Interpretations of Quantum Mechanics

[alexepascual]

Thanks for the reply alexepascual since I thought my comment had been lost in the general discussion, hence my delay in responding. However I still think that the MWI doesn't do what it set out do do since in your first suggestion one has to insert collapsing waves which obviously gets us back to the Copenhagen interpretation. Also, I can see no difference between ghost waves & probability waves which I thought the MWI was trying to avoid. The second suggestion is that the parallel worlds are not truly separate but different states that result in a superpostion but this also seems like back to square one & probability waves.

I think Dmitry has made this clear for you now. I think I didn't express myself clearly. What I meant is that the "splitting" happens at the point at which the standard interpretation would say that there was a collapse. It is true that MWI claims that there is no collapse, and this is simply because all the treads are supposed to continue their separate ways and each one continues to "exist" in the "multiverse" which includes all the worlds. In other interpretations, only one thread survives and all others cease to exist. I think it might happen that someone who likes the MWI may eventually discover something that those who prefer other interpretations would miss just because they are discarding the "other worlds" (real or not).
I think MWI provides a simpler explanation to many of the paradoxes of QM compared to other interpretations. But given the fact that there is no experiment so far that can distinguish, I think for the moment it is a mater of taste which interpretation you choose.

 

[Dmitry67]

I remember there is also partial decoherence.
For me this is a proof that MWI is true.
Branches don't get split instantly: we can observe how other branches disappear gradually.

 

[karatemonkey]

I'm reasonably close the bayesian view, but I think I'm even more radical, becuase a central thing in interence is the choice of rule for information the update. There are several ways here, bayes rule, but also various maxent rules with various choices of entropy. I think the rule for the information update is evolving, and it's exactly this that's subject to evolution.

/Fredrik

First sorry, for not getting back sooner. And even more sorry for skming the rest of the thread so fast, got really busy at work.

Second, in reference to the above quote, I'm not sure I understand what you are saying. So, let me ask another question to help me understand. Isn't "the rule for information update evolving" exactly what happens in the process of measurement and the predictions of the density matrix's when that is repeated?

On "no objective reality", I have a hard time not believing that there isn't an object reality because we can come up with a consensus on reality. We all may different views of what it is but, there is something there. That and we can share a description of physics, agree on it's ability to predict, and perform and report results, (in the future no less) of experiments seems to indicate that there is something outside of our selves.

And finally for the philosophers, I've just spent weeks on a problem trying to solve it. Why, if I am in my own little world, do I make mistakes? I like myself, why do I torture myself. :) (Ok that was tongue in cheek, I couldn't resist)

 

[Fredrik]

I remember there is also partial decoherence.
For me this is a proof that MWI is true.

Then your standards aren't very high.

 

[Fra]

So, let me ask another question to help me understand. Isn't "the rule for information update evolving" exactly what happens in the process of measurement and the predictions of the density matrix's when that is repeated?

Yes, the information update is the state change during interactions. But IMO there is no given static state space, sometimes the state space is also updated.

In my view a measurement process is an action followed by a reaction followed by an internal information update. The internatl information update is the revision of the observers state and microstructure in response to the reaction from the environment. This microstructure and microstate encodes the observers action.

In the same sense, the action of a proton, is encodes in the microstructure and microstate of the proton. But this is continously challanged by the environment.

For example I don't acknowledge the concept of observer independent hilbert spaces. Instead the effective objectivity we undoubtedly do witness, is a result (in my view) of an evolutionary equilibration process. Ie. a local objectivity is emergent when systems are interacting - rather than beeing fundamental in some realist sense.

On "no objective reality", I have a hard time not believing that there isn't an object reality because we can come up with a consensus on reality. We all may different views of what it is but, there is something there. That and we can share a description of physics, agree on it's ability to predict, and perform and report results, (in the future no less) of experiments seems to indicate that there is something outside of our selves.

I think there are degrees of objectivity. But there is no timless universal objective static objectivity, or more correctly, I see no evidence for it. I do not ban it, I just don't presume it. There is a difference there.

/Fredrik

 

[Fra]

I have a hard time not believing that there isn't an object reality because we can come up with a consensus on reality.

Yes, but "coming up with" is to me a physical inference process involving time. This is why I see emergent consensus among communicating/interacting systems. Any objective reality beyond what's "communicated" is not scientifically justified in my view.

/Fredrik

 

[Fra]

I think a common response to that is that for communication to make sense, there must exists an real objective communication channel. This is where I differ. The communication channels, are emergent along with the process, where the observer evolves. This translates into the standard forms with a belief that matter and spacetime must emerge together. You don't need one first, to make sense out of the other. Both can evolve together from a point where no one can distinguish them.

/Fredrik

 

[kote]

Any objective reality beyond what's "communicated" is not scientifically justified in my view.

It's amazing how someone can consistently sound like Bohm in one sentence and Bohr in the next .

in our description of nature the purpose is not to disclose the real essence of the phenomena but only to track down, so far as it is possible, relations between the manifold and aspects of our experience.

Niels Bohr. Atomic Theory and the Description of Nature. (London: Cambridge University Press, 1934) 18.​

But then again, the only basic difference I can find between Bohr and Bohm is that Bohm says we can only call the manifold real (or deeply real anyways) while Bohr allows aspects of our experience to be called real (in the deepest sense).

 

[DrChinese]

On "no objective reality", I have a hard time not believing that there isn't an object reality because we can come up with a consensus on reality. We all may different views of what it is but, there is something there.

Isn't that having it both ways? Some elements are objective: perhaps the *existence* of a particle/wave. But the facts say that what we see is consistent with an observer-dependent reality. I don't see the consensus. What we see is dependent on what we look for.

 

[Zarqon]

hello all (first post here!)

I have an issue with the MWI that I didn't see while skiming through this thread, and that regards energy conservation. It seems to me very strange that the outcome of any quantum experiment would create a new world, simply because of the fact that this new world and all the people that live their lives knowing a different result of the experiment than we, has to be sustained by some energy.

If new worlds keeps being created, and we assume that energy conservation is valid with respect to the whole universe, then where does the energy to sustain the new worlds come from? Although I haven't seen this answered anywhere, it seems to obvious a question to have been ignored, so I've probably just missed it. But still, I would appreciate to get an answer on it.

 

[Fredrik]

hello all (first post here!)

Hello, and welcome to Physics Forums.

I have an issue with the MWI that I didn't see while skiming through this thread, and that regards energy conservation. It seems to me very strange that the outcome of any quantum experiment would create a new world, simply because of the fact that this new world and all the people that live their lives knowing a different result of the experiment than we, has to be sustained by some energy.

If new worlds keeps being created, and we assume that energy conservation is valid with respect to the whole universe, then where does the energy to sustain the new worlds come from? Although I haven't seen this answered anywhere, it seems to obvious a question to have been ignored, so I've probably just missed it. But still, I would appreciate to get an answer on it.

There's nothing in "the MWI" (which I assume means Everett's MWI) that says that measurements lead to the creation of new universes. I can't tell you exactly what it says, and I don't think anyone can, because no one seems to have been able to write down a consistent set of axioms that defines the MWI. I would say that there is no MWI. (Comments to anyone who's offended by that: 1. Feel free to prove me wrong. 2. Don't even think about saying that all you have to do is to remove the Born rule from the standard formulation).

The best I can do is tell you that any MWI proponent would say that there's a Hilbert space with the property that any point in it represents a possible state of all the universes. Penrose calls this physical system "the omnium". The Schrödinger equation describes the time evolution of the omnium in the following sense. Given a state of the omnium (a point in the Hilbert space), the Schrödinger equation defines a unique continuous curve through that point. That curve tells you the state of the omnium at any time.

What I just described is often called the "bird's view" of time evolution. That part of the MWI is well-defined. The ill-defined part has to do with the "frog's view", i.e. a human observer's description of the time evolution of his "world". The idea is that in some subspaces* of the Hilbert space of the omnium, a short segment of the time evolution curve can be interpreted as describing a universe where an experiment is performed. Those subspaces have subspaces of their own, and some of them can be interpreted as describing a universe where the result of the experiment is A, and others can be interpreted as describing a universe where the result of the experiment is B. (If someone feels that I got this part wrong, let me know).

So there's no actual "creation" of different worlds. All that happens is that the time evolution in the bird's view is constantly changing which of the subspaces should be interpreted as different frog's views.

*) If you're unfamiliar with Hilbert spaces and other vector spaces, just think about a cartesian coordinate system for \mathbb R^3. Call the axes x,y and z. The x-y plane is a good example of a "subspace", and so is the y-z plane, the x-z plane, and the plane defined by the equation x+y+z=1. Those are all 2-dimensional subspaces. The x-axis and the line that consists of multiples of the vector (1,1,1) are examples of 1-dimensional subspaces. The subspaces I'm talking about are subspaces in the same sense, but they are infinite-dimensional subspaces of infinite-dimensional vector spaces.

 

[WaveJumper]

I would argue for "shut up and calculate!"

I wonder, if for at least part of its proponents, this strictly calculatory mathematical approach is implying that it's all there is and Hilbert space is reality, and as such is incomprehensible?

 

[kote]

I wonder, if for at least part of its proponents, this strictly calculatory mathematical approach is implying that it's all there is and Hilbert space is reality, and as such is incomprehensible?

"Shut up and calculate" is typically a statement of basic instrumentalism or logical positivism.

From Wikipedia: "A 1929 pamphlet written by Neurath, Hahn, and Rudolf Carnap summarized the doctrines of the Vienna Circle at that time. These included: the opposition to all metaphysics, especially ontology and synthetic a priori propositions; the rejection of metaphysics not as wrong but as having no meaning; a criterion of meaning based on Ludwig Wittgenstein's early work; the idea that all knowledge should be codifiable in a single standard language of science; and above all the project of "rational reconstruction", in which ordinary-language concepts were gradually to be replaced by more precise equivalents in that standard language."

Asking what your model means or what it represents is simply a misuse of language, according to this view. There is no meaning to the question "what is real" in ordinary-language. The Copenhagen Interpretation is simply the next step in the positivist program. It redefines reality, replacing the ordinary-language requirement that reality be separably objective with a "meaningful" definition of reality based only on experiential empirical results.

This, by the way, is the basis of the entire interpretational debate. Whether "reality" should be defined empirically or if it should be presumed to have a separable objective ontology. Bohr and Bohm both agree that all physics is necessarily instrumentalist with respect to "the real essence of phenomena" or "deeper reality."

 

[RUTA]

"Shut up and calculate" is typically a statement of basic instrumentalism or logical positivism.

Asking what your model means or what it represents is simply a misuse of language, according to this view. There is no meaning to the question "what is real" in ordinary-language. The Copenhagen Interpretation is simply the next step in the positivist program. It redefines reality, replacing the ordinary-language requirement that reality be separably objective with a "meaningful" definition of reality based only on experiential empirical results.

This, by the way, is the basis of the entire interpretational debate. Whether "reality" should be defined empirically or if it should be presumed to have a separable objective ontology. Bohr and Bohm both agree that all physics is necessarily instrumentalist with respect to "the real essence of phenomena" or "deeper reality."

These questions are not without relevance to progress in physics. Consider the method by which data is collected and analyzed in particle physics, for example.

Individual detector clicks (called “hits in the tracking chamber”) are first localized spatially (called “preprocessing”), then associated with a particular track (called “pattern recognition”). The tracks must then be parameterized to obtain dynamical characteristics (called “geometrical fitting”). See Fernow, R.C.: Introduction to experimental particle physics. Cambridge University Press, Cambridge (1986), sections 1.7.1, 1.7.2 & 1.7.3, respectively. Some assumptions are required, e.g., “Sometimes it is necessary to know the identity (i.e., the mass) of at least some of the particles resulting from an interaction (Fernow, 1986, p 17)” and “Within the errors tracks may appear to come from more than one vertex. Thus, the physics questions under study may influence how the tracks are assigned to vertices (Fernow, 1986, p 25),” but no one disputes the inference that "click-causing" particles are responsible for the trajectories in tracking chambers. This leads particle physicists to treat sets of detector clicks as the fundamental constituents in their experiments. They then function under this assumption for pattern recognition, throwing away "spurious noise hits" and stressing over whether hits really constitute tracks (Fernow, p 22).

What would happen to this enterprise if we rather believed there were no click-causing particles? I think it's safe to say particle physics would not occupy such a central position in unification. I'm not here to argue about the existence of particles, I'm simply trying to illustrate that these questions are answered explicitly or tacitly in order to collect "objective data." Thus, the answers to such questions bear directly on progress in physics.

 

[nikman]

I just looked at these papers... and I'm sorry, but they are just completely wrong. Analytic propositions can't be proven a posteriori. Experiments can't serve as mathematical proofs.

Or maybe I missed the point of the papers.

Based on my understanding of the master project -- and we're talking not only Zeilinger and Brukner but also Karl Svozil, Greg Chaitin and Chris Calude -- the missing link here is Chaitin's Omega, which is the mathematical equivalent of quantum stochasticity. (It's actually been computed to 64 digits ... probably the limit for a long time to come.)

At any rate, mathematics is just as physical as is computation. Calculation requires physical media (brain cells, pencil and paper in their various analogs including abaci). Also maths is an extrapolation from adding and subtracting natural numbers. Try this experiment: here, I'm giving you nine marbles. Give me back seven and tell me how many you have left. Two? ... that's correct.

I claim that was both a physical experiment and a mathematical proof.

Anyway:

http://arxiv.org/PS_cache/quant-ph/pdf/0402/0402197v6.pdf

http://arxiv.org/PS_cache/quant-ph/pdf/0611/0611029v2.pdf

 

[kote]

What would happen to this enterprise if we rather believed there were no click-causing particles? I think it's safe to say particle physics would not occupy such a central position in unification. I'm not here to argue about the existence of particles, I'm simply trying to illustrate that these questions are answered explicitly or tacitly in order to collect "objective data." Thus, the answers to such questions bear directly on progress in physics.

RUTA, I agree that a presumption of incompleteness is very practical. The idea that there could be a unified theory that completes or replaces QM is necessary for the hope of any progress. At the same time, however, presuming incompleteness in the current theory is admitting that its elements are not basic in nature. At best they are macroscopic approximations of basic entities, and at worst they are inconsistent with them.

Practically it's probably best to hold inconsistent views about the reality of particles .

 

[Albert V]

I think the success of quantum mechanics is remarkable. The fact that calculations often precedes observations suggests that the mathematical model is closer to reality than our mental concepts of a particle.

 

[nikman]

I think the success of quantum mechanics is remarkable. The fact that calculations often precedes observations suggests that the mathematical model is closer to reality than our mental concepts of a particle.

Eugene Wigner maintained that the success of science is remarkable, period. Or maybe it's the success of mathematics. Or both. This from "The Unreasonable Effectiveness of Mathematics in the Natural Sciences":

THERE IS A story about two friends, who were classmates in high school, talking about their jobs. One of them became a statistician and was working on population trends. He showed a reprint to his former classmate. The reprint started, as usual, with the Gaussian distribution and the statistician explained to his former classmate the meaning of the symbols for the actual population, for the average population, and so on. His classmate was a bit incredulous and was not quite sure whether the statistician was pulling his leg. "How can you know that?" was his query. "And what is this symbol here?" "Oh," said the statistician, "this is pi." "What is that?" "The ratio of the circumference of the circle to its diameter." "Well, now you are pushing your joke too far," said the classmate, "surely the population has nothing to do with the circumference of the circle."

Naturally, we are inclined to smile about the simplicity of the classmate's approach. Nevertheless, when I heard this story, I had to admit to an eerie feeling because, surely, the reaction of the classmate betrayed only plain common sense. I was even more confused when, not many days later, someone came to me and expressed his bewilderment with the fact that we make a rather narrow selection when choosing the data on which we test our theories. "How do we know that, if we made a theory which focuses its attention on phenomena we disregard and disregards some of the phenomena now commanding our attention, that we could not build another theory which has little in common with the present one but which, nevertheless, explains just as many phenomena as the present theory?" It has to be admitted that we have no definite evidence that there is no such theory.

 

[Fredrik]

I wonder, if for at least part of its proponents, this strictly calculatory mathematical approach[/color] is implying that it's all there is[/color] and Hilbert space is reality[/color], and as such is incomprehensible?

Aren't these two (red and blue) opposite viewpoints? The blue stuff is essentially Everett's MWI, and the red stuff can be described as "shut up and calculate", but is actually better described by my post #11.

 

[f95toli]

I wonder, if for at least part of its proponents, this strictly calculatory mathematical approach is implying that it's all there is and Hilbert space is reality, and as such is incomprehensible?

No, the whole point for most of us that prefer that approach is that it in QM (and physics/science in general) is meaningless to ask if there is anything. Period.
I.e. most of us are -strictly speaking- agnostic about whether or not there even is a reality, or indeed if if Hilbert space or any other part of QM represents something that is real (whatever that means).

I think it is wrong to say that there is any "deep" philosophical ideas behind this; it is merely a result of the opinion that the only requirements on a physical theory is that it should be able to predict the outcome of experiments; whether or not that theory has anything to do with a "reality" is irrelevant.
This is why we (or at least I) think that the debatte over various intepretations etc is more or less irrelevant, unless of course someone can come up with an experiment that can test which interpretation is correct.

 

[nikman]

Aren't these two (red and blue) opposite viewpoints? The blue stuff is essentially Everett's MWI, and the red stuff can be described as "shut up and calculate", but is actually better described by my post #11.

"Shut up and calculate" works, just as "Light the fuse and run" works.

But isn't it reasonable for people to wonder how it works and why it works the way it seems to work?

 

[RUTA]

RUTA, I agree that a presumption of incompleteness is very practical. The idea that there could be a unified theory that completes or replaces QM is necessary for the hope of any progress. At the same time, however, presuming incompleteness in the current theory is admitting that its elements are not basic in nature. At best they are macroscopic approximations of basic entities, and at worst they are inconsistent with them.

Practically it's probably best to hold inconsistent views about the reality of particles .

I agree that you should use whatever model of the theory helps you do calculations. My point concerns the experimental part of physics. Ontological assumptions determine how we look for and interpret data. Thus, changes in our ontological assumptions result in changes to our experiments. That's all I was trying to establish.

 

[nikman]

From an interview with Anton Zeilinger:

... Ultimately that implies something monstrous: namely that the particle had absolutely no characteristics before it was measured. The great Danish physicist Niels Bohr once said: no one has ever seen a chair. There is no objective reality. Only that which is measured exists. We construct reality, and only in the moment of measurement or observation.

I think you have to make a distinction: in my view there is something that exists independently of us – in physics we call that the singular event. For example the activity of a particle detector. Or the activity of a certain cell in my eye, which registers a certain number of light particles and then provokes a chemical reaction that is then registered in the brain. The images that we form on the basis of this are our constructs. Bohr's chair or on a much more abstract level, the quantum mechanics equation of states, are our concepts of an object. Of course they are very purpose-oriented, because they've been corroborated with repeated use.

So there is in fact something that exists independently of us. And the moon is also there when I'm not looking at it.

Something exists, but it is not directly accessible to us. Only indirectly. And whether this thing must really be called the "moon" is another question. That is also a construct.

But there is something up there...

... the word "there" is yet another construct. Space and time are concepts aimed at giving meaning to our world of appearances. So they are entirely reasonable constructs. By no means do I want to give the impression that I believe everything is just our imagination.

The world as a huge theatre that only plays in our heads.

That is certainly not my view of things.

http://www.signandsight.com/features/614.html

 

[Fredrik]

"Shut up and calculate" works, just as "Light the fuse and run" works.

But isn't it reasonable for people to wonder how it works and why it works the way it seems to work?

Sure it is. But it isn't reasonable to assume that QM "describes what actually happens", just because it makes accurate predictions about probabilities of possible results of experiments. That last part is just the minimium requirement for falsifiability, and it doesn't in any way imply that the mathematical model used by a falsifiable theory describes reality.

Without the assumption I mentioned, there's no reason to think that QM (a standard "Copenhagenish" formulation) needs an interpretation.

 

[Hurkyl]

Without the assumption I mentioned, there's no reason to think that QM (a standard "Copenhagenish" formulation) needs an interpretation.

Every physical theory needs an interpretation. Without an interpretation to connect them to experiment, your just pushing meaningless symbols around on paper.

 

[Fredrik]

Every physical theory needs an interpretation. Without an interpretation to connect them to experiment, your just pushing meaningless symbols around on paper.

I wouldn't use the word "theory" about something that doesn't already include such an interpretation. To me this is the difference between a theory and a model. I would say that a model is just a mathematical structure, and that a theory consists of a model and a set of axioms that tells us how to interpret the mathematics as predictions about the results of experiments.

The standard ("Copenhagenish") formulation of QM is a theory, not a model. What I'm trying to say is that its underlying mathematical model (Hilbert space) doesn't need to be reinterpreted.

This touches on something else that's been on my mind for a long time. A valid alternative interpretation technically defines a different theory. I would say that it's equivalent to the original theory if it makes the same predictions. Now, a theory can always be stated as a list of axioms, but for some reason no one seems to think that an "interpretation of QM" needs to be stated that way. Everyone seems to tolerate a few poorly worded comments as a definition of an "interpretation", probably because "it's just an interpretation". I think this is just ridiculous. We shouldn't be talking about "interpretations" at all. We should be talking about different theories that may or may not be equivalent.

One last comment about how I use the word "theory" here. I would be perfectly OK with using the word "theory" for an equivalence class of what I've been calling "theories" so far. If we use that terminology, I would say that the members of an equivalence class (i.e. a "theory") are different formulations of the theory. So instead of the last sentence of the preceding paragraph, I could have said that we should be talking about different formulations of QM and about formulations of slightly different theories.

I hope I have expressed myself clearly this time.

 

[Dmitry67]

Every physical theory needs an interpretation. Without an interpretation to connect them to experiment, your just pushing meaningless symbols around on paper.

Yes, except the very last step probably:
http://arxiv.org/abs/0704.0646

All these theories have two components: mathematical equations and “baggage”, words that explain how they are connected to what we humans observe and intuitively understand. Quantum mechanics as usually presented in textbooks has both components: some equations as well as three fundamental postulates written out in plain English
...
the ratio of equations to baggage decreases as we move down the tree, dropping near zero for highly applied fields such as medicine and sociology. In contrast, theories near the top are highly mathematical, and physicists are still struggling to articulate the concepts, if any, in terms of which we can understand them.
...
However, could it ever be possible to give a description of the external reality involving no baggage? If so, our description of entities in the external reality and relations between them would have to be completely abstract, forcing any words or other symbols used to denote them to be mere labels with no preconceived meanings whatsoever. A mathematical structure is precisely this: abstract entities with relations between them.

 

[Zarqon]

The best I can do is tell you that any MWI proponent would say that there's a Hilbert space with the property that any point in it represents a possible state of all the universes. Penrose calls this physical system "the omnium". The Schrödinger equation describes the time evolution of the omnium in the following sense. Given a state of the omnium (a point in the Hilbert space), the Schrödinger equation defines a unique continuous curve through that point. That curve tells you the state of the omnium at any time.

Thanks for the answer, it does clarify my issue. However, it does seem to apply, that at the creation of the universe (the omnium I assume), it was created already including all the many different worlds that would be needed, given all the quantum experiments that would be performed during the course of its existence. Is this correct?

There can't be less worlds than would be needed or we're back to energy conservation problem. There also can't be more worlds than would be needed, or we're back to a true probability of which would be used situation. The universe/omnium would have to contain exactly the number of worlds needed for the lifetime of the universe, and to me, this seems like an awfully big assumption to make. How would this be known in advance?

 

[nikman]

Sure it is. But it isn't reasonable to assume that QM "describes what actually happens", just because it makes accurate predictions about probabilities of possible results of experiments. That last part is just the minimium requirement for falsifiability, and it doesn't in any way imply that the mathematical model used by a falsifiable theory describes reality.

Without the assumption I mentioned, there's no reason to think that QM (a standard "Copenhagenish" formulation) needs an interpretation.

We're probably not in disagreement here. Bohr stressed two things: (1) We have no choice but to measure the quantum world with classical instruments and describe it in classical terms, and (2) What we measure and describe is not reality any more than a pencil sketch made at midnight of a mountain is a mountain.

Couple that with complementarity, uncertainty and the realization that to start dissecting the measurement process leads to infinite regress, and it seems to me you have a pretty profound philosophical interpretation of whatever it is that philosophical interpretations are meant to philosophically interpret. (Or maybe we should substitute "foundational" for "philosophical" here.)

Neo-Copenhagenists like Brukner and Zeilinger are busy trying to marry the above to avant-garde informatics and create a new synthesis based on the principle that in the deepest possible sense you can't separate a thing from what you know about that thing. I for one say more power to them.

 

[WaveJumper]

Thanks for the answer, it does clarify my issue. However, it does seem to apply, that at the creation of the universe (the omnium I assume), it was created already including all the many different worlds that would be needed, given all the quantum experiments that would be performed during the course of its existence. Is this correct?

There can't be less worlds than would be needed or we're back to energy conservation problem. There also can't be more worlds than would be needed, or we're back to a true probability of which would be used situation. The universe/omnium would have to contain exactly the number of worlds needed for the lifetime of the universe, and to me, this seems like an awfully big assumption to make. How would this be known in advance?

All this talk of a world is misleading. There is NO world except for our perceptions of it. How old is the world? 13.7 billion years? Wrong. There is no privileged frame of reference to ascertain that the universe is 13.7 b. years old. There are almost infinite frames of reference where the universe is 1000 years old, 1 billion years old, etc., etc., etc.

How big is the universe? 70 billion light years across? Wrong. Such an answer is homocentric. Unless you believe we are something extremely special, the size of the universe through the different FOR's vary from zero to 100s of light years in diameter.

What does cosmology say about the world? Metric expansion of the universe means the outside diameter of the universe has stayed the same since the Big Bang, because space expands(is created) between points, and so the universe is expanding into itself, not into nothingness. Let's move on - Quantum mechanics introduced even more uncertainty. In the subatomic realm, the entire concept of fixed particles in time and space fuzzes out into an ever-shifting haze of probabilities. As Harvard physicist Andrew Strominger says: "space-time is an uncertain concept, so you've lost your firm footing. And that is a deep conceptual issue we have not yet come to grips with."

Let's see what string theories are saying about the world:

"Space and time may be doomed" - Ed Witten

"I am almost certain that space and time are illusions. These are primitive notions that will be replaced by something more sophisticated." - string theorist Nathan Seiberg

"When we talk about space and time, we think there is something there, and we live in it, the idea that space-time is an illusion is very disturbing. Where are we? When are we?" - David Gross

"The notion of space-time is something we've cherished for thousands of years, and it's clearly something we're going to have to give up" - Andrew Strominger of Harvard University"The real change that's around the corner is in the way we think about space and time. We haven't come to grips with what Einstein taught us. But that's coming. And that will make the world around us seem much stranger than any of us can imagine." - David Gross
"All my attempts to adapt the theoretical foundation of physics to this new type of knowledge (Quantum Theory) failed completely. It was as if the ground had been pulled out from under one, with no firm foundation to be seen anywhere, upon which one could have built." - Albert Einstein

Personally, I hold a similar view as to that of Lee Smolin - "From the most sceptical critics to the most strenuous advocates of string theory, you hear the same thing: We are missing something Big."Without this missing Big, we don't know what we are talking about and all this talk of interpreting reality from what we currently know of it from physics, is nothing but a pipe dream.