmatic modelling. We can only have knowledge about reality via our conceptions.

Our models encourage us to create certain measuring devices and experimental set-ups with which to probe. But whatever we learn is always in terms of those familiar conceptions. We don't get outside our own self-created observer bubble to grasp the thing-in-itself. All we have is a system of signs that seems well behaved. We can stick our thermometer into the bath and read off some numbers. We understand that combination of events as evidence there exists "a temperature". Likewise we can probe the quantum realm with quantum set-ups and read off observations in terms of the behaviour of a particle. Or of a wave. Depending on the choices made as the observer.

So you set up questions in a certain way - a human way and not necessarily nature's way. That will result in a reading, a sign, that "collapses" your ignorance. But what went on "out there" is another mystery.

Heisenberg: ....we have to remember that what we observe is not nature in itself but nature exposed to our method of questioning. Our scientific work in physics consists in asking questions about nature in the language that we possess and trying to get an answer from experiment by the means that are at our disposal.

So yes. CI is often considered to claim collapse realism. But Heisenberg appears to aim at a sophisticated epistemic position that instead takes as primary the Kantian impossibility of naked realism in any form.

And the mystery unsolved is then why the quantum mode of inquiry works so "objectively". The collapse of our ignorance when we conduct our probes is so reliable that it tempts us make a stronger causal connection than our epistemological limitations would warrant. We want to say we ourselves collapsed the wavefunction by touching reality with our minds. Or that collapse really is objective and caused by the physical aspect of our probing - the way we jarred the wavefunction with our material devices.

Thermal decoherence seems to offer now a fairly natural view of how macroscale observers can act as the decohering contexts that "collapse" quantum-scale possibilities. But unfortunately decoherence is quite tied up with MWI fundamentalism about wavefunction realism and no collapses.

We always differentiated between instrumental interp from CI, though. — Moliere

As you say, even if you go back to Bohr and Heisenberg, you can't recover some pure CI position. And perhaps I should have said pragmatist or logical positivist rather than instrumentalist initially - even though instrumentalism is only Dewey and Popper trying to strip down Peircean pragmatism of its "unfortunate" metaphysical leanings.

So I find that when I talk to modern proponents of CI, they are essentially arguing pragmatism - all we can know is that the maths sure works. And then the metaphysics that lingers at the back of this is the idea that the mind of the observer works on the classical side of the equation, so something that sure looks like a definite collapse of quantum weirdness must be the case in that we manage to extract classically understood measurements from the world (within the bounds of uncertainty).

So even the instrumentalism relies on a background metaphyics which I would say should be troubling. And it certainly was for Peirce who was working on a "fuzzy logic" view of metaphysics for just that reason.

Generally, I struggle to draw sharp lines between interpretations. But when given some central issue - like wavefunction collapse - people are going to divide quite logically into the three camps of (1) it must do, (2) no, it can't, and (3) can't know so learning not to care.

CI as people currently use it seems more 3 than 1 these days.

What bugged Einstein is his native faith that reality was 'there anyway', whereas the Copenhagen advocates all said that in this matter, the line between observer and observed was no longer clear-cut. And I'm with them on that, as far as I can understand it. — Wayfarer

CI itself comes in a rainbow of variants. But the central idea in my view is that in the end what we can be sure of is that we don't know how to define what looks like a necessary division between observers and observables when it comes to quantum scale observations of observables. So we know there is an explanatory gap, but can see no watertight way to fill it.

So CI says there is a line for sure. We sit on its classical side. And where that line gets drawn to rule off the quantum side is something we can't answer.

And my response to that is that it is this notion of there being a definite line which is questionable. Instead, I see the classical and the quantum as complementary models of the two perfect limits on existence. So CI gets it wrong in persisting in believing in a dividing line. Although, as I say, CI comes in so many varieties that it can be seen as a "shrug of a shoulders" intrumentalism even about hard line vs fuzzy line ontologies. Who cares because we can use the maths to deal with the world and built great machinery?

Then Peirce comes in here because he was already dealing with this precise problem - the nature of observers. And he extended that epistemological question to make it a ontological answer. His semiosis is a way of defining soft dividing lines in worlds where observers and observables are fundamentally entangled, but can - thermally - develop robust habitual divisions.

So you keep claiming Peirce to be an idealist - someone somehow arguing that divine mind conjures the world into being. And at stages in his life, he may have well wanted to believe that.

But if you look at his actual metaphysics - his semiotic approach - then he was talking about signs rather than minds. Observers weren't localised experiencers but contextual habits of interpretance. The difference might be subtle, but it is also huge.

Rather than being defensive, why not critique Orzel from your point of view? That would be more interesting.

That's close to my own thinking, but was obviously written before the discovery that the second law of thermodynamics is violated more frequently the smaller anything becomes and completely ignores the Quantum Zeno Effect. — wuliheron

I'm hardly ignoring the quantum zeno effect. Remember that that too requires "perfect watching" to stop the particle ever decaying. So it is both remarkable that we could slow down a decay, impossible that we could create the energy-demanding experimental conditions that would stop a decay.

The simplest explanation is that time can flow both forwards and backwards because a context without significant content and any content without a greater context is a demonstrable contradiction. — wuliheron

I'm all for some version of retrocausality. But you are invoking a globally general version that again betrays perfect world thinking and not the fuzzy logic approach that I would take.

So our bulk model of time and causality is best described by this kind of thinking I would say - http://discovermagazine.com/2015/june/18-tomorrow-never-was

This thermal view of time says the past is pretty much solid and decohered, the future is a bunch of open quantum possibilities. And then quantum retrocausality would be about very local and individual events which are criss-crossing this bulk picture.

The bulk seems definitely sorted in having a sharp split between past context and future events. But on the fine grain, past and future are connected because - as with quantum eraser experiments - the context can take a "long time" to become fixed in a way that then determines the actual shape of the wavefunction. It is only in retrospect that we can see all that went into its formation.

So again, rather than time/causality being either absolute in a uni-directional classical sense, or instead absolute in a quantum non-local or "both ways" sense, the real world dangles somewhere between these two perfect limits. It emerges as the equilbrated bulk behaviour.

. Its enough to make Zeno's head spin, but its a more Asian metaphoric take on the issue. — wuliheron

The trouble with Asian metaphors is that culturally they lack mathematical development. So they are inherently fuzzy in being verbal descriptions. At best, using proto-logical arguments, they are proto-mathematical.

So yes, it is my own argument that all early civilisations shared a fairly organic, symmetry-breaking, perspective on metaphysics. There are strong parallels between Anaximander and Tao.

But you can't claim quantum physics to be the triumph of the Eastern way over the Western way. It was Zeno who crystalise the mathematical paradoxes of a way of thinking, and thus made possible their equally sharp counter-reaction. You couldn't develop calculus unless you knew there was some sharp problem when it came to differentiating a curve. And you couldn't develop quantum mechanics if Lagrangian mechanics wasn't already a result of being able to do such differentiation.

So Zeno sparked something usefully concrete in Western thought. It allowed us to speak mathematically about the opposing limits on being. Asian philosophy just spoke about the fact that Yin and Yang gave you the I Ching - a proto-maths that was too fuzzy to ever go anywhere after that.

So I don't undervalue Eastern metaphysics. But there are reasons why Western metaphysics - in its built-in capacity to be "utterly wrong" via axiomatic mathematical claims - became the actually productive intellectual tradition.

Zeno made everyone's head spin for the next 2300 years. Asian metaphysics has since gone down the nearest toilet/rabbit hole even in Asia. Universities over there don't teach quantum theory any differently.

You do realise that that makes you a super-strength pragmatist? :)

You aren't thinking of yourself as a CI proponent in the "consciousness causes collapse" sense? - https://en.wikipedia.org/wiki/Von_Neumann%E2%80%93Wigner_interpretation