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