Problems with Many Worlds Interpretation

[juanrga]

well that's a little bit strong (although I think I agree with you, it's a possibility that this statement causes a strong reaction of people who feel misjudged).
Maybe, to be a little arrogant, my poll is a better way to make a similar (tough a little less strong) point. Do I think it wouldn't be bad to read the website you mention.

Well in your poll in this same forum you add some of the responses that you received.

X1:

I think the many worlds interpretation is nonsense.

X3:

The many-worlds theory is a silly mistake

X5:

The theory is false because it is inconsistent.

I do not find too many difference with what I said:

Many worlds (MW) is a collection of nonsense as has been repeatedly showed in the literature.

But thanks by your post.

 

[eqblaauw2]

Well in your poll in this same forum you add some of the responses that you received.

X1:

X3:

X5:

I do not find too many difference with what I said:

But thanks by your post.

You make a good point.
And no thanks.

 

[juanrga]

Hi jtbell,

from: http://www.anthropic-principle.com/preprints/manyworlds.html

"Political scientist" L David Raub reports a poll of 72 of the "leading
cosmologists and other quantum field theorists" about the "Many-Worlds
Interpretation" and gives the following response breakdown [T].

1) "Yes, I think MWI is true" 58%
2) "No, I don't accept MWI" 18%
3) "Maybe it's true but I'm not yet convinced" 13%
4) "I have no opinion one way or the other" 11%

Amongst the "Yes, I think MWI is true" crowd listed are Stephen Hawking
and Nobel Laureates Murray Gell-Mann and Richard Feynman. Gell-Mann and
Hawking recorded reservations with the name "many-worlds", but not with
the theory's content. Nobel Laureate Steven Weinberg is also mentioned
as a many-worlder, although the suggestion is not when the poll was
conducted, presumably before 1988 (when Feynman died). The only "No,
I don't accept MWI" named is Penrose.

This is the 'highly unscientific' (Max Tegmark own words) poll taken at a 1997 quantum mechanics workshop, where Gell-Mann is listed as a believer in the interpretation, although he explicitly rejected the view, for instance.

 

[Ken G]

Your approach is not scientific, it is philosophical.

Not at all, what I am doing is separating the science from the philosophy. Often people get them all mixed up together.

The progress means the ability to meet and understand, even partially, the objects, not to make calculations about them.

What objects are you understanding?

I am of course aware that we are far away from being able to make sense of the physical world but I manage to make a room for it in the near or the far future. Because that's the true mission of science.

This is exactly the kind of "mixing up" philosophy and physics that I'm pointing out. We have no kind of basis to scientifically support these beliefs of yours, all we have any evidence of whatsoever is that we will continue to push new theories into domains where our predictions are currently suspect. That's it, that's what we can say. How do you know when you have made sense of the physical world? You expect a sign that reads "you have it correct-- you have reached your destination"? Every single scientific culture since Aristotle thought they were making room to make sense of the physical world in the near future! These are just the facts of the matter, as scientists, we should at least deal in facts.

I was right, you are a postmodernist who lives in "interpretations", "narrativities" and "metaphors".

Nah, I just know the difference between a scientifically demonstrable claim that is not liable to change in the future, and an interpretation that is.

What kind of effectivity could have a technology if we don't have the shadow of a clue of what things are... ? Magic, maybe ?

Let's examine your logic here. Your syllogism is apparently "we have effective technology, any effective technology must be based on understanding "what things are", ergo, we understand what things are." Does that really sound like a logically bulletproof argument to you? You can't think of any examples of technologies that worked fine being used by people who had no idea of why? Do we have any idea why two slits make a diffraction pattern, just because we can write an equation that predicts it? Why do you think we can build and fly airplanes without knowing any string theory?

 

[BruceW]

The standard interpretation is the Copenhagen one. Many worlds (MW) is a collection of nonsense as has been repeatedly showed in the literature. It is still maintained alive from people who do not understand QM.

Maybe you would take a look to Streater list of lost causes in physics, the section about MW: http://www.mth.kcl.ac.uk/~streater/lostcauses.html#XII

That website doesn't specifically rule out MWI, it just seems to say that MWI isn't useful. Also (sorry if I'm boring everyone with this point again), the 'no non-unitary collapse' version of MWI and the 'non-unitary collapse only happens for the end-user of the calculations' version of CI seem to be exactly the same thing (except the philosophical slant is different, but I don't really care about that either way).

 

[Ken G]

All interpretations of QM are the same except for the philosophical slant, so if you don't care about that, then what differences do you see in any of them? It's all the same theory, you realize!

 

[eqblaauw2]

This is the 'highly unscientific' (Max Tegmark own words) poll taken at a 1997 quantum mechanics workshop, where Gell-Mann is listed as a believer in the interpretation, although he explicitly rejected the view, for instance.

you seem to mix up two polls, the one cited by tegmark (which really says nothing very pro to mwi (in my opinion), and is in tegmark's own opinion highly unscientific, with people voting more then once, with 8 people voting for mwi, and in which copenhagen is still number one, if you don't count the instrumental version). And david raub's one, you're right when you say that 'Gell-Mann is listed as a believer in the interpretation, although he explicitly rejected the view, for instance' (unless you think consistent histories, that doesn't contain parallel universes and copies of everything on earth, is a version of mwi, which I think is kind of strange thing to argue for, since the many-worlds of the many-worlds interpretation aren't there in consistent histories).
just trying to get the fact straight, no real relevant criticism intended.

 

[juanrga]

That website doesn't specifically rule out MWI, it just seems to say that MWI isn't useful. Also (sorry if I'm boring everyone with this point again), the 'no non-unitary collapse' version of MWI and the 'non-unitary collapse only happens for the end-user of the calculations' version of CI seem to be exactly the same thing (except the philosophical slant is different, but I don't really care about that either way).

It says rather more than that. It says that the subject arose from a «misguided» point of view, remarks that «the idea of the wave-function of the universe is meaningless», that «there is nothing to the many-worlds theory», that is based in hopes «by its advocates», that they do not understand what they are trying («if this were possible, then we just arrive at quantum mechanics»)...

In short, it is a «lost cause» as the website title emphasizes.

 

[juanrga]

you seem to mix up two polls, the one conducted of david raub (which really says nothing very pro to mwi (in my opinion), and is in tegmark's opinion highly unscientific, with people voting more then once, with 8 people voting for mwi, and in which copenhagen is still number one, if you don't count the instrumental version). And david raub's one, where you're right when you say that Gell-Mann is listed as a believer in the interpretation, although he explicitly rejected the view, for instance.
just trying to get the fact straight, no real relevant criticism intended.

You are welcome

 

[eqblaauw2]

You are welcome

haha thanks I edited it (if that's what you tried to make me aware of)
greetings Edo

 

[BruceW]

All interpretations of QM are the same except for the philosophical slant, so if you don't care about that, then what differences do you see in any of them? It's all the same theory, you realize!

I see. I was thinking of objective collapse theory as one of the interpretations of QM. But I guess it is a separate theory to QM. (Since it makes different predictions compared to the other interpretations of QM).

So 'interpretation', by definition, means that there is no way to experimentally distinguish between different interpretations?

 

[Ken G]

So 'interpretation', by definition, means that there is no way to experimentally distinguish between different interpretations?

Yes, I would say that is true. If it makes different predictions, it's a different theory, not a different interpretation of a theory. However, different interpretations might stimulate different new theories, so they are not moot.

 

[BruceW]

Yes, I would say that is true. If it makes different predictions, it's a different theory, not a different interpretation of a theory. However, different interpretations might stimulate different new theories, so they are not moot.

I get you. That makes sense.

 

[Fra]

However, different interpretations might stimulate different new theories, so they are not moot.

I agree. Thus one can say that the "constructive" sense of "interpretations" is different ways to ask or construct the OPEN questions.

In QM for example, there are a certain domains where there is hard experimental confirmation. But there are other domains where it's not confirmed at all.

Unification is a good example. It's simply ambigous exactly HOW to "extrapolate" current measurement theory from the well tested domain of subsystems (except a full GUT is still lacking) to the not at all tested domain of cosmological systems (or open systems).

These are the areas where I find the discussion intersting. It's exactly what you take to be the CORE of quantum mechanics, that determines the most plausible extrapolation it to new territory.

/Fredrik

 

[BruceW]

It says rather more than that. It says that the subject arose from a «misguided» point of view, remarks that «the idea of the wave-function of the universe is meaningless», that «there is nothing to the many-worlds theory», that is based in hopes «by its advocates», that they do not understand what they are trying («if this were possible, then we just arrive at quantum mechanics»)...

In short, it is a «lost cause» as the website title emphasizes.

If we're talking about the interpretations of QM as being equivalent in their predictions, then how is MWI a 'lost cause'? We could equally well choose to use MWI instead of CI. (Or use any of the other interpretations). I think Ken G puts it well when he wrote that 'different interpretations might stimulate different new theories'. So maybe the website is saying that MWI is unlikely to lead to any new predictions/theories?

 

[eqblaauw2]

If we're talking about the interpretations of QM as being equivalent in their predictions, then how is MWI a 'lost cause'? We could equally well choose to use MWI instead of CI. (Or use any of the other interpretations). I think Ken G puts it well when he wrote that 'different interpretations might stimulate different theories'. So maybe the website is saying that MWI is unlikely to lead to any new predictions/theories?

I think that's why david deutsch call's mwi a theory (not that is an argument in it's favor by any means), because it does make predictions: predictions of (now) unobservable universes, that's a prediction (he thinks that one day there will be observational evidence for this, but even if there will be not, it predicts a lot of unobservable universes).

that being said, I have stopped taking david deutsch serious. In an email he said this to me:Unfortunately, even that is not as simple as it sounds.

The rejection of Everett's theory is in my opinion mainly a sociological phenomenon, unlike any other in physics. I suspect that it is rooted in the intellectual intimidation of physics students, and in a complex niche that yearns for quantum mysticism in the general public. As a result, many physicists are reluctant to discuss the issue at all, and they couch their opinions in platitudes or equivocation. Further relevant issues are discussed in Chapter 12 of *The Beginning of Infinity*.

IRONY ALERT
yes and the aliens have caused 9/11 in a complex niche between the cia and al qaida.
ENDING OF IRONY ALERT

p.s.
his book 'the beginning of an infinity' is a theory of everything that combines the qm interpretation of Hugh Everett (that's to say it lightly a bit controversial, but ok you're free to believe in it), with the interpretation of the evolution theory by Dawkins (that's also controversial), with the theory of Popper (in my humble opinion completely misinterpreted by david deutsch), and that all together mixed by david deutsch.
To say that is a lot of names and interpretations (and no 'generaly excepted' interpretations/theories by 'the' scientific community) (except popper, but he messes that, again in my humble opinion, completely up, and the evolution theory, but not with the interpretation of dawkins), seems an understatement.

 

[Ken G]

If we're talking about the interpretations of QM as being equivalent in their predictions, then how is MWI a 'lost cause'?

Yeah, in my view that section of the article translates to "here's why the many-worlds interpretation does not fit into my own personal philosophical priorities about what science is", but it is not actually framed that way. The article would do much better to simply analyze what those philosophical priorities are, and then it follows rather immediately whether MWI fits into them. This would put the focus on its proper place.

 

[eqblaauw2]

Yeah, in my view that section of the article translates to "here's why the many-worlds interpretation does not fit into my own personal philosophical priorities about what science is", but it is not actually framed that way. The article would do much better to simply analyze what those philosophical priorities are, and then it follows rather immediately whether MWI fits into them. This would put the focus on its proper place.

well I think d.d. en others' theory is scientific without the positive connotation,
if you think bad science isn't science, then I think it isn't (see my previous post).
if you think speculations that aren't necessary at all is philosophy, then I think it's philosophy

 

[Ken G]

In mathematics, one does not argue the axioms, one simply identifies the axioms and tracks their ramifications. Physicists have something to learn from that model.

 

[BruceW]

I think that's why david deutsch call's mwi a theory (not that is an argument in it's favor by any means), because it does make predictions: predictions of (now) unobservable universes, that's a prediction (he thinks that one day there will be observational evidence for this, but even if there will be not, it predicts a lot of unobservable universes).

Again, it depends what you mean by MWI. Not all versions of MWI require many universes. The MWI with many literal, separate universes is one particular way of explaining the probabilities of outcomes.

But even the version of MWI with many universes doesn't make different predictions to CI. It does make different predictions to objective collapse theory, but that's because objective collapse theory is not standard QM.

Edit: To explain further, in the MWI with many universes, these universes are supposed to be completely noninteracting, so there is no way (even in principle) to be able to do an experiment to show their existence. This is one of the reasons why I don't like this version of MWI.

 

[eqblaauw2]

Again, it depends what you mean by MWI. Not all versions of MWI require many universes. The MWI with many literal, separate universes is one particular way of explaining the probabilities of outcomes.

But even the version of MWI with many universes doesn't make different predictions to CI. It does make different predictions to objective collapse theory, but that's because objective collapse theory is not standard QM.

Edit: To explain further, in the MWI with many universes, these universes are supposed to be completely noninteracting, so there is no way (even in principle) to be able to do an experiment to show their existence. This is one of the reasons why I don't like this version of MWI.

that's why I said david deutsch and others', not everyone's mwi,
p.s. It would be helpfull if there would be one definition of mwi, in physics there's seems to be a bit of a problem with definitions, so everyone can make the most strange claims about what's been generally accepted or not. I suggest we call mwi, the one with mw that extually exist in a strong sense (because the weak sense can mean anything).
greetings Edo

 

[BruceW]

Good idea.
I don't know much about the MWI of many literal universes, could you help me on an explanation?

Its often said on the web that these different universes are non-interacting. So are they simply a statistical justification of the probability in QM?

Or are they meant to represent each component of the state vector in some basis? For example, if we had ldead cat> + lAlive cat> then does one universe have ldead cat> and the other have lAlive cat> and the two universes would in fact interact (but only slightly, since decoherence has happened)?

 

[eqblaauw2]

well I could direct you to david deutsch and tegmark and you can google david bryce, but then again I think I would direct you to a lot of bull

 

[Ken G]

For example, if we had ldead cat> + lAlive cat> then does one universe have ldead cat> and the other have lAlive cat> and the two universes would in fact interact (but only slightly, since decoherence has happened)?

I think that is very much the idea. The point of MWI is not just to give a statistical basis to the interpretation of a probability (as being N events out of M possibilities, because the ensemble interpretation allows that just fine), it is to have a mathematical description of any closed system that maintains both unitarity and completeness. So that's why the "alive cat" and the "dead cat" must both be equally real in MWI, regardless of what we see when we open the box, because nothing else would allow us to interpret unitarity as giving a complete description of the reality of closed systems (including closed systems that involve observers).

 

[juanrga]

If we're talking about the interpretations of QM as being equivalent in their predictions, then how is MWI a 'lost cause'? We could equally well choose to use MWI instead of CI. (Or use any of the other interpretations). I think Ken G puts it well when he wrote that 'different interpretations might stimulate different new theories'. So maybe the website is saying that MWI is unlikely to lead to any new predictions/theories?

Because, as explained before in this thread, many-worlds is not an interpretation of QM but a collection of nonsense arising from misunderstandings of QM [*]. Re-read the quote that you are citing, and the associated website, paying special attention to clever words as «belief», «misguided», «meaningless»...

[*] The confusion in the many-worlds literature is evident on that some advocates claim that this is another interpretation of QM, whereas others claims this is a different theory leading to (never tested) new 'predictions'.

 

[juanrga]

I have stopped taking david deutsch serious. In an email he said this to me:Unfortunately, even that is not as simple as it sounds.

The rejection of Everett's theory is in my opinion mainly a sociological phenomenon, unlike any other in physics. I suspect that it is rooted in the intellectual intimidation of physics students, and in a complex niche that yearns for quantum mysticism in the general public. As a result, many physicists are reluctant to discuss the issue at all, and they couch their opinions in platitudes or equivocation. Further relevant issues are discussed in Chapter 12 of *The Beginning of Infinity*.

Many physicists are reluctant to discuss the issue, because it has been discussed in detail up to extenuation and simply they have better things to devote their limited time than to correct mistakes already corrected, not one, but several times in the literature.

 

[eqblaauw2]

Many physicists are reluctant to discuss the issue, because it has been discussed in detail up to extenuation and simply they have better things to devote their limited time than to correct mistakes already corrected, not one, but several times in the literature.

I'm sorry in my post that is partly about the mail d.d. send me I was a little bit sloppy. This can lead to a minor misunderstanding (not a misunderstanding by you specifically juanrga). The 'unfurtionally this is also not as simple as it sounds' is from d.d. not from me.
The rest of the (in my opinion very vague and slightly ridiculous) conspiracy theory is also from d.d.

greetings Edo,

p.s. Does anyone know how I can fully unsubscribe my account?, I think I've said what I wanted to say about this subject, and I do not intend to say anything at other threads at this moment.

 

[juanrga]

So that's why the "alive cat" and the "dead cat" must both be equally real in MWI, regardless of what we see when we open the box,...

This reflects the main MWI position very-well and explains why MWI has been labeled as unscientific, for very good reasons, by some.

 

[juanrga]

I'm sorry in my post that is partly about the mail d.d. send me I was a little bit sloppy. This can lead to a minor misunderstanding (not a misunderstanding by you specifically juanrga). The 'unfurtionally this is also not as simple as it sounds' is from d.d. not from me.
The rest of the (in my opinion very vague and slightly ridiculous) conspiracy theory is also from d.d.

greetings Edo,

p.s. Does anyone know how I can fully unsubscribe my account?, I think I've said what I wanted to say about this subject, and I do not intend to say anything at other threads at this moment.

I interpreted the last paragraph as d.d. and (curiously) added the first line for avoiding anyone to attribute the paragraph to you instead of to d.d.

About your question I have no idea. Why do not you ask the Staff?
Regards

 

[Ken G]

This reflects the main MWI position very-well and explains why MWI has been labeled as unscientific, for very good reasons, by some.

I feel it should really be labeled as "unempiricist" rather than "unscientific." Most people feel that science is deeply rooted in empiricism, that's true, but quite a few scientists, probably most notably some of the great theoretical physicists, see it as more deeply rooted in rationalism (i.e., the mathematical models are the reality, the observations are just how we check those models). If you adopt the latter view, you say that observations can falsify models, but observations do not falsify that the cat is both alive and dead because the observations are coming from within the system, and may not have access to complete information about the system. But the empiricist view is that observations must have access to complete information because they define complete information. Rationalists say that complete information is whatever we think it is, not whatever we observe it to be. Consider the question in the book by the celebrated astrophysicist Mario Livio, "is God a mathematician?" (http://plus.maths.org/content/god-mathematician) So it's not exactly "unscientific" to be rationalistic-- the relative fortunes of empiricism and rationalism have demonstrably ebbed and flowed many times in the fledgling history of our physics.

 

[juanrga]

I feel it should really be labeled as "unempiricist" rather than "unscientific." Most people feel that science is deeply rooted in empiricism, that's true, but quite a few scientists, probably most notably some of the great theoretical physicists, see it as more deeply rooted in rationalism (i.e., the mathematical models are the reality, the observations are just how we check those models). If you adopt the latter view, you say that observations can falsify models, but observations do not falsify that the cat is both alive and dead because the observations are coming from within the system, and may not have access to complete information about the system. But the empiricist view is that observations must have access to complete information because they define complete information. Rationalists say that complete information is whatever we think it is, not whatever we observe it to be. Consider the question in the book by the celebrated astrophysicist Mario Livio, "is God a mathematician?" (http://plus.maths.org/content/god-mathematician) So it's not exactly "unscientific" to be rationalistic-- the relative fortunes of empiricism and rationalism have demonstrably ebbed and flowed many times in the fledgling history of our physics.

Empirical method is not a synonymous for experimental method. And this latter is only a part of the scientific method.

Using your «may not have access to complete information about the system» as basis for your «So that's why the "alive cat" and the "dead cat" must both be equally real in MWI, regardless of what we see when we open the box» is another instance of why MWI has been labeled as «unscientific» by most scientists. Other reasons are the internal inconsistencies. See quotes and polls given before. References analyzing MWI and its flaws are multiple. See also the website «lost causes» given before.

No physicists would confound physical reality with the mathematical models used to represent part of that reality. It is curious that Mario Livio discusses Euclidean geometry in his book, because Feynman in his course in physics (with Leighton and Sands) precisely explains the differences between physics and maths using a light ray and Euclidean geometry. Feynman emphasizes how the mathematical (geometric) model is only an approximation to physical reality (the physical object) and how answering what is the range of validity of that approximation is a subject of experimentation and not of reasoning only.

Finally, I want to add that the history is full of rationalist who believed that they could explain the world by reasoning only. I can now recall the father of «rational thermodynamics», a mathematician very polemic with the work of physicists and chemists working in thermodynamics (He used the term «Onsagerists» in pejorative ways, although Onsager won a Nobel for his remarkable work in thermodynamics). He and his coworkers used the term «rational» to emphasize that the thermodynamics developed by others was 'irrational' (of course, using their own criteria and definitions). The funny part was when his 'rational' formulations were confronted with experimental data and miserably failed in a number of tests; whereas the 'irrational' theories of physicists and chemists worked and continue to be taught at universities of all the world.

 

[Ken G]

References analyzing MWI and its flaws are multiple. See also the website «lost causes» given before.

Nothing in that "lost causes" website was at all convincing tht MWI has flaws, that website was merely categorizing the philosophical priorities of its author. Given those priorities, it is obvious that MWI would not be looked on favorably. That's the point-- one can only judge interpretations subject to a set of philosophical priorities. We don't argue axioms, we merely identify them, and track their ramifications.

No physicists would confound physical reality with the mathematical models used to represent part of that reality.

But that isn't true. A strongly rationalistic physicist, like say Max Tegmark or Steven Weinberg, will do exactly that. They may well recognize that any given model has shortcomings, but they view the "actual truth" as simply a deeper model that is very much along the same lines as the existing one but with some improved features. Above all, they view the truth about the reality as being described by a mathematical model, because to them, that's just exactly what truth is. There's just no point in arguing axioms like that, only in identifying them, and tracking their ramifications.

It is curious that Mario Livio discusses Euclidean geometry in his book, because Feynman in his course in physics (with Leighton and Sands) precisely explains the differences between physics and maths using a light ray and Euclidean geometry. Feynman emphasizes how the mathematical (geometric) model is only an approximation to physical reality (the physical object) and how answering what is the range of validity of that approximation is a subject of experimentation and not of reasoning only.

Feynman always tended toward empiricism, which is one reason I like his approach. But a rationalist could easily counter that Euclidean geometry is only one brand of geometry, and no one ever said reality had to be Euclidean. They would still hold that reality is fundamentally geometric, whether Euclidean or some other.

Finally, I want to add that the history is full of rationalist who believed that they could explain the world by reasoning only.

Indeed, they always tend to "go overboard" in interpreting the ramifications of each new theory, I agree. All the same, every theorist dons a "rationalist hat" pretty much every time they sit down to try and conjure a new theory. So there is no question that rationalism is a useful angle from which to view reality, even if one does not have to take it quite as seriously as the "God is a mathematician" camp does.

I can now recall the father of «rational thermodynamics», a mathematician very polemic with the work of physicists and chemists working in thermodynamics (He used the term «Onsagerists» in pejorative ways, although Onsager won a Nobel for his remarkable work in thermodynamics).

And there's the rub right there-- he won a Nobel. So there is a demonstrable value to being able to think rationalistically. But I agree that rationalism is probably not a good way to build a world view that transcends what science can demonstrate-- it's just too unlikely to be right.

He and his coworkers used the term «rational» to emphasize that the thermodynamics developed by others was 'irrational' (of course, using their own criteria and definitions). The funny part was when his 'rational' formulations were confronted with experimental data and miserably failed in a number of tests; whereas the 'irrational' theories of physicists and chemists worked and continue to be taught at universities of all the world.

The way I put that earlier in the thread is, the problem with rationalism is that the theories keep changing but the observations don't. Still, the rationalist counters that a good theory is always a good theory-- for whatever it is good at. To me, the bottom line is, "don't take the theory too seriously." Or how this is often said, "the map is not the territory."

 

[BruceW]

Nothing in that "lost causes" website was at all convincing tht MWI has flaws, that website was merely categorizing the philosophical priorities of its author. Given those priorities, it is obvious that MWI would not be looked on favorably. That's the point-- one can only judge interpretations subject to a set of philosophical priorities. We don't argue axioms, we merely identify them, and track their ramifications.

That's true. I feel that MWI doesn't match my philosophical preference, but I can see that it is a viable interpretation.

One more question: What if we said that non-unitary collapse doesn't happen, and we also said there is only one 'world'? I guess from there we could say that the wavefunction only tells us about a large statistical ensemble of similarly-prepared systems (ensemble interpretation). Or we could say the wavefunction is real, and then we need some way to make sense of the probabilities of individual outcomes.

MWI makes sense of it by saying that each component of the (pure) state vector in the measurement basis represents a different 'world'. Are there any other ways to make sense of measurement without resorting to the subjective non-unitary collapse which CI advocates?

 

[Ken G]

What if we said that non-unitary collapse doesn't happen, and we also said there is only one 'world'? I guess from there we could say that the wavefunction only tells us about a large statistical ensemble of similarly-prepared systems (ensemble interpretation).

Yes, that's the "ensemble interpretation", it simply holds that QM is not a complete description for individual systems.

Or we could say the wavefunction is real, and then we need some way to make sense of the probabilities of individual outcomes.

Yes, there is quite a tension between definiteness and indefiniteness in quantum mechanics. The two seem to be halves of the same coin.

Are there any other ways to make sense of measurement without resorting to the subjective non-unitary collapse which CI advocates?

The deBroglie-Bohm approach holds that the initial state is already collapsed, we just don't know it. It places a level of mathematics beneath the wave function, interpreting the wave function like we interpret the density of a gas-- an emergent equilibrium property of a more complicated underlying system. The emergent equilibrium is treated statistically, but the underlying system is deterministic and inaccessible in practice. It is the closest to classical, but still has an "angels on a pin" feeling because it equilibrates so readily that we never encounter anything else.

 

[juanrga]

Nothing in that "lost causes" website was at all convincing tht MWI has flaws, that website was merely categorizing the philosophical priorities of its author. Given those priorities, it is obvious that MWI would not be looked on favorably. That's the point-- one can only judge interpretations subject to a set of philosophical priorities. We don't argue axioms, we merely identify them, and track their ramifications.
But that isn't true. A strongly rationalistic physicist, like say Max Tegmark or Steven Weinberg, will do exactly that. They may well recognize that any given model has shortcomings, but they view the "actual truth" as simply a deeper model that is very much along the same lines as the existing one but with some improved features. Above all, they view the truth about the reality as being described by a mathematical model, because to them, that's just exactly what truth is. There's just no point in arguing axioms like that, only in identifying them, and tracking their ramifications.
Feynman always tended toward empiricism, which is one reason I like his approach. But a rationalist could easily counter that Euclidean geometry is only one brand of geometry, and no one ever said reality had to be Euclidean. They would still hold that reality is fundamentally geometric, whether Euclidean or some other.
Indeed, they always tend to "go overboard" in interpreting the ramifications of each new theory, I agree. All the same, every theorist dons a "rationalist hat" pretty much every time they sit down to try and conjure a new theory. So there is no question that rationalism is a useful angle from which to view reality, even if one does not have to take it quite as seriously as the "God is a mathematician" camp does.
And there's the rub right there-- he won a Nobel. So there is a demonstrable value to being able to think rationalistically. But I agree that rationalism is probably not a good way to build a world view that transcends what science can demonstrate-- it's just too unlikely to be right.The way I put that earlier in the thread is, the problem with rationalism is that the theories keep changing but the observations don't. Still, the rationalist counters that a good theory is always a good theory-- for whatever it is good at. To me, the bottom line is, "don't take the theory too seriously." Or how this is often said, "the map is not the territory."

The lost causes in physics website gives technical arguments against MWI.

Evidently, the criticism of MWI, which I have pointed out before is purely technical and has been published in journal of physics (e.g., Int. J. Mod. Phys. A 5 1745-1762 1990), not in philosophical magazines, as you seem to believe.

It is very ironic that you write about the role of axioms, because precisely one of the main criticism of the MWI literature is that its main advocates either lack to give a complete set of axioms, from which one could explain the physical world (reason for which the theory has been labeled «unscientific») or them give us a set of self-contradictory axioms (reason for the which «The theory is false because it is inconsistent»; quote X5 in this same thread).

Max Tegmark confounds physics with philosophy in his post-modern Radical Platonism: MUH.

Steven Weinberg is also aware of the differences between physics and maths. Precisely in his textbook gravitation and cosmology, Weinberg explains why he follows what he calls a non-geometrical presentation of the subject, and remarks in the preface how the electromagnetic interaction cannot be understood in geometrical terms.

You have completely misinterpreted Feynman's point of view. He was not talking about the limitations of Euclidean geometry in regard to more general geometries. He was talking about the limits of mathematics and the differences with physics. He chose Euclidean geometry as an simple illustrative example adequate to his audience (people taking an introductory physics course).