I think 'we don't know' is the superior answer. Physics is getting hopelessly entangled in pseudo-metaphysics, Everett's being the most egregious example. A dose of humility and a sense of the limitations of science might be preferable. — Wayfarer

By all means keep an open mind. Nonetheless, Everett's is the only theory that explains why we see quantum interference effects. So it is the theory to beat.

By all means keep an open mind. Nonetheless, Everett's is the only theory that explains why we see quantum interference effects. So it is the theory to beat. — Andrew M

And as a result of MW being the ONLY explanatory theory that can reproduce all the results of QM, it is also the only testable theory.

https://arxiv.org/abs/1508.02048

except for it's not 'a theory', it is a metaphysic.

The metaphysics is realism, which brings us back to Einstein and Bohr.

except for it's not 'a theory', it is a metaphysic. — Wayfarer

No, it's a testable theory:

https://arxiv.org/abs/1508.02048

It is different from standard treatments of QM in that does not have the Born rule as an axiom. The Born rule is derived.

It has also made far reaching predictions - quantum computing, and predictions regarding conscious agents running on reversible quantum computers.

A rudimentary quantum computer is capable of performing vastly more calculations in parallel than if all the matter in the visible universe was made into a classical computer. In fact, that is an understatement. Where these parallel calculations occur, is not a metaphysical question.

only for 'weak' mwi; for the strong version there really are countless separate or parallel universes. And that is metaphysics.

predictions regarding conscious agents running on reversible quantum computers. — Tom

Also metaphysics. Assumes that 'conscious agents' are something that can be engineered. But it's probably beyond debate in your mind.

The metaphysics is realism, which brings us back to Einstein and Bohr. — Andrew M

The realism is required by the epistemology of science.

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.

But the point that I want to make, is that the Pythagorean theorem can only by known by a mind. So it's not mind-dependent, in the sense of being reliant or this or that mind, but in the sense of only being perceptible by a mind. So, what is, includes or implies a mind capable of grasping the truth! But that is what had been bracketed out of the scientific method by Galileo and his successors; this is where the idea of 'mind-independent' came from. So I think Einstein's conception of realism is at fault. Essentially, it doesn't want to recognize the limitations of science; saying that science sees 'things as they truly are' is a conceit.

Nice summary. I never understood all the confusion around CI, surely it's obvious that what will be observed is a facet determined by the capacities of the instrument being used to do the observing. The fact that those facets appear inconsistent is only due to it being a random snapshot of the facets.

To jump from there to a waveform collapse etc etc is assumption upon assumption while wearing blinkers. None of it follows.

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.

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.

If we were to survey physicists, what percetage do you think would say that they buy MWI instrumentally versus buying it as making a realist ontological commitment?

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.

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.

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. — apokrisis

My book is an attempt to bring that kind of mathematical formalism to Asian philosophy. Essentially, it assumes the law of identity goes down the nearest rabbit hole or toilet of your personal preference allowing even the mathematics to always remain context dependent. Rather than a metaphysical approach that builds from the ground up, it takes the top down approach of merely sorting all the metaphors for any humble and elegant simplicity to make both more and less sense out of observations without requiring any assumptions other than that the law of identity must vanish into indeterminacy.

From what I read his vision of time is merely begging the question and splitting semantic hairs. Calling something random is like saying it has no properties and does not exist. He is circling the drain, so to speak, and attempting to do much the same thing that I am doing with my own writing using a more western metaphysical approach. The problem is he is mixing metaphysics and metaphors leading to a contradiction. Without a demonstrable definition for what random means he is essentially using metaphors in an attempt to describe everything metaphysically.

Again, the second law of thermodynamics has proven to be violated on micron scales and smaller meaning that entropy can decrease. A scrambled and fried quantum egg will reassemble itself and there's just no way metaphysics can explain the inexplicable any better than mysticism can. God may be able to see the back of their own head without a mirror, but the rest of us don't have that luxury. The implication is that all of fuzzy logic implies a yin-yang systems logic is required that can express both causal and acausal perspectives with a common shadow being an example of the acausal.

Whether we see a shadow as the absence of light just depends upon the context and, for example, in a dark room what was a shadow can become a faint blob of light because it isn't so much an effect of scale as it is how humble the specific context and its contents are relative to the observer and each other. Mathematically speaking, photons experience isomorphic space-time meaning they don't distinguish between forward or backwards in either space or time just as we might say that shadows don't distinguish between space or time. Photons are also instantly absorbed and emitted and appear to have no independent identity of their own merely conveying any energy and information with perfect fidelity just as a shadow can be said to merely convey the lack of energy and information instantaneously with perfect fidelity. The opposite is also true and in a dark shielded vacuum chamber virtual particles will appear out of nowhere because a context without any significant content is both physically and conceptually gibberish. Mother nature's mindless sense of beauty and humor can resemble that of a toddler, yet, the human eye is sensitive enough to detect a single photon ensuring that nobody is ever left completely in the dark.

Shadows express the same principle that can be applied to everything that a context without significant content and vice versa is simply physically and conceptually impossible. It would mean that thermodynamics need to be reformulated along the lines of Adrian Bejan's Constructal Theory, but as a systems logic that expresses retro-causality. The past merely represents more of the geometry of the universe that we can perceive and the future more of the time, but the two can exchange identities. In order to prevent the past from dominating the future its own synergy leads to the future normalizing any individual contributions of its contents.

Synergy itself becomes context dependent because it can be perceived as normalization.

What I am calling into question is the principle of 'mind-independence' or 'scientific realism'.

I notice from the Orzel blog, 'The fundamental problem with Many-Worlds is that every argument about it devolves very quickly into stoner dorm-room bull session nonsense about parallel worlds and identity and morality. But none of that is physics.'

'The physics' can be understood solely in terms of mathematics, without delving into what it means in philosophical terms - whether there are many worlds, or how to think about what that means. But insofar as physics is purported to be about what is real, then dorm-room bull is inevitable, as far as I am concerned. I noticed in an earlier post about this, the Worlds were spelled with a capital W. So I think that 'many worlds' is actually morphing into a form of popular or science-fiction metaphysics (with David Deutsch as it's cult hero and the Quantum Computer as the cult object. Sure that's dorm-room bull, but that can be said of a lot of 'cultural artefacts').

I never understood all the confusion around CI, surely it's obvious that what will be observed is a facet determined by the capacities of the instrument being used to do the observing. — Punshhh

As quantum physics developed, it undermined common-sense realism or even scientific realism. Einstein wanted to see a fundamental material unit, not all of this wave-particle ambiguity and now-you-see-it now-you-don't magic tricks. It offended his sense of propriety.

From the Aeon article that Orzel says is terrible:

An existence where? This is where the many worlds come in. ...You measure the path of an electron, and in this world it seems to go this way, but in another world it went that way.

That requires a parallel, identical apparatus for the electron to traverse. More – it requires a parallel you to measure it. Once begun, this process of fabrication has no end: you have to build an entire parallel universe around that one electron, identical in all respects except where the electron went. You avoid the complication of wavefunction collapse, but at the expense of making another universe.

All the MWI advocates seem to be ignoring this point.

All the MWI advocates seem to be ignoring this point. — Wayfarer

Sure, Many World advocates ignore that point.

http://www.cheapuniverses.com/

Orzel is also wrong. by the way.

As quantum physics developed, it undermined common-sense realism or even scientific realism. Einstein wanted to see a fundamental material unit, not all of this wave-particle ambiguity and now-you-see-it now-you-don't magic tricks. It offended his sense of propriety. — Wayfarer

Many Worlds is realist.

only for 'weak' mwi; for the strong version there really are countless separate or parallel universes. And that is metaphysics, — Wayfarer

I'm guessing by 'weak' mwi, you mean instrumentalism. An instrumentalist would say that they don't know what summing over paths really means or, more strongly, that it doesn't mean anything. But it works extremely well for predicting phenomena, so we should use it.

But why does the math work? The straightforward realist explanation is that the world really is as the math describes it. There are paths that split off and interfere.

BTW, MW doesn't imply parallel universes, but instead paths (branches) within the universe. And these paths are observed in quantum interference experiments.

MW doesn't imply parallel universes — AndrewM

Tell me this, then - what does the "M" stand for in "MW"?

Orzel is also wrong — Tom

says you.

Obviously it stands for 'many worlds'. It refers to the many paths (or branches) that can be in superposition.

If we were to survey physicists, what percetage do you think would say that they buy MWI instrumentally versus buying it as making a realist ontological commitment? — Terrapin Station

The old argument from consensus.

Only a minority of physicists advocate Everett. It's a scandal, which future historians will recognise as being an obstacle to progress. In fact Deutsch is on record, not only stating that Bohm could have anticipated Everett entirely, if only he had not equivocated about what is real and what is not in his theory, but that the quantum computer could easily have been invented in 1950s for the same reason. All the quantum mechanics was there, plus an extraordinary collection of towering geniuses.

Strange as it may seem, the nature of reality doesn't trouble most physicists, and few have any understanding of the importance of realism. Most shut-up-and-calculate, and whether they admit it or not, they do so as if they were dealing with reality. Methodological (or unconscious) realism works up to a point.

But, where it matters, i.e. where pretending QM is not about reality makes no sense whatsoever - particularly in the fields of quantum cosmology or quantum computation - then Everett may be consensus. Hawking is on record stating it is "trivially true".

Of those working on foundations, if Oxford U Philosophy of Physics dept. is anything to go by, then Everettians make up 25%. http://www.philosophy-of-physics.ox.ac.uk/

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.

Andrew, 'Worlds' doesn't begin with 'M', does it. The question was, what does "M" stand for? And obviously the answer is 'many' - as in 'many worlds'. That is what it means, it refers to branching or splitting or multiple universes.

In the ‘multiverse’ of the Many Worlds view, says Tegmark, ‘all possible states exist at every instant’. That’s quite an ambiguous statement, since it might either mean all states that could evolve from some initial configuration, or all imaginable arrangements of all particles. But, either way, we face some nonsensical implications. You see, the MWI does some radical stuff to you and me.

‘The act of making a decision,’ says Tegmark – a ‘decision’ here being interchangeable with an experiment or measurement – ‘causes a person to split into multiple copies.’ Brian Greene, another prominent MWI advocate, tells us gleefully that ‘each copy is you’. In other words, you just need to broaden your mind beyond your parochial idea of what ‘you’ means. Each of these individuals has its own consciousness, and so each believes he or she is ‘you’ – but the real ‘you’ is their sum total.

Now, if it doesn't mean that, then there's nothing to debate. If the 'many' in 'many worlds' is simply an hypothetical mathematical construct or device, then it's back to 'shut up and calculate'. But the controversy is about the notion that it really does say there are many or parallel realms.

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. — Apokrisis

Right - decoherence, I get that. I think I'm more or less in agreement with your post, although I don't have the background to understand all of it.

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. — Apokrisis

And I think the first two points there are much nearer to Bohr and Heisenberg's attitude.

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. ;)

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. — apokrisis

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". Definitely nope, Nope, thrice NOPE!

Andrew, 'Worlds' doesn't begin with 'M', does it. The question was, what does "M" stand for? And obviously the answer is 'many' - as in 'many worlds'. That is what it means, it refers to branching or splitting or multiple universes. — Wayfarer

Sorry I misread and I've edited my earlier comment.

Now, if it doesn't mean that, then there's nothing to debate. If the 'many' in 'many worlds' is simply an hypothetical mathematical construct or device, then it's back to 'shut up and calculate'. But the controversy is about the notion that it really does say there are many or parallel realms. — Wayfarer

People simply use different terminology to refer to the same phenomena. What is being referred to is the many paths, or branches, that can be in superposition.

And, yes, the realists say those branches are real.

Hawking is on record stating it is "trivially true". — Tom

Right, but by that he doesn't mean that it's referring to anything real. He's a positivist, i.e., doesn't matter whether there really are many worlds. From the Wiki article on Many Worlds:

"But, look: All that one does, really, is to calculate conditional probabilities—in other words, the probability of A happening, given B. I think that that's all the many worlds interpretation is. Some people overlay it with a lot of mysticism about the wave function splitting into different parts. But all that you're calculating is conditional probabilities."

"I don't demand that a theory correspond to reality because I don't know what it is. Reality is not a quality you can test with litmus paper. All I'm concerned with is that the theory should predict the results of measurements. Quantum theory does this very successfully. — Stephen Hawking

My underline. So Hawking is saying, he doesn't know what is real (and the implication is, doesn't care.) So, it's all 'shut up and calculate'. MWI isn't about 'reality' at all. All you're doing is calculating possibilities - in which case there's nothing to debate.

People simply use different terminology to refer to the same phenomena. What is being referred to is the many paths, or branches, that can be in superposition. — AndrewM

I would have thought that the 'many paths' are not phenomena. They're inferences. But one cannot see 'the other paths', by definition - they're what's in the 'other worlds'. We only see one path - so that is the only 'phenomenon' being observed, the rest is inference.

Andrew, 'Worlds' doesn't begin with 'M', does it. The question was, what does "M" stand for?. And obviously the answer is 'many' - as in 'many worlds'. That is what it means, it refers to branching or splitting or multiple universes. — Wayfarer

Nope, it doesn't refer to that.

What Everett claimed is that the bare formalism of quantum mechanics may be treated in a straightforward realist way, without changing our general conception of science, or quantum mechanics.

So, here's the thing. According to text-book QM, when you have a macroscopic superposition, you declare indefiniteness. Under Everett, you accept multiplicity.

multiplicity of what?