Is MWI Self-Contradictory and Does Time Travel Need a New Approach?

[Demystifier]

Demystifier: did you check the two papers I posted on MWI in the Heisenberg picture?

Yes, and I agree with their content, but they are not about MWI.

 

[Fyzix]

Yes, and I agree with their content, but they are not about MWI.

What?
Yes they are about Deutsch's attempt at making MWI completley local by using the Heisenberg picture.
How is that not about MWI?

 

[Demystifier]

What?
Yes they are about Deutsch's attempt at making MWI completley local by using the Heisenberg picture.
How is that not about MWI?

I have not been reading the Deutch's paper they refer to, but they never use the words "many worlds". Just because something is about a paper written by Deutch does not immediately imply that it is about many worlds.

For example, I have also written a paper referring to a Deutsch's work
http://xxx.lanl.gov/abs/1006.0338
and yet neither my nor the Deutsch's paper is about MWI. In fact, in a sense the opposite seems to be the case with the Deutsch's paper. In that paper Deutch assumes that free will exists at a fundamental level, which is incompatible with the MWI idea that wave function satisfying a deterministic equation is ALL that exists.

 

[Fyzix]

Obviously as it is about QM it relates to MWI and is just as relevant?
By the way, yes everything Deutsch writes relates to MWI.
I also tried discussing this with him and showed Ruth Kastners paper to him, he rejected it based on something which turned out to be him misunderstanding / not reading the paper.

 

[rkastner]

To anyone who is interested: Deutsch has claimed (in an email, if I recall), that my criticism of his paper is irrelevant because his paper (near the end in one sentence) assumes that more than one outcome exists and that Bell's thm therefore does not apply, which is the key assumption of MWI. So he appears to intend his paper to apply to the MWI picture even though he does not make that explicit up front. As I note in my paper, the claim that D-H 2000 is only intended to apply to the MWI picture does not nullify my criticism, which basically points out that D-H overstate their case: a MWI picture with Rubin-type labeling of Heisenberg operators *must* be assumed to save locality, not merely factorization of the operators, which they present as the main argument of their paper.

 

[stefanbanev]

The MWI picture is getting elegant and natural once we recognize that it is not universe splits apart (it’s always in superposition state) but rather "observer" is constantly branching. Our memory perceives a single path from root to current node. In fact the "Time" from this point of view is not one dimensional – it seems one-dimensional only thanks to our perception.

 

[Fyzix]

The MWI picture is getting elegant and natural once we recognize that it is not universe splits apart (it’s always in superposition state) but rather "observer" is constantly branching. Our memory perceives a single path from root to current node. In fact the "Time" from this point of view is not one dimensional – it seems one-dimensional only thanks to our perception.

This "elegance" is a joke though and is exactly what this thread is dedicated to.
In this picture you can't get Born Rule, which is at the heart of QM, so basically MWI doesn't describe reality at this stage.

You also got more objections than just Born Rule.
How to get determinate outcomes and a physical ontology without local beables and a clear definition of "splitting" is not defined...

To quote Amit Hagar's review of the book "Many Worlds?" on this subject:

How are we then to reconcile the aforementioned claims with the fact that
quantum mechanics, taken literally, mentions neither branches nor a multiplicity of
worlds? According to Wallace, these elements should be regarded as “emergent” on a
par with haircuts or tigers. Not only the latter, says Wallace, are missing from the
mathematical formalism of our most fundamental physical theory, but also they are not
directly definable in the language of microphysics. Nevertheless, and this is the message,
no one would doubt their existence. Decoherence, as a mechanism that allows quasi--
classical structures to emerge from the underlying quantum theory, is what establishes
the existence of these structures, where by “existence” we mean no more (and no less)
than what we mean when we talk about the existence of other macroscopic entities that
presumably emerge from the microphysical world.
Proponents of alternative no-collapse interpretations to Everett such as Bohmian
mechanics are not impressed. For Bohmians, the wave function alone is insufficient to
account for the result of any measurement. To do so, says Tim Maudlin in the chapter
“Can the World Be Only Wavefunction?”, one must add particles, i.e., localized objects
in low--dimensional spacetime, into the ontology. Maudlin’s conclusion is that Everett’s
interpretation, and similarly collapse alternatives in which nothing but the wavefunction
exists, are epistemically incoherent: they do not make the connection between theory
and the results of experiments comprehensible, and yet these results are presumably
what serves to confirm these theories to begin with.
The worry here seems to be that if, according to the Everettians, the wave
function is all there is, and if, further, it ‘lives’ in an abstract, multidimensional space,
then it is unclear how such an object can account for our experience which is, roughly
put, the behavior of localized objects in the low--dimensional spacetime we inhabit.
Bohmians can easily address this problem, says Maudlin, because they simply postulate
such localized objects by adding them into the ontology. GRWf theory (collapse with
flash ontology) has a similar solution. But Everettians (and first generation collapse
theoreticians with them) face the serious challenge of coming up with a comprehensible
link between the state of wavefunction (which is all there is) and what warrants our
belief in the theory, namely, the behavior of localized objects in a low-dimensional
spacetime, which is our experience. Decoherence, argues Maudlin convincingly [p. 132],
simply cannot meet this challenge.
At this stage the attentive reader would have probably noticed that present day
Everettians and their opponents are engaged in two different sets of problems, and
simply talk past each other. While Wallace is busy defending the ontology of multiplicity
of worlds by presenting it as no more awkward than any other ontology of emergent
entities (call this tactic “emergence”), Maudlin saddles him with the problem of latching
that ontology to our everyday experience (call this problem “incoherence”).
And the point is that no matter how seriously one is willing to consider
“emergence” as a viable defense, it still falls short of solving “incoherence”.

Source: http://mypage.iu.edu/~hagara/MW.pdf

 

[stefanbanev]

>In this picture you can't get Born Rule, which is at the heart of QM,
>so basically MWI doesn't describe reality at this stage.

Well, not sure why you say such nonsense, Born Rule is perfectly derived from MWI...

 

[Fyzix]

>In this picture you can't get Born Rule, which is at the heart of QM,
>so basically MWI doesn't describe reality at this stage.

Well, not sure why you say such nonsense, Born Rule is perfectly derived from MWI...

No it is not :)

And what about the other objections?

Even if you could miraculously dervive Born Rule, the interpretation is still wrong without additional postulates.

However please feel free to share your breakthrough discovery of how to derive Born rule because all attempts by Deutsch, Wallace, saunders and greaves have been thoroughly debunked.

 

[Demystifier]

Well, not sure why you say such nonsense, Born Rule is perfectly derived from MWI...

Yes, but by adding additional assumptions/axioms, which destroys the initial elegance.

Even worst, there are several different derivations of the Born rule, each taking ANOTHER set of additional assumptions/axioms.

 

[Fyzix]

Yes, but by adding additional assumptions/axioms, which destroys the initial elegance.

Even worst, there are several different derivations of the Born rule, each taking ANOTHER set of additional assumptions/axioms.

Demystifier, read the Amit Hagar quote in my post above, do you share their view?
I actually feel this is even stronger than the objection regarding born rule

 

[Varon]

No it is not :)

And what about the other objections?

Even if you could miraculously dervive Born Rule, the interpretation is still wrong without additional postulates.

However please feel free to share your breakthrough discovery of how to derive Born rule because all attempts by Deutsch, Wallace, saunders and greaves have been thoroughly debunked.

Dear Dimetry67, other Pro-Many Worlders, Fyzix, Demystifiers, other Anti-Many Worlders, Fredrik, other neutrals, etc.

Pls. read the following paper "Many Mind Interpretation of Quantum Mechanics" as it offers radical solution to how to derive the born rule in Many Worlds. State honestly what you think is the problem with it. I've been analyzing it for a week and need input from others. Thanks.

http://www.ibiblio.org/weidai/Many_Minds.pdf

 

[Fyzix]

Dear Dimetry67, other Pro-Many Worlders, Fyzix, Demystifiers, other Anti-Many Worlders, Fredrik, other neutrals, etc.

Pls. read the following paper "Many Mind Interpretation of Quantum Mechanics" as it offers radical solution to how to derive the born rule in Many Worlds. State honestly what you think is the problem with it. I've been analyzing it for a week and need input from others. Thanks.

http://www.ibiblio.org/weidai/Many_Minds.pdf

I will take a look at the paper later today.
I've actually discussed MWI with the author through mail just some weeks ago.
He objects to MWI due to the probability problem and the fact that there is no way to say where a world starts/ends, which is really problematic.
However I'm not sure if his Many minds interpretation is the same as others, usually they require dualism of the mind.
Which I personally reject.
There is some brief information of it on wikipedia, if you google his name + many minds he also got a FAQ

 

[Varon]

I will take a look at the paper later today.
I've actually discussed MWI with the author through mail just some weeks ago.
He objects to MWI due to the probability problem and the fact that there is no way to say where a world starts/ends, which is really problematic.
However I'm not sure if his Many minds interpretation is the same as others, usually they require dualism of the mind.
Which I personally reject.
There is some brief information of it on wikipedia, if you google his name + many minds he also got a FAQ

The Many Minds versions by Albert and Loewer requires dualism of the mind. But Michael Lockwood's Many Minds (above) doesn't require dualism of mind. But what I can't seem to understand is how about complex objects without brains. How is born rule derived here.

 

[Delta Kilo]

http://www.ibiblio.org/weidai/Many_Minds.pdf

I hereby propose a new "Many Bricks" interpretation by replacing the words "Alice" and "Bob" in the above paper with "Brick 1" and "Brick 2" and no change in the underlying logic. The question "what's it like to be a brick" is no less well formed than the opening remark "what's it like to be Alice" on which the whole article is hinged. Furthermore, "consciousness" is replaced with "brickness" and if anyone have an issue with it, they better start with a universally accepted and unambiguous definition of the former

Seriously, assumption (II) on p. 178 postulating the existence of orthogonal basis of pure states of mind just does not ring true, [STRIKE]brick[/STRIKE]mind being a classical macroscopic system and all. Assumption (III) simply re-states Born rule with no hint why it should be so.

DK

 

[Delta Kilo]

On a serious note, have there been any objections to Zurek's http://arxiv.org/abs/0903.5082" ) to demonstrate the emergence of Born rule from first principles.

There was http://arxiv.org/abs/1102.2826" by Chris Fields mentioned before in this thread. While the title says categorically that "Quantum Darwinism does not explain the emergence of classicality", the paper itself is a lot milder basically agreeing with the premises but highlighting the difficulties in establishing boundaries between subsystems.

Of course, Zurek uses a kind of toy model for the measurement process where each of the observers and the environment are separate well-defined subsystems. It just makes one's life a lot easier. In practice one would have to show that moving the boundary back and forth, adding/removing extra bits, splitting/chaining observers and the environment etc. does not alter the end result as long as the einselected pointer basis remains intact.

DK (disclaimer: I'm really new to all this. please take my posts with a big grain of salt)

 

[Demystifier]

On a serious note, have there been any objections to Zurek's http://arxiv.org/abs/0903.5082" ) to demonstrate the emergence of Born rule from first principles.

Let me comment the last paper you give link to, which is the published one (in Phys. Rev. A).

I don't see a problem with this paper viewed from a "standard" interpretational* view of QM, according to which QM is about information available to observers. However, this paper does not help much to explain the Born rule in the MANY-WORLD interpretation of QM. That's because this paper is NOT about the many worlds. Moreover, regarding the probability issue, it is incompatible with the modern decoherence-based many-world interpretation. It can be seen from Theorem 2 (page 5), which attributes probabilities to ANY Schmidt states, not only to states that suffered branching through decoherence. In MWI, such general states are not "worlds" which could be observed as such, so no probability should be ascribed to them. It's fine to ascribe probabilities to such states in the "standard" interpretation (which this paper is really about), but not in the many-world interpretation.

* The author of the paper is adherent of his "existential" interpretation, which is a variant of the information interpretation.

 

[Delta Kilo]

It can be seen from Theorem 2 (page 5), which attributes probabilities to ANY Schmidt states, not only to states that suffered branching through decoherence.

I think what happens is when he introduces Theorem 2 he just uses the word "probability" as a label for a number that is associated with particular basis vector in Schmidt decomposition and follows the usual probability rules, and shows how to compute it from symmetry under swaps. At this moment this "probability" is not yet connected to the outcome of measurement. This is done later in section V where he considers multiple memory-record states. But yes, it is rather confusing, I'm not sure I get it.

this paper does not help much to explain the Born rule in the MANY-WORLD interpretation of QM. That's because this paper is NOT about the many worlds. Moreover, regarding the probability issue, it is incompatible with the modern decoherence-based many-world interpretation.

I'm not sure why you say that. Zurek certainly stresses the "no-collapse" assumption and refers to Everett's Relative States often enough. He may have been avoiding explicit mentioning of DeWitt's "branching" or "splitting" because these expressions [STRIKE]are a can of worms[/STRIKE] do not describe what happens accurately enough.

To me, an interpretation is (assumes, implies) MWI if all "branches" of a wavefunction in superposition are treated on equal footing. This is what you get by default. To make interpretation non-MWI, one has to somehow suppress all branches but one. Different ways to do it are:

• Postulate objective collapse (out of fashion)
• Tag one branch only with particle trajectories in configuration space
• Invoke anthropic principle down to outright solipsism
• etc.
• Just ignore them, they are not worth talking about (I'm sort of ok with this one)

But the main reason I look favourably at MWI is the mindboggling hugeness of the Hilbert space. It just feels too big compared to the size of the configuration space for a single world, but probably just the right size for the entire multiverse I mean the nature has to compute the wavefunction for the entite multiverse anyway as a side effect of running our world. It seems a shame to throw most if it away

DK
PS My favourite interpretation of QM is http://hitchhikers.wikia.com/wiki/Whole_Sort_of_General_Mish_Mash"

 

[rkastner]

The Born Rule is perfectly transparent in Cramer's Transactional Interpretation (TI), so you don't need MWI and its associated difficulties with obtaining the Born Rule. It is sometimes alleged that 'absorber' is not well-defined in TI. I have developed TI further (including into the relativistic domain); and absorption (i.e., generation of confirmation waves (CW)) is easily accounted for in terms of the microscopic coupling between currents and fields (e.g. as in a scattering vertex). CW are generated upon the action of destruction operators, just as offer waves (OW) are generated by action of creation operators. A macroscopic 'absorber' is a collection of large numbers of microscopic currents, for which generation of a confirmation wave is virtually assured, even if one cannot identify which microscopic current generated it.

My forthcoming book on TI will present this latest development. It is based in part on Davies' QED extension of the Wheeler-Feynman absorber theory. TI also has no problem with 'emergence' of the classical since the latter is just the set of actualized transactions, which are genuine collapses. Such collapses are based on a kind of spontaneous symmetry breaking.

 

[gpran]

Pl. see: http://physics.about.com/od/quantumphysics/f/manyworldsinterpretation.htm. As per many worlds interpretations ‘every time a random event takes place, the universe splits between the various options available. Each separate version of the universe contains a different outcome of that event.’ I wish to ask some basic questions.

1) How to define a world/universe? Does it mean that laws of physics are different in two distinct worlds?
2) Are these worlds completely independent? If humans are in one world then can they get idea of what is happening in other worlds?
3) If action in one world can produce some effect in other world then the two should be treated as interdependent/interconnected worlds and it may not be appropriate to treat them as two distinct worlds. A human being can experience two worlds, first when he is awake and second in his dreams when he is asleep. In his dream the person believes that the dream world is the real world. But here the same person experiences two worlds even though not simultaneously. Therefore some may not think even these two worlds as distinct worlds. Are we suggesting these type of worlds for this theory?
4) I believe that the many worlds interpretation does not, in any way, allow for communication between the parallel universes that it proposes. The universes, once split, are entirely distinct from each other. Is this process also random and what stops the universes from joining again?

In my opinion MWI seems to be the most complex but interesting interpretation and I request for guidance. I also request physics experts to suggest good learning material.

 

[Fyzix]

gpran, please delete your post.
This thread is about TECHNICAL PROBLEMS in the MWI.
In other words, this is not where you come to ask what MWI is.
There are plenty of FAQ's.
Google: MWI FAQ and atleast 2 will come up.

 

[stefanbanev]

I think what happens is when he introduces Theorem 2 he just uses the word "probability" as a label for a number that is associated with particular basis vector in Schmidt decomposition and follows the usual probability rules, and shows how to compute it from symmetry under swaps. At this moment this "probability" is not yet connected to the outcome of measurement. This is done later in section V where he considers multiple memory-record states. But yes, it is rather confusing, I'm not sure I get it.


I'm not sure why you say that. Zurek certainly stresses the "no-collapse" assumption and refers to Everett's Relative States often enough. He may have been avoiding explicit mentioning of DeWitt's "branching" or "splitting" because these expressions [STRIKE]are a can of worms[/STRIKE] do not describe what happens accurately enough.

To me, an interpretation is (assumes, implies) MWI if all "branches" of a wavefunction in superposition are treated on equal footing. This is what you get by default. To make interpretation non-MWI, one has to somehow suppress all branches but one. Different ways to do it are:

• Postulate objective collapse (out of fashion)
• Tag one branch only with particle trajectories in configuration space
• Invoke anthropic principle down to outright solipsism
• etc.
• Just ignore them, they are not worth talking about (I'm sort of ok with this one)

But the main reason I look favourably at MWI is the mindboggling hugeness of the Hilbert space. It just feels too big compared to the size of the configuration space for a single world, but probably just the right size for the entire multiverse I mean the nature has to compute the wavefunction for the entite multiverse anyway as a side effect of running our world. It seems a shame to throw most if it away

DK
PS My favourite interpretation of QM is http://hitchhikers.wikia.com/wiki/Whole_Sort_of_General_Mish_Mash"

Very well said! The ingenuity to avoid the obvious is the major technical problem of MWI ;o) The irony is that everybody gets what he/she is looking for; the multiverse is huge to accommodate all consistent realizations so the opponents may struggle for a while and eventually master some working ugly model without explicit "multiverse" agenda but it will be different from mine branch of reality.

 

[Fyzix]

Very well said! The ingenuity to avoid the obvious is the major technical problem of MWI ;o) The irony is that everybody gets what he/she is looking for; the multiverse is huge to accommodate all consistent realizations so the opponents may struggle for a while and eventually master some working ugly model without explicit "multiverse" agenda but it will be different from mine branch of reality.

Stefan, I made a long post about technical difficulties in MWI in response to your post.
Where is the response?

Either defend the interpretation or accept that it's wrong.

Either way, stop acting like a arrogant idiot when you can't even defend your own "beliefs", it makes you look dumber than Kent hovind, atleast he (tried) to defendh is position

 

[stefanbanev]

Dear Fyzix,

Fyzix>Either way, stop acting like a arrogant idiot

I used to avoid to communicate and/or confront with impolite people unless I really want to "educate" them; you are definitively not such case.

All the best,
Stefan

 

[Fyzix]

So in other words, because I stumped your favoured interpretation and rebutted it completely, you are now speechless?
Check.

 

[stefanbanev]

Check.

Actually it is a checkmate (joke). No need to reply; I really respect your beliefs and see no reasons to argue with you. I wish you all the best... Stefan

 

[Fyzix]

Check as in "Is this correct ? Check"
Not as in checkmate, so no, fail again.


Anyway moving on, this isn't about "beliefs" (atleast not for me) this is SCIENCE and philosophy.
MWI was put forth as one of many potential solutions to the measurement problem.
It has been shown to fail on many technical levels, I ask you defend these, and you can't.
Infact you don't even try because you know you can't...

So why keep acting like MWI is right? As I have given you sources you can check, it's not.
The "pure MWI" is wrong and infact CAN'T work.
Unless you can answer to these questions, you don't belong on this forum as this forum is about rational discussion, when someone has rebutted your argument you can't just say "thats your belief".
That sort of **** belongs in church.

 

[Delta Kilo]

...As I have given you sources you can check...

Which ones would that be? I just rescanned the entire thread and I can see only two links.
One arguing that QM is non-local (duh!) and another is just random blog musings with no physical content.

The "pure MWI" is wrong and infact CAN'T work.

This strong statement requires very strong proof. Please provide.

For example, while I personally favour MWI, I wouldn't go as far as saying other interpretations cannot work. They sure can since at the end of the day they all produce the same results. While I might object to notions that I consider unnecessary, I cannot conclusively prove their absence.

And I don't get why people are so obsessed with Born rule in MWI. It is so obviously correct It's part of the math of QM, it works equally well in all interpretations, it has been proven to be the only sensible measure that works. It is intuitively well understood (in thermodynamics sense as a ratio of the number of microstates leading to different macrostates). Yes, counting those microstates is a pain because it all comes from the measurement and measurement is a complicated multi-stage process, but the progress has been made in this direction. Actually this problem (going from micro to macro) applies equally to all interpretations, at least those that try to study the process of measurement rather just postulate it as in Copenhagen.

 

[Fyzix]

Which ones would that be? I just rescanned the entire thread and I can see only two links.
One arguing that QM is non-local (duh!) and another is just random blog musings with no physical content.

Sigh...
The paper was about trying to make MWI local in Heisenberg picture, which failed...
I also quoted a long segment which brings up a lot of technical criticism of MWI, in it Amit Hagar referes to Tim Maudlin's paper "can the world be only wavefunction?" which you can google for your self...

So unless you can show how you get worlds out of a "pure" wavefunction, you do not have a interpretation of our world...
I demand that you reply back with REAL arguments of how to get this out of this "interpretation", if you want to be taken serious.

This strong statement requires very strong proof. Please provide.

I guess you skipped Logic 101 ?
MWI is the claim, you are the claimant, burden of proof lies on your shoulders.
MWI has been thoroughly rebutted in this thread...

And I don't get why people are so obsessed with Born rule in MWI. It is so obviously correct It's part of the math of QM, it works equally well in all interpretations, it has been proven to be the only sensible measure that works.

NO, Born Rule is obviously correct, yes, MWI can't derive Born Rule...
If you got 75+ IQ this adds up to MWI being wrong

Want some sources?

Adrian Kent
http://arxiv.org/PS_cache/arxiv/pdf/0905/0905.0624v2.pdf

Jacques Mallah
http://onqm.blogspot.com/2009/09/decision-theory-other-approaches-to-mwi.html
http://arxiv.org/abs/0808.2415

Meir Hemmo
http://edelstein.huji.ac.il/staff/pitowsky/papers/Paper45.pdf

Patrick Van Esch
http://aflb.ensmp.fr/AFLB-321/aflb321m515.pdf

Peter J. Lewis
http://philsci-archive.pitt.edu/archive/00002636/01/Uncertainty_(revised).doc

Huw Price
http://arxiv.org/PS_cache/arxiv/pdf/0802/0802.1390v1.pdf

Should I keep going?

 

[Delta Kilo]

The paper was about trying to make MWI local in Heisenberg picture, which failed...

So what? The keyword here is "local", not MWI.

I also quoted a long segment which brings up a lot of technical criticism of MWI, in it Amit Hagar referes to Tim Maudlin's paper "can the world be only wavefunction?" which you can google for your self...

Yes you did and no it does not.You have quoted a review that tells us that there are different opinions on the topic (duh! who would have thought!) and which in turn refers to Maudlin's paper which - have you actually read it? - is another kind of review (duh!). While reviews like this one do bring forth interesting points they are not meant to argue them conclusively. You are supposed to refer to the sources.

MWI is the claim, you are the claimant, burden of proof lies on your shoulders.

Negative. No theory can ever be proven right, but any theory can be proven wrong. You said it's wrong, you prove it.

Note that I myself have avoided making such strong claims: no matter how skeptical I might be about other interpretations, I'm in no position to disprove them since they all agree with experiments. About the only thing I can do is to mutilate them with Occam's razor

Want some sources?

Thanks, I'll check them out in due course...

DK

 

[Demystifier]

And I don't get why people are so obsessed with Born rule in MWI. It is so obviously correct It's part of the math of QM, it works equally well in all interpretations, it has been proven to be the only sensible measure that works. It is intuitively well understood (in thermodynamics sense as a ratio of the number of microstates leading to different macrostates). Yes, counting those microstates is a pain because it all comes from the measurement and measurement is a complicated multi-stage process, but the progress has been made in this direction. Actually this problem (going from micro to macro) applies equally to all interpretations, at least those that try to study the process of measurement rather just postulate it as in Copenhagen.

The question is not whether the Born rule can be incorporated into MWI. Of course it can, in many ways. The question is whether incorporation of the Born rule ruins the initial beauty and simplicity of MWI. The answer is that it does! Perhaps not more than in other interpretations, but not less either. So if MWI with the Born rule incorporated is no simpler or more beautiful than other interpretations, then why one should prefer it over other interpretations? I'm sure one can find many reasons to still prefer it, and that is fine, but the point is that the initial STRONGEST argument for preferring MWI is now lost. If there was no such a loss, then MWI could easily dominate on the world-interpretation map, and that's why people are so obsessed with the Born rule, in both MWI and anti-MWI camps.

 

[Fyzix]

First off: no Tim Maudlin's paper is not a "review" it's a direct response to the problem of ontology in MWI...

Also, you are completley wrong.
MWI isn't a theory, it's a idea, but that idea makes certain claims, which IT HAS TO PROVE.
It's not up to the skeptic.
If I state "There is a God" is it up to other people to disprove it? No, it's up to me who claim this God exists.
If I make my statement more detailed like "God moonwalks on the moon 3:50 am each night" we could test this claim.
Exact same way we can test Born Rule in QM and show it doesn't work in MWI means YES MWI as a "pure interpretation" is disproved.

Like Demystifier just said, SURE you can introduce ADDITIONAL POSTULATES to get Born Rule, such as particles, wavefunction collapse, many minds dualism of mind etc.
However would you still call this many worlds? It's no longer pure wavefunction and this is what is being discussed here.

The claim that pure wavefunction taken as ontologically real can somehow make worlds (which is questioned by many) and that these worlds correspond to Born Rule (which is downright disproved at this point).
So in this sense Bohm is also a "many worlds" interpretation in that it has the wavefunction, but also particles.
The particls allow the Bohmian interpretation to get both of the things MWI can't: a physical ontology that makes sense in 3-Space (local beables) and it can derive Born Rule.
However you wouldn't call this many worlds, it's not even inspired by Everett.
Hell deBroglie was thinking about this back in the 1920's...

 

[Hurkyl]

It's not up to the skeptic.

You're not expressing skepticism of MWI -- you're denying MWI. A denial is a claim which has a burden of proof.

Like Demystifier just said, SURE you can introduce ADDITIONAL POSTULATES to get Born Rule

MWI doesn't need to add postulates -- anything "core" MWI postulates were already there in ordinary quantum mechanics.

Besides, I've always found it baffling that people would criticize any interpretation for assuming "the probabilities computed by the mathematics match the probabilities observed by experiment".

 

[Fyzix]

You're not expressing skepticism of MWI -- you're denying MWI. A denial is a claim which has a burden of proof.

Which I've provided in sources...

MWI doesn't need to add postulates -- anything "core" MWI postulates were already there in ordinary quantum mechanics.

Besides, I've always found it baffling that people would criticize any interpretation for assuming "the probabilities computed by the mathematics match the probabilities observed by experiment".

read the papers please...

 

[Delta Kilo]

The question is whether incorporation of the Born rule ruins the initial beauty and simplicity of MWI. The answer is that it does!

Could you please elaborate on that? How does it ruin the beauty?

I agree that it is difficult to introduce Born rule in MWI without circularity. But there is a reason or it. Typically, in order to derive Born rule one would have to set up some sort of toy model, show that it works (eg. from symmetry arguments), then generalize to more complicated scenarios. But to do that in MWI one needs Born rule to set the stage (to pin down the slice of reality if you wish). In other words, one needs macroscopic objects (pointer states, observers) to operate on but these objects are emergent, not given. It's a bootstrap problem.

DK

 

[IllyaKuryakin]

I've never been able to accept the concept that the entire universe splits in two every time a leaf falls to the ground face up or face down. Even if the math can be made to work, the concept is silly. Considering the number of particles that have made quantum choices over the history of our universe, it would take a number of universes much greater than the number of particles in our universe, and of course, every time a leaf falls to the ground in one of those, it splits in two as well, ad infinitum. Occams razor slices this to ribbons. This reminds me of the solution to string theory, if you suppose an infinite number of universes; one will surely fit the theory. Since we can never observe anything outside our universe, this can never be confirmed by experiment. Surely if you grant infinite degrees of freedom, just about anything can work out. But nothing, other than crackpot theories, ever has infinite degrees of freedom. It falls into the category of religion in my opinion.

 

[stefanbanev]

I've never been able to accept the concept that the entire universe splits in two every time a leaf falls to the ground face up or face down.

Well, it was a bad popularization of MWI. "Quantum universe" remains in its superposition state and it is not the universe you perceive as such. The branching describes the evolution of observer in this quantum realm, actually the picture is more complicated since observer as you perceive it is just one of slices of this realm.

 

[Fyzix]

Stefan: ready to defend your view ?
Or are you just going to continue to "ignore" these technical difficulties and keep the faith?

 

[Delta Kilo]

I've never been able to accept the concept that the entire universe splits in two every time a leaf falls to the ground face up or face down. Even if the math can be made to work, the concept is silly. Considering the number of particles that have made quantum choices over the history of our universe, it would take a number of universes much greater than the number of particles in our universe, and of course, every time a leaf falls to the ground in one of those, it splits in two as well, ad infinitum.

This picture is misleading and that's why I don't like terms "branching" and "splitting". Instead, picture the multiverse as a turbulent flow. Close trajectories represent similar worlds. A single macroscopic state is represented by a compact parcel of gas or water where differences between trajectories are so small that they are unobservable on macroscopic level. As the parcel goes with the flow it gets split into smaller parcels which go different ways, and again and again. If the observer had perfect memory of past events then the size of it parcel (or the proportion of the flow cross-section) would shrink every time the observer learns new fact, in the limit shrinking into a single point which represent the exact configuration of the world with no fuzziness at all. However, real observers are not perfect and tend to forget things. Once a piece of information is forgotten, the corresponding "worlds"/"branches" join back together. However from the global point of view its just a flow of water under the bridge.

And please don't take this analogy too literally. In my opinion it is better than the everbranching tree of life but still it will only carry you that far before it breaks down.

Another way of looking at it: first consider Bohm model. In there you have your wavefunction which evolves all by itself and then you have a single point that dances around in configuration space, representing single definite solution. But in order to make this single point move, the wavefunction has to be computed everywhere. So you get all the motion of other points basically for free. So instead of a lone point moving around, you get a field that flows.

Occams razor slices this to ribbons. ... Surely if you grant infinite degrees of freedom, just about anything can work out.

But this is exactly the issue! Hilbert space is just too darn big! You get all these degrees of freedom out of the box whether you like it or not. Just check how much memory you need to simulate 32 bits. Now do that for 32 qubits. Feel the difference? What do you do with all these numbers, where do you stick them all? (officers! silence!).

 

[Varon]

I will take a look at the paper later today.
I've actually discussed MWI with the author through mail just some weeks ago.
He objects to MWI due to the probability problem and the fact that there is no way to say where a world starts/ends, which is really problematic.
However I'm not sure if his Many minds interpretation is the same as others, usually they require dualism of the mind.
Which I personally reject.
There is some brief information of it on wikipedia, if you google his name + many minds he also got a FAQ

Fyzix, pls give comment on the Michael Lockwood paper which is not based on dualism. Which part of it don't you agree? It is supposed to explain the born rule.

 

[Delta Kilo]

Adrian Kent
http://arxiv.org/PS_cache/arxiv/pdf/0905/0905.0624v2.pdf

The author considers several attempts at deriving Born rule in MWI by counting branches. The branching is taken as granted, no attempt is made to look at the branching process in details. No wonder it does not work. As I said the probabilities have to come out as a ratio of microstates per indistinguishable macrostates during conversion from quantum to classical. The ppaper is nowhere near that.

Jacques Mallah
http://onqm.blogspot.com/2009/09/dec...es-to-mwi.html
http://arxiv.org/abs/0808.2415

Same as above. I may like MWI and at the same time I don't have to like decision-theoretic approach.

Meir Hemmo
http://edelstein.huji.ac.il/staff/pi...rs/Paper45.pdf

The problem is to derive Born’s rule from the many worlds theory without assuming directly or indirectly a notion of typicality or a measure over branches.
Our aim is to show that this is impossible.

Cannot argue with that. A sensible measure of branch "thickness" is required. But that by itself does not disprove MWI.

 

[ExcessRed]

I apologize in advance if this has already been said. I only read the first page of this (kind of lengthy) thread, and felt the need to comment on this:

Nono, ofcourse I don't think the experimentalist will see both.

he splits just like whole world including the experiment.
However,

Pre-experiment you got:

1 Experimenter
A experiment with 2 possible outcomes

After the experiment

You got 2 experimenters each observing one of the 2 outcomes.
They repeat the experiment and this occurs again.

However unless MWI ASSUMES that there is something very special about consciousness that makes the universe somehow put the observers in the universe which would then correspond to the correct probability, they will see 50/50.

It's that simple.

Just draw it on a piece of paper and you will understand exactly what I mean (this thought experiment is Putnam's not mine originally).

90% chance that a blue light occurs, 10% chance that a red light occurs.

Unless you know ahead of time which experimenter to choose from the theoretically infinite number of realities, there is a good chance (in our case, 90% x 90% = 81%) you'd randomly grab two blue-lighters - we can't just choose two at random.

In contrast, if you somehow knew ahead of time that the two experimenters you choose are going to express different results, then the argument is about as relevant as saying... look in a bag of marbles (90% blue, 10% red), remove one marble of each color. From that new set of two, randomly choose one marble and you would have a 50% chance of picking blue.

In essence... wouldn't a single event with a precisely 90% chance of success result in 10 branched realities - 9 successes and 1 failure - thus preserving the global probability?

EDIT: Moved my edit to a new post, since someone had replied by the time I edited. Sorry!

 

[Fyzix]

The author considers several attempts at deriving Born rule in MWI by counting branches. The branching is taken as granted, no attempt is made to look at the branching process in details. No wonder it does not work. As I said the probabilities have to come out as a ratio of microstates per indistinguishable macrostates during conversion from quantum to classical. The ppaper is nowhere near that.

Same as above. I may like MWI and at the same time I don't have to like decision-theoretic approach.

could you give us a paper showing the technical details of this approach you are talking about?

 

[Fyzix]

I apologize in advance if this has already been said. I only read the first page of this (kind of lengthy) thread, and felt the need to comment on this:



90% chance that a blue light occurs, 10% chance that a red light occurs.

Unless you know ahead of time which experimenter to choose from the theoretically infinite number of realities, there is a good chance (in our case, 90% x 90% = 81%) you'd randomly grab two blue-lighters - we can't just choose two at random.

In contrast, if you somehow knew ahead of time that the two experimenters you choose are going to express different results, then the argument is about as relevant as saying... look in a bag of marbles (90% blue, 10% red), remove one marble of each color. From that new set of two, randomly choose one marble and you would have a 50% chance of picking blue.

In essence... wouldn't a single event with a precisely 90% chance of success result in 10 branched realities - 9 successes and 1 failure - thus preserving the global probability?

No and that's the whole point.

At each single event, the universe (if we look at it from MWI) would branch into 2 realities.
1 where the red light goes on
1 where the blue light goes on

This would happen each time and would always add up to 50/50.
There is no escaping it.

Take a piece of paper and draw a line, now pretend that you conduct a experiment and that it branches into blue on one side, red on the other, now branch a blue and red from each of those again and continue doing it.
How the hell are you going to say that there is a 10 vs 90% chance of one of them being observed if the experimenter pre-experiment will end up with BOTH branches and continue to do so at each experiment?

 

[ExcessRed]

No and that's the whole point.

At each single event, the universe (if we look at it from MWI) would branch into 2 realities.

I don't think the idea is that a branch occurs when a human eye observes it - that would be silly. An "observation" occurs any time a particle interacts with another particle in a way that requires it to have a definite quantum state.

Perhaps a more kosher way of describing this phenomenon would be that non-binary probabilities are the result of n binary subdivisions wherein 2 to the n-th worlds would be created.

If an experiment has success rate of approximately 90%, it might result in 1,048,576 different realities. 943,719 of these realities we would observe the result of as "blue light", and the other 104,857 we observe as "red light" - even though the observations of one blue light world and another blue light world are functionally the same, there are subtle differences below the observed level. In this case there were 20 subdivisions resulting in 2^20 worlds.

EDIT: Basically, this:

As I said the probabilities have to come out as a ratio of microstates per indistinguishable macrostates during conversion from quantum to classical.

 

[Hurkyl]

In essence... wouldn't a single event with a precisely 90% chance of success result in 10 branched realities - 9 successes and 1 failure - thus preserving the global probability?

Taking the the decoherence-based philosophy that we should accept the statistical mixture as being reality rather than assuming collapse, the math tells us this is a weighted mixture of two states, with the weights being 90% and 10%.

While we could invent hidden degrees of freedom for the sole purpose of splitting the mixture into a uniform distribution with roughly 90% of the micro-states containing a blue event and the remaining 10% containing a red event, I think it's a bad idea for two reasons:

1. This moves us away from the fundamental idea of MWI -- to understand wave-functions undergoing unitary evolution. (This is the most important of the two reasons)
2. There is absolutely nothing to suggest probability is quantized, and to the best of my knowledge this approach doesn't solve any real problems.

(I don't count an attack on MWI by person who steadfastly refuses to even conceive the idea of a weighted mixture a "real problem")

 

[Lost in Space]

If the MWI theory is wrong, does this mean that consciousness does collapse wave functions? If so, how could the universal wave function collapse at the Big Bang if there were no observers around to collapse it?

 

[Hurkyl]

If the MWI theory is wrong, does this mean that consciousness does collapse wave functions?

If MWI is wrong, it means one of:

• Some aspect of quantum mechanics is wrong
• Experimentally observed statistics in subsystems are not the result of unitary evolution in larger systems
• There are other components to physical state beyond the wave-function which contribute to observations
• Some other mode of failure I didn't think of

The difference between physical state collapsing to a single outcome versus remaining a statistical mixture is not a physical difference -- no observation can distinguish between the two possibilities.

Consciousness has pretty much nothing to do with any of the above. Anything that talks about consciousness is a separate thing layered on top of the basics.

 

[rkastner]

If MWI is wrong (which I think it is), that does not imply that "some aspect of quantum mechanics is wrong". It simply implies that our interpretational approach has been limited by an unrecognized artificial barrier: we haven't gotten outside the nonrelativistic box. Keep in mind that nonrelativistic qm cannot be the whole story anyway. A big problem for most of the 'mainstream' interpretations is that they cannot define what an 'observation' is in the sense of ExcessRed's statement that "An "observation" [i.e., measurement] occurs any time a particle interacts with another particle in a way that requires it to have a definite quantum state." Well, what is this 'way' without resorting to an appeal to 'consciousness,' or an implicit human choice of what to observe as in decoherenc-based approaches? It is explained unambiguously in PTI with reference to the *relativistic* domain: a 'measurement' occurs when an annihilation operator acts on a quantum state -- i.e., when a quantum state is destroyed. The point is that the measurement problem cannot be solved within the nonrelativistic limit -- you have to get outside the nonrelativistic box to solve it. This will all be explained in detail in my forthcoming book on PTI.

 

[Fyzix]

If MWI is wrong, it means one of:

• Some aspect of quantum mechanics is wrong
• Experimentally observed statistics in subsystems are not the result of unitary evolution in larger systems
• There are other components to physical state beyond the wave-function which contribute to observations
• Some other mode of failure I didn't think of

Hurkyl you know this is ********, so why do you keep saying it?

Even wavefunction taken as all there is doesn't yield MWI, so, yeah...

Also what were your solution to the probability problem? The failed Desicion Theoretic approach?