Why is this reality apparent as opposed to other possible worlds?
So, in the Many Worlds Theory of QM the wavefunction doesn't collapse. Instead, we have decoherence and the branching out of possible worlds.
However, what puzzles me about this interpretation of QM is how is this reality (the one here, at this moment which you are reading here on Earth) real as opposed to other possible worlds?
However, what puzzles me about this interpretation of QM is how is this reality (the one here, at this moment which you are reading here on Earth) real as opposed to other possible worlds?
Comments (215)
Why is this one real as opposed to the others I'm not experiencing where I instead went to sleep instead of replying to your post, now?
Because in this one you're replying to the post. In another one, you're sleeping. What you're asking is why you're experiencing posting and not going to sleep. That's because you're not that "version" of you. That other you experienced it.
Common!
You will notice that frequently in this discussion, the reality of the other worlds is put in quotes- 'other', or 'real'. A typical example is the Wikipedia entry on Many Worlds, the second sentence of which reads:
Note the scare quotes around world and universe. So are they 'worlds' - or worlds? Are they real - or 'real'?
I don't think we will ever know.
I have often asked the question, both here and on Physics Forum, that if Many Worlds is the solution, then what is the problem? And that is a question I never get a straight answer to.
http://xxx.lanl.gov/abs/quant-ph/0104033
If it's not true, then what? That is the philosophical question.
But that isn't the first sentence, is it?
...."led Everett..."
I don't think you are even attempting to be honest.
The question I am asking is, if 'parallel universes or histories is the solution, what is the problem?' Why is it necessary to postulate such an apparently bizarre notion in the first place? What problem is it trying to solve?
If Many-Worlds is proven false, we will know for sure that the worlds are not real.
Quoting Wayfarer
I think the problem is that physicists are trying to understand the true nature of real possibility, with an inadequate understanding of the nature of time. In other words, their understanding of physical activity has come to the limits allowed, by their understanding of the non-physical time. Since time is what makes physical activity possible, and physicists do not have an adequate understanding of time, physicists do not have adequate premises for understanding the possibility of physical activity.
Speculations such as Many-Worlds are just examples of what comes about when a science pushes the limits of its premises. When premises are taken to the point where they produce absurd conclusions, what is demonstrated is a need to revisit the premises. In the case of quantum physics, what is glaringly obvious, is the inadequate understanding of time.
This isn't to suggest that I support "many worlds," that I think it's not just nonsense applied as a way to understand a particular set of mathematical constructions, but nevertheless, that's the idea.
You could ask what problem does entanglement solve? What problem does superposition solve? What problem does the Heisenberg Uncertainty Principle solve?
Or, when dealing with General Relativity, what problem do black holes solve? What problem do gravitational waves solve?
Parallel "universes" are a prediction of unitary i.e. Everettian quantum mechanics, which, as a by product, solve a number of other problems: e.g.
The Measurement Problem.
The nature of probability.
The arrow of time.
The meaning of counterfactuals.
The meaning of complexity.
A couple of other discoveries that were made within Everettian QM, but are arguably theory-neutral ( I disagree)
The possibility of quantum computers.
The existence of decoherence.
So, taking QM seriously as a theory of reality solves many problems, and renders it testable. Parallel "worlds" are a prediction.
In what sense is this particular prediction "testable"? What specific experiential consequences can we deductively explicate from it? How would we then go about inductively evaluating whether there really are parallel "worlds"?
Um, perhaps you've not been paying attention, but we know the other worlds exist because they interact with each other and with our world.
https://arxiv.org/abs/1508.02048
The only known theory that can reproduce the results of QM, at least up to quantum field theory, is Many Worlds.
I concede that I am not fully up to speed on QM, but it strikes me as a bit presumptuous to claim that we know the other worlds exist, and that they interact with our world. To be honest, I am not even sure what that would mean, or how one would demonstrate it.
In any case, the OP asked about distinguishing the world that we are actually experiencing from the "other" possible worlds. I was merely suggesting one terminological option for doing so.
Well, what if they're not? What if you refuse to entertain the notion? I think Neils Bohr refused to entertain it. Sure, it leaves all kinds of unanswered questions, but the lack of an answer migh be better than a clever fallacy.
And sure it's true that other interpretations are not testable - but that might just be an indication that we're dealing with a problem which is on the border of what is knowable. Again it might be better to acknowledge that than to build an edifice on fantasy.
Thank you.
Perhaps you are in a different world? It seems like every participant in this thread is in one's own world. At least we are somewhat capable of interacting though.
But, the laws of physics are the same for all of us and we occupy the same space. So, hypothetically we are all experiencing the same history of the world (or what can be called the evolution of the wavefunction).
I think the issue is that if Everettian QM both explains our observations and solves a bunch of problems, as Tom points out, then on what grounds are you dismissing it?
In terms of consequences, we can continue to hold the same kinds of views around personal identity and decision-making as we always have. It's just that the world would be larger than previously thought.
Haha, it's disturbing to imagine what you'd be willing to do in the presence of Deutsch.
Anyway, the first big problem with the paper you linked to is that in section 2, what he describes as essentially the Popperian approach is not at all at odds with the Bayesian, instrumentalist or positivist approach to experimentation, yet Douche describes the latter as contradictory to the former.
That particular prediction is tested in every quantum interference experiment, and every experiment involving "non-locality". Quantum computing is also a test, as are certain proposed experiments involving reversible quantum computers.
A particularly striking and simple test is the Elitzur-Vaidman Bomb-Tester, in which you get to blow up a laboratory and perhaps kill yourself in a parallel world.
https://arxiv.org/abs/hep-th/9305002
If you dismiss Many Worlds, what theory do you replace it with?
Everett never mentioned Many Worlds in his publications, he focused on solving the measurement problem thus formulating quantum mechanics in a manner suitable for addressing quantum gravity.
Because you have never studied quantum mechanics, you keep claiming the many worlds are an assumption. This is pure ignorance. I'm getting a bit tired of repeating that the branching nature of the wavefunction - which gives rise ultimately to the many worlds - is a prediction of the theory. It can't be avoided without ad-hoc modification of unitary quantum mechanics.
Try this book:
https://www.amazon.co.uk/Emergent-Multiverse-Quantum-According-Interpretation/dp/0198707541
I said that quantum physics is on the border of what can be known. Maybe there will be no theory to replace it with. Maybe it's something we'll never know.
Quoting tom
This is a philosophy forum. Papers published in the technical journals of physics are not part of the curriculum. Besides, I think that many physicists are engaging in metaphysics without even knowing that they are doing that. Sean Carroll is arguing that untestable predictions ought to be regarded as scientific merely because they're mathematically elegant.
Imagine how the world would look if all the imaginary elbow room provided by many worlds and multiverses were swept away. Imagine if we had to face the cold light of day knowing there were implications of physics that we simply can't understand, instead of inventing fantastic mathematical extravaganzas to 'make sense' of them.
Here he is talking.
https://podcasts.ox.ac.uk/plurality-worlds
Wallace is committed though to a very particular view. Here is part of Chapter 1 of his book:
Personally I am content with that and find Wallace's view of the philosophy of science overblown and too dismissive of alternatives. But then I am a die-hard empiricist, and don't accept that the desire for an elegant theory should override scepticism about metaphysical claims. Obviously, Wallace goes on to express his discontent with what he calls an 'instrumentalist' view of science, and his argument for metaphysical (scientific) realism.
Peter Woit's blog is an entertaining alternative that treats multiverse claims with some scepticism, while insisting on scientific rigour, if anyone is interested: http://www.math.columbia.edu/~woit/wordpress/
I think we should at minimum be clear that the Deutsch view is a minority position within physics; it doesn't stand for science against ignorant philistines masquerading as amateur philosophers.
They would be no solution at all. But this would imply the QM formalism being either wrong or incomplete. And QM is a very well tested theory.
QM is counterintuitive to humans because we don't knowingly encounter things in superposition in everyday life. People intuitively think we live in an classical world where particles have precise positions and momenta at the same time. But we don't - we live in a quantum world and so it's really our intuitions that need to change.
Once we stop thinking of superposition states as possible states that the particle can be in (the classical intuition) and instead as actual states that interfere with each other (the quantum intuition), then the idea of parallel worlds (or branches or paths) naturally follows.
The philosophical issue is whether mathematical equations provide insight into the world we live in, or whether they are mere Platonic abstractions that nonetheless may have instrumental value.
Quoting Andrew M
ONLY given a particular, and physicalist, notion of what constitutes 'reality'. There are alternatives that are not based on materialist premisses - for example, Bernard D'Espagnat's 'Vieled Reality' which is nearer to Neo-Kantianism. Werner Heisenberg favoured a Platonist approach. And I don't think any of the MWI advocates have any grasp of Platonism or Kant, because they're too committed to physicalism. It really is a metaphysical problem, masquerading as scientific theory.
Notice that in David Wallace's podcasts on MW, it states upfront the fact that among the problems that are solved is that of the requirement for there to be an observer - the crux of the measurement problem. MWI disposes of that by saying that there is 'no collapse', i.e. all the observations are equally real in some parallel world. Doesn't that just strike you as being a monumentally bizarre idea - that there are endless replicas of the universe? If you can't see how bizarre it seems, then I'm afraid we do live in different worlds after all.
I keep an eye on Woit's blog. I only understand a fraction of what he says, but what I understand I'm generally in agreement with.
Quoting mcdoodle
...which is well on its way to becoming a new religious movement, complete with iconic heroes (Deutsch, Everett, Tegmark), and eschatology (i.e. realisation of human consciiousness in silicon.)
What you're not allowing for is the possibility of 'real abstractions'. In your view 'abstractions' are simply 'mental phenomena', which must be consequent to the physical, right? Mental phenomena are the products of the brain, which is the product of evolution, which is ultimately governed by physical laws, right? So there is no way to understand how 'abstractiions' can be real in any objective sense.
But, note this passage from Heisenberg, in his lecture The Debate between Plato and Democritus'. Democritus (and Leuccipes) founded atomism, the idea of an ultimate material point or particle; Plato on the other hand, represents objective idealism, the philosophy that ideas precede forms.
Underline added. Heisenberg is suggesting that sub-atomic particles can't be said to exist in the way stones or flowers exist. In what way do they exist? Elsewhere, he says they are:
Heisenberg called this "potentia," a concept found in Aristotle. So in this framework, the observation made by the physicist 'actualises' the potentially-existing 'object' into a particle, which doesn't really exist prior to that observation.
Now I don't think realism can cope with this, because something like a sub-atomic particle either exist or they don't. And if they don't exist, then what is at the foundations of our purportedly material reality?
The 'Copenhagen Interpretation' doesn't solve the issue. It simply points it out. It's not a school of thought, it's not a philosophy or a method. All it consists of, are various observations from those associated with Bohr's institute in Denmark, concerning what can and can't be said on the basis of quantum mechanics. But as I said before, I think the admission of there not being an answer, is preferable to speculative metaphysics which purports to provide an answer based on questionable premisses.
But you know that is an understatement by a very long way! Ignoring the fact that our culture and technology is based on QM -we spend hours a day interacting with it and through it, not even the LHC can detect a hint that there might be the slightest problem.
Then of course there is the fact that QM is full of surprises. How is it possible that a conjectured law to explain atomic spectra, should also reveal entanglement, superposition, teleportation, quantum computing and the multiverse? Luck?
Quoting Andrew M
Instrumentalism, apart from being wrong for other reasons, cannot explain the surprises.
Yes, it sounded bizarre when I first encountered it. But having worked through the math, there's really no way around it. The other interpretations are just creative attempts to avoid the straightforward implications of QM.
Everettian QM is unitary, local, causal, realist, parsimonious, explanatory and testable - just the sorts of things one would expect of a robust scientific theory. On the other side is Copenhagen QM, which just shrugs and says the math is meaningless and the world is intrinsically unknowable.
So that is the context for judging these two interpretations. Everettian QM violates our natural intuitions, but has all the hallmarks of a correct theory.
I think of abstractions in an Aristotelian sense, not Platonic sense. That is, universals exist when they are instantiated in things. In this sense, abstractions existed prior to people being around to talk about them. They are something we discover, not create.
Quoting Wayfarer
It's a creative theory. But what does it mean? Do potentially-existing objects interfere in the double-slit experiment?
Indeed. But I'm leaving open the possibility of extra postulates. For example, QM would be incomplete if there were demonstrated to be disappearing worlds, per Copenhagen.
I assume you understand that there is a distinction between past and future. An actually existing object owes its actual existence to the fact that it has been actualized. The act which causes its existence is in the past. A potentially existing objects is one that has not yet been actualized. It is in the future. The act to cause its existence has not yet occurred. Do you recognize the difference between a past act and a future act? The past act has already occurred, and so it has existence in time. The future act has not yet occurred and so it does not exist in time.
But it may not be simply a mathematical issue. What is measurable might be only one aspect of what is there. Notice this comment that Wallace makes (quoted by McDoodle):
I think it's much more likely that there's something basic that we don't understand, than parallel universes.
Quoting Andrew M
Hey, we're discussing Werner Heisenberg. He's not simply 'a creative theorist' but one of the founders of quantum physics. I don't claim any kind of deep knowledge of his philosophy of physics but I think he probably has good 'street cred' on the subject.
But as I understand it, such things as sub-atomic particles are not 'existents' in the way that we intuitively understand such things. That is actually the import of the passage I posted. He says when say of flowers and stones and the like that they exist, we can't use the same terminology about sub-atomic entities. They're on the borderline between existence and potentiality. So when you ask of them 'do they exist', the answer is neither yes nor no; it's 'it depends on what you mean by "exist"' or 'it depends on what question you're asking'. So their existence is not un-ambigious, which is what is the real problem for physicalism and realism. On the other hand, if one is not a scientific realist, then it's not that big a problem.
Quoting Metaphysician Undercover
Earlier on the other thread on this topic, there was a discussion about the interference pattern in the double-slit experiment. I noted that the interference pattern is independent of the rate at which electrons are fired. So I put that question to Physics forum, and also Stack Exchange, and sure enough, the physicists there said that 'time is not a boundary condition' of the interference pattern.
The question I then asked was, are other kinds of wave-functions also independent of time? What is the significance of a timeless wave? That question didn't produce a response. I think it's significant, but to prove it, I would probably have to go and re-enroll in physics and spend 5 years on it. But, intuitively, what it tells me is that the probability wave is not a function of time, and I think that has profound philosophical significance.
Quoting tom
What about the so-called Nightmare scenario? This is a hard thing to summarise but describes the possibility that if there are no super-symmetric particles, that the standard model seems 'unnaturally fine-tuned'.
So actually, even though physics produces highly accurate results, there are huge conceptual gaps.
Why not?
The basic thing that we don't understand is the nature of time. There is One fundamental principle which is well proven by experience, and therefore produces the most sound base for any ontology, which is ignored, neglected, or even dismissed by most physicists. This is the basic assumption that there is a substantial difference between future and past. We know that this is true, because things in the past have already occurred, and things in the future have not yet occurred. This simple fact has far more influence over the way that we live our lives than any other definable fact. It permeates all aspects of all our actions, languages, and concepts. For some reason, at the level of theoretical physics, and metaphysical speculations carried out by physicists, there is a tendency to deny this simple fact. I see it as an unwarranted attempt to simplify the complex, an unjustified application of Occam's razor.
The substantial difference between future and past necessitates the assumption of two distinct types of substance, one proper to the past, the other proper to the future. We cannot assign substantial existence (the existence of substance) to the present, because the present appears to us as a division between future and past, and such a division has not temporal extension. Substance necessarily has temporal extension. So we have two distinct types of substance which bear the labels actual (past) and potential (future). Of course one must be transformed into the other, and this is what occurs at the present, actualization, what we call activity. This produces the concept of "becoming", which refers to the activity at the present.
Now we have another difficulty to overcome. Activity necessarily requires time, temporal extension. But we've already relegated temporal extension to the past and to the future, producing a timeless boundary at the present. The boundary between past and future, the present, can no longer be considered to be timeless, because we must allow that becoming occurs at the present, and becoming is a concept with temporal extension inherent within it, just like substance has temporal extension inherent within. The only logical option is to assume another dimension of time, which is proper to becoming.
So we temporal extension, in the classical sense, which refers to the tradition concept of time. This assumes a non-dimensional point in time, derived from the non-temporal point which separates future from past. We can map out many different time periods, containing duration of time, in the classical sense. But this non-dimensional, non-temporal point, dividing two periods of time, is artificial. And, it is an inadequate representation. It is derived from the assumption of a non-temporal division between past and future, "the present is a point in time". It is inadequate, because from this assumption "becoming" is unintelligible, it defies the laws of logic. This problem with becoming has been demonstrated over and over in different ways by different philosophers. In order to render becoming as intelligible, we must be able to assign to it a temporal order. This is a passing of time which occurs at the present, within that artificial point, that divides future from past. This newly found dimension of time is completely different from time as referred to in the classical sense, because it is ongoing within the point which divides between two classically separated durations of time. The challenge is to establish principles of consistency between the two, to create one concept of time, consisting of these two dimensions.
Quoting Wayfarer
So from my perspective, there really is no "timeless wave". The wave-function must be measured according to the other, undeveloped, dimension of time. It is proper to the realm of becoming, as all energy is. "Energy" refers to a relationship between what actually is (past), and what potential is (future), so its existence is proper to becoming, which can only be measured according to the new dimension of time. What this perspective opens up to the mind, is the vast realm of unknown, which lies on the other side of that newly dimensioned point in time, the present. This is the realm of the not yet actual, the future. Since it is prior to the passing of time at the present, it is truly timeless. Our only means of access to it, is to develop the dimension of time which is proper to the present, becoming and the wave-function. By doing this, we can establish a mathematical relationship between the realm of what actual existence (past), and the realm of potential existence (future, 2nd type of substance). But without this relationship, which can be defined as a unified concept of time, we have no approach to this non-empirical realm.
Your explanation needs to account for the double-slit experiment. What goes through the slits, if anything, such that an interference pattern is observed on the back screen?
Who is 'we'? I know for sure I don't understand it, and I'm pretty sure I'm not going to find out the solution on a philosophy forum. (Not wanting to be rude, or anything like that.)
As I said - outside of time. Sub-atomic particles belong to a different order to that of pheneomena, which always appear in time.
The slits are an object, and so have actual existence. Their existence justified by past observation. Objects have substantial existence, and I divided substantial existence into two categories, past and future, actual and potential respectively, such that the two are fundamentally incompatible. What goes through the slits is energy, and as I explained in my post, energy exists in the realm of becoming, which occupies the boundary, or separation between the two types of substance. It exists at the present. Therefore nothing substantial goes through the slits. That something moves through the slits is just our way of describing relationships between substances.
This is how we understand motions, as relationships between different substances. When we deal completely with actual objects, we deal with different types of objects, all within one category, observed existence, that of the past. We establish relationships between these objects and this is what we call motion. Notice that motion is completely conceptual. It is not necessary that any objects "really move", it is just the case that the observed relationships change, and this we call motion.
Now, introduce the second type of substance, future existence. All substance of the future is potential rather than actual, so there is a boundary which separates these two principal categories. The concept of energy allows that not only actual objects are related to one another, but potential objects as well are admitted into these relationships. The deficiency in this concept is that the proper separation between the two fully incompatible categories is not respected. Thus actual objects, may be related to potential objects, as if they are both one classification, objects, without accounting for the categorical separation. If the categorical separation I describe is real, then it seems impossible that potential objects "really move", because there is no real object to move. And if this is the case, the status of the movement of actual objects is also thrown into doubt.
So consider that energy is just an extension of the concept of motion, and as I said, motion refers to the relationships between objects. These relationship change, and we call this motion. "Motion" refers to our descriptions, not the objects themselves. If all the objects being related to each other, are observed objects, actual, in the past, then then we can maintain consistency in our descriptions of the relationships. But if some of the objects are actual objects, and some are potential, and they are related through the concept of energy, then there is a deficiency according to the failings in maintaining this categorical separation. The described motion, energy through the slits, is a description which relates things on one side of the slits to things on the other. But as I said, the concept of energy is deficient as it does not properly provide for the categorical separation between actual things and potential things. Therefore we have no determination of what goes through the slits, an actual thing or a potential thing. If it's a potential thing, then it is impossible that it really moves through the slits. If it is an actual thing, it is doubtful that it really moves through the slits.
In this case, what I refer to with "we" is what I believe to be every human being in the world. None of us have the adequate understanding of the nature of time, which is required to produce a coherent understanding of the nature of existence. And as I said, the modern tendency is to insistently produce simplifications. You might say, it keeps the mathematics eloquent. But to over-simplify something very complex is a mistake if you are attempting to understand that complex thing.
Where else, other than a philosophy forum would you expect to find out the truth about these matters? You know that it is a metaphysical issue rather than a physical issue, so a metaphysician is more highly qualified to tackle such problems than a physicist. But there is no funding to hire a metaphysician to bring issues against established institutions of science. So you might only find one taking advantage of a public forum, at one's own will, occupying one's own free time. Also, consider that physicists such as Lee Smolin for example, who advocate for the "reality" of time, and advance notions which question the completeness of special relativity tend to get ridiculed and ostracized: http://motls.blogspot.ca/2009/08/why-lee-smolin-is-immoral-double-faced.html Pay particular attention to the final paragraph where the blogger is concerned about influence over the general public who control the funding agencies.
Modern speculative physics is the very same thing, sophistry. It is highly educated individuals simply seeking money to support their stream of false information. If they are to be rousted, as the sophists which they are, where else to start this movement other than a philosophy forum?
Fair enough, point taken. I'm aware of Lee Smolin's books, but I don't know if I'm up to reading them.
Quoting Metaphysician Undercover
I agree with you, but I don't think the likes of you and I sounding off about on forums is going to make the least difference.
He's into Loop Quantum Gravity, did some work on string theory, but seems to think that may be a dead end. I read Time Reborn. I liked it because it challenges physicists to take seriously the idea that time is something real. It brings to light real problems in physics which lead toward the idea that time must be something real. However I was somewhat disappointed with the book because it offers no speculation as to what time is. The title hints that the book might go that way. If time is real, it must be something describable.
Quoting Wayfarer
Oh come on, please don't shatter my illusions. This is my little fantasy world here, let me live it and leave me to my pleasures. If it's not hurting anyone, leave me in my deluded state. It's not like I'm trying to force you to join me.
As you probably know by now (even if you don't like it!), local realism works just fine under Everettian QM. If you measure one of the photons and its polarization is horizontal, you can then deduce that the polarization of the other photon is also horizontal. That's because the initial measurement entangles you on the same branch as that pair of photons (and not the vertically-polarized photon pair). So QM respects space and time - no superluminal effects required.
It works, given that there are 'branches'. But then Ptolmaic epicycles worked, given that there were crystal spheres.
It preserves time and space at the cost of introducing parallel worlds.
The branching is intrinsic to QM. So it's dynamical collapse and hidden variables that are ad hoc, in order to preserve classical single-world intuitions.
But it's not. It is the result of a simple conjecture: 'hey, what if the wave collapse DOESN"T OCCUR?' That's all it is. One of the implications of the wave function not occuring is that there must be gadzillions of different universes, or that the universe 'splits' whenever a measurement is made. But those who advocate it, don't seem to get how bizarre this is. 'Look at the math', they say.
Here is where I get off the bus. I just think it's conjecture gone mad. Sure, given that there are all these branches, then 'the math works'. But there's something the matter with the basic intuition behind it.
That article I'm quoting from, on Scientific American, notes that Neils Bohr did eventually agree to speak to Everett.
It was in doing the math for the 'deployment of nuclear weapons' that Everett made his fortune. Not that it did him a lot of good. He died aged 51, an embittered alchoholic hardly on speaking terms with his family, leaving instructions in his will to have his ashes put in the garbage.
Sure, he might have been a brilliant mathematician, but there was something seriously wrong with his intuition, in my opinion.
So in this case perhaps we should be looking for the worth of the funding, are the money dispensers taking it all on faith? What is the worth they are expecting to arrive?
You are misrepresenting QM:
Copenhagen - Wavefunction collapse does not occur.
Many Worlds - Wavefunction collapse does not occur
De Broglie-Bohm - Wavefunction collapse does not occur
Modal Theories - Wavefunction collapse does not occur
Relational Theory - Wavefunction collapse does not occur
Statistical Interp. - ....
Ensemble ...
Many Minds
Consistent Histories
Get the idea?
The only theories that ever employed wavefunction collapse as a process in nature are von Neumann's theory of consciousness causing collapse, GRW - which is NOT quantum mechanics and does NOT work, and the Transactional interpretation.
Oh, but of course, wavefunction collapse also happens to be falsified.
The WIkipedia entry on the subject states that:
Further down in the same article, it is stated that:
The reference there is to this quote by Heisenberg:
Sure sounds like 'wave function collapse' to me. But, as you know, Wikipedia is a user-edited resource, so if you believe it's wrong, go ahead and edit it.
Such joy being reduced to selecting quotes from the same wikipedia page!
Copenhagen, and neo-Copenhagen theories such as Consistent Histories, are purely epistemic. The wavefunction is not part of reality, and certainly collapse is not.
Do we really have to repeat these threads over and over again? Local realism and non-local realism have been falsified by several no-go theorems. Copenhagen survives because it is not a theory about what is real, rather it is a theory about what can be said about what is real. Many Worlds survives because the no-go theorems do not apply to it.
This is the whole point of the famous Bohr-Einstein debate. Einstein could not accept that QM was not about "elements of reality", whereas Bohr claimed "the quantum world does not exist".
And, as we have repeated, and repeated, a theory that is explicitly anti-realist cannot provide an explanation. The ONLY explanatory theory that exists, which agrees with QM all the way up through field theory and the Standard Model is Many Worlds.
A famous quote from Bohr:
Of course, Einstein, Everett disagree, though I think Deepak Chopra agrees.
This blog is worth a look.
http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/
So, the first quoted passage is incorrect, in your view? (I ask because it seems to contradict what you said in the post before).
Quoting tom
But these are all intepretations. When you say that something has or hasn't been falsified, all you're doing it is interpreting it in accordance with your chosen metaphysical view, which any statement about what the theory means must be. Everyone sees the same data, the only thing being discussed here is what it means.
Quoting tom
I interpret the wave-function as a distribution of probabilities. Is that not correct?
Quoting tom
That's only because of a pre-commitment to the kinds of explanations that must be real. Again, it's a metaphysic masquerading as science. It all comes down to a very literalistic understanding of what must be considered 'real'.
Shocking statement, isn't it. But probably not as shocking as the Bohr Family Coat of Arms:
I'm sure Deepak would think that was cool. ;)
Well stated, that is exactly Socrates' attitude, and the position we should all take, including the high level physicists. Many already have this attitude with respect to limited branches in the field, the key is to expand this principle to all areas, even fundamental assumptions. Start with the premise "I know nothing", and justify every premise before proceeding.
Knowledge is a journey which proceeds into the unknown. The destination is unknown. Each premise, or assumption, is a fork in the road, the option to proceed or not. Do I take this road or not? There's a map of sorts, because I can look ahead, with my limited comprehensive capacity, and see where it has brought others. Are they coming to a dead end? What other options do I have? Have some others taken other roads? The nature of possibility is that there are always other options. The roads less travelled are not so well cleared, they must be sought. Where they might be exposed, who knows (tpf?). Perhaps I'm already beyond the turn off, I missed it because it was the less travelled road, so I have to go back and find that fork. Perhaps individuals slip off the well travelled road at different points all along, seeing the dead end ahead, adopting different assumptions which are not the same as each other, but are inconsistent with the well travelled road, then they start to come together again on a different well traveled road, off there in the distance somewhere, as they establish consistency with each other. Should I create my own turn off, or go all the way back looking for a more well travelled turn off?
It is better to have no understanding than a misunderstanding. Misunderstanding is the illusion of understanding, the believe of understanding which is really not understanding, it is mistaken. Misunderstanding robs one of the capacity of choice. All appears as understood, but it is not. Under the illusion which is called misunderstanding, there is no choice as to which road to take, the certitude involved with the confidence of knowing, and the appearance of understood, denies that possibility. But the confidence is misplaced, involved with misunderstanding rather than understanding.
Quoting Punshhh
It's really always taken on faith, the western system is an honour system, built on strong moral principles, honesty, with trust and faith entwined with honesty. Though there are some exceptions to the rule, honesty is not the problem, physicists who are being funded to do their research truly believe that they are proceeding in the right direction. The vast majority of the money comes from the consumers, industry follows this, and hires physicists and engineers to get the competitive edge. In universities, learning institutions, and publically funded research centres, there is more freedom of direction for the researchers. Here, it is probably not so much the case that the physicists go in the direction that the money is, but the money goes in the direction of where the physicists' minds are.
The real issue I believe is misunderstanding, and this is honest mistake. The sophistry which Socrates exposed was real honest misunderstanding, at the institutionalized level. The sophists truly believed that they knew these things, and were proceeding in the honest and good way by educating others. What he demonstrated was that they really did not know what they professed to know. This opens the door to doubt and skepticism. But the point is that unlike deception which is relatively easy to determine, honest mistake is extremely difficult to identify. Fundamental principles are firmly believed, and maintained by the community, to the same degree whether or not they are actually true. There is no essential difference between a true fundamental principle and a false one, they both play the exact same role in the community. To expose a false one requires applying the principle to something outside of the system within which it is currently employed. That's what Socrates did, he took fundamental principles which were being employed in various fields of technology, and said look what happens when I employ this principle in another field, absurdity results. Why do you cling to this principle as if it is a truth? Clearly it is not.
It's just standard guff written about an theory whose sole purpose is obfuscation and denial. I really couldn't care less about it, so can't be bothered forming an opinion. Save to say, the article makes the epistemic nature of Copenhagen explicit later on.
Quoting Wayfarer
Your primary source of knowledge, Wikipedia, has articles on Bell's theorem etc.
Bell - local realism falsified
Leggett - non-local realism falsified
It has been shown by experiment that both local and non-local realist theories disagree with Reality. Quantum Mechanics has never been shown to disagree with Reality.
PBR - The wavefunction cannot be interpreted as a probability distribution over real states.
I don't believe any experiment has been performed to test PBR - i.e. to test whether reality agrees with Quantum Mechanics or any theory that regards the wavefunction as real probabilities, but no one doubts the result.
Actually, PBR does have implications for Many Worlds - it means Many Worlds is correct.
Quoting Wayfarer
To claim you have an "interpretation" of a topic you know so little about is bizarre.
Meanwhile my impression of MWI is that it's ad hoc to preserve determinism.
That is almost funny.
I made a list of the rather low-quality "criticisms" of many worlds, but I'm not sure where this fits in.
It doesn't seem to fit precisely with "criticism by personal incredulity" which cover almost everything. This one seems to be a combination (or should that be superposition) of "ignorance" + "willful misrepresentation".
Here's a test too see if I'm correct:
1. Name the ad-hoc modifications to QM employed by Many Worlds
2. Identify where it is non-deterministic.
I like how you respond to that, but completely ignore the problem that Deutsch only defines "computational equivalence" for machines in the paper that supposedly "proves" the CTD principle.
Why is that a problem?
Oh I get it, how do you know the machines exist when you're not looking at them.
Because the CTD principle isn't supposed to be only about machines, is it?
It's only about machines.
What does "disagree with Reality mean"? Do you have an assumed Reality which a theory either agrees with or disagrees with?
Why the capitalised 'Reality'?
I thought it was claiming that a universal computing device can simulate every physical process? Not every physical process involves a machine, unless he's claiming that everything is a computing device, but you explicitly denied that he was stating that.
That refers to the Wikipedia article on the 'Copenhagen Interpretation.' This is an open-source encylopedia, so anyone is entitled to edit it. But apparently it is 'so incorrect' that it's not even worth an opinion about, let alone editing or updating it.
Let's not forget that the main claim of 'many worlds' is that there are, in fact, many worlds. It's not simply mathematics, it's a metaphysic.
Quoting tom
You can learn a lot by asking questions and gauging the responses.
it's not a claim, it is a testable deduction...for the umteenth time.
Some intellectual honesty would be a peasant surprise!
The universal machine can simulate every finite physical process.
A deduction is only as sound as its premises. What is your definition of Reality?
Whenever you go into detail of what it's 'testability' amounts to, it is always along the lines of a deductive argument about 'what the observations mean'. Deductive arguments are by nature not amenable to falsification. Nobody disputes the accuracy of the predictions made by quantum physics, but it is precisely 'what the observations mean' which is at issue. If you google the term 'wave-function metaphysics' you get a number of books, and a wide range of interpretations. So if it's a matter of intellectual honesty, you're obliged to acknowledge that dissenting interpretations exist. Repeating your belief over and over again does nothing to change that.
There is a lot more to the issue than that. There is nothing at all in QM that implies or predicts wave function collapse. Copenhagen doesn't postulate wave function collapse, it wholesale denies that the wave function is real. That is, the philosophy of the Copenhagen Interpretation is anti-realism. It's worth repeating the quote by Bohr which makes it very clear what anti-realism entails:
The determinism is built-in to QM - the wave function evolves deterministically according to the Schrodinger Equation. And self-locating uncertainty is a prediction of QM.
Copenhagen has to deny the reality of the wave function to avoid that determinism and it cannot explain measurement uncertainty. If you take the pilot wave route, determinism is preserved, but it posits hidden variables which, as you may guess from the name, there is no evidence for.
Just to clarify this, Everettian QM is a local realist theory. What Bell's theorem falsifies are realist theories that depend on local hidden variables.
The second edition of Everett's thesis was published as “Wave Mechanics Without Probability'. Why do you think it was called that?
Because Everett considered the wave function to be real and the world as not inherently probabilistic.
Why do you think the probabilistic nature of the wave-function is sufficiently troublesome to consider such an alternative?
You might like this:
From ~25mins for the purely QM stuff.
So re the Schrodinger equation, do you disagree with this statement: "The associated wavefunction gives the probability of finding the particle at a certain position"?
I agree that the ontology of probability is interesting. This 'from 25 mins on' wasn't 'purely QM stuff' at all, though, it was a prolonged lecture about metaphysics. My view of philosophy is that you imagine all the best arguments people can put up against you, and you rebut them. In this lecture Deutsch seems instead to be imagining a series of feeble opponents who haven't considered the slightest subtlety in their position. Even an actuary has a defence to the notion of probability, let alone proponents of statistical mechanics and so on. I don't see how this sort of stuff furthers the debate. Plenty of people who disagree with Deutsch's interpretations of MWI will agree that probability is epistemic, especially scientific realists, for they don't want 'the world' at heart to be indeterministic. And, it must be something you're not seeing because you admire Deutsch, but to the uncommitted outsider the lecture seems to show a pompous man over-reaching himself. Why isn't all this in a peer-reviewed paper where his intellectual equals like Wallace and Timpson could respond and critique it?
It's redundant to say there is no evidence for hidden variables. If there was evidence, they wouldn't be hidden. But "evidence" is a property of the mind which seeks relationships, it is not a property of the physical world. So evidence may be right in front of one's eyes, or even right on one's list of observations, but if that individual does not establish the appropriate relationships, it is not seen as evidence, and so it is claimed, "there is no evidence".
Evidence is a funny thing. If we are looking for evidence, we must create logical relationships in advance, to know what we are looking for. Without this, nothing is evidence, because there is nothing which we are looking for evidence of. So let's say that we are looking for evidence of "hidden variables". Well, the variables are hidden, we know not what they are, so we have no idea of what we are looking for evidence of. Until the possible variables are brought out into the open, and exposed as possible variables, we cannot even begin to look for evidence.
I submit to you, that there is an immense quantity of evidence of hidden variables. The variables are hidden in the mathematics. That is the way in modern physics, and it's become epidemic since the practises of general relativity. Whenever a variable pops up, mathematics is created to work it into the theory, and it becomes lost into the theory, hidden by the mathematics. Let's consider general relativity as the prime example. Special relativity is a particular theory, gravity is a variable in relation to this theory. The mathematics of general relativity allow this variable to become hidden within the theory, so that it doesn't appear to be a variable any more. It is a hidden variable, hidden by the mathematics. That is the practise in modern physics, create mathematics to deal with the variables, this obscures their presence, such that they become hidden variables, hidden by the mathematics.
Yes it's counterintuitive. That's not a valid argument against it. If that's the way the world is, then we should change our intuitions.
Quoting Wayfarer
Energy is conserved. I recommend Ask a Physicist's excellent answer on this.
Quoting Wayfarer
I think for much the same reasons that Einstein found Copenhagen troublesome. Lack of causality, non-locality and anti-realism. Contra Bohr, I think the task of physics is to find out how nature is.
Quoting Terrapin Station
No I don't disagree. That's the self-locating uncertainty that I mentioned. The wave function assigns a complex number (called an "amplitude") for each measurement outcome. Per the Born Rule, the probability of seeing a particular measurement outcome is the square of the amplitude.
Okay, but that's the probability I'm talking about there being a desire to remove. There's still a probability of what one will observe in one's world, but it's no longer a probability that only one outcome will obtain (via measurement) while others do not obtain.
But you haven't addressed a single one of his arguments.
Quoting mcdoodle
Try this paper by Marletto.
https://arxiv.org/abs/1507.03287
or this paper where Deutsch invented the idea.
http://xxx.lanl.gov/abs/quant-ph/9906015
or this paper where Wallace defends Deutsch
https://arxiv.org/pdf/quant-ph/0303050.pdf
or this paper where Wallace improves Deutsch's argument
https://arxiv.org/pdf/quant-ph/0312157.pdf
or this paper where Wallace establishes the formal proof of Deutsch's idea
https://arxiv.org/pdf/0906.2718.pdf
Or chapters 5 and 6 of this book by Wallace:
https://www.amazon.co.uk/Emergent-Multiverse-Quantum-According-Interpretation/dp/0198707541
So, the point Andrew M, I am a metaphysician, not even a physicist, and I can identify numerous possible hidden variables, such as gravity, expansion of space, dark matter, dark energy, so I don't know how many possible hidden variables there really is. Very many I would say. From my perspective there is massive evidence for hidden variables.
Hidden variable theories are ruled out by the many no-go theorems: Bell, Leggett, Kochen-Specker, Free Will Theorem, PBR.
There is no existing hidden variable theory that is able to replicate the results of Quantum Mechanics up to electrodynamics and field theory. They don't work or don't exist.
All hidden variable theories disagree with quantum mechanics, so they are wrong.
What you have demonstrated is that you haven't the first clue what is meant by the term "hidden variable". Look it up!
There doesn't need to be a valid argument against it. I already quoted the passage where Everett, 'after a slosh or two of sherry', sat around with a couple of mates thinking of 'ridiculous things you could say about quantum'.
@Metaphysician Undercover - here's a good video on hidden variables/pilot waves:
So there isn't a desire to remove that probability in Everettian QM, which would amount to an ad hoc change to QM.
As an example, consider a particle in a superposition of spin-up and spin-down. The wave function includes the particle in superposition, and also the external environment which includes Alice. Now Alice measures the particle spin. The wave function evolves to a superposition of (Alice measures spin-up) and (Alice measures spin-down). Each of these superposition states are assigned an amplitude which, per the Born Rule, are convertible into equal probabilities that Alice measures spin-up and spin-down. Both measurement outcomes are present in the wave function.
Dynamical collapse theories add an ad hoc postulate to remove one of those measurement outcomes. Copenhagen goes further and denies the reality of the wave function. Whereas Everettian QM leaves the wave function intact and explains Alice's reported measurement as the natural consequence of self-locating uncertainty.
As Tom mentions, hidden variables have a particular history in a quantum context. In particular, Bell's Theorem shows why no physical theory of local hidden variables can reproduce all of the predictions of quantum mechanics.
I have looked it up. And I've watched the clip Wayfarer provided above, thank you Wayfarer. Furthermore, I know very well what a variable is, and I know very well what it means for a variable to be hidden. And as I explained, I see many variables hidden behind mathematics, the mathematics making them appear as constants.
Quoting tom
You seem to be in some sort of state of denial, afraid to face the possible reality of non-locality. You deny that hidden variable theories are even applicable just so that you can claim that MWI is the only realist interpretation. Do you really think that Many Worlds is a more plausible interpretation than non-locality? Are you afraid to face the fact that special and general relativity may be wrong? Clearly they do not provide us with an adequate representation of time.
Quoting Andrew M
The fact remains that the best theory which physics has, for dealing with gravity is general relativity, and this is far from adequate from a metaphysical stand point.
But in MWI, the probability that both are measured is 100%, no? One is measured in one world. The other is measured in another world.
Yes. The point is that there is no ad hoc modification to QM to preserve determinism. Everettian QM is just the natural interpretation of the wave function evolution.
The ad hoc part is that we posit the ontological ridiculouslessness of parallel worlds.
So in a double-slit experiment with a particle, name the hidden variable.
Quoting Metaphysician Undercover
Name a non-local hidden variable theory that agrees with the results of quantum mechanics up to at least quantum field theory.
The predictions are supplied by the mathematics, correct?
The hidden variable is the concept of activity itself. Notice how you say, "in a double slit experiment with a particle". You are misrepresenting the experiment, because what is there in that experiment is activity. That activity may be expressed as energy or it may be expressed as a wave, and that is a variable.
There are two distinct types of activity. One is called change, and it is internal to an object. The other is called motion and it is objects changing in relative position. Relativity theories cannot be applied to change unless that change is represented as motion. Relativity theories represent change as objects moving relative to each other. The modern concept of energy is intrinsically tied to relativity theories, and therefore relative motions. In understanding activity as energy, that activity is represented as motion, and relativity theory is applied. If internal change is an activity, that activity must be understood, or represented as motion, in order that it can be expressed as energy. Therefore in order to understand any activity as "energy", that activity must be represented as motion.
A wave is an internal activity of a substance. It is a change, not a motion. If one desires to represent this internal wave activity as energy, then it must be rendered conceptually as a motion. Relativity theory does not do this, it only allows that energy is the property of moving objects, there is no wave energy. The method by which wave activity (which is an internal change to an object) is transformed to energy (relative motion of objects) is the hidden variable here.
Thanks for the list, Tom. I don't have access to the book, but David Wallace has lots of papers on his Academia page so it's easy enough to read his arguments. What I'm not clear about is what the up to date arguments are. I'm looking at 'Many worlds', a 2010 collection of essays by people of all sorts of opinion, including Wallace, though some of the essays seems to have had online updates later.
Both Wallace and Deutsch along the way have offered 'proofs' relating to their approach, which you have tended to gloss as 'They have proved...' I don't have the maths to spot the problems in the proofs, or not, but it seems clear once you read around the literature that the key issue is what assumptions one brings to the party before proposing a so-called 'proof'. It's all, for the moment, metaphysical debate of one kind or another. Some ideas lack empirical support and have fallen by the wayside, but there are many that are alive and kicking.
The strongest critic of Wallace in the book above is Adrian Kent, a Reader in quantum physics at Oxford. Here is how he summarises his criticism:
I've got to say, because I didn't know much about this field before being stimulated by the frequent forum debates to have a closer look, I'm amazed the Deutsch-Wallace approach hinges on decision theory and assumptions about rationality. Decision theory is quite a hotly-debated topic in its own right so I wouldn't build a mountain on it. Well, maybe a rough algorithm for how people act, but no 100% right view.
They (D-W) end up arguing, as I understand it, that we can by fiat state what rational agents should do (and therefore by implication do do) in certain situations, including the knock-on situations - the first 'sub-branch' in one language beyond the initial branching. And if certain probabilistic arguments are empirically sound, then the 'weights' of the supposed branches in the Everettian world(s) are, as Kent says, going to have known values, and there are rational-for-agents decisions that don't fit Wallace's axioms.
I'm not clear that they do then answer the question that opened this particular thread? I don't see how an idealization dissolves the question of echoing footfalls - where do the other branches go? It seems in some of them our laws of nature won't apply? - most elegantly put by T S Eliot:
Yes. Consider, for example, an emitted particle in the double-slit experiment.
The Schrodinger wave equation describes the evolution of the particle and its surrounding environment, including the apparatus and the observer. Particle paths through both slits must be included in order to predict the observed interference pattern on the back screen.
If only one of the paths through one of the slits is included then the prediction changes.
They're very strong assumptions about what must be considered real. It's the ambiguity of the interpretation which realism can't stand - something has to be either real (1) or not (0). It can't cope with the idea that there are 'degrees of reality'. So the move is to export the uncertainty to a whole set of putative 'worlds', in each of which the outcome is certain or definite.
Right. And how are you seeing any mathematics as amounting to any sort of ontological commitment whatsoever?
What about this and this?
It's difficult to address a criticism which is just a slur.
Anyway, Kent doesn't like MW. His solution is to append some extra mathematical structure to QM in order to make it a single-world theory. He is thus an advocate of hidden variables. The trouble with this is that no hidden variable theory that does not contradict QM exists.
So, Kent advocates changing the physics, because he does not like the implication of currently known physics.
Quoting mcdoodle
Maybe you should watch the video I linked to. Stochastic theories are normative! Very weird.
Maybe you could briefly describe those theories and indicate to what extent they are capable of dealing with particle interactions etc.
I don't understand them. I only know (from what's been said of them) that they add to the de Broglie–Bohm theory the one thing that it doesn't normally explain; particle creation and annihilation. If that is indeed what they do then they are non-local hidden variable theories that agree with the results of quantum mechanics up to at least quantum field theory.
The ambiguity is expressed by the premises of special relativity as the relativity of simultaneity. If we consider that "reality" refers to what "is" the case, then the relativity of simultaneity defines the ambiguity of reality. In QM time and energy are canonically conjugated variables. However, due to the ambiguity of time expressed by special relativity, the positioning of time, within QM is not so straightforward. Apparently, von Neumann sought to place time as a quantum operator, with point particles existing in three dimensional space. At this time it had been impossible to establish consistency between relativistic principles and QM. But canonical positioning of particles (positioning within a given system) is conceptually different from spatial co-ordinates, due to that ambiguous nature of time, so this was problematic. Physicists now use 4d space-time fields, so that rather than attempting to resolve the ambiguity it is incorporated into the fields.
I see. You don't have an argument, but you like playing buzzword bingo for points.
Here are some buzzwords:
Bell - local hidden variable theories do not agree with QM
Leggett - non-local hidden variable ...
Kochen-Specker - non-contextual hidden variable ...
Free Will Theorem - any hidden variable theory whatsoever ...
PBR - probabilistic distributions of any type of hidden variable theory ...
There is also a an experiment that had slipped my mind - the famous Before-Before experiment which refutes any Bohmian theory including relativistic versions.
That's what it means to regard QM as an explanatory scientific theory. The alternatives are to either change the theory (e.g., dynamical collapse or Bohmian mechanics) or to abandon realism (Copenhagen, instrumentalism).
You didn't ask for an argument, and nor did I claim to have one. You asked for a hidden variable theory that agrees with the results of quantum mechanics. I provided what seems to be just that.
The only mention of that I can find is by Antoine Suarez. I can't find any other sources that corroborate his findings, but I can find several that say that no experiment refutes Bohmian mechanics.
I don't at all agree, and it wouldn't at all be agreed upon in the consensus of physicists, or scientists in general, that what it means to regard something an an explanatory scientific theory is to assign ontological commitments to mathematical models. Mathematical models on their own, sans ontological commitments, are taken to be sufficient for explanatory scientific theories.
This is essentially taking an instrumentalist approach to mathematical models, but it's neither an alternative nor a rejection of realism--it's rather noncommittal on the question because it's avoiding any ontological commitments.
Reading the Schrodinger equation as implying real, parallel worlds, rather than simply being a mathematical model that allows accurate predictions, is making ad hoc assumptions that are not implied by the mathematical model.
Every mathematical model is a diagrammatic representation of an ideal state of things. As such, any ontological commitments are manifested in the mapping of the model - as well as the accompanying rules for its analytical transformation - to something in experience. The model itself embodies only the relations that the one doing the modeling has judged to be significant, and ignores everything else. The analysis of it is intended to simulate contingent events with necessary reasoning, so its "accuracy" is limited by that of the underlying assumptions.
First I want to make sure that I'm clear on what you're claiming in this sentence and why you're claiming it. What is the source for that being what mathematical models are?
As you might have guessed, it is something that I picked up from Peirce. He favorably cited his father Benjamin's definition of mathematics as "the science that reasons necessarily," and added that necessary reasoning only strictly applies to ideal states of things. A diagram is an icon that embodies the significant relations among the parts of its object; both geometrical figures and algebraic equations qualify.
Haha--okay.
Saying that all mathematical models would be examples of necessary reasoning seems dubious to me.
To clarify--constructing the model requires creativity and imagination (retroduction), but processing the model is entirely a matter of necessary reasoning (deduction). Once the model is created, the results are inevitable, given the transformation rules that govern the analysis.
Wait, why are we saying that models involve transformation rules and analysis?
For example, let's pick something simple. Say F=ma as a mathematical model of force.
F=ma is a diagrammatic representation that embodies the relations among force, mass, and acceleration--all of which are concepts that we have defined in order to facilitate this mapping of an idealized state of things to something in experience. The transformation rules are such that we can rewrite the equation as a=F/m or m=F/a. Analysis in this case is merely a matter of finding the third value when we only know two of them initially.
Quoting aletheist
The problem I see with this is that we're not mapping F=ma to F equaling m times a in experience, because there is no mathematical equality or multiplication in experience--mathematics isn't an empirical science.
We are mapping F=ma to the real relations that we observe in experience among force, mass, and acceleration.
Quoting Terrapin Station
This is true, in the sense that mathematics only pertains to ideal states of things. It is false, in the sense that mathematics is an observational science; we manipulate diagrams in accordance with transformation rules and observe what other relations become apparent that were not part of the diagram's original construction.
I don't buy that we can observe a multiplicative relation or that mathematics is observational.
You deny that we can observe (through experimentation) that force is directly proportional to both mass and acceleration? How else have we ascertained that the equation is an accurate representation of reality?
As for mathematics being observational, I suggest looking into what Peirce called theorematic (as opposed to corollarial) reasoning.
If a scientific theory, per instrumentalism, makes no ontological commitments (i.e., is neither true nor false), then neither can it be offering an explanation. In Duhem's words, "A physical theory is not an explanation; it is a system of mathematical propositions whose aim is to represent as simply, as completely, and as exactly as possible a whole group of experimental laws."
Quoting Terrapin Station
OK, but...
Quoting Terrapin Station
This is akin to saying that the heliocentric model makes accurate predictions but it's an ad hoc assumption to suppose the model implies that the earth orbits the sun.
What you're calling an ad hoc assumption just is the implication of the model, whether or not you choose to be agnostic or instrumentalist about it.
Multiplication is a scaling transformation. An example of observing this is when we see a car moving towards us from 200 meters to 100 meters away and consequently appears twice the size.
I'm an anti-realist on mathematics. I don't believe that any mathematics is an accurate representation of reality, because I don't believe there is anything like mathematics in reality. ("Real" here is referring to the extramental or objective world.) Mathematics is rather just a way that we conceptualize relations on an abstract level.
It's just a matter of what people consider an explanation or not. And a large percentage of relevant academics consider mathematical equations read instrumentally to be explanations.
All is not what it seems!
Quoting Michael
Nicolas Gisin performed the remarkable experiment, and yes Bohmians are full of claims, but none has ever made any progress in quantum mechanics - unlike the Everettians who can claim several remarkable discoveries. The lack of progress by Bohmians is discussed in this otherwise positive paper by Gisin:
https://arxiv.org/abs/1509.00767
But science (unlike philosophy it seems) does in fact progress, and a recent experiment involving entangled histories falsifies Bohm and supports Everett. It was the idea of Nobel prize winning physicist Frank Wilczek. This is a very easy to follow article with some explanation:
https://www.quantamagazine.org/20160428-entanglement-made-simple/
This is a good example, the model follows from the success of prediction. So let's say that the successful predictions lead to a Many Worlds model. Now, it's when the model which is necessitated by the successful math, does not make sense, as is the case with MW, that we have to turn back to the principles whereby the mathematics is applied, to see where the mistakes are.
The geocentric model followed from very successful mathematics and predictions. Yes the mathematics was more primitive at that time, but the predictions were very successful. However, the model did not make sense. There were too many issues which could not be worked out to complete the model. The model was missing many aspects necessary to be complete and coherent, as is the case with MW. So we have to go back to the principles which underlie the application of the mathematics to determine why the very successful mathematics produces an unacceptable model.
Yes, that is what I would have guessed. Just curious, then - how do you explain the element of surprise, the fact that there are genuine discoveries in mathematics?
Right, it is a matter of how we are mapping the (ideal) diagram to the (actual) universe - both in formulating the model, along with its accompanying transformation rules, and in interpreting the results. In other words, like so much of philosophy, it comes down to our assumptions.
That's simply playing a game of sorts per rules that one has set up beforehand. The rules are complex enough (and vary enough per different sorts of starting assumptions--for example, Euclidean vs Riemannian geometry)) that future constructions can be unpredictable, one can come to realizations about present constructions that weren't apparent at first, etc.
Right, and my point was that this happens because mathematics is observational - manipulating and then reexamining a diagram can reveal new information. The difference, of course, is that we are observing our own (ideal) constructions, rather than something "out there" in the (actual) universe.
Ah--well, I wouldn't use "observational" in that way, since it's rather a construction, but if you use "observational" so that it would fit that, then okay.
It's like the scientific method never happened!
No instrumentalists regard equations as explanations. That is the entire point of their philosophy; the purpose of a theory is to predict the outcome of experiments. Instrumentalists build the LHC for no other reason than they want to predict what the LHC does. The experiments, and more importantly the theories, tell us nothing about the Reality.
The scientific method is fundamentally based on the conception of theories as explanation - statements about what exists in reality, how it behaves, and why. This conception is necessary for a coherent epistemology.
As every instrumentalist knows, there are an infinite number of "theories" i.e. non-explanatory mathematical equations that agree with observations. This is a feature of the underdetermination of the laws of physics.
By contrast, good explanations are extremely difficult to come by!
Based on your ideas, how do you explain the discovery of quantum entanglement?
I don't know if there's a single sentence in your post that's not confused or just plain wrong.
Let's take it sentence by sentence.
Quoting tom
This is confused because just how we interpret mathematical equations as theories and just what we do or do not count as an explanation has no implications for whether it is or isn't like "the scientific method never happened."
Explanation is an account of why something happens. I've just quoted Duhem, probably the main proponent of instrumentalism in the 20thC, who rejects that physical theories are explanatory. Do you have any cites to back up your contrary claim?
So what about MW does not make sense, or is mistaken, on your view?
Because you are confused and wrong, let me spell it out:
Scientific theories are expressed in mathematics because that is the means by which deductions are most easily made - i.e. it is the expression of the theory that is most amenable to testing.
Of course, despite Galileo's proclamation, the theory of Evolution has not yet been expressed mathematically. The theory of Evolution is expressed in ordinary language, and is nonetheless as successful as any other fundamental theory - it provides a good (the only) explanation of what it purports to explain.
You are ignoring the scientific method. For you, it is as if it never happened.
Maybe you could explain the discovery of quantum entanglement in your instrumentalist terms?
Not offhand--I'd have to search for some. What I had in mind is both people I personally know or have known and statements I've encountered over the years where there's no way I'd remember particular titles of papers. But all a citation would tell you anyway is that different people have different opinions and use words differently. Do you really doubt that?
We were talking about discoveries in (pure) mathematics, not physics.
So on your view, how we interpret mathematical equations as theories has implications for whether it's as if the scientific method never happened because _____ ?
It's quite extraordinary. Everyone, both supporters and detractors of Instrumentalism know what it means, except supporters on this forum.
Strangely enough, it is possible even to treat Evolution instrumentally, despite there being nothing to shut-up-and-calculate.
I know coherence is not your strong point, but could you translate that into something less incoherent?
Maybe you could explain how the discovery of entanglement is a discovery in "(pure) mathematics" and not "physics" and why it therefore exist in the Reality?
Not really interested. You should be able to understand what I wrote in the context of the current conversation.
Why would you expect me to explain something that I never claimed? I have not said anything at all about quantum entanglement.
So mathematics is "observational", whatever that means. We are "observing our own (ideal constructions)"
OK, so how did we manage to "observe our own ideal constructions" of phenomena that took 50 years to observe after their discovery?
Sure, I figured that out long ago.
I have no idea what this means, or how it relates to anything that I have said here.
It's a contradictory notion that all possible worlds are actual. In my understanding of possibilities, any possibility must be actualized before it can become an actuality. If all possible worlds are assumed to have actual existence, without a cause (source of actualization), then this is contradictory to my understanding of "possible".
I realise that.
MW is a causal theory - the wave function evolves deterministically with the parallel branching and merging built in. I've been making just your argument that possibilities - an epistemic term - cannot be invoked to explain interference effects. Only real superposition states can cause real interference effects.
The interference effects are phenomenal. The phenomenon is described as possibilities. So the possibilities are epistemic. The possibilities are the epistemic representation of the phenomenon. We cannot invert this and say that the phenomenon is the actual existence of these possibilities, because the epistemic possibilities are simply a representation of the phenomenon. There is no principle which allows us to say that the phenomenon is the actual existence of the possibilities.
For example, we have an activity, a phenomenon, which is the flip of a coin. We can represent that as possibilities, one possibility of heads and one possibility of tails. We cannot invert this now, to say that the phenomenon which is the flipping of the coin, is the actual existence of both these two possibilities, such that in the flipping of the coin there exists the actuality of heads and also the actuality of tails. The fact that one cannot devise the means to determine the outcome, heads or tails, does not justify the claim that the phenomenon itself consists of the actuality of both the possibilities.
Quantum interference effects are real and are predicted by Schrodinger's equation. You won't find any mention of possibilities or probabilities in the Schrodinger equation.
I don't think you describe this correctly. I believe that the Schrodinger equation is an interpretation of interference effects, which expresses the possible positioning of particles. Therefore the equation does represent possibilities. It is produced as an interpretation of the real phenomenon, interference effects, which renders that phenomenon as epistemic possibilities, the possible positions of particles. If a possible position is observed, it can be claimed to be actual. Otherwise there is no principle which allows us to affirm that possible positions are actual.
The Schrodinger Equation describes the deterministic evolution of the wave function of a quantum system. In the double-slit experiment, the system evolves from the initial state when the particle is emitted, to states at both slits and finally to states at the back screen.
This process is fully deterministic. There are no probabilities in the system, only amplitudes for each quantum state which are represented as complex numbers.
That is the ontology of the system. Probabilities only arise when making predictions about measurements within the system and this is governed by the Born rule.
Note the word "measures".
Probabilistic language relates to the measurement of the system, not its ontology, which is what the Schrodinger equation describes. Here's Wikipedia:
Quoting Andrew M
In order to apply the Schrodinger, there must be some initial measurements of energy which is attributed to the system. Probability is inherent within the way that this energy is represented in the equation, it is the energy of the particles. The entire system is described in "probabilistic language". That is inherent in the Hamitonian operator which is an essential part of the description. It may be true, as you say, that the Schrodinger describes the evolution of the wave function, but it describes it in terms of particles, which is a probabilistic description.
Not true. We can easily observe that three sets of four trees equals twelve trees, for example.
How would you observe that? Wouldn't you have to actually count them, as one group of twelve, to reach that conclusion?
Could you explain why probability is "inherent within the Hamiltonian?
Quoting Metaphysician Undercover
Could you explain how the initial measurement is made in say a two-slit experiment, and what difference the result makes?
Quoting Metaphysician Undercover
If probability is "the energy of the particles", why are different words used to state the same thing?
No it is easy enough to visualize three groups of four or four groups of three, and to see that it equals twelve. Of course it's not possible with larger numbers of objects. But really the idea of simple multiplication is just an extension of the idea of simple addition. For the simplest case where you have two objects it can be intuitively understood that one plus one equals two or that two times one equals two.
Personally, I find it easiest to visualise the negative inverse of the sum of all positive integers, when I think of 12.
I told you this already, the energy of the system is expressed as probable locations of particles.
Quoting tom
There is an amount of energy introduced into the system, as you say, a photon particle or number of particles are "fired". The energy of that system is expressed as particles. This expression is used in the Hamiltonian, and therefore the Schrodinger.
Quoting tom
Have you ever heard of wave/particle duality? Two different words to express the same thing.
Quoting John
Say you visualize such groups, how would you know that there was twelve there without counting them or performing the math?
Because twelve is a small enough number to be visualized, either as three groups of four or four groups of three. If you can't visualize twelve then just consider the example of two or three objects; which can be visualized either in terms of addition or multiplication.
The Hamiltonian tells you how a quantum state will (deterministically) evolve. When it is applied in the Schrodinger equation, it produces a superposition of states which are expressed as probability amplitudes (complex numbers), not probabilities.
This matters. If states in a quantum superposition were merely probabilistic, with only one state being real as with a coin flip, then they could not constructively or destructively interfere with each other to produce interference patterns. That is why all of those states must be real.
It is only the Born rule, which is not part of the Schrodinger equation, that enables us to extract the probabilities for observing those states when a measurement is made.
But as we learned from the video on probability, the exact same results are achieved - i.e. we obtain the same Value, without invoking the Born Rule or probability.
Probabilities are not fundamental to QM, they are simply useful.
You claim that the Hamiltonian operator expresses the "probable locations of particles".
What is the wavefunction for?
Quoting Metaphysician Undercover
If you "fire" a particle into a twin-slit experiment with an "energy" 3, what difference does that make to the outcome of the twin-slit experiment compared to an energy of 2?
Quoting Metaphysician Undercover
You claim that wave/particle duality is just two words to express the same thing - and that "probability" and "energy of the particles" also express the same thing.
But you also claim that "the energy of the system is expressed as probable locations of particles"
You seem to be going round in circles.
Yes, you can use the magic of mathematics to turn possibilities into realities if you like, but I think that if the magician is convinced my the magic, that's a problem And I am not convinced by that magic. Logic, of which mathematics is a type, cannot produce anything contrary to its premises. The Hamiltonian operator describes the system in terms of probabilities due to the reality which the uncertainty principle is supposed to represent. How do you think that the Schrodinger equation converts these probabilities into realities? Even the Wikipedia article you referred me to clearly discusses probability amplitudes in terms of probabilities. It says in the first line of the article: "The modulus squared of this quantity represents a probability or probability density." Then the entire article discusses things like probabilities, probabilistic laws, and probability densities.
Quoting Andrew M
I don't see the premises whereby you make this conclusion. If we have a coin toss of 50/50 probability, and add another coin to the toss with a 50/50 probability, the fact that the two coins could interfere with each other in the air does not produce the conclusion that our description of the toss is not probabilistic.
But you seem to be missing something fundamental in your reference to "one state being real". When the system is described in terms of probabilities, this does not imply that one state must be the real state. There is no such thing as a "state" within a system, it is an active system. A "state" and an active "system" are two incompatible descriptions. Consider the coin toss, the 50/50 probability refers to the outcome of that activity. It is describing the activity, the coin in the air, with reference to the outcome. There is no "state" being referred to, except the outcome, but the outcome has not yet occurred, so it is probabilistic. It is not a "real state", it is a future potential state. The activity described, being the coin in the air, is an activity, it has no real states. To represent the activity as a state is to stop the activity, and this negates the essence of "activity".
So in our quantum example, the Hamiltonian operator recognizes that the system has no real states. What is real is the activity. So now we can produce a wave function, and the wave function is assumed to be a description of the activity of the system, the activity of the system being what is real. That description describes something real, but the something real is an active system, not a state. Specific spatial temporal positions of particles is a description which refers to a state. So there is an inherent incompatibility between describing an active system and the possible states of that system.
You could ask, which is real, the active system, or the states of the system, and the answer depends on your perspective. The term "energy" refers to the activity of a thing, so if energy is believed to be real, and the system is described in terms of energy, the activity of the system is what is real. The wave function describe the reality, the activity, the coin in the air, and any states are just possible states, produced if we stop the activity. But if the activity is stopped, then the wave function is no longer real. The problem being that there is no principle whereby we can represent both as real.
However, one could take an alternative perspective, and claim that energy, activity, is not real, it is merely conceptual. Activity and energy are how we describe changing states. From this perspective, we would say that "the system" is just a conceptual representation of what is real, and what is real is particular definitive states, which change from one moment to the next. Then we could say that the reason why these states must be represented as possible, or probable states, is that the reality of the system is being represented as energy, activity, and this representation is incapable of reproducing the states, due to the incompatibility expressed above. We do not have the means to say that both of the descriptions, the activity, and the states, are real, because the incompatibility between these two has not been resolved.
The criticism was not 'just a slur'. It was a chapter of reasoned argument of which I gave you the summary and another paragraph of exposition. You didn't address the criticism at all, you just went on to say 'Anyway...' - and then began an entirely different point. The criticism is, to start with, that the axiomisation is invalid in certain reasonable circumstances. It's hard to discuss if you won't answer reasonable points raised. Your entirely different point may be interesting in its turn, but there remains a substantial argument Kent made which you hadn't addressed.
You went to re-recommend me to watch Deutsch's video on probability, which for some reason you find convincing. I've already told you I disliked it, and thought it was particularly weak in that he never represents any of the positions he disagrees with fairly. It's the polemics of a lecture. I doesn't mean it's wrong, I just mean it's obviously a diatribe not a carefully-reasoned piece. I'm happy to read essays which interact with other essays in an academic fashion, but I've never understood why a superficial video is an adequate substitute.
You do, you know, regard 'just a slur' as a reasonable way for you to speak to other people on this forum. It's not ok. If you don't like slurs, I don't think you should make them at other people's expense either.
What axiomatisation?
That is an interesting paragraph as it encapsulates to me the philosophy-of-science debate going back and forth here. Mathematically states in a quantum superposition are probabilistic. 'Merely' is a matter of taste. A measurement occurs, the outcomes are mathematically understood.
You quote Duhem in arguing that putting things merely mathematically like that is not 'an explanation', but Duhem is long dead and there are new sorts of empiricists about who might happily use the word 'explain' about mathematical models. I think here it's realists who are also being rigid about what an explanation must involve; it can be a circular demand, in that if one isn't some sort of realist then what is one explaining? I do think that's a fruitless side-alley.
The realist in turn only feels ok if like you they can point to what is 'real' (albeit hypothetical in that it's unobservable) in order to apply something like ordinary language to what happens in the maths. It *is* hard to talk about. I've a friend who's doing some physics which assumes entanglement in order to try and model what happens in PET scans, for instance. In explaining it to a layperson like me he juggles between talking as if it's all real and then adding, 'or at least that's what the maths says'. I don't see that in remaining agnostic about 'the real' in such cases I'm somehow being anti-scientific, or failing to understand something. I am just a wary sceptic.
So, the "Hamiltonian operator describes the system in terms of probabilities". How does it do that? Where in the Hamiltonian operator are the probabilities? I'm particularly interested as, having applied the Hamiltonian, typically in systems of interest, one obtains a scalar quantity, not a probability distribution.
Quoting Metaphysician Undercover
How do YOU think the Schrödinger equation achieves that? More pertinently perhaps, why do you think the Schrödinger equation does that, particularly as no one else does?
How do they affect each other?
I'm afraid the detail of the arguments is impossible to summarise in a short space.
In what way is that relevant to what I was saying to AndrewM? I was making an epistemic/ontological distinction, not arguing about what hypothetical entities do or don't do.
Really!
You claim that
Quoting mcdoodle
Do these states affect each other? Seems to me a one word answer.
Try Google, it's very helpful, but let me try, maybe I can describe it. The Hamiltonian operator describes a system in terms of the energy of all the particles within the system. There is a time-energy uncertainty, so any derived time evolution is inherently probabilistic.
Quoting tom
Clearly I don't believe that, that seemed to be Andrew M's position, which I objected to.
Google is a bit too hard for me, so if you don't mind, perhaps you could clarify a couple of questions:
What does the Hamiltonian operator operate on?
When you apply the Hamiltonian operator "H" to a ket in Hilbert space "|psi>" what do you get?
Agreed. Probabilities relate to observer predictions, not the world itself.
You're misunderstanding that sentence. The modulus squared is the probability that that particular quantity (the amplitude) will be measured.
The amplitude is a complex number associated with a quantum system. It's about the ontology. Whereas the probability (a real number between 0 and 1) is the predicted likelihood that that quantum system will be observed if a measurement were made. It's about the epistemology.
Quoting Metaphysician Undercover
I'm referring to a coin that has already been flipped, where there is a single state that is unknown (e.g., it's hidden under my hand). Whereas a coin held in a superposition of heads and tails has two superposed states.
In both cases, the 0.5 heads/0.5 tails probabilities are predictions about what state will be observed, not about what states actually exist prior to observation.
Mathematically, the states in a quantum superposition are represented as probability amplitudes (complex numbers), not probabilities (real numbers between 0 and 1).
Quoting mcdoodle
I don't think it's unreasonable to ask why quantum interference effects occur or what nature is really like. I don't see the point in calling interpretations like Copenhagen "explanatory" if they deny that there can be answers to such questions.
Quoting mcdoodle
Sure, it is hard to talk about. We don't knowingly encounter superpositions in everyday life, so QM is counterintuitive. But that doesn't mean that we should abandon ordinary language and realism. That's the crucial philosophical issue. Mathematical models help us to correct our intuitions and find the language we need to better reflect the world we find ourselves in.
On this we can (partly) agree, and thanks for the correction regarding probability amplitude; we are at the outer limit of my ability to talk maths/physics here, but I still hope that it doesn't require postgrad work in the subjects to debate the philosophical issues. I think my version of 'realism' is different from yours but I understand what you're saying. I'm sceptical that we can know 'what nature is really like', which is why I keep asking for the agnostic option in science: what is the minimum ontological commitment involved in such and such a proposition? It feels as if people of a scientific bent sometimes drift from the minimum to a greater 'metaphysical' realism that is to my mind just a metaphysical claim, not something that's necessary to agree on the proposition in question.
I don't understand your distinction between ontology and epistemology. It's all mathematics, therefore it's all epistemology. You have arbitrarily singled out a part of the mathematics to say that this is the ontology. But I think you're going in the wrong direction. Instead of following me towards the fundamental principles, which the numbers refer to, and this is where you will find the ontology, for some reason you believe that you will find ontology in some complex mathematics. But that is backward.
Quoting Andrew M
This is a misrepresentation though. What is being referred to is an active system. So you cannot represent this as a case of the coin having been tossed, and the result is hidden under your hand. The system is an active system, so there are no states, there is no result. The ontology of the system must be represented as if the coin is in the air. That is your mistake, you want to represent states, talk about states, when there are no real states in an active system, it is inherently active. The idea that there are particles moving within the system makes you think that the particles must have definitive spatial-temporal positions, and the mathematics represents this. The uncertainty principle demonstrates that this is not the case, there are no definitive positions of particles. So you'll propose "superposition", and desire to assign some ontological status to this.
However, you're not addressing the true ontology of the active system, that it is active, and this is inherently incompatible with states. Consider that under special relativity, electromagnetism is pure energy. There is energy which moves from A to B, but it is impossible that a physical object moves from A to B, because an object cannot move at the speed of light, and this energy moves at the speed of light. The photoelectric effect demonstrates that energy leaves A and gets to B as particles, objects. The question is, how should you represent that energy which is moving from A to B. If you assume a particle, then you look for intermediate states, the positions of the particle. But there is no need to assume a particle. If the energy leaves A and appears at B as a particle, moving at the speed of light, and special relativity states that it is impossible for an object to move at the speed of light, why would you believe that a particle moves from A to B? This is the ontological question, why is the energy within the system represented as moving particles, that makes no sense.
Don't you find it bizarre that you can (supposedly) go from an ontic state in Reality, to an epistemic state in a mind, just by taking the modulus squared?
As it happens, Many-Worlds does involve the minimum ontological commitment (albeit more of the same ontology we are already familiar with) - it's bare-bones QM without extra postulates. Whereas it requires extra effort to take the branches out of QM. Other approaches either change the philosophy (Copenhagen, instrumentalism) or change the physics (Bohmian Mechanics, Dynamical Collapse theories).
Regarding knowing 'what nature is really like', this is where translating mathematical models into understandable language is useful. QM is generally regarded as being not merely difficult, but inherently confusing and incomprehensible. Which is a philosophical issue.
The mathematics of QM describes the world. That is what is being modeled. It is not a description of people's knowledge.
Quoting Metaphysician Undercover
It's difficult to discuss this when you won't accept a simple, familiar example like the outcome of a coin toss. Of course there can be states in an active system, just as there can be frames in a movie.
Quoting Metaphysician Undercover
The uncertainty principle does not demonstrate this. It shows that an object can't have a precisely-defined position and precisely-defined momentum at the same time.
I see the Born rule as an empirical result that is useful for making predictions about the state that will be observed. But I don't have an explanation for the rule. Do you?
For sure, there could be states like frames in a movie. But this is a completely different premise, not consistent with QM, it's a completely different ontology. If this is the case, then we have to account for a completely different type of activity, the activity of exchanging one frame for the next. This implies that the whole world would be in state X at one moment, and in state Y at the next moment. There would be no "movement" as we now conceive of it, "activity" would be a switching of one frame to the next. The mathematics of QM describes activity as motion though, it doesn't describe a switching of one frame to the next.
Quoting Andrew M
Have you ever considered that according to relativity theory, "at the same time" is relative, and, everything is moving. Therefore it's impossible that anything has a precisely defined spatial-temporal position. The uncertainty principle demonstrates this in practise.
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There are three unrelated derivations of the Born Rule that I'm aware of: Deutsch-Wallace, Zurek, Carrol and Sebens. But after checking Wallace's book "The Emergent Multiverse", there seem to be a variety of arguments of various degrees of formality.
Of course, in all of these derivations, only unitary evolution occurs, and in the end you get something ontological - i.e. branch weights.
I found it perplexing that you were willing to defend Many Worlds against a barrage of repetitive, uninformed criticism of extremely low quality, yet are willing to go all Copenhagen when it comes to the Born Rule! Anything as important as BR that is not an axiom, needs to be derived, and it is!
Quantum states are fundamental to QM. The Schrodinger equation describes how the quantum state of a quantum system changes with time.
I think you may have misunderstood my comments on the Born rule (or I could have expressed them better) - I certainly agree that it should be derivable in principle from the ontology of QM. Anyway, I've just read through Carroll's blog post on his and Seben's derivation and it makes sense to me.
Basically the Born probabilities are explained in terms of self-locating uncertainty just after a measurement has been taken and decoherence has occurred. For branches with equal amplitudes, we should be indifferent about the branch we find ourselves on and so assign them equal probabilities. Whereas (as Zurek shows) branches with unequal amplitudes can be mathematically reduced to many more branches with equal amplitudes (which, as it happens, will be in proportion to the square of the amplitude). So that seems like an intuitive result.
We're going around in circles. These quantum states are inherently probabilistic. That's the issue here, you want to say that they are not, but it's inherent to the way that states are assigned to the active energy of an active system, due to uncertainty, that these states are probabilistic. That is why they are epistemological rather than ontological, the epistemology has not overcome uncertainty to enable such an active system to be represented as states.
The Carroll / Seben derivation does seem to hinge on just a different purported version of 'rationality' to Wallace's derivation via decision theory, and an equally disputable one:
I appreciate this is the simple version of the supposed principle (Epistemic Separability Principle). It does seem open to pretty obvious objections. I wouldn't bet the house on 'credence' just as I wouldn't bet it on the definitions of rationality in decision theory. For instance, how can one know what is and isn't 'affecting' the observers? The supposed derivation certainly comes in for criticism from various quarters. I'm just expressing sceptical doubt, not disagreement, here.
The ESP seems to me just a version of a common-sense principle that we apply in everyday life. Suppose we are predicting whether it will rain this afternoon. We look at local factors and ignore irrelevant or remote factors.
There are also strong constraints in play, such as speed-of-light limits and isolation between branches.
Well, to invoke 'common sense' seems quite a weird thing to do,in the context of many worlds and the quantum universe. Some of the anti-many-worlds view is based on 'common sense', and advocates of many worlds give such common sense, when they disagree with it, short shrift. See earlier in this thread.
Obviously these things aren't however, deal-breakers in any way. This is another, like the David Wallace, attempt to derive the Born rule from what you call 'the ontology of QM'. (I see that the very enterprise of 'wanting to derive' is a disputed idea among the critics of many-worlds)
The maths still works, whatever words we bracket it within.