Is the Many-Worlds Interpretation truly deterministic?

[bhobba]

I suppose it is possible in principle for a scientist to adhere to the same standards of rigor in informal communications like pop science articles or TV specials as he does in formal communications like textbooks or peer reviewed papers. But in practice it rarely if ever happens.

It happens all the time. I was a programmer for 30 years - 20 at the team leader level and I attended many meetings with users who knew nothing about the technicalities - nor should they. They wanted to know what we could do for them. I was very 'loose' with all sorts of stuff.

Same here - when scientists speak informally they are often, like I was, a bit loose. The reason I know Gell-Mann adhered to DH is he wrote papers on it. The reason I know Feynman was converted to it is Gell-Mann described how he discussed it with him and attended his lectures o it. This is the type of evidence you want.

Thanks
Bill

 

[mfb]

I agree with this... mwi doesn't solve the initial problem of why measurement/ consciousness seems to trigger the collapse (or in the case of mwi, the universal split)

There is no "trigger" necessary because the process is continuous in MWI, but decoherence shows why those worlds split.

 

[PeterDonis]

when scientists speak informally they are often, like I was, a bit loose.

In other words, they don't adhere to the same standards of rigor as they do in formal communications. Which is what I said.

Your analogy with a programmer explaining things to a user isn't valid IMO, because the user is not trying to learn programming; they're just trying to get work done. So an informal, "loose" explanation is good enough. People who ask questions here on PF are trying to learn the actual science--at least, that's the assumption that underlies the PF rules on acceptable sources (and if we find out people aren't really trying to learn the actual science, we cut the discussion short if possible). An informal, "loose" explanation isn't enough for that.

 

[PeterDonis]

This is the type of evidence you want.

If I'm interested in who favors what interpretation, yes. But not if I'm interested in what a given interpretation actually entails.

 

[nikkkom]

mwi doesn't solve the initial problem of why measurement/ consciousness seems to trigger the collapse (or in the case of mwi, the universal split)

It does solve it.

The thing it, MWI in fact does not precisely say that there are "splits". There are no splits at all. In Schrödinger's cat situation, unobserved "cat in a box" system exists in a superposition (even in Copenhagen) - it does not split into gazillions of branches, it is still one system.

What MWI says is that a similar superposition situation arises when you observe the box. The "you + opened box" system does not split into gazillion branches - instead, now this system is in superposition of "you see a dead cat" and "you see a live cat". It is still one system. (If you disagree, then you must be agreeing that Copenhagen interpretation of the "unobserved box" system also includes world splits).

No collapse happened when box was observed. Thus, no concept of measurement needs explaining. In MWI, measurement is merely "interaction which entangles observer with the observed subsystem".

You can think about "gazillion of branches" method of describing it as a way to explain superposition to laymen.

 

[secur]

Well, I think the first example would be Murray Gell-Mann's famous declaration (apparently appropriated from T.H.White) that "Everything not forbidden is compulsory." https://en.wikipedia.org/wiki/Totalitarian_principle

The totalitarian principle is not about MWI - it is an uncontroversial statement about renormalization in quantum field theory.

That principle applies throughout QM (/QFT), including renormalization and MWI. Murray Gell-Mann originally thought of it in relation to particle decay but its relevance to MWI is direct and important. It's precisely the main point of this thread (one of them anyway): that "every possible possibility" must be realized in a branch, or universe, of the many worlds wavefunction.

Gell-Mann "appropriated" the phrase from White but White knew nothing about QM, talking about an unrelated topic (dictatorial government). The principle is inherent in QM and was known from the beginning, but Gell-Mann was the first to single it out (AFAIK) and emphasize its importance and applications. IMHO he deserves the entire credit for it.

It does solve it.

Such a statement should never be made in reference to MWI. It really doesn't matter what is supposed to be "solved" but it's especially true if it has anything to do with measurement, collapse, observers, and consciousness, as in the present case.

All these statements are acceptable: "It may possibly solve it"; "according to some advocates it does solve it"; "it offers a solution which of course is not proven, well-defined, or entirely accepted by the physics community"; "IMHO it solves it, but of course many physicists would disagree". And similar variations.

If we all understood and agreed to the above, then the simple, direct "it does solve it" would be acceptable as shorthand. But since we don't all understand and agree it seems necessary to flag this statement as a mistake.

 

[nikkkom]

MWI does not have and does not need a concept of "measurement" as something special and distinct from all other interactions in quantum systems.
MWI does not postulate any "collapse" to be happening.
Thus, it does not have "problem of why measurement/ consciousness seems to trigger the collapse".

I don't see what are you arguing against.

 

[secur]

I shouldn't have referred to your post, @nikkkom. I had been glancing through "The Beginning of Infinity" by David Deutsch and accidentally vented my annoyance on your statement, for which I apologize. My comments are actually meant for DD and others of that ilk. This book is NOT bad science; it's not even bad pop-science: it's bad science fiction.

 

[n01]

I have three small questions that I figure can be answered here instead of cluttering the forum with them.

Under MWI, how is it that this reality (the sum total of logical relations between objects in the universe interacting with each other) is apparent (or real) as opposed to being none other than what it is itself?

Is Occam's Razor superseded or discredited by Everettian QM in explaining an infinitude of events?

And finally, can the Church-Turing-Deutsch principle ever hope to amount to anything more than a theory? Can it be proved?

 

[bhobba]

Under MWI, how is it that this reality (the sum total of logical relations between objects in the universe interacting with each other) is apparent (or real) as opposed to being none other than what it is itself?

Its easy.

Due to interactions you end up with what's called a mixed state that is written as ∑pi |bi><bi| - the |bi> are the outcomes of the observation, interaction etc etc. This is from the formalism of QM - every interpretation has it. Now in MW the |bi><bi| are interpreted as separate worlds and everything just keeps evolving - no single outcome is singled out - they all just occur. Using decision theory you can show the pi are the probability that if you randomly pick a world what is the probability it will be |bi><bi|. Its really is that simp;le. Of course the details are technical and mathematical and can be found here:
https://www.amazon.com/dp/0198707541/?tag=pfamazon01-20

I don't know enough about the Church-Turing-Deutsch principle to know the current state of ply - but predicting future progress is a mugs game so who knows.

Thanks
Bill

 

[n01]

Thank you Bill,

I will try and buy the book if I find myself in a possible world where I have enough money to...

All kidding aside, isn't the most probable event the one that dictates the evolution/behavior of the wavefunction and thus presents us with this reality as opposed to any other (less probable, eg. one where I won the lottery)?

 

[secur]

Is Occam's Razor superseded or discredited by Everettian QM in explaining an infinitude of events?

No. Applied to theories Occam's doesn't call for fewer "real" objects, but fewer statements, axioms, or assertions. Which is simpler: "everything has property A", or "everything which is red, Belgian, with mass between 10 and 20 kg, has property A"? The first applies to "infinitely" more objects, but the second is much more complicated. Similarly, "every possible outcome becomes real" vs. "only one outcome becomes real, because of the wavefunction collapse, which means {long explanation omitted}". The first, MWI (or, "Everettian QM"), is (on the face of it) much simpler, even though it instantiates "infinitely" more "real" branches.

can the Church-Turing-Deutsch principle ever hope to amount to anything more than a theory? Can it be proved?

No, although it depends what you mean by "proved". With the normal, naive meaning, C-T can be proved because it's mathematics (or, formal logic). C-T-D can't be proved because it's physics, a statement about the "real" world. Judging by your avatar (Wittgenstein) I suppose you don't like Popper, but you could read him for more insight on this topic.

Under MWI, how is it that this reality (the sum total of logical relations between objects in the universe interacting with each other) is apparent (or real) as opposed to being none other than what it is itself?

No offense, but that doesn't actually make sense. And it will probably be hard to rephrase it so that it does.

 

[n01]

No, although it depends what you mean by "proved". With the normal, naive meaning, C-T can be proved because it's mathematics (or, formal logic). C-T-D can't be proved because it's physics, a statement about the "real" world. Judging by your avatar (Wittgenstein) I suppose you don't like Popper, but you could read him for more insight on this topic.

I don't understand why you use quotations when describing the "real" world.

I have read Popper; but, I subscribe to the notion that every physical law or physics can be understood through a formal system, eg. logic, and mathematics. This is a statement that I believe can either be "proved" to be true, false, undecidable if it fulfills or fails to fulfill the C-T-D principle. I'm kind of assuming the consequent; but, that is only due to not having enough information/knowledge on the matter.

No offense, but that doesn't actually make sense. And it will probably be hard to rephrase it so that it does.

Hypothetically, why haven't I won the lottery yet?

 

[bhobba]

isn't the most probable event the one that dictates the evolution/behavior of the wavefunction and thus presents us with this reality as opposed to any other (less probable, eg. one where I won the lottery)?

Its determined by some deep theorems found in the book.

Take for example going to two worlds. You may think it 50-50 what world you will experience. Now imagine in one of the worlds you do the same thing. So you have worlds - 50- 25 -25. Yet you have three worlds so you would think its 1/3, 1/3, 1/3. It consistency requirements like this that leads to the Born rule being the corrrect probability - its tied up with non-contextuality and Gleason's theorem - but that is for a whole new thread.

Thanks
Bill

 

[mfb]

Hypothetically, why haven't I won the lottery yet?

In MWI you have won in some branches, in those branches you ask why you won the lottery.

 

[secur]

I don't understand why you use quotations when describing the "real" world.

Because you're discussing philosophy (of science). Almost the whole point of this study is, precisely, to figure out what "real" means. So to use the word as though we already know what it means is to commit the fallacy of petition principii. Considering I'm dealing with people who respect someone like David Deutsch, you might ask, why bother to be accurate, to reason correctly - no one can tell the difference anyway. Actually, I've been wondering the same thing myself.

I have read Popper; but, I subscribe to the notion that every physical law or physics can be understood through a formal system, eg. logic, and mathematics.

There's no question that every physical law can be understood that way. A law is a limited, very finite statement written in a book. But the reality underlying that law is something else entirely. I perceive that you still think you can "figure out" life and reality. Have fun, but a word of advice: don't play the stock market! In particular, stay away from options trading.

Hypothetically, why haven't I won the lottery yet?

I don't know that you haven't.

 

[n01]

In MWI you have won in some branches, in those branches you ask why you won the lottery.

That much I understand.

I may be uneducated on the matter; but, why is this timeline where I'm asking these questions apparent to me and not any other? I'm not sure if I'm being clear enough.

Thank you.

 

[secur]

I may be uneducated on the matter; but, why is this timeline where I'm asking these questions apparent to me and not any other? I'm not sure if I'm being clear enough.

MWI says that your consciousness "splits" so that different versions of you exist on every timeline. You see one outcome of an experiment, while your "twin (s)" will see the other (s). The "split" is well-defined in QM math terms. The experimenter is entangled with the wave function, just like any other subsystem can be entangled. However the way consciousness does this, in detail, is not so well-defined.

Anyway, your "twin" right now is probably asking the same question, "why am I on this timeline?" - but it's a different branch he's asking about. According to MWI.

 

[n01]

MWI says that your consciousness "splits" so that different versions of you exist on every timeline.

I know I'm repeating myself; but, I am only aware of one timeline and not others. The wavefunction seems to evolve in a deterministic fashion in that I am experiencing this timeline and not another. How come?

 

[bhobba]

I know I'm repeating myself; but, I am only aware of one timeline and not others. The wavefunction seems to evolve in a deterministic fashion in that I am experiencing this timeline and not another. How come?

That is the assumption of MW.

What you are talking about is a history. In MW all histories happen but you experience just one - by assumption.

Thanks
Bill

 

[n01]

but you experience just one

Can you tell me why do I experience just one? Quite curious.

 

[bhobba]

Can you tell me why do I experience just one? Quite curious.

Its an assumption from the definition of a history - that's why.

The theory assumes that all histories occur and each is a separate world. By the definition of a history you only experience it.

In science some things are assumed - this is one of them. No reason - its just assumed. You have versions of MW where you experience all at once - but your brain only is aware of one. That's called many minds interpretation:
https://en.wikipedia.org/wiki/Many-minds_interpretation

Thanks
Bill

 

[n01]

Its an assumption from the definition of a history - that's why.

The theory assumes that all histories occur and each is a separate world. By the definition of a history you only experience it.

In science some things are assumed - this is one of them. No reason - its just assumed. You have versions of MW where you experience all at once - but your brain only is aware of one. That's called many minds interpretation:
https://en.wikipedia.org/wiki/Many-minds_interpretation

Thanks
Bill

So, the fact that I, or I think I can use the word 'we' without assuming anything, experience the same history means that we are experiencing a super deterministic world as opposed to a less probably one. I've just got it stuck in my head that the most probably stochastic event is what dictates the evolution of 'this' (the one we are both experiencing) world/reality.

 

[bhobba]

So, the fact that I, or I think I can use the word 'we' without assuming anything, experience the same history means that we are experiencing a super deterministic world as opposed to a less probably one. I've just got it stuck in my head that the most probably stochastic event is what dictates the evolution of 'this' (the one we are both experiencing) world/reality.

No.

MW is mathematically very beautiful. You should study the math - not try to semantically analyse it.

Thanks
Bill

 

[PeterDonis]

Can you tell me why do I experience just one?

Because the physical thing in which your experiencing happens is entangled with the physical things you are experiencing. In different branches ("worlds"), these entangled systems are in different states, so the copy of you in those branches experiences different things. But in each individual branch, the entangled systems are each in some particular state, and so you have a certain experience and the things you are experiencing are in the state that is consistent with that experience.

 

[n01]

Because the physical thing in which your experiencing happens is entangled with the physical things you are experiencing. In different branches ("worlds"), these entangled systems are in different states, so the copy of you in those branches experiences different things. But in each individual branch, the entangled systems are each in some particular state, and so you have a certain experience and the things you are experiencing are in the state that is consistent with that experience.

The state space we both occupy (since you are entangled in some manner by replying to this post by me) is evolving non-stochastically? Or are we literally evolving in different state spaces?

 

[n01]

I don't see anything deterministic about the wavefunction evolving in an infinite amount of ways.

If every reality is real then that makes the world "reality" lose its meaning and becomes a vacuous existential (or universal?) quantifier denoting nothing in reality.

 

[PeterDonis]

The state space we both occupy (since you are entangled in some manner by replying to this post by me) is evolving non-stochastically?

The state space doesn't evolve at all. In the usual formulation of the MWI, the evolution of the quantum state, which is a particular vector in the state space, is unitary, hence information-preserving and deterministic. The description in terms of different "worlds" comes from picking a particular basis in which the state vector is a superposition of terms, and viewing each term as a separate world.

Or are we literally evolving in different state spaces?

No. See above.

If you have not spent any time studying the actual math underlying the MWI (and QM in general), I would strongly suggest that you do so. Even better, study several different treatments of it from different viewpoints.

 

[n01]

I would strongly suggest that you do so. Even better, study several different treatments of it from different viewpoints.

If you can recommend any particular books on the matter, I would appreciate for satisfying my curiosity on the matter.

Thank you.

 

[PeterDonis]

If you can recommend any particular books on the matter,

I have found Ballentine to be a good treatment.

https://www.google.com/search?q=ballentine+quantum+mechanics&oq=ballentine+quantum+mechanics

Others here can no doubt suggest other references.