Many Worlds Interpretation and act of measuring

[atyy]

No, I haven't read that or any Deutsch or Wallace. I was hoping you guys could save me having to do that. I started reading this link and see that it's 47 pp, so it would take me awhile to get through it. Have you read it? Can you summarize anything?

Yes, everyone's view seems to make sense on a first pass - but if you start asking whether you have missed some subtlety by trying to find a robust core to the argument, that answer is hard to find, because everyone's argument is different and seems incompatible.

Wallace summarizes the situation in http://arxiv.org/abs/0712.0149.

"It is useful to split this problem in two:

The Incoherence Problem: In a deterministic theory where we can have perfect knowledge of the details of the branching process, how can it even make sense to assign probabilities to outcomes?

The Quantitative Problem: Even if it does make sense to assign probabilities to outcomes, why should they be the probabilities given by the Born rule?"

Regarding the incoherence problem, he writes " The Subjective Uncertainty Program aims to establish that probability really, literally, makes sense in the Everett universe: that is, that an agent who knows for certain that he is about to undergo branching is nonetheless justified in being uncertain about what to expect. ... If the Subjective Uncertainty program can be made to work, it avoids the epistemological problem of the Fission Program, for it aims to recover the quantum algorithm itself (and not just to account for its empirical success.) It remains controversial, however, whether subjective uncertainty really makes sense. For further discussion of subjective uncertainty and identity across branching, see Greaves (2004), Saunders and Wallace (2007), Wallace (2006a) and Lewis (2007)."

Regarding the quantitative problem, he says "The third, and most recent, strategy has no real classical analogue (though it has some connections with the ‘classical’ program in philosophy of probability, which aims to derive probability from symmetry). This third strategy aims to derive the principle that weight=probability from considering the constraints upon rational action of agents living in an Everettian universe. It was initially proposed by Deutsch (1999), who presented what he claimed to be a by Barnum et al (2000), and defended by Wallace (2003b). Subsequently, I have presented various expansions and developments on the proof (Wallace 2007,2006c), and Zurek (2003b, 2005) has presented another variant of it. It remains a subject of controversy whether or not these ‘proofs’ indeed prove what they set out to prove."

 

[Rodrigo Cesar]

Why not accept that no one understands quantum physics and move on ? rather than create theories that don't make any sense... no math will solve this, each time someone tries to solve the problems of quantum physics more problems appear, srsly.. Quantum physics is beyond our logic..understanding classical physics is enough!

 

[bhobba]

rather than create theories that don't make any sense... no math will solve this,

Its the exact opposite - mathematically its very beautiful and makes a lot of sense. Its just to many, including me, it's too weird. But weirdness is purely a personal reaction - nothing to do if its true or not.

BTW its a myth that no-one understands QM. We certainly understand it these days eg:
http://arxiv.org/pdf/quant-ph/0101012.pdf

What it means, what are its basic primitives, what it explains and what it doesn't - that's what this interpretation stuff is about.

Thanks
Bill

 

[Rodrigo Cesar]

In math makes sense, but in reality is very tasteless, we must have a balance between both

 

[DennisN]

In math makes sense, but in reality is very tasteless, we must have a balance between both

Why? Science is not like art, literature, architecture etc (and "tasteless" is an opinion, which actually is completely irrelevant). If the mathematics and the models work, they work, that is the only thing that matters in the end. If you want art instead, you go to an art museum . Here's what Feynman had to say about it (with toungue-in-cheek):


Edit: Another way to put it is basically like this: In science, if we are to choose between a beautiful inaccurate theory and an ugly accurate theory, we choose the ugly one, not because it is ugly but because it is accurate.

 

[atyy]

Why? Science is not like art, literature, architecture etc . If the mathematics and the models work, they work, that is the only thing that matters in the end. If you want art instead, you go to an art museum . Here's what Feynman had to say about it (with toungue-in-cheek):

Rubbish! It wasn't tongue in cheek. Not all universes have observers, however, since recoherence is inevitable, some observers will end up in another universe.

 

[Quantumental]

This is a nice take down of the decision-theoretic approach of Wallace. The author even offers an attempt to solving the problem: arxiv.org/pdf/0808.2415

 

[bhobba]

Why? Science is not like art, literature, architecture etc (and "tasteless" is an opinion, which actually is completely irrelevant).

Exactly. I find it too weird for my tastes - but that means diddley squat. The only thing that matters is correspondence with experiment.

Thanks
Bill

 

[bhobba]

This is a nice take down of the decision-theoretic approach of Wallace. The author even offers an attempt to solving the problem: arxiv.org/pdf/0808.2415

Can you give a précis of its argument in simple terms? The last paper you posted I couldn't make sense of - it looked like philosophical goobly gook to me.

Thanks
Bill

 

[bhobba]

Rubbish! It wasn't tongue in cheek. Not all universes have observers, however, since recoherence is inevitable, some observers will end up in another universe.

Bearing in mind that in MW an observation occurs when decoherence happens what universe will not have observers ie what universe will not allow decoherence?

Thanks
Bill

 

[Rajkovic]

when will we have a final position on MWI, if it is correct or not?

 

[DennisN]

Exactly. I find it too weird for my tastes - but that means diddley squat. The only thing that matters is correspondence with experiment.

Just to clarify, my reply was actually a general reply to post #177 and #179 by the OP, which I interpreted to be about quantum physics in general. Regarding MWI I feel the same as you, but that also means diddley squat (I also have some more scientific issues with MWI in general, but I'm not keen to go into those at the moment; if I would, I'd like to be more thorough than I could be a the moment. AND have more knowledge than I have at the moment. Maybe some other time ).

 

[bhobba]

when will we have a final position on MWI, if it is correct or not?

Of course its correct. Disproving would be big news. Nothing here has done that.

Thanks
Bill

 

[Rajkovic]

Ok, but, what's the best interpretation of MWI? I know there are many..could you explain to me ?

 

[bhobba]

Ok, but, what's the best interpretation of MWI? I know there are many..can you explain to me ?

I only know one - Wallace's as detailed in his book on it:
https://www.amazon.com/dp/0198707541/?tag=pfamazon01-20

But if this type of interpretation appeals then take a look at Consistent Histories:
http://quantum.phys.cmu.edu/CHS/histories.html

It's described by Gell-Mann as many worlds without the many worlds. Also, again according to Gell-Mann, Feynman was very positive towards it, sitting in the back of seminars and asking quite penetrating questions. Basically its the stochastic theory of histories - which are basically a coarse grained sequence of worlds in MW parlance - but in Consistent Histories you only have one.

I like Consistent Histories - my only objection is for me it looks like defining your way out of problems rather than facing them head on.

Thanks
Bill

 

[Quantumental]

Of course its correct. Disproving would be big news. Nothing here has done that.

I always get the feeling that you really believe MWI, but don't want to accept the implications of such a belief ;p
Saying "of course it's correct", is a bit weird. It's correct like every other interpretation is correct, but then again all interpretations has scientific and technical difficulties that make them incorrect.

Nearly all refutations of David Wallace's decision-theoretic programme will include what you call "philosophcal goobly gook", simply because the entire decision-theoretic approach is hopelessly philosophical and outside the realm of science itself. So in order to take it apart, you have to go down to it's level and dissect it. This is also why it is borderline impossible to cook it down to a short paragraph.
There is a simple argument put forth by David Albert called the "fatness measure", it's summarized here: https://books.google.com/books?id=V9yQrUQW6O0C&pg=PA181&redir_esc=y#v=onepage&q&f=false

There are so many arguments put forth against the decision theoretic approach that is a lot more solid than the derivation itself, so to me the Born Rule issue is wholly unsolved. There are other attempts, but all of those have pretty much been shown to be circular/flawed in some fatal way. Which is why even amongst the proponents of MWI, they do not agree at all.

Couple this with the factorization problem and other issues mentioned (by you too Bhobba), I do think it's fair to say that MWI fares no better than any other interpretation, one might even argue that it's one of the interpretations that is pretty bad off. The idea of just taking the wavefunction and then saying "every outcome is real" sounds very elegant and simple, but then you realize that's not what MWI is and what MWi does not work with current understanding of physics and philosophy, suddenly it's not so elegant anymore. I would also suggest you read Jeffrey Barretts recent paper where he defends the emperical adequacy of pure wave mechanics (pure Everett). http://www.socsci.uci.edu/~jabarret/bio/publications/everett4.pdf He also picks apart Wallace's approach quite well in this article by showing how much additional "stuff" and assumptions Wallace add to quantum mechanics in order to defend his "emergence" argument.

 

[bhobba]

Nearly all refutations of David Wallace's decision-theoretic programme will include what you call "philosophcal goobly gook", simply because the entire decision-theoretic approach is hopelessly philosophical and outside the realm of science itself.

That's exactly the issue I have. Decision Theory is a well developed area of math used in a number of mathematical areas such as Actuarial Science. It has a number of key theorems from its axioms - one being that its notion of probability, which I gave previously, is equivalent to the Kolmogorov axioms. That being the case its a perfectly valid basis as an interpretation of probability in QM, just like Bayesian or frequentest, or even just using the Kolmogorov axioms themselves.

This philosophy stuff leaves me cold because no agreement is ever reached. Previous things like Kant's idea that Euclidean geometry was a-priori true proved a crock - in fact it was clear, logical, mathematical reasoning that proved it so - not philosophical mumbo jumbo.

Thanks
Bill

 

[Rodrigo Cesar]

maybe in another universe I love this theory lol

 

[julcab12]

Its the exact opposite - mathematically its very beautiful and makes a lot of sense. Its just to many, including me, it's too weird. But weirdness is purely a personal reaction - nothing to do if its true or not.

... Well. In QM math is deliberate and literal -- "what you see is what you get. It appears to be random - Let's make use of the randomness and create probability solutions that is mathematically beautiful. -- It offers prediction-- Ok, fair enough. BUT I'm always reminded that any interpretation in QM are dynamic consequence and not categorized as physical theory. In the classical view. We deal weirdness with caution. We don't take phenomenon's very literal and construct something that is not limited to that axiom like the usual QM does (Who could blame them. They don't have a choice anyways -- We can't make anything cohesive about randomness/multiplicity but view and used it as literal).

... I respect optical theorem in the basis of unitary or some evolution operator that is time dependent including the weird things that time brings to the table. I view multiplicity as optical phenomenon or some sort of false image and respect very much unitarity. Why it looks random/multiple? We really don't know so the simplest way is to take it literal. Until now we only took this paradigm to make probabilistic predictions and not what it really is. IMO. The field breaks the pointer state allowing it to appear as multiple false images/pointers or time slices in a 1 Hilbert space/ 1 universe.

 

[bhobba]

BUT I'm always reminded that any interpretation in QM are dynamic consequence and not categorized as physical theory.

Come again. An interpretation is a physical theory.

and not what it really is. IMO.

That's the precise problem. In QM we have far too much of this 'what it really is' and 'IMHO'. Science isn't concerned with such. For example some believe the math literally is the reality. Its purely philosophical mumbo jumbo believing or refuting such a position. We all do it - but its not science.

Thanks
Bill

 

[julcab12]

Come again. An interpretation is a physical theory.Bill

"Interpretations of quantum mechanics aren't physical theories. There is no testable prediction of the MWI, for example, that would allow us to falsify it (except in the trivial sense that we could falsify quantum mechanics in general, which would also falsify the CI and every other interpretation).

That's the precise problem. In QM we have far too much of this 'what it really is' and 'IMHO'. Science isn't concerned with such. For example some believe the math literally is the reality. Its purely philosophical mumbo jumbo believing or refuting such a position. We all do it - but its not science.

Not really my intention. If you've read my point. I'm a realist. "what it really is" -- in all honestly, is that we really tried to know what it is exactly. That's what it meant by interpretation in QM -- no added baggage. My version of 'IMO' is conducive to real events and not a subjective whatnots. Literal viewpoint is not always the go to in nature simply because we've seen similar events that happens naturally and has natural explanations. If you appeared to me as multiple bhobba. I don't simply look at you as bhobba in a multiple version in a multiple worlds but i have to look also "WHAT MAKES YOU APPEAR THAT WAY'. Ins't that a legit question? This is exactly how we evaluate events in reality.

 

[bhobba]

"Interpretations of quantum mechanics aren't physical theories. There is no testable prediction of the MWI, for example, that would allow us to falsify it

Their is no requirement for all aspects of a theory to be falsifiable.

Not really my intention. If you've read my point. I'm a realist. "what it really is" -- in all honestly, is that we really tried to know what it is exactly.

That's exactly why it a useless criteria. What some accept as 'it is exactly' varies widely eg Penrose believes the math literally is what it is exactly. You probably don't. But in supporting your position you will find its philosophical discourse, and, as I have pointed out innumerable times, that discipline never reaches any conclusions accepted as 'true' like science does.

Thanks
Bill

 

[Quantumental]

Ok let's move the discussion (temporarily at least) away from the probabilities issues since it's so heavily loaded with philosophy and instead move over to the ontological issues of the factorization issue. Why isn't his sufficient enough to disuade you from thinking that MWI is a solid interpretation?

 

[bhobba]

Why isn't his sufficient enough to disuade you from thinking that MWI is a solid interpretation?

Because it hasn't been proven to be fatal to the theory as I have explained many many times eg that paper claiming nothing happens in MW needs to have a bit of a look at spontaneous emission and what causes that.

It has been thrashed out innumerable times in many threads - no need to do it again. And I will not be drawn into another long winded thread about it that goes nowhere.

Thanks
Bill

 

[julcab12]

Ok let's move the discussion (temporarily at least) away from the probabilities issues since it's so heavily loaded with philosophy and instead move over to the ontological issues of the factorization issue. Why isn't his sufficient enough to disuade you from thinking that MWI is a solid interpretation?

.. Depends on how you evaluate each problems which often leads to circular. If it is viewed as direct postulate or ontological approach (universally). MWI has the advantage.

 

[julcab12]

..

That's exactly why it a useless criteria. What some accept as 'it is exactly' varies widely eg Penrose believes the math literally is what it is exactly. You probably don't. But in supporting your position you will find its philosophical discourse, and, as I have pointed out innumerable times, that discipline never reaches any conclusions accepted as 'true' like science does.

.

What about Penrose? Regardless of his belief. He made a very good argument and/or mathematical structure about a possibility of universe in a continuum using simple dynamics. Is it consistent? It depends on the criteria. In the context of QM's postulate its weak due to inconsistencies -- unless certain postulate is realized. In GR it is a natural solution. Multiplicity is also well handled in GR as a natural phenomenon.

Of course. Science never reaches any conclusion but we have temporal results, constants and constraints that is workable and consistent to a point. So we consider it as 'true' to the limit of our understanding/science. I think your referring to absolutes?

 

[bhobba]

..In the context of QM's postulate its weak due to inconsistencies -- unless certain postulate is realized. In GR it is a natural solution. Multiplicity is also well handled in GR as a natural phenomenon.

What QM postulate would that be?

Of course. Science never reaches any conclusion but we have temporal results, constants and constraints that is workable and consistent to a point. So we consider it as 'true' to the limit of our understanding/science. I think your referring to absolutes?

I am referring to exactly what I said. In science, at any point in time we have a generally accepted picture - it may be true or false - who knows what future research will bring. In philosophy we have all sorts of views and no generally accepted answer to the type of questions it asks. Indeed history shows philosophical views are generally way off the mark as far as future scientific progress is concerned eg Gauss vs Kant on non Euclidean geometry- Kant was wrong - Gauss correct.

Thanks
Bill

 

[kith]

Ok let's move the discussion (temporarily at least) away from the probabilities issues since it's so heavily loaded with philosophy and instead move over to the ontological issues of the factorization issue. Why isn't his sufficient enough to disuade you from thinking that MWI is a solid interpretation?

Non-rhetorical counter question: how exactly does the factorization problem trouble you?

 

[RUTA]

Why not accept that no one understands quantum physics and move on ? rather than create theories that don't make any sense... no math will solve this, each time someone tries to solve the problems of quantum physics more problems appear, srsly.. Quantum physics is beyond our logic..understanding classical physics is enough!

Most physicists are of that mindset, actually. "Shut up and calculate!" per Mermin. But, many of us in foundations of physics believe a deeper understanding of quantum physics will lead to new physics altogether.

 

[Quantumental]

Non-rhetorical counter question: how exactly does the factorization problem trouble you?

Well without a solution it diretly contradicts physical reality, so even if you had ignored the probability problem, you're still left with an incomplete hypothesis. You could obviously say that: "Let's just postulate the perference". And that'd be alright, just like Bohmians postulate a pilot wave or Copenhagenists postulate collapse. But for a theory that is supposed to be the underlying final answer to reality such postulates that fly in the face of what the initial hypothesis says? That's ugly in my opinion.

Let me ask the question back:why doesn't it trouble you?

 

[julcab12]

What QM postulate would that be?

As i told you earlier postulate in QM (1-6 incl abstract) are built upon a literal mathematical framework or to satisfy certain mathematical conditions because of probabilistic interpretation. In consequence, we assign operators and eigenstates to act as if it is real in a sense but in reality we don't know if it's the ONLY case. Anyways QM --normalization techniques is built upon that. The wavefunction boils into a sum of position "eigenstates" - simpler wavefunctions which correspond to the particle(s) having definite positions which is the more general rule, is that -- to get predictions for some observable property, you break the wavefunction into a sum of eigenstates or eigenfunctions for that particular observable property. BUT that is only on a mathematical basis. We assign worlds to each values as consequence of math. Same is true in GR's limit's assumption on flat Minkowski space.

I am referring to exactly what I said.

You have a general way of saying so. And i don't disagree. Truth/true to me is temporal and accountable to the limit of our scientific endeavor that doesn't include any unverified predictions -- multiverses and MWI's. However, i don't see them as without merit.

 

[RUTA]

The discussion so far has involved only the probabilistic nature of MW (of which I'm dubious at this point). What does MW have to say about quantum non-locality?

 

[atyy]

That's exactly the issue I have. Decision Theory is a well developed area of math used in a number of mathematical areas such as Actuarial Science. It has a number of key theorems from its axioms - one being that its notion of probability, which I gave previously, is equivalent to the Kolmogorov axioms. That being the case its a perfectly valid basis as an interpretation of probability in QM, just like Bayesian or frequentest, or even just using the Kolmogorov axioms themselves.

This philosophy stuff leaves me cold because no agreement is ever reached. Previous things like Kant's idea that Euclidean geometry was a-priori true proved a crock - in fact it was clear, logical, mathematical reasoning that proved it so - not philosophical mumbo jumbo.

Thanks
Bill

But why can decision theory be applied in the first place? Decision theory requires uncertainty, but it is unclear why there is any uncertainty here. To justify it, there are two approaches, but as these two papers discuss, neither is uncontroversial.
Wallace, http://arxiv.org/abs/0712.0149 (section 4.5)
Greaves, http://users.ox.ac.uk/~mert2255/papers/pitei.pdf (section 3.1)

Also, the derivation assumes decoherence in order to get apparent collapse, which requires the application of the Born rule before any decision has been taken.
Zurek, http://arxiv.org/abs/quant-ph/0405161 (long comment on Deutsch/Wallace on p27)
Dawid and Thiebault, http://philsci-archive.pitt.edu/9542/1/Decoherence_Archive.pdf

 

[kith]

Well without a solution it diretly contradicts physical reality, so even if you had ignored the probability problem, you're still left with an incomplete hypothesis. You could obviously say that: "Let's just postulate the perference".

Why do we need a preference? Why is the arbitrariness of the factorization a problem?

Let me ask the question back:why doesn't it trouble you?

Since I haven't understood what exactly bothers you, I can't answer yet.

 

[bhobba]

As i told you earlier postulate in QM (1-6 incl abstract) are built upon a literal mathematical framework or to satisfy certain mathematical conditions because of probabilistic interpretation. In consequence, we assign operators and eigenstates to act as if it is real in a sense but in reality we don't know if it's the ONLY case.

I quite likely have missed something - but I can't find the axiom you are talking about. Can you tell it to me again?

My axioms are along the lines of the following - see post 137:
https://www.physicsforums.com/threads/the-born-rule-in-many-worlds.763139/page-7

That's the most elegant I know of. My preferred ones are the following though:
http://arxiv.org/pdf/quant-ph/0101012.pdf

It shows QM is basically the simplest generalised probability model that allows continuous transformations between pure states.

Thanks
Bill