"Intuitive" perspective for quantum entanglement?

[Yakk]

So neither the amplitude or the probability has any effect on the model? Is there a graph to show the probability against the amplitude to help me visualise them?

How can there be both a greater probability to end up with all heads, yet less outcomes ending up with all heads? I thought the two correlated.

I think you are lost. Lets do a really simple case.

We have a coin with a 51% chance of landing heads. We flip it twice.

There are 4 universes.
TT: .49^2 = 0.2401
HT: .49*.51 = 0.2499
TH: .51*.49 = 0.2499
HH: .51*.51 = 0.2601

Notice how the highest probability verse is the HH one. However, if we ignore order, the verses where there is 1 head and 1 tail has a 0.4998 chance, higher than the HH one.

All 4 of these verses are "real".

We flip another coin. There are now 8 verses:
TTT: .49^3 = 0.2401 * .49 = 0.117649
TTH: .49^2*.51 = 0.122451
HTT: .49^2*.51 = 0.122451
HTH: .49*.51^2 = 0.127449
THT: .51*.49^2 = 0.122451
THH: .51^2*.49 = 0.127449
HHT: .51*.51*.49 = 0.127449
HHH: .51^3 = 0.132651

You'll notice that the highest probability verse is the HHH one.

However, the verses where you have 2 heads and 1 tail, and 2 tails and 1 head, are rather overwealmingly more popular collectively.

Imagine if we didn't care what order the heads and tails came in. Even though it happened, all we cared about on a macro scale was the count of heads and tails. Then the verses where there where 2H1T and 2T1H are the ones that are by far the most common.

When you hit 100 coin flips, the one that is HHHHH...HHH is still the individually most common verse, even though its actual individual probability is really low (like 10^-30 or so). 95% of the verses have 51+/-10 heads.

In our experience, when we run such kinds of tests, we don't end up in the single highest amplitude verse. Instead, we end up somewhere in the "almost certain" cluster around 51. In our experience, unless we manage to run the experiment on the order of 10^30 times, we don't see the 100 heads in a row case.

Ie: our macro-state experience tends to be the ones that are macro-state similar. One particular one happens, and it is individually no more common than the "ridiculous" 100 heads in a row one, but the MWI says that there are far, far more such verses (that are the "common" ones) than the rare ones with 100 heads in a row (if the coin flip was the only events, then there is exactly 1 such 'verse, while there are on the order of 10^30 verses with between 41 and 61 heads. It doesn't seem unexpected that the ones we experience are the ones that are the common ones, under the MWI.)

[Technical Ben]

Yes, thanks, that is what I was getting at. The confusion was over "amplitude" I thought it had a bearing over which universe we were more probable to end up in. Turns out it did not, I'd jumped ahead a step by mistake.

So the previous MWI was that there was 4 universes, and a 1/4 (25%) chance to be in each one. This is the model I had trouble with, because we would have an even probability to end up in the universes with the ridiculously improbable outcomes. The more complete description of MWI is there are 26% of the universes with HH (with a 51% bias coin) but our probability to end up in a different universe to that one is 74%? That works mathematically.

So the "ridiculously improbable" universes are still ridiculously improbable? I'm still uneasy about the resultant universes where unicorns exist (because the maths says they do ) but I'm a lot more confident about the maths.

[Xanthir]

How to recover the Born rule in MWI is an important current research topic. I have no idea what the answer is.

Then you must admit that many worlds simply isn't a full-fledged interpretation. Its might "feel good", but it gives you no way of making measurements. What is preferable- a non-unitary collapse, or a total inability to make predictions? Naive many-worlds will give you the wrong answers for experiments the majority of the time (the probability is high you find yourself in a maverick world with a non-born probability).

Right now we can just take the Born rule as an axiom based on experimentation. We don't necessarily need it to fall out of the interpretation itself, though it would be nice. Like I said, there is ongoing research on how to recover it directly from the interpretation.

I assume by "naive MWI" you mean something like "one world, one vote", or that every world has an equal amount of "reality". Yes, this is naive and gives incorrect results; it's roughly equivalent to assuming that every binary outcome is 50/50. That's irrelevant to the actual forms of MWI that physicists believe in. (I'm not a physicist, but I play one on the internet.) Like lightvector said, while the total "number" of worlds that can't derive the born probabilities is much larger than the number of worlds that can, the "amount of reality" of the two groups has the opposite ratio. (This assumes the Born probabilities, but fuck it, let's just roll with it.)

There's also probably a bit of anthropic principle at play here. A lot of the worlds in which you can't derive the born probabilities are pretty strange and may very well be inimicable to life, at least as we know it.

But if you do not get the born rule 100% of the time, you do not have identical predictions as other interpretations. Which means you aren't an "other interpretation" anymore, you're a distinct theory.

You don't have a 100% chance of getting the Born rule in collapse-based interpretations, either. The chance of things occurring in such a way that you can't do that is miniscule, but so is the chance that you find yourself in a world where the Born rule isn't derivable.

Hmm, you're still attaching too much ontological significance to this whole "worlds" things.

Indeed! What else is an "interpretation" supposed to be? I'm down with Hilbert space, but it says nothing about how (where, through what mechanism) its superpositions are to be embedded in actual physical reality, that's just not in Hilbert's lexicon.

So how does MWI inform your personal intuitive ontology of qm? Or are you saying that it has nothing to say about your intuitive ontology of qm, and by "interpretation" you mean something other than that?

I've tried to answer a few times, and we're not quite communicating properly. Hopefully this post by Charlie! helps, as it's a very clear statement of what I'm trying to say:

Where do the probabilities come from in MWI, then? If there are two outcomes from an event, does that mean the expectation is necessarily 50%? How can it possibly make the right predictions in that case?

Important question of quantum mechanics: if you're at one spot in possibility-space and the world is left to evolve, what will the world look like later? The answer is probabilistic, regardless of interpretation. And it's not "half one way, half the other." The universe can be represented by a complex function in possibility-space: the bigger the function at a certain point in possibility-space after the universe is left to evolve, the bigger the probability of the world looking like that later.

The "universes splitting" picture is common in some popularizations, but totally misleading. Especially for continuous variables! What you might call "splitting" is really just the universe becoming more spread out in possibility-space.

Thats fine, but why don't we evolve over time into an area where the born rule stops working?

"We" do. "We" also evolve into areas where it keeps working. The "we" that do the latter are more likely/"real" than the "we" that do the former.

One other quick note, is there any reason MWI can't be stated to accommodate for differing probabilities? For example, suppose I have a wavefunction^2 with a 2/3 bump at point A and a 1/3 bump at point B. I agree it's an awkward solution to say that "there are two worlds resulting from this and you're twice as likely to find yourself in A" due to the invisible hand of qm (don't. I regretted saying it even as I was typing it). But what would be wrong with interpreting it instead as "three worlds split off from this, and you have equal probability of finding yourself in either of them, it's just that two of the worlds are identical. Does that harsh the "it's literally Hilbert space" ontological interpretation's charm too much?

The MWI *is* stated to accommodate differing probabilities. Only naive pop-science versions of it don't, and that's more due to lack of detail than an explicit or purposeful lack. It's not "the invisible hand of qm" that does, but the fact that different worlds have different amounts of reality (or, equivalently, that different regions of hilbert-space have different distributions/densities of amplitude).

That's pretty much the way that David Deutsch describes it. In his version of MWI, the number of universes doesn't increase: it started as an infinite ensemble and always remains infinite, but at the start all the universes were in the exact same location of the configuration space, and thereafter tended to move in tandem. Each "splitting" event merely involves universes that had traveled in parallel up to that point diverging from one another.

Right. Whether you refer to it as (infinite) distinct universes or as an infinitely-divisible amount of "reality" is just a naming issue.

I'm not really satisfied with the playing around in Hilbert space aspect. That doesn't really feel like an "interpretation" in the usual sense; it's almost tautological from the bare math.

That's precisely why I prefer it. You don't need any extra concepts - you just look at the math, and lo, that's reality! Yay! Like doogly says, there is still a philosophical difference between MWI and "the bare math", but it's small.

So the previous MWI was that there was 4 universes, and a 1/4 (25%) chance to be in each one. This is the model I had trouble with, because we would have an even probability to end up in the universes with the ridiculously improbable outcomes. The more complete description of MWI is there are 26% of the universes with HH (with a 51% bias coin) but our probability to end up in a different universe to that one is 74%? That works mathematically.

So the "ridiculously improbable" universes are still ridiculously improbable? I'm still uneasy about the resultant universes where unicorns exist (because the maths says they do ) but I'm a lot more confident about the maths.

Yes, they're exactly as ridiculously improbable as collapse-based interpretations would say.

[Malconstant]

I've tried to answer a few times, and we're not quite communicating properly. Hopefully this post by Charlie! helps, as it's a very clear statement of what I'm trying to say:

Where do the probabilities come from in MWI, then? If there are two outcomes from an event, does that mean the expectation is necessarily 50%? How can it possibly make the right predictions in that case?

Important question of quantum mechanics: if you're at one spot in possibility-space and the world is left to evolve, what will the world look like later? The answer is probabilistic, regardless of interpretation. And it's not "half one way, half the other." The universe can be represented by a complex function in possibility-space: the bigger the function at a certain point in possibility-space after the universe is left to evolve, the bigger the probability of the world looking like that later.

The "universes splitting" picture is common in some popularizations, but totally misleading. Especially for continuous variables! What you might call "splitting" is really just the universe becoming more spread out in possibility-space.

I feel as though appealing to "possibility space" is ducking the ontology question, and that's the only one I care about. Does your view of MWI have a preferred timeline? Such that others may exist as possibilities, but ultimately when the present comes to shove, there's only one that is meaningfully existent? Or is your MWI one with infinite pre-existing universes, the sum of which spell out every possible way in which the universe could have been, and none are more or less meaningfully existent than any others?

Basically, describe for me the way in which you visualize this interpretation personally. As far as I can tell there are three kinds of pictures that have been put forth so far:
1) infinitely-many independent universes which do not interact and the sum of which spell out every possible way the universe could have gone. You can toy around with the numbers to account for probabilities however you like.
2) Just one universe, with one real time-line, and other "universes" existing in possibility space. This one is virtually indistinguishable from a collapse-based world view, understanding that collapse still includes path integrals for self-interaction.
3) A merger of these pictures, with just one super-universe that has a single unambiguous initial state but "flowers" out as time goes on to extend infinitely many different time-lines for every quantum possibility. This picture is where the idea of "splitting" would most naturally fit.

These are what I mean by ways in which MWI might inform an ontology. Do you agree that these are the kinds of worldviews supported by MWI, and do you prescribe to any or some other option I didn't consider? Or do you not have any accompanying visualization of it, but rather live entirely in Hilbert space, call it MWI, and don't pretend that it extends to any further meaning at all?

[Xanthir]

#1 doesn't reflect reality. The universes *do* interact - that's what superposition is.

If you correct that part, then #1 and #3 are just differences in terminology. That said, I prefer the terminology of #3. I consider that basically equivalent to the "Hilbert space" idea.

[Malconstant]

#1 doesn't reflect reality. The universes *do* interact - that's what superposition is.

If you correct that part, then #1 and #3 are just differences in terminology. That said, I prefer the terminology of #3. I consider that basically equivalent to the "Hilbert space" idea.

You mean "self-interaction", not superposition right? As in, path integrals. Even so the whole point is that so far as observation is concerned, you'll measure the same thing, so it reflects reality as much as anything else. Where would you get the idea that isolating one timeline would yield results that would violate what we know experimentally? The whole idea is that you would pick a "stem" of the greater super-universal "flower", set it aside and call it its own universe. The distinction is topological, it's in a totally isolated space (or at least embedded in a higher-dimensional space, but definitely not "stitched in" to the other universes as is the model for #3)

And there are huge differences in the way a universe like #1 and #3 would need to be created and thought of. That's exactly the level which I'm arguing here. The whole point of having an interpretation is to have an ontology, and that's what it means. So, okay, you go for the eternal super-flower uberverse version of MWI, that's fine. Now do you admit that there aren't any guidelines set forth by Hilbert space for how these world stems diverge topologically? I get that you can create stuff with 0 energy because their total energy is 0, but what's the mechanism? My whole point, that I've stated quite a few times now, is that these are points where MWI is an incomplete theory. Because it doesn't satisfactorily describe a mechanism for making other worlds in order to satisfy the a "superliteral" Hilbert space ontology, nor where the worlds go topologically.

I honestly don't think my objections as such should be offensive to someone with MWI inclinations. These shouldn't be considered subtle nuance points. It's akin to saying "you say many worlds eh? I have a hard enough time wrapping my head around just one. How do you figure these infinitely-many others are made physically and where do they go?" If you respond with "oh it's just possibility space" you're completely ducking the ontological question being asked, and in effect claiming (not unreasonably) that there is no meaningful ontology, that there is only Hilbert space and that's really all there is in a meaningful way. It's just the poison you pick, and I've got my own poison to chew on with collapse.

Though actually, are you sure that's not what you're actually saying? That there is no ontology, there is only Hilbert space? Cause that's fine if that's what you're saying. It's a profound statement, a bold stance, it's one I can admire the courage to accept. But that would explain my perception of your trying to wiggle out of the meaningful ontological questions I'm asking about your sense of MWI. Because in your heart of hearts you believe that there is no meaningful ontology at that level, that quantum mechanics, though true, describes a world with fundamentally no physical reality being modeled.

As Dooglie was saying about this earlier:

Well, if you take it as an interpretation, "the bare math is all you need," then you are saying something rather profound - you are giving up on the idea that the math is modeling something, you're saying that it is the thing. My level of comfort with this is variable.

[SU3SU2U1]

Right now we can just take the Born rule as an axiom based on experimentation.

If you do that you get an interpretation known as the Copenhagen interpretation (or an ensemble interpretation depending on the details.)

I assume by "naive MWI" you mean something like "one world, one vote", or that every world has an equal amount of "reality".

I fear we are talking past each other because you have some other definition of many-worlds. What axioms does your version use? In particular, what is your framing of the measurement postulate? Please list the axioms of your MWI formulation of quantum mechanics. I don't understand how you propose to add the born rule. Adding it in the traditional way obviously gives you the copenhagen interpretation- how do you add a "no-collapse" collapse postulate?

Keep in mind that interpretations of quantum mechanics are actually formulations of quantum mechanics- they change the axioms. I feel like you are asserting things with words that aren't actually true about the math of the interpretation- hopefully laying your formalism will make this more clear.

[Xanthir]

#1 doesn't reflect reality. The universes *do* interact - that's what superposition is.

If you correct that part, then #1 and #3 are just differences in terminology. That said, I prefer the terminology of #3. I consider that basically equivalent to the "Hilbert space" idea.

You mean "self-interaction", not superposition right? As in, path integrals.

No, I mean superposition. When we see a superpositioned particle (before we entangle ourselves with it and trigger decoherence), the "quantum stuff" that happens is due to close worldlines interfering. In the simple case where the superposition is of two states, before we've interacted with it we're spread across two threads in amplitude-space with a miniscule distance between them (just the distance between the particle's two states). (Remember, the worldlines are branches of the universal wavefunction, and so are defined by the product of all the universe's quantum variables, even before "we" have interacted with a particular variable.) Then, when we entangle ourselves with the particle via something like a detector, the difference between the two states gets massively blown up in a cascade of differences across billions of variables. This separates the two threads by a massive distance (tiny changes in billions+ of dimensions adds up to a large absolute magnitude of separation), so they no longer interfere and you see the particle in only a single state.

Even so the whole point is that so far as observation is concerned, you'll measure the same thing, so it reflects reality as much as anything else. Where would you get the idea that isolating one timeline would yield results that would violate what we know experimentally? The whole idea is that you would pick a "stem" of the greater super-universal "flower", set it aside and call it its own universe. The distinction is topological, it's in a totally isolated space (or at least embedded in a higher-dimensional space, but definitely not "stitched in" to the other universes as is the model for #3)

If you isolate the universes then you have to explain superposition and such by some separate mechanism. That loses the primary reason for MWI in the first place; you might as well believe in wavefunction collapse at that point.

And there are huge differences in the way a universe like #1 and #3 would need to be created and thought of. That's exactly the level which I'm arguing here. The whole point of having an interpretation is to have an ontology, and that's what it means. So, okay, you go for the eternal super-flower uberverse version of MWI, that's fine. Now do you admit that there aren't any guidelines set forth by Hilbert space for how these world stems diverge topologically? I get that you can create stuff with 0 energy because their total energy is 0, but what's the mechanism? My whole point, that I've stated quite a few times now, is that these are points where MWI is an incomplete theory. Because it doesn't satisfactorily describe a mechanism for making other worlds in order to satisfy the a "superliteral" Hilbert space ontology, nor where the worlds go topologically.

The hilbert space just describes the geometry. Quantum operators define how things move around in that geometry.

I honestly don't think my objections as such should be offensive to someone with MWI inclinations. These shouldn't be considered subtle nuance points. It's akin to saying "you say many worlds eh? I have a hard enough time wrapping my head around just one. How do you figure these infinitely-many others are made physically and where do they go?" If you respond with "oh it's just possibility space" you're completely ducking the ontological question being asked, and in effect claiming (not unreasonably) that there is no meaningful ontology, that there is only Hilbert space and that's really all there is in a meaningful way. It's just the poison you pick, and I've got my own poison to chew on with collapse.

Though actually, are you sure that's not what you're actually saying? That there is no ontology, there is only Hilbert space? Cause that's fine if that's what you're saying. It's a profound statement, a bold stance, it's one I can admire the courage to accept. But that would explain my perception of your trying to wiggle out of the meaningful ontological questions I'm asking about your sense of MWI. Because in your heart of hearts you believe that there is no meaningful ontology at that level, that quantum mechanics, though true, describes a world with fundamentally no physical reality being modeled.

As Dooglie was saying about this earlier:

Well, if you take it as an interpretation, "the bare math is all you need," then you are saying something rather profound - you are giving up on the idea that the math is modeling something, you're saying that it is the thing. My level of comfort with this is variable.

I expressed earlier that I believe that amplitude-space is the "really real" reality, and thus the physical universe we experience is an emergent phenomenon. True reality is a lump of amplitude spread out in 10^big-dimensional space mutated by quantum operators. This isn't quite the same as saying "the math is the thing", but it ends up looking pretty similar. This exact position isn't required for a MWI, but I think it's the simplest consistent version.

Right now we can just take the Born rule as an axiom based on experimentation.

If you do that you get an interpretation known as the Copenhagen interpretation (or an ensemble interpretation depending on the details.)

Everett and other QM physicists who support a MWI disagree with you.

Adding it in the traditional way obviously gives you the copenhagen interpretation- how do you add a "no-collapse" collapse postulate?

The Born probabilities have nothing directly to do with the collapse postulate. In terms of MWI, the Born probabilities predict the likelihood that you find yourself in a particular world when you interact with a superpositioned system. In my particular flavor of MWI, it corresponds to the relative amount of amplitude in the "humps" of a quantum variable's amplitude distribution, and thus how much amplitude each world-line will have.

[Malconstant]

The hilbert space just describes the geometry. Quantum operators define how things move around in that geometry.

I expressed earlier that I believe that amplitude-space is the "really real" reality, and thus the physical universe we experience is an emergent phenomenon. True reality is a lump of amplitude spread out in 10^big-dimensional space mutated by quantum operators. This isn't quite the same as saying "the math is the thing", but it ends up looking pretty similar. This exact position isn't required for a MWI, but I think it's the simplest consistent version.

There we go. That's all I wanted. By my lexicon your position is indistinguishable from "the math is the thing", whereas a defining quality of MWI is an ontological distinction. But then I'm not even terribly fond of MWI, so who am I to tell you what it is and is not.

[SU3SU2U1]

Everett and other QM physicists who support a MWI disagree with you.

No, they don't. Please ACTUALLY READ the wikipedia article you linked to.

A consequence of removing wavefunction collapse from the quantum formalism is that the Born rule requires derivation

Which supports what I said- adding the Born postulate in by hand gives you wavefunction collapse, therefore removing wavefunction collapse requires a derivation of Born. The physicists who want a many worlds (or any no-collapse) interpretation all work on derivations of born from the rest of the formalism, starting with Everett.

Everett did attempt a derivation, I've already commented on it- it only works for infinitely many interactions, which is a problem. You yourself have said this is still an active area of research. Deutsch has done a fair amount of work on it recently, but none of it is particularly convincing (at least to me), and most importantly Deutsch's many-worlds doesn't look like what you are describing. Thats why I've asked you to let us know the actual axioms you are using- I'm honestly confused as to what your axioms are and what your interpretation looks like formally.

In my particular flavor of MWI, it corresponds to the relative amount of amplitude in the "humps" of a quantum variable's amplitude distribution, and thus how much amplitude each world-line will have.

You don't get to just make up rules, you have to have an actual formalism. What does it mean if the ratio of two humps is 3/4 i? How do you propose moving from amplitudes to probabilities?

[Dopefish]

It's not clear to me how taking the born rule as an axiom implies collapse, although I acknowledge that wiki at least seems to concur with you in that it does. Are there any links to material that actually shows how taking it as an axiom in an otherwise MWI implies collapse, and yet if it were derived within MWI it wouldn't lead to that implication?

How viable is the notion of having collapse built-in, but only in such a way that someone external to the wavefunction could give rise to that collapse, such that an additional consequence of the theory is that that collapse can never happen, as I suggested in an earlier post (although I admit without much deep thought, as it was late)?

My interpretation of "interpretation" has generally been working with the notion that it only interprets the math, but doesn't change it's form or what it makes as predictions. You seem to be suggesting otherwise (potentially correctly), which throws me off a tad. I appreciate that there are MW theories which go beyond just a MWI but function as (perhaps incomplete) theory in of itself, but it seems to me that one could have a Many-worlds flavoured interpretation and go on doing things in the standard way and not be stuck with any logical inconsistancies. This is without taking on a stronger view where Many-Worlds would form a full theory, which is the camp where I'm guessing most of the individuals working to derive the Born rule fall, so there might be wiggle room allowing someone to adopt a weaker form of Many worlds, without needing to answer especially difficult questions.

Is the standard collapse based interpretation considered complete, despite not having any particularly satisfying answer for entanglement witchcraft?

Is it it a fair stand that someone might take the born rule as emperically valid and consider that as sufficient evidence that it is in fact derivable, and handwave the derivation as "something for the mathematicians to worry about"*? (This isn't necessarily my stand, but it seems like one that someone could take, and as I don't belive it's been shown that Born can't be derived from MW it seems valid.)

*= Something I've seen a number of QM texts do, and something a number of my professors do when teaching. Although I appreciate that in those cases the actual derivations have actually been done.

[SU3SU2U1]

It's not clear to me how taking the born rule as an axiom implies collapse, although I acknowledge that wiki at least seems to concur with you in that it does.

The important part of the Born rule is that any measurement performed results in only ONE value (an eigenvalue) proportional to amplitude mod squared. Many worlds says that "measurements" don't happen, everything evolves via Schroedinger. What then, do the amplitudes mean?

How viable is the notion of having collapse built-in, but only in such a way that someone external to the wavefunction could give rise to that collapse, such that an additional consequence of the theory is that that collapse can never happen, as I suggested in an earlier post (although I admit without much deep thought, as it was late)?

This is somewhat related to David Deutsch's approach and is generally how quantum information theoretic approach the problem. Think of how a quantum computer works- you process and only cause a wavefunction collapse when data is read out.

My interpretation of "interpretation" has generally been working with the notion that it only interprets the math, but doesn't change it's form or what it makes as predictions. You seem to be suggesting otherwise (potentially correctly), which throws me off a tad.

As another poster said, physical theories come with a set of definitions that tell you how to get numbers out for predictions. Every major interpretation (Copenhagen/Ensemble, Many worlds, Bohm, Consistent Histories, transactional) involves modifying those definitions to tell a new "story" with the math. Bohm adds new degrees of freedom (particles and pilot waves), consistent histories adds a class operator for histories, transactional approaches involve interplay between forward and retarded Green's functions, etc.

Is the standard collapse based interpretation considered complete, despite not having any particularly satisfying answer for entanglement witchcraft?

Yes. Even many worlds people tend to use standard copenhagen when dealing with actual problems. "Shut-up-and-calculate" is copenhagen, which is probably why one of the previous posters called it "no interpretation."

There are mathematically hairy questions like "whats constitutes a measurement?" that can lead to circularity, and using the theory in practice almost always starts from quantizing a classical theory (which should help point you to the circularity- classical mechanics is a limit of quantum BUT quantum mechanics usually relies on a classical apparatus for a measurement).

Is it it a fair stand that someone might take the born rule as emperically valid and consider that as sufficient evidence that it is in fact derivable, and handwave the derivation as "something for the mathematicians to worry about"*?

I would say no- a physicist is a physicist because he cares about getting the numbers out/making predictions. You need the born rule to make empirically valid predictions. No-collapse quantum mechanics is an elegant theory that useless for predictions. Hence, happy mathematician, sad physicist.

[Technical Ben]

Spoiler:

How to recover the Born rule in MWI is an important current research topic. I have no idea what the answer is.

Then you must admit that many worlds simply isn't a full-fledged interpretation. Its might "feel good", but it gives you no way of making measurements. What is preferable- a non-unitary collapse, or a total inability to make predictions? Naive many-worlds will give you the wrong answers for experiments the majority of the time (the probability is high you find yourself in a maverick world with a non-born probability).

Right now we can just take the Born rule as an axiom based on experimentation. We don't necessarily need it to fall out of the interpretation itself, though it would be nice. Like I said, there is ongoing research on how to recover it directly from the interpretation.

I assume by "naive MWI" you mean something like "one world, one vote", or that every world has an equal amount of "reality". Yes, this is naive and gives incorrect results; it's roughly equivalent to assuming that every binary outcome is 50/50. That's irrelevant to the actual forms of MWI that physicists believe in. (I'm not a physicist, but I play one on the internet.) Like lightvector said, while the total "number" of worlds that can't derive the born probabilities is much larger than the number of worlds that can, the "amount of reality" of the two groups has the opposite ratio. (This assumes the Born probabilities, but fuck it, let's just roll with it.)

There's also probably a bit of anthropic principle at play here. A lot of the worlds in which you can't derive the born probabilities are pretty strange and may very well be inimicable to life, at least as we know it.

But if you do not get the born rule 100% of the time, you do not have identical predictions as other interpretations. Which means you aren't an "other interpretation" anymore, you're a distinct theory.

You don't have a 100% chance of getting the Born rule in collapse-based interpretations, either. The chance of things occurring in such a way that you can't do that is miniscule, but so is the chance that you find yourself in a world where the Born rule isn't derivable.

Hmm, you're still attaching too much ontological significance to this whole "worlds" things.

Indeed! What else is an "interpretation" supposed to be? I'm down with Hilbert space, but it says nothing about how (where, through what mechanism) its superpositions are to be embedded in actual physical reality, that's just not in Hilbert's lexicon.

So how does MWI inform your personal intuitive ontology of qm? Or are you saying that it has nothing to say about your intuitive ontology of qm, and by "interpretation" you mean something other than that?

I've tried to answer a few times, and we're not quite communicating properly. Hopefully this post by Charlie! helps, as it's a very clear statement of what I'm trying to say:

Where do the probabilities come from in MWI, then? If there are two outcomes from an event, does that mean the expectation is necessarily 50%? How can it possibly make the right predictions in that case?

Important question of quantum mechanics: if you're at one spot in possibility-space and the world is left to evolve, what will the world look like later? The answer is probabilistic, regardless of interpretation. And it's not "half one way, half the other." The universe can be represented by a complex function in possibility-space: the bigger the function at a certain point in possibility-space after the universe is left to evolve, the bigger the probability of the world looking like that later.

The "universes splitting" picture is common in some popularizations, but totally misleading. Especially for continuous variables! What you might call "splitting" is really just the universe becoming more spread out in possibility-space.

Thats fine, but why don't we evolve over time into an area where the born rule stops working?

"We" do. "We" also evolve into areas where it keeps working. The "we" that do the latter are more likely/"real" than the "we" that do the former.

One other quick note, is there any reason MWI can't be stated to accommodate for differing probabilities? For example, suppose I have a wavefunction^2 with a 2/3 bump at point A and a 1/3 bump at point B. I agree it's an awkward solution to say that "there are two worlds resulting from this and you're twice as likely to find yourself in A" due to the invisible hand of qm (don't. I regretted saying it even as I was typing it). But what would be wrong with interpreting it instead as "three worlds split off from this, and you have equal probability of finding yourself in either of them, it's just that two of the worlds are identical. Does that harsh the "it's literally Hilbert space" ontological interpretation's charm too much?

The MWI *is* stated to accommodate differing probabilities. Only naive pop-science versions of it don't, and that's more due to lack of detail than an explicit or purposeful lack. It's not "the invisible hand of qm" that does, but the fact that different worlds have different amounts of reality (or, equivalently, that different regions of hilbert-space have different distributions/densities of amplitude).

That's pretty much the way that David Deutsch describes it. In his version of MWI, the number of universes doesn't increase: it started as an infinite ensemble and always remains infinite, but at the start all the universes were in the exact same location of the configuration space, and thereafter tended to move in tandem. Each "splitting" event merely involves universes that had traveled in parallel up to that point diverging from one another.

Right. Whether you refer to it as (infinite) distinct universes or as an infinitely-divisible amount of "reality" is just a naming issue.

I'm not really satisfied with the playing around in Hilbert space aspect. That doesn't really feel like an "interpretation" in the usual sense; it's almost tautological from the bare math.

That's precisely why I prefer it. You don't need any extra concepts - you just look at the math, and lo, that's reality! Yay! Like doogly says, there is still a philosophical difference between MWI and "the bare math", but it's small.

So the previous MWI was that there was 4 universes, and a 1/4 (25%) chance to be in each one. This is the model I had trouble with, because we would have an even probability to end up in the universes with the ridiculously improbable outcomes. The more complete description of MWI is there are 26% of the universes with HH (with a 51% bias coin) but our probability to end up in a different universe to that one is 74%? That works mathematically.

So the "ridiculously improbable" universes are still ridiculously improbable? I'm still uneasy about the resultant universes where unicorns exist (because the maths says they do ) but I'm a lot more confident about the maths.

Yes, they're exactly as ridiculously improbable as collapse-based interpretations would say.

Yes. But MWI is the only scientific theory currently telling me to believe in fairies and unicorns. This is not helping it.

Say for example I have a universe made of 2 bits. I write it down as a multi-verse with 4 universes. They are as follows; 1,1; 1,0; 0,1; 0,0.
Now, to have that in a mathematical sense is fine. I have no problems with the mathematics of a MWI. However, to make a working program from those bits, I need to do something with them. IE, I need to make a calculation, change or application of some sort. From what I have seen of QM theory, it says the bits are random, unmeasurable and not local-hidden variables etc. MWI says those bits always existed, and did not change. If the bits are not changing, how can an existence (as in a layman's own conclusions) or our measurements (something purely mathematical or scientific) even happen?

[Edit]
I've just read the further details posted. I guess my roadblock is the "measurements" don't happen one. Is there any maths to suggest an alternative model to measurements?
I also like the "shut up and do the math" example given. I totally agree! I may be rubbish at the math, but if pointed in the right direction, I'll give it a go. As my example above, I may work my way to infinite space from something smaller though.

Would my questions on the basics still be welcome when the thread has moved onto the deeper things?

[Malconstant]

Yes. Even many worlds people tend to use standard copenhagen when dealing with actual problems. "Shut-up-and-calculate" is copenhagen, which is probably why one of the previous posters called it "no interpretation."

Oh no, Copenhagen says "the state is all there is, and that includes being a superposition", but it also says "but when you measure that shit it collapses the wavefunction". Another way of stating it is that, before observation an observable had no meaningful value beyond superposition, that "God doesn't know whether that electron will be measured spin up or spin down before it's measured". It's interpreting amplitude space (squared) as probability space. It's very much an interpretation in the usual sense.

[Xanthir]

Everett and other QM physicists who support a MWI disagree with you.

No, they don't. Please ACTUALLY READ the wikipedia article you linked to.

A consequence of removing wavefunction collapse from the quantum formalism is that the Born rule requires derivation

Which supports what I said- adding the Born postulate in by hand gives you wavefunction collapse, therefore removing wavefunction collapse requires a derivation of Born. The physicists who want a many worlds (or any no-collapse) interpretation all work on derivations of born from the rest of the formalism, starting with Everett.

Everett did attempt a derivation, I've already commented on it- it only works for infinitely many interactions, which is a problem. You yourself have said this is still an active area of research. Deutsch has done a fair amount of work on it recently, but none of it is particularly convincing (at least to me), and most importantly Deutsch's many-worlds doesn't look like what you are describing. Thats why I've asked you to let us know the actual axioms you are using- I'm honestly confused as to what your axioms are and what your interpretation looks like formally.

So, we're clashing on this point about the Born rule. It may just be because I Am Not A Physicist, but I really don't think you're right. (It's also very difficult to distinguish confidence from bravado when talking with strangers on the internet, so I can't tell whether I should trust you and update my knowledge or challenge you so you can update yours.)

The Born rule simply states that, upon observing a quantum system, you will observe it to be in one of its component states with a particular probability. (/handwave) Collapse-based interpretations choose a particular state that the system "actually" ends up in, and when you work through the math this corresponds to the Born probabilities. MWI naively loses the ability to invoke this as a feature. You can just add it as an axiom that the worlds split in such a way as to preserve the Born probabilities, so that you have a chance to find yourself in one world or another with the correct probability distribution. The attempts by MWI theorists to derive the Born rule purely from the interpretation are just an attempt to make the formalism more beautiful, as far as I understand.

In my particular flavor of MWI, it corresponds to the relative amount of amplitude in the "humps" of a quantum variable's amplitude distribution, and thus how much amplitude each world-line will have.

You don't get to just make up rules, you have to have an actual formalism. What does it mean if the ratio of two humps is 3/4 i? How do you propose moving from amplitudes to probabilities?

I Am Not A Physicist, but what's wrong with the obvious way ("square" it)?

[Xanthir]

It's not clear to me how taking the born rule as an axiom implies collapse, although I acknowledge that wiki at least seems to concur with you in that it does.

The important part of the Born rule is that any measurement performed results in only ONE value (an eigenvalue) proportional to amplitude mod squared. Many worlds says that "measurements" don't happen, everything evolves via Schroedinger. What then, do the amplitudes mean?

When you say things like this, it makes me think that either we're talking past each other somehow, or you just don't understand MWI properly (like Malconstant earlier in the thread, when he thought that looking around his room spawned the creation of billions of new universes).

The important part of the Born rule is that we *observe* only one value. It says nothing about the underlying reality; it doesn't claim that the superpositioned system *actually* transforms into a single-state one. That's a collapse-based interpretation. What matters is just that the observables end up matching the Born probabilities, and can happen without any problem in MWIs that take the Born rule as an axiom. (Theory dictates the observables, the observables constrain, but don't dictate, the theory.)

In MW with assumed Born, you start with a superpositioned system, like an electron with superpositioned spin. You put it in a detector. If the spin is up, a photon goes HERE; if it's down, a photon goes THERE. If a photon shows up HERE, it triggers a photomultiplier; if it shows up THERE, it's absorbed by non-responsive matter in the detector. Etc., until eventually one world has a detector spewing out photons, while the other doesn't. The two worlds were *always* separate (the split occurred as soon as you superpositioned the electron), but now they're *more* separate. It's a difference in quantity that looks like a difference in kind to us macroscopic beings; it previously looked like a single world with a superpositioned electron, while now it looks like two worlds each with a classical electron.

The amplitudes of the component states define the relative reality of each world-line. When the two worlds peel away from each other and you can distinguish the two, you find yourself in one or the other relative to the original amplitude.

[gavin]

No, that doesn't work. If two events are spacelike separated rather than timelike (timelike being the sort where you can say one is in the past/future of the other), then to ALL observers the events are spacelike separated. Two different observers X and Y might see A and B happen 'before' or 'after' each other, with before and after measured according to X and Y's clocks, but nobody ever sees A in the past of B or vice versa.

The above is a basic special relativity fact. Making sense of entanglement and relativity requires, for starters, the relativistic formulation of quantum mechanics -- quantum field theory. Things get very unintuitive. I don't think there's any good way around it.

So, what you're saying is that a space hobo riding a space train with his legs hanging over the side of an open compartment who pulls his legs inside just before the compartment slams shut (from his perspective) will never be viewed as having had his legs slammed on by the compartment door from any angle?

[Malconstant]

So, what you're saying is that a space hobo riding a space train with his legs hanging over the side of an open compartment who pulls his legs inside just before the compartment slams shut will never be viewed as having had his legs slammed on by the compartment door from any angle?

Well yeah. Otherwise you'd have a really inconsistent reality. This is the idea with any special relativistic paradox. You may be thinking of something like the barn and ladder paradox, in which the barn thinks the ladder fits inside the barn, and the ladder thinks otherwise, and it turns out they're both right. The thing is that if you were to make a bomb mechanism that would explode the barn and ladder if the ladder fits, then you have a pretty objective situation you can check out, either everything explodes or it doesn't and they'll agree on that one. In this case what matters is how you design the bomb. If you put the bomb on the barn, it'll explode, and if you put it on the ladder it won't explode. But either way they'll both agree on whether or not they were exploded. Relativity doesn't have any superposition.

[gavin]

So, what you're saying is that a space hobo riding a space train with his legs hanging over the side of an open compartment who pulls his legs inside just before the compartment slams shut will never be viewed as having had his legs slammed on by the compartment door from any angle?

Well yeah. Otherwise you'd have a really inconsistent reality. This is the idea with any special relativistic paradox. You may be thinking of something like the barn and ladder paradox, in which the barn thinks the ladder fits inside the barn, and the ladder thinks otherwise, and it turns out they're both right. The thing is that if you were to make a bomb mechanism that would explode the barn and ladder if the ladder fits, then you have a pretty objective situation you can check out, either everything explodes or it doesn't and they'll agree on that one. In this case what matters is how you design the bomb. If you put the bomb on the barn, it'll explode, and if you put it on the ladder it won't explode. But either way they'll both agree on whether or not they were exploded. Relativity doesn't have any superposition.

Makes sense to me. I agree.

[SU3SU2U1]

When you say things like this, it makes me think that either we're talking past each other somehow, or you just don't understand MWI properly

See, here I am thinking just the same, but about you. My fear is that you don't have a consistent set of axioms you are working with, rather you are just qualitatively handwaving. Any no-collapse interpretation needs to rewrite the measurement postulate in some way, I still do not understand what rewrite you propose.

It would clarify tremendously if you would please tell me what set of postulates you are calling "many worlds." (I've asked for this a few times now). I generally assume many-worlds to be an Everett picture (copenhagen quantum - the measurement/Born postulate) but you apparently mean something different- so what is it that you mean?

[gmalivuk]

The amplitudes of the component states define the relative reality of each world-line. When the two worlds peel away from each other and you can distinguish the two, you find yourself in one or the other relative to the original amplitude.

But what does this mean, when you consider the fact that there's a version of you in *both* worlds? I can get an interpretation where the number of worlds is proportional to the probability distribution, but if every two-outcome situation results in two universes, what does it mean for one to have "more reality" than the other?

[Xanthir]

When you say things like this, it makes me think that either we're talking past each other somehow, or you just don't understand MWI properly

See, here I am thinking just the same, but about you. My fear is that you don't have a consistent set of axioms you are working with, rather you are just qualitatively handwaving. Any no-collapse interpretation needs to rewrite the measurement postulate in some way, I still do not understand what rewrite you propose.

It would clarify tremendously if you would please tell me what set of postulates you are calling "many worlds." (I've asked for this a few times now). I generally assume many-worlds to be an Everett picture (copenhagen quantum - the measurement/Born postulate) but you apparently mean something different- so what is it that you mean?

Here's the thing - I am just qualitatively handwaving. As I've said twice before in this thread, I Am Not A Physicist. However, I've synthesized a lot of discussions and explanations from people who seemed clueful (and who in many cases *are* physicists), and believe I understand things in a consistent manner. Further, I know from experience that even actual physicists can have a naive pop-science understanding of MWI, and not realize it.

Thus, I'm not sure whether I'm wrong and I should update my beliefs, or you're wrong and I should try and help you update yours. Based on my current understanding, your claims that the Born rule automatically implies collapse seems wrong on its face. I understand the Born rule to dictate your observables, but there are many possible interpretations that would produce observables consistent with the Born probabilities.

However, I'm limited in how precisely I can explain myself because my formal physics education is somewhat limited.

The amplitudes of the component states define the relative reality of each world-line. When the two worlds peel away from each other and you can distinguish the two, you find yourself in one or the other relative to the original amplitude.

But what does this mean, when you consider the fact that there's a version of you in *both* worlds? I can get an interpretation where the number of worlds is proportional to the probability distribution, but if every two-outcome situation results in two universes, what does it mean for one to have "more reality" than the other?

It means you're more likely to find yourself in it.

[Technical Ben]

No, that doesn't work. If two events are spacelike separated rather than timelike (timelike being the sort where you can say one is in the past/future of the other), then to ALL observers the events are spacelike separated. Two different observers X and Y might see A and B happen 'before' or 'after' each other, with before and after measured according to X and Y's clocks, but nobody ever sees A in the past of B or vice versa.

The above is a basic special relativity fact. Making sense of entanglement and relativity requires, for starters, the relativistic formulation of quantum mechanics -- quantum field theory. Things get very unintuitive. I don't think there's any good way around it.

So, what you're saying is that a space hobo riding a space train with his legs hanging over the side of an open compartment who pulls his legs inside just before the compartment slams shut (from his perspective) will never be viewed as having had his legs slammed on by the compartment door from any angle?

(Sorry, can't find doogley's origional post)

Ok, thanks. I'll have to revisit the barn/ladder problem. Been a while. Still not 100% sure why we can't separate spacelike as we can timelike.

I know my following comment is probably wrong, please take this as a student putting his hand up and going "ok, what tells us this is so?" After all, I thought it WAS space-time. Being able to reverse space-like space just means we loose the ability to seperate it time-like. (Hello black hole time/space calculation reversal! Nice to meet you.)
[The answer was given in another thread. Now I'm gonna read up Minkowski space. Heard of it, did not realise it's implications.]
[edit]
At risk of messing up my well prepared question to the tutor with a silly remark that will get me expulsion, I say...
Xanthir, define "find".

[Malconstant]

Now I'm gonna read up Minkowski space. Heard of it, did not realise it's implications.

Minkowski diagrams are the greatest thing that ever happened to special relativity. Though it may not be immediately clear why, or how they ought to work. But suffice it to say, it's a way of drawing out a single diagram which is implicitly built upon hyperbolic/Lorentzian geometry structure in a way that allows every special relativistic paradox to be made crystal clear. It's a single diagram that puts two seemingly contradictory reference frames on the same plot in a way that everyone can agree and understand what's going on with a single coherent picture. Which, to someone new to SR, seems like an impossible task.

[SU3SU2U1]

Here's the thing - I am just qualitatively handwaving. As I've said twice before in this thread, I Am Not A Physicist.

Its fine to not be a physicist- its another to claim some understanding of a theory. If you don't have a formalism you can work with, all your arguments are just appeals to other people's authority. You seem to have an interest, why not sit down with some textbooks and learn some theory?

As I'm fond of telling students- if you can't do calculations with a theory, you don't really understand it.

[Technical Ben]

Yep, Malconstant, I guess it's a needed diagram for refuting paradoxes and those who argue "oh, but there may be a possible solution we have not thought of". Without strong irrefutable theories and proofs, it's hard to learn the full implications.

Once I understood that space, time and the lightcone are separated, I could see you can't join them. Even more so when you add position/velocity restrictions of measurements is it apparent these things are exclusives, I can't argue "but there may be a way to do both". I did not realise these other ways were being excluded mathematically. The maths and physics are saying "these things are logically exclusive". To have one, is to exclude the other. We only have 2 possible options, exclusive or inclusive.

With QM, Bell's theorem proves the exclusivity of hidden variables. We can have hidden variables, but the results of experiments would be different. We cannot try to argue "there may be universes where we have different results" or "there may be other possibilities". We already have all the possibilities available. There are 2. We can check the outcome of both. We cannot have both the same results and hidden variables. With our current results the only option is for the variables not to be local and hidden. So they must be non-local or must not exist until measurement.

When we start with a logical exclusivity of "existence/non-existence" as an axiom (and the easiest one to accept, as we have no choice in the matter ) the rest is progressive. Just like a computer, though complex, runs on single binary exclusive or inclusive operations. I hope others can see when the proofs in QM, relativity or even standard macro events are given, these can be absolute and without exception.

[Malconstant]

Yep, Malconstant, I guess it's a needed diagram for refuting paradoxes and those who argue "oh, but there may be a possible solution we have not thought of". Without strong irrefutable theories and proofs, it's hard to learn the full implications.

Once I understood that space, time and the lightcone are separated, I could see you can't join them. Even more so when you add position/velocity restrictions of measurements is it apparent these things are exclusives, I can't argue "but there may be a way to do both". I did not realise these other ways were being excluded mathematically. The maths and physics are saying "these things are logically exclusive". To have one, is to exclude the other. We only have 2 possible options, exclusive or inclusive.

Huzzah!

With QM, Bell's theorem proves the exclusivity of hidden variables. We can have hidden variables, but the results of experiments would be different. We cannot try to argue "there may be universes where we have different results" or "there may be other possibilities". We already have all the possibilities available. There are 2. We can check the outcome of both. We cannot have both the same results and hidden variables. With our current results the only option is for the variables not to be local and hidden. So they must be non-local or must not exist until measurement.

When we start with a logical exclusivity of "existence/non-existence" as an axiom (and the easiest one to accept, as we have no choice in the matter ) the rest is progressive. Just like a computer, though complex, runs on single binary exclusive or inclusive operations. I hope others can see when the proofs in QM, relativity or even standard macro events are given, these can be absolute and without exception.

Once you go around invoking "other universes", well it's really hard to say what actually goes on in a totally different universe. You can make sensible multiverse models, and work out the consequences, but just the idea of "other universes" is more waxing poetic.

Specifically, "Bell's Theorem" is a mathematical theorem, so it'll hold in any universe where logic holds, BUT the experiments done on a different universe might as well yield different results, in which case the implication is totally different. What I'm getting at is that you seem to be having an epiphany where all of modern physics is knowable from a priori reasoning, and I can't emphasize enough how much that misses the point of the philosophy of science. Generally speaking, the scientific community doesn't even think that our current theories are perfect ones which totally get to the heart of how the universe works. They're good ones, that's for damn sure, and experimentally verified, but Newton's theories were also experimentally verified. We do know this, however. Any theories which come to replace our current understanding of GR and QM will have to be more crazy because they will have to demonstrate the same reproducible, experimentally-verified results of GR and QM.

[Technical Ben]

I'm not saying we know it all. But that most if not all can be described as either/or statements. We either have multi-verses or don't. Then after the statement, we have to prove the maths behind it.
When it comes to "universes which follow logic" it's starting to leave the science and into the philosophy. As in, if you throw out all the axioms, your left with nothing. It's a pointless consideration such as "what is a universe existed that did not exist".

I don't see the "oh, but a universe might exist that does have..." arguments as fruitful. If the other universes exist, they follow the same rules this one does. We just have to extend the rules, not ignore them.

[Malconstant]

Well yeah, talking about totally hypothetical universes with arbitrary properties is more story telling time than anything else. The thing is there are multiverse theories, many of which will play around with fundamental constants and such, and so the universe as you know it may well not be very much at all like other universes in these theories.

Now, I personally wouldn't recommend that you try and get knee deep in legit multiverse theory right now, but rather content yourself with the rich and fulfilling GR and QM that we know and love. And then once you've reached a point in your studies, re-approach the multiverse theories from a position to truly understand what they're getting at.

[Technical Ben]

Well, I have no requirement of MWI. Neither do current collapse based theories. So I'll keep note of it, it's helpful to know the for and against arguments.

[Malconstant]

Oh! Real quick distinction. Multiverse theories are totally different from MWI. Multiverse theories are trying to figure out a mechanism for creating universes, from a cosmology perspective. MWI is just a way of interpreting QM formalism. I totally understand confusing them superficially, but they are vastly different monsters.

[Technical Ben]

Well, as long as the term "an entire universe is created" [is not used in MWI], then I guess I have no problem. As mentioned further up in the thread, saying that the multi-verses do interact at the point of observation is one thing, but we need the maths to back it up. Unless I've missed something, no mathematical model was offered for how these interactions apply. One was offered to list them, but that's stamp collecting, not physics.

[ Edited in the sentence I missed off. Sorry, very tired from a long weekend and a cold. ]

[Charlie!]

Well, as long as the term "an entire universe is created" at each moment/point/observation then I guess there is no problem. As mentioned further up in the thread, saying that the multi-verses do interact at the point of observation is one thing, but we need the maths to back it up. Unless I've missed something, no mathematical model was offered for how these interactions apply. One was offered to list them, but that's stamp collecting, not physics.

This post made no sense. For example, the first sentence needs a verb.

[Technical Ben]

Sorry, fixed it.
I would liken saying "there is a corresponding universe for each probability" is like stamp collecting. We know something is there, we want to know how it works (the physics).

All science is either physics or stamp collecting.

[Malconstant]

The maths are just the quantum formalism, Hilbert space. Though I suspect that what some people mean by "different universes interacting" is a way of reconciling self-interaction and path integrals as well.

[Technical Ben]

Would I be correct to say that the Hilbert space of a string requires the string to wobble/vibrate?
If I ask how the multi-verse interacts, I'm asking how it "vibrates" so as to self interfere. Just as a vibrating string would.

Currently, the model of multi-verses is just a set of lists to me. A stationary one at that.

[Malconstant]

String theory has nothing to do with qm formalism or interpretations (including MWI)

Pick up Feynman's QED (Quantum Electrodynamics). It's short, brilliant, and written such that an interested amateur physicist can follow while providing penetrating insight into self-interation of QM. I think you'll find forum responses increasingly dissapointing at this point if you only want to examine these questions superficially (as in, without actually bothering to read some books.)

[SU3SU2U1]

String theory has nothing to do with qm formalism or interpretations (including MWI)

At its most basic level, with string theory you take the Lagrangian for a fundamental string and quantize it. In that sense, it has very much to do with the qm formalism.

[doogly]

Oh, I think this is meant in the sense that if string theory is accurate, it does not cause you to in any way rethink or retool the quantum mechanical formalism.

[Technical Ben]

Hey, I did not mean string theory! I mean Hilbert Space, a subset of which is describing things vibrationing.
So, to rephrase the question, if we have a string trampoline vibrating as an example of Hilbert Space, do we not need "vibrations" in the multi-verse to be able to describe it in Hilbert space?
If there is no interaction or vibration we do not have Hilbert Space, we have a set/list/counter of universes. Or am I missing something?