Problems with Many Worlds Interpretation

[juanrga]

And evidently, I'm missing the bold-faced sentence where Penrose actually says what you keep claiming he is saying: that MWI is inconsistent with any theory that can make the same tested predictions as the current postulates of QM that can be found in standard textbooks. Your argument lacks evidential support in a very blatant and obvious way, yet in all your posts, you cannot correct this gaping flaw.

Therefore your argument has moved from Penrose-agrees-with-me to show me a sentence where Penrose-agrees-with-you.

Sorry, but I do not need to find a sentence from Penrose supporting my claim that MWI is nonsense. I already supported my claim.

Maybe you missed this point again, but the reason which I cited Penrose was because you pretended him to support your philosophy, when he just agrees with me that MWI is both inelegant and not-working. Read the quotes again.

It's really quite simple-- you can't get R from U, but the MWI proponent doesn't think you ever get R. You only get R when you adopt certain philosophical assumptions

This very much summarizes the point.

Effectively, as I repeated and repeated R cannot be derived from U (because is irreducible). That is the reason which QM includes both R and U.

Although for decades the MWI community has done claims that they have an alternative interpretation of QM using only U, their theory is internally inconsistent and disagrees with QM predictions.

Now you finally agree that the R that cannot be obtained from U can be 'obtained' from U when, your own words, «you adopt certain philosophical assumptions»

I am really satisfied and this point.

Thank you.

 

[Ken G]

Therefore your argument has moved from Penrose-agrees-with-me to show me a sentence where Penrose-agrees-with-you.

Actually, I already presented the evidence that Penrose agrees with me-- the problem is that you have presented none that he agrees with you. As this is the crux of your entire position here, I think that is a serious flaw in your stance.

Sorry, but I do not need to find a sentence from Penrose supporting my claim that MWI is nonsense. I already supported my claim.

As I expected, you still cannot provide evidence that the Wiki article was wrong when it claimed that Penrose thinks MWI is consistent with current QM, but that current QM is missing something important, and so by implication MWI is missing something important. I agree with the Wiki, it completely checks with all the evidence presented in this thread, nor have you refuted it with a shred of evidence.

Maybe you missed this point again, but the reason which I cited Penrose was because you pretended him to support your philosophy, when he just agrees with me that MWI is both inelegant and not-working. Read the quotes again.

Yet again you are imagining something that never had anything to do with this thread. It is clear you have no idea what I'm saying every time you attempt to summarize it. You would actually do much better sticking with my words.

This very much summarizes the point.

I know that R, a well-defined physical and mathematical entity, cannot be derived from U (because is irreducible).

That has never been the source of the disagreement. Read my words again. The source of the disagreement is whether or not we can take it as a scientific fact that we do get "R". I have told you that this "fact" actually requires certain philosophical assumptions and priorities that are not required to adopt, and indeed MWI proponents generally do not, which is pretty much the entire point. There is no experiment that requires that R be part of the reality that QM postulates are trying to describe, there is just the observer perception, which as I said is not part of your theory, or any theory, of QM. Until that problem is fixed, if it can be fixed, the issue will always reduce to philosophical priorities-- largely around the role of rationalism and empiricism in asserting what a physics theory is trying to do.

Although for decades the MWI community has done bogus claims that they had derived, all the 'derivations' have been showed to be wrong.

That is also not the least bit relevant to this thread. The issue was not whether MWI could derive R from U according to some set of laws (we should know that is impossible), it was simply whether or not MWI is a consistent interpretation with the fact that we perceive R. That is entirely different-- for example, CI never makes any effort whatsoever to "derive R" from some deeper principles, yet obviously CI is consistent with R because it simply includes it as an ad hoc postulate (something Penrose sees as a big problem, and Hawking does not, both for philosophical reasons). Similarly, MWI includes the ad hoc postulate that R is perceived because of the action of the perceiver, and the fact that it has not succeeded in connecting that to any deeper principles seems to me like a perfectly obvious extension of the problem of having no theory of perceivers. Nor do you, nor does Penrose.

So given the absence of a theory of quantum gravity that can do what Penrose would like it to do, and given the absence of a theory of perceivers that can do what I am saying would be necessary to do, what these "proofs" actually accomplish is simply tracking the logical ramifications of the various philosophical priorities in concert with what has been experimentally established about quantum systems. That is what I have been trying to tell you all along.

As a mathematician working in foundations of QM has said «MWI is a smokescreen without a consistent mathematics behind.»

That is also irrelevant to the thread. Nowhere did I claim that MWI gives a mathematically closed accounting of the predictions of QM, I said it is an interpretation that is consistent with those predictions. The predictions require nothing beyond the mathematics of how to do them, which there is no disagreement about. What there is disagreement about is how to find a set of postulates that put those predictions on a sound and rigorous mathematical footing, which simply does not exist at present (because of the problem of no dynamical accounting of the perception of collapse). That's why Penrose, and others, are trying to create one! Why on Earth would they need to do that if one already existed?

I am really satisfied and this point I have stopped from reading the rest of your post.

Thank you.

Unfortunately you still have understood nothing I said. Pity, your inability to understand these nuances will continue.

 

[fellupahill]

Hello,

While the majority of physicists embrace the Many Worlds interpretation of quantum decoherence, I am holding out hope for the Copenhagen interpretation or better yet, a undiscovered interpretation.

Please allow me to pose three problems I have with the MW interpretation.

1) There is a nonzero prob of me spontaneously becoming a miniature sun. Let me elaborate. Since I am made of atoms, there is a nonzero prob that all of the subatomic particles comprising each of the nuclei of my atoms are all one kilometer away except for a single proton and single electron in each atom. I.e. I am now spontaneously comprised of only hydrogen atoms. Now let's say that since even the exact position of these hydrogen atoms is uncertain they are close enough that gravity overpowers all and nuclear fusion takes place. I.e. I have become a miniature sun.

The probability of this happening is obviously miniscule, but nonzero. With the CI interpretation this will never happen because the probability is so small that the universe is not old enough for such a low probability to have been realized. However with MWi since the probability is nonzero, it has happened. Moreover it has been happening every second of every day since the minute I was born in some parallel universe.

2) My second problem with MW intepretation is how can an interference pattern result in a double slit experiment if the particle is actually traveling through a different slit in separate universes. Shouldn't the interference only occur if the particle is traveling through both slits simultaneously in the same universe?

3) My third problem with MW is that it really does away with the concept of probability although many quantum experiments have shown that the concept does exist. For example, take a weighted coin which is 99% more likely to flip heads, than tails. CI predicts that a 100 flips would yield 99 heads and 1 tail. With a single flip, one is much more likely to get a head than a tail. However with MW, one flip will result in head in one universe, tail in another so therefore 50-50 probability.

Can someone help me to understand these issues any better? Thanks!

Finally. I found someone who agrees.

I think along the same logic.

What is the chance that we live in the one universe were NONE of the crazy but possible outcomes happen. We seem to be made of what is predicted will happen.

 

[notnews32]

My question for many-worlds proponents would be how the laws of quantum mechanics are reconciled in these outliar universes. How can intelligent life observe these fundamental laws of nature for which we have accounted for 100% of possible outcomes given that they do not observe the same distribution of outcomes that we do? Would you suggest that there is no universe in which every event is unprobable, and that these unprobable events scatter themselves through an infinite number of universes?

 

[kith]

If you agree with the MWI you also have to acknowledge that the laws of physics appear different in a very small fraction of the multiverse. I don't think this is a problem for a person who accepts the existence many worlds in the first place.

You can also expand this idea. What forbids that the laws of physics can actually be different in other universes? Maybe your universe is a very unlikely one and you only perceive it to be normal, because you need very special conditions for the emergence of the ability to perceive? (->anthropic principle)

Such verbal ramblings can be done endlessly with a MWI background. This is probably why it is so popular in pop science.

 

[Ken G]

If you agree with the MWI you also have to acknowledge that the laws of physics appear different in a very small fraction of the multiverse. I don't think this is a problem for a person who accepts the existence many worlds in the first place.

Is it essential to accept a multiverse if you accept MWI? In my view, those two ideas are quite different, and you could have either one without the other (though holding one certainly makes it easier to hold the other!). The multiverse is used to "explain" why the parameters (and maybe even laws) of our universe are what they are, within the "landscape" of other possibilities. The "many worlds" are not the multiverse, they would be aspects of a single universe with a single set of parameters and laws, but many islands of mutually incoherent processing agents trying to figure out those laws. All of the "many worlds" would have the same cosmological parameters, for example, because I don't think those parameters are thought of as dynamically evolving in statistically distributed ways, but rather as being stochastically distributed over the multiverse right from the start, independently of any subsequent evolution. That's my understanding anyway, it all seems a bit far-fetched to me and I'm not sure if I could even count anthropic reasoning as an "explanation" of how things are, but merely as an observation that must be true. Explanations shouldn't have to be true.

You can also expand this idea. What forbids that the laws of physics can actually be different in other universes? Maybe your universe is a very unlikely one and you only perceive it to be normal, because you need very special conditions for the emergence of the ability to perceive? (->anthropic principle)

Right, and that's what makes it so hard to use anthropic reasoning for anything constructive-- can we really say what the distribution is we are selecting from? Are universes that obey laws likely or unlikely? If life that thinks in ways that leads to anthropic principles requires a universe that obeys laws, how could we ever tell if we are in a majority or minority universe just because ours appears to respect laws? And does ours really respect laws, or is it natural that intelligence finds something that it can interpret that way?

 

[bohm2]

This is another paper that just came out today discussing some of the arguably less well-known criticisms against MWI:

The Many World Interpretation is therefore rather a No World Interpretation (according to the simple factorization), or a Many Many Worlds Interpretation (because each of the arbitrary more complicated factorizations tells a different story about Many Worlds...The state vector of the universe in the EI (Everett Interpretation)has no environment or observer it can relate to, and is therefore completely meaningless. The appearance of interacting subsystems of the universe are only due to a choice of a “samsara” basis, which is however completely arbitrary, just like a slicing of Minkowski spacetime is possible, which makes it look like an expanding universe . One has to add something to give the state vector and QM a meaning.

Nothing happens in the Universe of the Everett Interpretation
http://lanl.arxiv.org/pdf/1210.8447.pdf

 

[Hurkyl]

The appearance of interacting subsystems of the universe are only due to a choice of a “samsara” basis, which is however completely arbitrary, just like a slicing of Minkowski spacetime is possible, which makes it look like an expanding universe . One has to add something to give the state vector and QM a meaning.

Based on your quote, the abstract, and skimming the introduction, there is a very straightforward response to the paper: it forgot about dynamics.

 

[Demystifier]

Based on your quote, the abstract, and skimming the introduction, there is a very straightforward response to the paper: it forgot about dynamics.

Dynamics is nothing but a unitary transformation from one point in the Hilbert space to another. As long as all points in the Hilbert space look the same (which is one of central claims in the paper), such dynamics does not bring anything interesting.

 

[Quantumental]

Based on your quote, the abstract, and skimming the introduction, there is a very straightforward response to the paper: it forgot about dynamics.

Forgot about dynamics? He mentions dynamics specifically 11 times.

 

[Quantumental]

Dynamics is nothing but a unitary transformation from one point in the Hilbert space to another. As long as all points in the Hilbert space look the same (which is one of central claims in the paper), such dynamics does not bring anything interesting.

What are your take on the paper?
Seems to be a very interesting one, but seeing as how many papers have been written about MWI I struggle to believe he has found a new "fatal" flaw

 

[Demystifier]

What are your take on the paper?
Seems to be a very interesting one, but seeing as how many papers have been written about MWI I struggle to believe he has found a new "fatal" flaw

I have similar feelings, but let me not further comment it before I study it in detail.

 

[Dmitry67]

The appearance of interacting subsystems of the universe are only due to a choice of a “samsara” basis, which is however completely arbitrary

It is not arbitrary: there is an "unfair" selection of basis with "consciousness", whatever it means. If we accept AP in cosmology we should also accept the similar principle in MWI, there is nothing wrong with it.

 

[Demystifier]

It is not arbitrary: there is an "unfair" selection of basis with "consciousness", whatever it means. If we accept AP in cosmology we should also accept the similar principle in MWI, there is nothing wrong with it.

I don't think that many adherents of MWI would agree that consciousness is the key to solve the basis problem.

 

[martinbn]

I am probably missing something very basic, but it seems to me that the point that the vectors of the same norm all look the same is very important, at the same time he points out that the theory comes with more than just the Hilbert space, there is a distinguished operator (the Hamiltonian). That operator gives extra structure, the vectors don't look the same any more, some are eigenvectors some are not, for example. So it isn't true that the vectors look the same. This may be irrelevant for his arguments but at least as far as I read he did not make any comment on it. Also why is the factorization needed? They way I understand the MWI, very superficially, factorizations have nothing to do with the interpretation.

 

[kith]

This quote is from the introduction of the paper:

The Everett Interpretation (EI, also known as Many Worlds) [1, 2, 3] is in a sense the minimal interpretation of quantum mechanics (QM): It basically claims that only the state vector |ψ> of the universe and the global Hamilton operator H are fundamental. Everything else follows from the dynamics given by the Schrödinger equation. In particular, the state vector does not represent the state of some objects. It is the object itself.

The state vector is the universe? This sounds quite odd. I don't think this is a correct discription of MWI.

 

[Quantumental]

This quote is from the introduction of the paper:

The state vector is the universe? This sounds quite odd. I don't think this is a correct discription of MWI.

His description sounds like the typical Everettian account.
What way would you describe it differently?

 

[kith]

His description sounds like the typical Everettian account.

This is something general. We have objects and we have states of them. A state of an object can't be the object itself. Or is this just nitpicking?

What way would you describe it differently?

I have only a vague idea of the MWI. I imagine it like this: |ψ> is the state of the universe. In the beginning, the universe consisted of distinct physical systems. Their existence, states and interactions are the initial conditions of the universe. After time evolution, we have entanglement and many worlds. Maybe this is not the standard view? If so, what is it?

 

[Dmitry67]

I don't think that many adherents of MWI would agree that consciousness is the key to solve the basis problem.

Everything, absolutely everything you perceive is based on that very specific basis – your consciousness (note that it is not the same as basis of your physical brain, and many similar states of your brain can be mapped into the same state of your consciousness – consciousness is not aware of some minor movement of individual molecules, for example. So it is more like an ensemble of QM states). How can one deny a central role of it?

 

[Demystifier]

Everything, absolutely everything you perceive is based on that very specific basis – your consciousness (note that it is not the same as basis of your physical brain, and many similar states of your brain can be mapped into the same state of your consciousness – consciousness is not aware of some minor movement of individual molecules, for example. So it is more like an ensemble of QM states). How can one deny a central role of it?

Yes, but MWI people want to DERIVE everything (including consciousness) from the wave function.

 

[Demystifier]

I am probably missing something very basic, but it seems to me that the point that the vectors of the same norm all look the same is very important, at the same time he points out that the theory comes with more than just the Hilbert space, there is a distinguished operator (the Hamiltonian). That operator gives extra structure, the vectors don't look the same any more, some are eigenvectors some are not, for example. So it isn't true that the vectors look the same. This may be irrelevant for his arguments but at least as far as I read he did not make any comment on it. Also why is the factorization needed? They way I understand the MWI, very superficially, factorizations have nothing to do with the interpretation.

Later in the paper he explains that only the wave function is what matters, in the sense that if wave function at all times is given, then the Hamiltonian is irrelevant. The Hamiltonian only serves to determine wave function at all times for the case when it is not already known.

 

[Demystifier]

The state vector is the universe? This sounds quite odd. I don't think this is a correct discription of MWI.

More precisely, in MWI the state vector is the multiverse - the collection of all "universes".

 

[Demystifier]

What are your take on the paper?
Seems to be a very interesting one, but seeing as how many papers have been written about MWI I struggle to believe he has found a new "fatal" flaw

After the reading of the whole paper, I want to say that I am simply impressed.

The argument he presents is not new, but, in my opinion, nobody ever presented this argument so clearly.

In a nutshell, the argument by Jan-Markus Schwindt in
http://arxiv.org/abs/1210.8447
is this:

To define separate worlds of MWI, one needs a preferred basis, which is an old well-known problem of MWI. In modern literature, one often finds the claim that the basis problem is solved by decoherence. What J-M Schwindt points out is that decoherence is not enough. Namely, decoherence solves the basis problem only if it is already known how to split the system into subsystems (typically, the measured system and the environment). But if the state in the Hilbert space is all what exists, then such a split is not unique. Therefore, MWI claiming that state in the Hilbert space is all what exists cannot resolve the basis problem, and thus cannot define separate worlds. Period! One needs some additional structure not present in the states of the Hilbert space themselves.

As reasonable possibilities for the additional structure, he mentions observers of the Copenhagen interpretation and particles of the Bohmian interpretation. Consciousness which Dmitry67 likes to talk about could also be such an additional structure. But whatever the additional structure is, it is no longer pure MWI. It is MWI with an additional structure, which may be fine, but then one cannot use the typical MWI argument that it is the simplest interpretation without an additional structure, period.

 

[kith]

More precisely, in MWI the state vector is the multiverse - the collection of all "universes".

After skimming the paper, I saw that Schwindt also has commented on this. The argument for identifying the physical objects with the mathematical structure seems to be nothing inherent to the MWI but affects all self-sufficiant physical theories. So if we say that the state vector is the multiverse, we also have to say that a trajectory in phase space in classical mechanics is the particles. I don't think this is appropriate because the meaning of a mathematical structure is always given by the person who uses it to describe an already existing object. This is similar to the conclusion of Schwindt in section 6.3.

Of course, this hasn't much to do with his mathematical argument about the factorization which is definitely interesting.

 

[Quantumental]

After the reading of the whole paper, I want to say that I am simply impressed.


To define separate worlds of MWI, one needs a preferred basis, which is an old well-known problem of MWI. In modern literature, one often finds the claim that the basis problem is solved by decoherence. What J-M Schwindt points out is that decoherence is not enough. Namely, decoherence solves the basis problem only if it is already known how to split the system into subsystems (typically, the measured system and the environment). But if the state in the Hilbert space is all what exists, then such a split is not unique. Therefore, MWI claiming that state in the Hilbert space is all what exists cannot resolve the basis problem, and thus cannot define separate worlds. Period! One needs some additional structure not present in the states of the Hilbert space themselves.

Ok, but why isn't David Wallace's FAPP and arguments from functionalism sufficient?
I noticed that the author mentioned something against Dennett's view of mind, so I hope his argument isn't hinging upon rejecting functionalism?

I also noticed that the author didn't cite any paper more recent than 2003, this seems to ignore all the work of Wallace and Saunders since the early 00's

 

[Fredrik]

The state vector is the universe? This sounds quite odd. I don't think this is a correct discription of MWI.

Sounds standard, but as Demystifier already mentioned, the "universe" in that sentence refers to a physical system that contains all the worlds. However, I would like to make another correction. Since ψ and cψ represent the same state for all complex numbers c, it's more accurate to say that each 1-dimensional subspace is a possible state of our world.

This is something general. We have objects and we have states of them. A state of an object can't be the object itself. Or is this just nitpicking?

When we're dealing with small subsystems of the universe that can be isolated from their environments, a state is (a mathematical representation of) an equivalence class of preparation procedures. (Two preparation procedures are considered equivalent if experiments can't determine which one was used). Some of those states (the "pure" states) can be represented by wavefunctions. So it's an interpretation-independent fact that wavefunctions can be thought of as representations of equivalence classes of preparation procedures. What this author is telling you is that a definition of an MWI includes an assumption about what else a wavefunction represents: It represents all the properties of the system, or to put it differently, it represents the system itself.

After skimming the paper, I saw that Schwindt also has commented on this. The argument for identifying the physical objects with the mathematical structure seems to be nothing inherent to the MWI but affects all self-sufficiant physical theories.

It's definitely not obvious that it makes sense to think of quantum theories this way.

So if we say that the state vector is the multiverse, we also have to say that a trajectory in phase space in classical mechanics is the particles.

What you should say is that each point in phase space (they are what correspond to the 1-dimensional subspaces of a Hilbert space) represents all the properties of all the particles in that classical particle theory.

 

[Fredrik]

To define separate worlds of MWI, one needs a preferred basis, which is an old well-known problem of MWI. In modern literature, one often finds the claim that the basis problem is solved by decoherence. What J-M Schwindt points out is that decoherence is not enough. Namely, decoherence solves the basis problem only if it is already known how to split the system into subsystems (typically, the measured system and the environment). But if the state in the Hilbert space is all what exists, then such a split is not unique. Therefore, MWI claiming that state in the Hilbert space is all what exists cannot resolve the basis problem, and thus cannot define separate worlds. Period! One needs some additional structure not present in the states of the Hilbert space themselves.

This is something I've been thinking for years, but I don't think I've heard anyone other than me say it.

My own interpretation of what this means is that it's wrong to assume that the 1-dimensional subspaces spanned by preferred basis vectors are the only ones that represent worlds. I think a proper definition of a MWI should start with the assumption that every 1-dimensional subspace is a world.

This changes the role of the decoherence argument that's used to identify the preferred basis associated with a given split into subsystems. I suspect that when done right, this argument will show that the basis vectors identify the worlds where the subsystems' ability to store information about each other is at a maximum. Information storage is a crucial part of consciousness, so the worlds singled out by the preferred basis are the worlds where conscious observers are the most likely to exist. So consciousness kind of has a role to play here. It doesn't actually do anything. It just gives us a reason to not care about most of the worlds. We're not particularly interested in the worlds where consciousness can't exist, because none of them is our world.

 

[kith]

What this author is telling you is that a definition of an MWI includes an assumption about what else a wavefunction represents: It represents all the properties of the system, or to put it differently, it represents the system itself.

Yes, I get this. I also get that he tries to prove that we can't get our 3D world experience out of it. What I don't get is why this should be something inherent only to the MWI. As Schwindt himself mentions in section 6.3, how do we get our 3D world experience from the point in 3n-dimensional configuration space of Bohmian mechanics? And I'd like to add: how do we get our 3D world experience from the point in 6n-dimensional phase space of classical mechanics?

Please forgive my sloppiness regarding some technical details, I appreciate your corrections. ;-)

 

[Dmitry67]

To define separate worlds of MWI, one needs a preferred basis, which is an old well-known problem of MWI.

But why do you need to separate the worlds?

Do taxons "really" exist in biology or do one need to "separate" them? Do different cat breeds exist because we, humans, assign them different labels or are they an objective reality?

Universe wavefunction evolves the same way no matter how you artificially "separate" the "worlds". In fact, it does not care how you "define" the "worlds". It does not care about "splitting"... It just evolves... I am sure you agree with me because BM shares with MWI the same wavefunction...

All these problems with the "worlds", "splitting", "preferred basis" etc are artificial because this is how our human mind works - we want to stay on a solid ground, we got used to split reality into pieces and to give these pieces names and definitions... But once again, our common sense reasoning is wrong...

P.S.
Another example. Go back to the very beginning, say, 10^-20sec after the Big Bang. Hot quark plasma filled the whole Universe. No solid objects, no separate systems... Can you separate "worlds" in that chaos? What "preferred basis" can you choose in hot plasma? If you have to work without these notions at 10^-20sec, why do you think they become obligatory in colder Universe? (Note that my approach with consciousness doesn't have any problems with world at t=10^-20s)

 

[Fredrik]

Yes, I get this. I also get that he tries to prove that we can't get our 3D world experience out of it. What I don't get is why this should be something inherent only to the MWI. As Schwindt himself mentions in section 6.3, how do we get our 3D world experience from the point in 3n-dimensional configuration space of Bohmian mechanics? And I'd like to add: how do we get our 3D world experience from the point in 6n-dimensional phase space of classical mechanics?

I don't know Bohmian mechanics well enough to comment about that, but each point in the phase space of a classical particle theory specifies the position and momentum of each particle. So if you know the point (and the Hamiltonian, which determines the time evolution), you have a very clear picture of what's happening in the world described by the theory.

QM doesn't tell us (unambiguously) what is actually happening to physical systems. It just associates probabilities with possible results of experiments. The MWI on the other hand claims that the wavefunction (or rather the 1-dimensional subspace it spans) is a description of what's actually happening to a physical system that's large enough to include the observers. The problem is that this description involves superpositions, and we know that observers never experience superpositions directly. So how can the MWI's claim be true?

This is why it will be hard to take the MWI seriously unless it can explain what sort of experiences the observers can have. At the very least, it should be able to explain why an observer always perceives a cat to be either dead or alive, and never |dead> + |alive>.