Problems with Many Worlds Interpretation

[Hurkyl]

In this case, I'm using it to call into question the use of the theory to justify an elaborate world view of invisible other outcomes to every experiment. That is not at all "what a theory says", so I'm certainly not doing what you claim.

No more invisible than coordinate charts or forces or fields.

On the contrary, I see exchanges like that all the time. Are you an educator?

Professor? No. I have been been of the "outside help" variety, though, before I joined PF.

I've only really encountered the "it's just an X" argument form for rationalizing not listening to something here on the internet, though.

And you see a problem with Bob's position?

Yep. So you don't, then? I thought you might not -- I chose this one specifically because it is defensible even at the same time it's clear that there's something seriously wrong about it.

Sounds fine to me.Your analogy has unravelled at this point, it bears no resemblance any more.

Ah, the old "this form of argument is valid as long as it's used to come to conclusions I like, but it's invalid as soon as it's used to come to conclusions I don't like".

Consider this sentence: "I flipped a coin, and it came up heads." Shocking claim that, but quite nonunitary.

Eh? I don't see it.

Now we have your version: "I flipped a coin, and it appeared to come up heads, but I can't really tell that it didn't come up both heads and tails because I'm a radical anti-empiricist and don't believe my senses."

Huh?

You've joined two separate ideas together. If your version is

I flipped a coin and saw heads​

then my version is also

I flipped a coin and saw heads​

But if my version is

I flipped a coin and saw heads. But I can imagine the bird's eye the outcome is indefinite, and see how unitary evolution can be involved, and would predict the statistics of repeated experiments​

then your version is

I flipped a coin and saw heads. In the god's eye, the coin is also heads and you're being ridiculous (albeit internally consistent) for even entertaining any other thought​

Trouble is, hypothesis Y includes angels on the pin.

No more so than hypothesis X. At least my angels aren't so central to my world-view that it's impossible for me to imagine that they aren't there.

What you don't get about empiricism is that it holds that observations don't exist to test theories, they exist to tell us what is true.

"What is true" is about theories.

But even ignoring that, in of itself all observing Z tells us is Z. It doesn't tell us X, nor does it tell us Y.

 

[Ken G]

No more invisible than coordinate charts or forces or fields.

Exactly. To the empiricist, the "many worlds" have exactly the same claim on reality as a coodinate chart does. They are both rationalist tools for conceptualizing, but they are not real because they are maps not territories. To an empiricist, MWI is like a book of maps, where one page is labeled "reality", and the rest are "other," but including them allows the book as a whole to have some aesthetic property.

Professor? No. I have been been of the "outside help" variety, though, before I joined PF.

I just mean that the exchanges you say never happen are exactly like the exchanges between a student and a teacher. You must have had a thousand exchanges like that on here, in your role as theory explainer.

I've only really encountered the "it's just an X" argument form for rationalizing not listening to something here on the internet, though.

I realize that the "just" in that sentence can easily be used to misconstrue. The classic example is that Darwinian evolution is "just a theory". What does the "just" in that sentence really mean? To me, it doesn't mean "so we have to teach the controversy in classrooms", but it does mean "so we should not be too surprised if at some point in the future the theory requires substantial revision or replacement." But that doesn't mean we have to pay any attention to vastly inferior theories just because Darwin's is "just a theory like any other", that's the misconstrual.

Yep. So you don't, then? I thought you might not -- I chose this one specifically because it is defensible even at the same time it's clear that there's something seriously wrong about it.

Actually, I think our best theory of orbital motion, GR, is quite clear on the issue of whether or not the Earth really revolves around the Sun. It's off topic, but GR says that both the Sun and the Earth are moving inertially, they are just doing so in a curved spacetime. The curvature is due to the Sun, but that doesn't make the Earth "go around the Sun" or the Sun "go around the Earth", they just go around each other, like two ants crawling on an apple that happens to be curved because one of them chewed a hole in it.

Ah, the old "this form of argument is valid as long as it's used to come to conclusions I like, but it's invalid as soon as it's used to come to conclusions I don't like".

As opposed to your mode here, "any analogy I draw can be used to support my position, regardless of how completely I need to change the facts."

Eh? I don't see it.

OK, try this one. The second law of thermodynamics.

then your version is

I flipped a coin and saw heads. In the god's eye, the coin is also heads and you're being ridiculous (albeit internally consistent) for even entertaining any other thought​

No, my version is "there is no god's eye, you made it up."

"What is true" is about theories.

Indeed, and we come right down to it-- I know that is your perspective, that's why I have said you are a rationalist. Quite a die-hard on at that, perhaps more so than I've ever conversed with.

 

[Hurkyl]

Indeed, and we come right down to it-- I know that is your perspective, that's why I have said you are a rationalist. Quite a die-hard on at that, perhaps more so than I've ever conversed with.

Ah, I think I know where this idea that I'm a "die-hard rationalist" came from -- you're misinterpreting formalism.

When I see heads, I don't see any inherent value in attaching any significance to that fact beyond "I saw heads". The decision^* to infer some "truth" about "reality" is just that -- a decision, and an inference -- and I intend to acknowledge both.

*: whether conscious or not

And rather important to formalism is the principle "If it looks like a duck and it quacks like a duck, it's a duck".

If some form of "anti-empiricist radical rationalism" looks like someone using experiment to gain knowledge, and it acts like someone using experiment to gain knowledge, then as far as I concerned, it is someone using experiment to gain knowledge -- and any thoughts you have on whether they are actually using experiences, or have forgotten them and replaced them with pure reason simply aren't relevant.


Ironically, this is a form of experimentalism -- if you can't show me an actual, observation difference between two things, then the only value I see in anything you have to say on the topic of contrasting them is as a matter of pedagogy.

And really, this is where I think you have empiricism dead wrong -- when faced with a conflict that experiment can't help you with, you claim that empiricism has chosen a side for you. (and, miraculously, your side happens to be the one empiricism picked)



This last point, I think, is an example of the severe harm that comes from a "it's just information" approach to QM, or any sort of "don't interpret, just compute" approach to any technical matter.

Whether you like it or not, as you use a theory you form connections and associations, you will develop abstract notions, and your intuition will develop -- but by thoroughly convincing yourself that you aren't doing those things, and have lost both the ability to guide them, and the ability to differentiate between the theory and your own beliefs and intuition.

And worse, you may have even lost the ability to correct errors in your beliefs and intuition or otherwise improve them -- "You have an argument that contradicts my intuition? Well, it's just information, I shouldn't care!"

 

[Ken G]

Ah, I think I know where this idea that I'm a "die-hard rationalist" came from -- you're misinterpreting formalism.

Anyone who promotes MWI is quite certainly a die-hard rationalist, I hardly think that's controversial.

If some form of "anti-empiricist radical rationalism" looks like someone using experiment to gain knowledge, and it acts like someone using experiment to gain knowledge, then as far as I concerned, it is someone using experiment to gain knowledge -- and any thoughts you have on whether they are actually using experiences, or have forgotten them and replaced them with pure reason simply aren't relevant.

Look, you already self-identified as a radical anti-empiricist rationalist when you said "what is true is about theories." It just doesn't get any clearer than that, why can't you accept it? Again: to the empiricist, what is true is about what is observed and measured, never what is in a theory. Period, end of story, definition of empiricism. No empiricist ever views any theory as "true", only "effective" or "useful." Deal with it, you aren't one.

Whether you like it or not, as you use a theory you form connections and associations, you will develop abstract notions, and your intuition will develop -- but by thoroughly convincing yourself that you aren't doing those things, and have lost both the ability to guide them, and the ability to differentiate between the theory and your own beliefs and intuition.

No empiricist ever had to deny "abstract notion" or "intuition", obviously. Do you think Nils Bohr had no intuition, no ability to manipulate abstract notions? That's just silly, of course he did. But he never mistook his intuition or abstract notions for what was true, he merely used them as tools to help him grasp what was true. He was a classic empiricist. Note that Richard Feynman is also what I would call a classic empiricist. In almost every situation where he is about to describe a theory, he always started with a description of the observations first. He never said, "here's the theory, and here is the observational test that proved it", he always said, "here's the observation we are trying to understand, and here is a way you can understand it." What's more, Feynman once said "A philosopher once said, 'It is necessary for the very existence of science that the same conditions always produce the same results.' Well, they don't!" Note how that is both empiricist, and anti-MWI. I guess you think Feynman had no access to intuition or abstract notions?

And worse, you may have even lost the ability to correct errors in your beliefs and intuition or otherwise improve them -- "You have an argument that contradicts my intuition? Well, it's just information, I shouldn't care!"

I find it quite ironic that you think rationalism is the escape from the limits of intuition! There is intuition based on experience, and intuition based on a belief in the aesthetics of a theory. The only thing that doesn't change is the observations.

 

[jensa]

EDIT: Upon rereading the quote below I realize that I misread/misinterpreted what you wrote and the response doesn't apply to the quote. Still the point I wanted to make stands on it's own, and I vaguely recall you writing about the interpretation of experiments in earlier posts, so I'll leave the post as it is.

Whether you like it or not, as you use a theory you form connections and associations, you will develop abstract notions, and your intuition will develop -- but by thoroughly convincing yourself that you aren't doing those things, and have lost both the ability to guide them, and the ability to differentiate between the theory and your own beliefs and intuition.

Of course you are right that the way we interpret our experimental data is based on experience, knowledge and intuition that we have slowly developed over years of studying theories. This is unavoidable. What you seem to propose is IMO something more radical. If I am being provocative, I would call it "fabricating experimental data".

Take the following example:
I pull out a coin from my pocket, flip it, and say:
"Hey look, heads came up."
You look at it and say:
"Yes it appears so. However, I know from MWI that there is a parallel universe where tails came up. Therefore, in reality, both heads and tails came up."

Here you used theory to enhance the experimental data by adding an imaginary result with tails up. You say there is no way to distinguish having made a definite observation of only heads or an indefinite observation of both heads and tails.

Now here is the turn. I ask you "Are you certain this is what reality is?" You say "Of course!". Then I turn the coin and it turns out it was a tampered coin with two heads.

Of course I cheated you by not giving you all the information*, and had you had the full information you could have constructed a theory for this case which made perfect sense. The point is that you created a "reality" based on a theory which turned out to be inaccurate. We could repeat the experiment several times and you would likely think it was weird that heads kept coming up, but it would not contradict your version of reality - we simply are part of an improbable branch. The only way to realize that your construction was wrong would be to acquire the full information (take the coin from me and examine it).
You might say that CI has similar problems - we cannot tell whether our model (a coin with both heads and tails) is wrong or not, since it could just be a fluke that we keep getting heads.
The difference is that reality in the CI interpretation is simply that we keep getting heads (observation=reality), and if our theory is wrong it doesn't change reality, contrary to your approach.

The above example illustrates the problem I have with your approach to science which I would schematically draw as:

Theory --> Observation(Interpreted to fit theory)

as opposed to the more traditional approach

Observation --> Theory(Interpreted to fit observation)* Note that when conducting experiments we never have the full information.

 

[Hurkyl]

Anyone who promotes MWI is quite certainly a die-hard rationalist, I hardly think that's controversial.

Really? You don't think that controversial? You honestly believe that nobody interested in studying the consequences of the Schrödinger equation was motivated by its fantastic empirical success? Nor that they think connecting said consequences to our observations is of the utmost importance?


Well, despite your belief, I certainly believe I am motivated by the fantastic success of the Schrödinger equation, and I certainly believe that I think connecting its consequences to observation is important. And that anyone I've seen who's serious about it appears to feel the same way.


Or... maybe I just don't know what you mean by "die-hard rationalist"? I interpret it as adhering to what I call "strict rationalism" -- that reason is the only source of knowledge. But I can't see what that has to do with MWI. (and I think it's a silly philosophical position anyways)

Look, you already self-identified as a radical anti-empiricist rationalist when you said "what is true is about theories."

Talking about truth is the act of assigning truth values to propositions, no more and no less.

You may believe there is some deep meaning beneath the act of assigning truth values to propositions, but that doesn't change the fact that that's what you're doing.

Again: to the empiricist, what is true is about what is observed and measured, never what is in a theory. Period, end of story, definition of empiricism.

This is what I would call strict empiricism -- and in this discussion I would probably call an adherent a "radical empiricist". A strict empiricist believes that observation is the only source of knowledge. I think it's just as silly of a position as strict rationalism.

As an aside, I've never figured out how a radical empiricist can adhere to his devotion to strict empiricism while still having any confidence at all in his ability to make predictions about the future.

No empiricist ever views any theory as "true", only "effective" or "useful." Deal with it, you aren't one.

Honestly, I don't care about really care about the philosophical notion of "truth". By my observation, it's only real use seems to be as a way for people to try and trump up the importance of their claims.

And I greatly lament the difficulty in actually excising it from the language.

An empiricist is someone who "creates" knowledge via experiment. A rationalist is someone who "creates" knowledge by making an inference from already-existing knowledge. A scientist needs to be both.

I bet that if you described to me what you mean by a theory being "effective" or "useful", it would look like creating knowledge through inference, and it would behave like creating knowledge through inference.

In almost every situation where he is about to describe a theory, he always started with a description of the observations first.

Honestly, I don't see what this has to do with empiricism or rationalism. This is just plain pedagogy. To educate someone on any subject, you must give them knowledge and experience applying the knowledge. Historical information is often useful as well. And you must pique their curiosity enough so they stay engaged in their education.

If the first words out of your mouth are motivated by philosophical notions of science rather than what makes for effective pedagogy, then you're doing it wrong.

I find it quite ironic that you think rationalism is the escape from the limits of intuition!

Where did this come from?

There is intuition based on experience, and intuition based on a belief in the aesthetics of a theory.

I don't believe in the latter. I don't believe in the former either if you are using "experience" to refer to empiricism.

Intuition comes from doing, and it can be created, honed, refined, corrected, and trained.

The only thing that doesn't change is the observations.

Observations change the same way theories do. e.g. new observations are always being created, and the importance attached to certain observations varies over time.

 

[Ken G]

Really? You don't think that controversial? You honestly believe that nobody interested in studying the consequences of the Schrödinger equation was motivated by its fantastic empirical success? Nor that they think connecting said consequences to our observations is of the utmost importance?

There is still a great deal of misunderstanding around the terms "empiricist" and "rationalist", and it is causing lots of problems in getting what I am saying. Here's what I mean and what I don't mean:
Empiricist:
Does mean: One who thinks that scientific reality is what is measured and observed, and that theories are used to understand, organize, and predict observations. When observations are used to test theories, that is only to judge the value of the theory, never to assert what is real-- the observations already do that all by themselves. Nature does not obey laws, but we gain power over nature by idealizing it and approximating it in terms of imperfect laws.
Does not mean: One who never avails themself of any form of abstract thinking, and thinks all theories are a complete waste of time.

Ratonalist:
Does mean:
One who thinks that scientific reality is what scientific theories can say about reality, because access to knowledge comes from thinking about reality, from conceptualizing it, from making sense of it. Of course rationalists don't stare at blank walls, they avail themselves of experimental outcomes, but only as a guide to finding the correct theory that describes the truth. Observations exist only to motivate and test theories, nature obeys perfect laws, observations are imperfect approximations to what is really going on.
Does not mean:
One who is disinterested in experimental outcomes, or anything else you just said.

Well, despite your belief, I certainly believe I am motivated by the fantastic success of the Schrödinger equation, and I certainly believe that I think connecting its consequences to observation is important.

Actually, I never said anything of the kind, you are imagining a strawman every time I mention the differences between rationalism and empiricism. It is perfectly obvious to me that you are impressed by the empirical success of Schroedinger's equation, and it is also perfectly obvious to me that you are a die-hard rationalist (see the above definitions).

Or... maybe I just don't know what you mean by "die-hard rationalist"? I interpret it as adhering to what I call "strict rationalism" -- that reason is the only source of knowledge.

Yes, that is not what I mean by a die-hard rationalist, there really haven't been anyone who thinks like that for a long time, certainly not any scientist. Next to Parmenides, you might be considered empiricist it's true, but Parmenides was no scientist (he would have loved MWI though). Nobody today thinks that knowledge can be achieved only by rational thought, it must be informed by observations. The axis that distinguishes scientific rationalism from scientific empiricism is simply the arrow of logic that is used, much like the arrows that jensa gave above. To sum up:
scientific rationalist: theory is truth, observations are only needed to help adjudicate between theories.
scientific empiricist: observations are truth, theories are only needed to help unify and predict observations.
So when I mean "die-hard", I don't mean off the scale, I just mean at the far end of the scale where it is fair game to reinterpret the observations to make the theory seem correct (like saying that observed outcomes are still mixed states even after they are registered). If one starts with the theory, then MWI works fine-- the theory passes the observational tests, so any interpretation of that theory is valid, so the rationalist may choose the most rationalist interpretation. If one starts with the observations, then the MWI doesn't make sense right from the get-go. Remember, if one starts with the observations, there isn't even any theory yet, and there is no need for a theory to say what reality is-- the observations do that already. The theory comes in only later, to understand the reality, not to dictate a new reality. The latter is rationalistic.

Talking about truth is the act of assigning truth values to propositions, no more and no less.

That's just a tautological connection, essentially defining "assigning truth values." It doesn't say what truth is regarded as.

This is what I would call strict empiricism -- and in this discussion I would probably call an adherent a "radical empiricist". A strict empiricist believes that observation is the only source of knowledge. I think it's just as silly of a position as strict rationalism.

I agree-- one can be too radical of an empiricist. For one thing, almost any observation requires some degree of interpretation to be considered a measurement. So one must always temper empiricism with some rationalistic thinking, but one must not generate a rationalistic world view and deny doing it.

As an aside, I've never figured out how a radical empiricist can adhere to his devotion to strict empiricism while still having any confidence at all in his ability to make predictions about the future.

Yes, it is certainly a rationalistic principle that future events will act like past ones did. To the strict empiricist, physics does not predict the future, it predicts past events before they happened. Living one's life as if the future were predictable is both an important survival trait, and rationalistic in nature. But it's a very weak amount of rationalistic tempering-- the strict empiricist will simply say that the only reason they expect future events to play out like past ones did is because of the empirical fact that this has been true in the past-- past predictions worked, so it is empirically supported to predict the future. Since the rationalist thinks nature obeys laws, they might imagine it is a rationalist principle that the future should play out like the past, but the empiricist counters that if observations showed the laws changed, the rationalist would simply seek a law of how laws change.

Honestly, I don't care about really care about the philosophical notion of "truth". By my observation, it's only real use seems to be as a way for people to try and trump up the importance of their claims.

Methinks thou doth protest too much. Do you or do you not think MWI is "true"?

And I greatly lament the difficulty in actually excising it from the language.

I actually agree with you here-- I don't think human intelligence has anything like access to truth. I just think we are safer from fooling ourselves if we adopt empiricism, because the observations don't change. I love Feynman's definition of science-- a way of not fooling ourselves, given that we are the easiest ones to fool.

An empiricist is someone who "creates" knowledge via experiment. A rationalist is someone who "creates" knowledge by making an inference from already-existing knowledge. A scientist needs to be both.

I agree, I would simply add that a scientist also needs to not take their own concept of truth too seriously. It's always just going to be a stage in a very long process of enlightenment, one that most likely never reaches a final destination. That's why I don't believe in using science to build world views that go beyond what we actually observe to be elements of the world, it just seems too futile to me.

I bet that if you described to me what you mean by a theory being "effective" or "useful", it would look like creating knowledge through inference, and it would behave like creating knowledge through inference.

Yes it would-- the knowledge would be that the theory works, it serves its purpose to unify and understand observations. But it would not look like building a world view that falls apart if the theory breaks down two decimal places past where we have ever tested it. It would not look like MWI.

Where did this come from?

It comes from the fact that you keep painting the rationalistic perspective, such as the one that supports MWI, as the way to keep from falling into closed-minded thinking. But rationalism is always a form of closed-minded thinking, because it always comes from a place where the postulates of some theory are regarded as actually true. Not just useful, not just approximate, but true. What is MWI if the postulates of QM are not true? So that's the source of closedmindedness, right there. Empiricism is never a source of closedmindedness-- the observations don't change, no one ever had to shake themselves loose from some observed body of knowledge. But plenty of times, they had to shake themselves loose from some accepted set of postulates that made it almost impossible for them to think any differently!

Observations change the same way theories do. e.g. new observations are always being created, and the importance attached to certain observations varies over time.

Ah, but a new observation is not changing or replacing an old one! A new theory is.

 

[Hurkyl]

Methinks thou doth protest too much. Do you or do you not think MWI is "true"?

I think decoherence-based interpretations are the superior to collapse-based interpretations for understanding quantum mechanics. Among those, MWI appears to be the most promising approach for understanding the quantum-classical interface -- but that purpose does remain conjectural until quantum thermodynamics is sufficiently well-developed.

Also, I suspect that the MWI has more ways to fail than the CI. Since it hasn't failed, that would imply MWI enjoys a greater share of empirical support than CI.

Insomuch as one uses science to understand reality, MWI seems to be the understanding that QM tells us.

 

[Dmitry67]

Ken G, I am curious, how do you classify MUH (Mathematical Universe Hypotesis) - as radical platonism?

 

[Ken G]

I think decoherence-based interpretations are the superior to collapse-based interpretations for understanding quantum mechanics.

All interpretations are fully consistent with decoherence, there is no such thing as a decoherence-based interpretation! Decoherence is just quantum mechanics, it is all over well before there is any need for an interpretation. The intepretations serve a strictly ontological function, essentially choosing what to make of the mixed states when they get perceived. None of that has anything to do with decoherence, because decoherence is what creates the mixed substates, not what collapses them. The idea that decoherence is somehow an alternative to collapse is just plain wrong, the two are completely separate.

Among those, MWI appears to be the most promising approach for understanding the quantum-classical interface -- but that purpose does remain conjectural until quantum thermodynamics is sufficiently well-developed.

This will have to serve as our point of agreement then: "the MWI is conjectural." I can live with that.

Also, I suspect that the MWI has more ways to fail than the CI. Since it hasn't failed, that would imply MWI enjoys a greater share of empirical support than CI.

That is a completely unsupported claim. Since you have never suggested any predictions that are any different in MWI than CI, I hardly see how either can claim more empirical support. However, CI is motivated by empiricism, which is saying something different.

Insomuch as one uses science to understand reality, MWI seems to be the understanding that QM tells us.

Again, only if one is a rationalist. If one uses science to understand reality the way an empiricist does (i.e., by adopting empiricist axioms like "reality is what we measure"), then MWI is rejected immediately as anti-axiomatic.

 

[Ken G]

Ken G, I am curious, how do you classify MUH (Mathematical Universe Hypotesis) - as radical platonism?

Yes, I think there is no question at all that this is an example of radical platonism. It is also quintessentially rationalistic, and highly anti-empiricist. (Hurkyl: that doesn't at all mean it ignores observations, the distinction is that Tegmark is constructing a theory that is not ruled out by observations, whereas empiricists begin with the observations and allow the observations to dictate, not the set of all things that could be, but rather what is.)

In my view, it is a wonderfully provocative idea, but it is entirely based on a cheat, which is the same cheat that is evident when invoking the anthropic principle as an explanatory agent-- the idea that if a rationalist can assert a principle that is neither suggested by observations, nor ruled out by them, and has few or no free parameters associated with the assertion, then the assertion is good science. I can give an assertion like that right now: "everything that happens is the will of an almighty, and that will includes everything we can possibly imagine, just in some other worlds if necessary." Done, no free parameters, not contrary to any observations.

 

[Dmitry67]

Ken G, So you completely deny the role of mathematical beauty in physics?
What if we find TOE equations - so beautiful, being able to explain everything, but almost impossible to prove because near-Plancks energies would be required?

 

[Ken G]

Ken G, So you completely deny the role of mathematical beauty in physics?

Er, how do you get that? If I said that a world view that held that everything that has ever been painted depicts something that really happened is "radical", you'd say I was denying the role of beauty in art?

What if we find TOE equations - so beautiful, being able to explain everything, but almost impossible to prove because near-Plancks energies would be required?

Unification of the observations we have is always the goal of theory.

 

[Dmitry67]

Because if you base everything on observations/experiments, you always get just a reflection of the underlying mathematical reality, and the beauty of equations will be always spoiled by measurement errors and noise.

And even with very precise measurement, you won't be able to chose between 2 versions of a theory:

A. World = BeautifulFormula()

and

B. World = BeautifulFormula() + s*UglyAddition()

if small value of s makes the value of UglyAddition() beyond measurement.

 

[Hurkyl]

All interpretations are fully consistent with decoherence, there is no such thing as a decoherence-based interpretation! Decoherence is just quantum mechanics, it is all over well before there is any need for an interpretation.

Consistent with decoherence is not the same thing as being decoherence-based. On the topic of the quantum-classical interface:

• A collapse-based interpretation roughly says that quantum states collapse into a pure"eigenstate", which we see in the classical realm as a non-parm state.
• A decoherence-based interpretation roughly says that quantum states decohere into a mixture of "eigenstates", which we see in the classical realm as a parmstate.
  
  This classification is independent of other features, such as the collapse-based question^* of just information (a wave-function is just a new way to encode ignorance that can't be thought of as a set of possibilities!) versus something real (there's some new physics to discover that violates unitary evolution to produce non-parmness in the limit).
  
  *: I'm not sure I believe the two answers to this question are actually different in any relevant way
  
  Bohm, I think, is a "new physics" interpretation on the decoherence-based side (but one that actually exists rather than being hypothetical), with the interesting feature of retaining the parmness of the quantum state, but couching observations in terms of non-parm Bohmian particles.
  
  

  That is a completely unsupported claim.

  Hence "suspect". The motivation for my suspicion is that MWI will be falsified if observations are made that cannot be explained as unitary evolution of a larger system.

  (i.e., by adopting empiricist axioms like "reality is what we measure"), then MWI is rejected immediately as anti-axiomatic.

  I'm thoroughly unconvinced that sharing your prior philosophical biases about "what we measure" is a requirement for being an empiricist or for adopting axioms like "reality is what we measure".
  
  Show me a derivation of "there are no parmstates" from the hypothesis "reality is what we measure".

 

[Hurkyl]

There is still a great deal of misunderstanding around the terms "empiricist" and "rationalist", and it is causing lots of problems in getting what I am saying. Here's what I mean and what I don't mean:

Let me describe another position. (actually, positions on at least two different topics are being combined)

Knowledge is a repository of propositions one has acquired over time and has ascribed levels of confidence to. The role of observation is as a method of inference -- it is a means of producing a piece of knowledge. The role of reason is also as a method of inference -- combining pieces of knowledge together to produce a new piece of knowledge. (Also, to create new pieces of knowledge in the form of tautologies)

Science ascribes particular importance to Bayesian inference (or similar) -- when we obtain a new piece of knowledge X, it adjusts our confidence in other pieces of knowledge Y based on our confidence in the knowledge "Y implies X".

Nature is said to obey laws in the practical sense that we have confidence in knowledge of predictions about what will be seen 'in nature'.

One major role of theory is to provide for the ideas and concepts we use to think about things -- especially[/i] on topics we can't expect to have confidence in our intuition.

Another major role of theory is to provide a means to translate our intuition into forms we can reason with.

 

[Ken G]

And even with very precise measurement, you won't be able to chose between 2 versions of a theory:

A. World = BeautifulFormula()

and

B. World = BeautifulFormula() + s*UglyAddition()

if small value of s makes the value of UglyAddition() beyond measurement.

We can all agree on what attributes we are looking for in theories-- even empiricists. But we don't always agree on how to interpret those theories-- an interpretation is already an "ugly addition" to any theory, but we need them because "shut up and calculate" really just doesn't cut it.

 

[Ken G]

Consistent with decoherence is not the same thing as being decoherence-based. On the topic of the quantum-classical interface:

• A collapse-based interpretation roughly says that quantum states collapse into a pure"eigenstate", which we see in the classical realm as a non-parm state.
• A decoherence-based interpretation roughly says that quantum states decohere into a mixture of "eigenstates", which we see in the classical realm as a parmstate.

• But it is purely your own claim that your approach is "decoherence based." I see no evidence for it-- I think CI is completely "decoherence based" because the entire purpose of an observation, from the CI perspective, is to achieve decoherence. Perception of the outcome comes later, but it is also an essential part of interacting with our reality (imagine the football game where the referee tosses the coin but no one looks at it-- "red team calls heads, it's a mixed state, game cancelled." The empiricist says, if you try to decohere something to gain information about it, and if every time you do that you also get a collapse, then the "decoherence based" interpretation is to conclude that collapse is a natural consequence of perceiving decoherence. But either way, collapse is certainly something separate from decoherence, because it only appears when you add the concept of perception to the concept of decoherence.
  
  I view the decoherence as already having happened by the time we perceive the outcome, and it is only that perception that requires an interpretation, so I don't see any interpretations as having anything in particular to do with decoherence-- including MWI.

  This classification is independent of other features, such as the collapse-based question^* of just information (a wave-function is just a new way to encode ignorance that can't be thought of as a set of possibilities!) versus something real (there's some new physics to discover that violates unitary evolution to produce non-parmness in the limit).

  I'm not sure what you are saying here, but it sounds like something I agree with-- I agree with that first characterization of the wave function, and I find it highly likely that there is indeed some new physics to discover that will reveal unitarity as only nearly unbroken. It's nearly unbroken status will explain why QM works, and breaking it will explain the collapse, but to get there, we need to understand what perception is. Or maybe, by getting there, we will finally figure out what perception is.
  

  Bohm, I think, is a "new physics" interpretation on the decoherence-based side (but one that actually exists rather than being hypothetical), with the interesting feature of retaining the parmness of the quantum state, but couching observations in terms of non-parm Bohmian particles.

  I view Bohm's approach as angels on a different pin. The problem is how to retain determinism (instead of just chucking it as CI does), and the price is those angels-- MWI's angels are those other worlds, which maintain the deterministic evolution of the unitary state (and ultimately saying that closed systems don't change at all, Parmenides would be proud) but are not observed (you claim they are, I say that shows you are not at all an empiricist). Bohm's angels are the unknowable elements of the "initial condition" that determine the outcomes which we, not having access to the unknowable information, see as probabilistic.
  
  The three interpretations are really all a question of what you are distributing over (I'm reminded of Bob Dylan's lyrics: "it may be the devil, or it may be the lord, but you got to serve somebody."). CI distributes over identical trials of the same experiment. MWI distributes over observers in the many worlds. Bohm distributes over unknowable information in the initial condition. Perhaps Bob would put it, "it may be the experiments, or it may be the observers, but you got to distribute over something." Three interpretations, three distributions, all the same physics-- the only thing that changes is the world view they inspire. Maybe we just shouldn't use physics theories to inspire world views in the first place!
  

  Hence "suspect". The motivation for my suspicion is that MWI will be falsified if observations are made that cannot be explained as unitary evolution of a larger system.

  All interpretations of QM will be falsified if QM is falsified, but we'll feel less silly if we didn't build a world view around it first.
  

  I'm thoroughly unconvinced that sharing your prior philosophical biases about "what we measure" is a requirement for being an empiricist or for adopting axioms like "reality is what we measure".
  
  Show me a derivation of "there are no parmstates" from the hypothesis "reality is what we measure".

  Simple: we don't measure parmstates, we measure eigenvalues that associate with eigenstates. You keep saying that doesn't prove there aren't parmstates, but that's not what I said.

 

[Ken G]

One major role of theory is to provide for the ideas and concepts we use to think about things -- especially[/i] on topics we can't expect to have confidence in our intuition.

Another major role of theory is to provide a means to translate our intuition into forms we can reason with.

I agree with every single thing you said in that post, and not a word of it adjudicates between MWI and CI. That is simply because not a word of it is controversial for either a rationalist or an empiricist. The key issue you didn't address is at the crux of the matter: how seriously do you take those concepts as you are using them in the ways you state. Tegmark, as complete a rationalist as can possibly exist, takes them so seriously as to flat out assert that the concepts spawn realities, rather than the other way around (the empiricist view). If you will take MWI as your world view, then Tegmark is your oracle, and how this cannot make crystal clear the difference between rationalism and empiricism I just don't get. I think you are a dyed-in-the-wool rationalist who for some reason hesitates to self-identify as such. It isn't a bad word, though I admit I have been critical-- I have no doubt that Tegmark's contributions to human thoughts about reality will leave a far more lasting mark than any of mine will, even if just as a warning of what can happen if one goes a bit overboard on rationalism!

 

[Hlafordlaes]

Ken G... But either way, collapse is certainly something separate from decoherence, because it only appears when you add the concept of perception to the concept of decoherence.

I view the decoherence as already having happened by the time we perceive the outcome, and it is only that perception that requires an interpretation, so I don't see any interpretations as having anything in particular to do with decoherence-- including MWI.

Hi, Ken G, if you get a chance to digress for a sec can you go on about these two paragraphs a bit? Not sure I get it. Actually, I am sure I do not!

If, as from http://en.wikipedia.org/wiki/Quantum_decoherence" : "Decoherence occurs when a system interacts with its environment in a thermodynamically irreversible way," what more is needed for collapse to be said to also occur? And if as you say decoherence has already happened prior to perception, then how is perception required to explain collapse?

I mean, what's going on here?

 

[Ken G]

Hi, Ken G, if you get a chance to digress for a sec can you go on about these two paragraphs a bit? Not sure I get it. Actually, I am sure I do not!

If, as from http://en.wikipedia.org/wiki/Quantum_decoherence" : "Decoherence occurs when a system interacts with its environment in a thermodynamically irreversible way," what more is needed for collapse to be said to also occur? And if as you say decoherence has already happened prior to perception, then how is perception required to explain collapse?

I mean, what's going on here?

Irreversibility is a weird subject, to be sure. If you watch a movie in which 100 coins, variously heads and tails, are lying on a platform, and the platform jumps up suddenly and sends the coins to flipping, and they all settle on "heads", you are quite likely going to conclude you are watching a movie run backward. If there are 1000 coins, even more certain will you be. But why is this? The actual state you observed, before the "all heads" state, is no more or less likely than all heads, if you distinguish each of the coins individually. So you are watching a movie in which one incredibly unlikely state flips into another equally incredibly unlikely state, so how do you know the movie is being run backward?

All the same, I'll bet if you actually do see that, then indeed the movie will have been run backward. The reason has to do with how difficult it is to get a configuration of all heads in any way but manually, whereas any state of various combinations of heads and tails will serve as the final state of the flips, for making a movie like that. There is something "non-generic" about all heads, stemming from the smallness of the information we need to specify that state (two words!). So the irreversibility of the movie stems entirely from the information content, because there is a connection between the amount of information you need to describe the state, and the number of states belonging to the class that can be described with that much information (the former is the natural log of the latter).

So where does this leave collapse? Well, there's the rub-- the nature of information in quantum mechanics is very much what is being disputed in this thread. In MWI, any closed system is a stationary state (it matters little if it is treated as a mixture of stationary states, they're independently stationary because their relative phase is not defined), so there is no such thing as either reversibility or irreversibility. But that's because the information there is not extractable. In CI, or an empiricist approach, we do have access to information about subsystems with which we interact, so we can define a concept of irreversibility. Decoherence will appear to involve extracting information if we ignore the coherences that persist-- so in that interpretation, "decoherence" means "we no longer care about the coherences", more so than the "coherences are really gone." But in MWI, those coherences are still there-- the decoherence is an artifact of the projection onto the substate, the whole closed system is still stationary and has zero entropy at all times.

Bottom line: the Wiki entry is from the CI standpoint, and there, taking a subsystem in an initially pure state, and decohering it by attaching it to a measuring device, is irreversible-- the resulting mixed state has more entropy than the original pure state, whereas the entropy of the measuring device is not treated separately from what it measures. But perceiving the definite outcome, which is what I mean by "collapse", returns the state to one of zero entropy. The reduction in entropy can happen because the act of perception includes increased entropy in the observer.

 

[Dmitry67]

an interpretation is already an "ugly addition" to any theory, but we need them because "shut up and calculate" really just doesn't cut it.

This is true for any interpretation except MWI. MWI is NULL interpretation, all wordy stuff in it is just an explanation (for humans) that no extra stuff is needed and pure QM math is enough. This is the only interpretation compatible with MUH.

 

[Hurkyl]

But it is purely your own claim that your approach is "decoherence based."

To the best of my knowledge, "collapse-based interpretation" and "decoherence-based interpretation" are standard phrases in the taxonomy of interpretations. I'm 99% sure I didn't invent the terms.

I see no evidence for it-- I think CI is completely "decoherence based" because the entire purpose of an observation, from the CI perspective, is to achieve decoherence.

But the distinguishing point is that you don't interpret the resulting mixed state as referring to a parmstate, but instead interpret it as expressing ignorance.

I'm not sure what you are saying here,

I believe my intent was to preempt some response I had imagined was possible. But I'm glad I made it because of your response.

and I find it highly likely that there is indeed some new physics to discover that will reveal unitarity as only nearly unbroken. It's nearly unbroken status will explain why QM works, and breaking it will explain the collapse, but to get there, we need to understand what perception is. Or maybe, by getting there, we will finally figure out what perception is.

This touches on the underlying motivation that I think drives many CI devotees -- and is one of the aspects associated with CI that I have the most contempt for. I feel like people are effectively saying:

I don't like quantum mechanical view, so I will try my best to make do with pre-quantum views until the next scientific theory comes along, which I tacitly hope with be more palatable.​

For the record, I think "QM-style theories keep working all the way up", "new physics that produces collapse and works all the way up" and "new physics diverges even further from the classical intuition but works all the way" are all perfectly good outcomes.

As an aside, doesn't this position essentially boil down to "I think that QM is explained by a hidden-variable theory?" It's been a while since I thought about this matter -- isn't the known problems with hidden-variable theories a rather serious blow to the prospects of this position?

we'll feel less silly if we didn't build a world view around it first.

You keep saying this. But why should we feel silly?

Making mistakes is normal. And even if you put a lot of effort into something that ultimately turns out to be in error, you can still usually salvage lots of useful stuff.

And even if it turns out that a quantum mechanical world view would need to be discarded 25 years down the road, so what? You're almost surely better off having used a quantum mechanical world view for those 25 years than you would have been struggling along with a pre-quantum world view.

(And, of course, your pre-quantum world view might not be useful at all for the next theory after quantum mechanics!)

Simple: we don't measure parmstates, we measure eigenvalues that associate with eigenstates.

As far as I can tell, the observed eigenvalue is parm.


Remember, Einstein said "make the theory as simple as possible -- but no simpler!" Rejecting parmstates makes things too simple, because parmstates are needed to fully evaluate how QM connects to observation.

 

[Fyzix]

This is true for any interpretation except MWI. MWI is NULL interpretation, all wordy stuff in it is just an explanation (for humans) that no extra stuff is needed and pure QM math is enough. This is the only interpretation compatible with MUH.

I just can't let this blatant lie fly..
There is no way to get the Born rule in the math
There is no way to get a preferred basis in the math, the math does NOT give you a branching structure.
Decoherence is not enough to explain branching...

Also as for your MUH, not even David Deutsch supports it.

Also it blows my mind that you make the error of not even understanding that whatever the true theory underlying QM is, it will have the correct math, that's just logic 101.
As for MWI we know it does not have the right math.
So it is INCONSISTENT with MUH.

 

[Dmitry67]

Lets not start it over again. Born rule had been derived by Max Tegmark.
And please don't confuse people with your misconceptions. MWI does not have any math except the one QM and Decoherence provide. If you don't agree, provide any 'MWI-specific formula'

 

[Dmitry67]

I just have my opinion. Having an opinion does not mean 'trying to believe desperately in something'. You have a different opinion, which is normal, but please stop injecting into thread the emotional stuff, telling me what I should 'desperately' do.

As you did not reply to my question in your post above (good example of what Max Tegmark calls 'word baggage' - mostly it contains names you want to hide behind), I have to repeat it and to add another one.

1. Please provide any 'MWI-specific' formula which does not exist neigher in standard QM nor in the derivation of the Qunatum Decoherence. Formula does mean formula, not a wordy stuff.
2. Please name the 'additional postulates' of MWI (except the Born riule, which is derived by Max Tegmark). To be specific, 'postulate' is an axiom, which can't be derived from the theory. For example, Quantum Decoherence is not an axiom.

Frankly, I don't expect any answers, except 'In my private conversations with Deutsch, Wallace, Newton and Einstein they all had mentioned that they hated MWI' :)

 

[Fyzix]

I literally JUST TOLD YOU which postulates YOU have to come up with.
That's not my job...

No Born Rule is not derived by Tegmark, at best with his additional infinite universe(+1 postulate) he MIGHT have managed to get the Born Rule within that speculative picture.
So no and even if you want to keep insisting on it, it added a additional postulate to achieve it. (although I realize that you probably don't have anything against postulating infinity when u already accept MUH).

As for "private conversations", yes I have had them with both Deutsch and Wallace, but both are strong adherents of MWI, I have never said anything else.
If you want Deutsch's newest thoughts on the matter read his book and then read this critical review of his book: http://physicsworld.com/cws/article/indepth/47021 which shows how it reintroduces the preferred basis problem and still haven't solved the Born Rule.

As for Wallace he keeps changing axioms to get the Born Rule in his decision theoretic approach and he constantly changes the whole ontology of his MWI.
He has some vague "emergence" assumptions, but Maudlin has pointed out why this doesn't work.
Which you can read in the Many Worlds? book or Maudlin's new book.

Zeh openly says he postulate the Born Rule (read the papers on his site)

 

[Dmitry67]

Thank you for mentioning 'infinite universe' - yes, sure, it is an additional postulate, and it was my mistake for not mentioning it. Our universe is nearly flat and current observations can't tell us if it is finite or infinite. However, that postulate sounds very reasonable for me for the reasons of mathematical beauty, also described by Max Tegmark in his work.

So I think it is much easier to accept the 'Infinite Universe' and to derive the Born Rule postulate than postulate to the Born Rule explicitly.

Do you know if Wallace or Zeh have any motivation for not accepting the derivation by Max Tegmark?

 

[Fyzix]

Thank you for mentioning 'infinite universe' - yes, sure, it is an additional postulate, and it was my mistake for not mentioning it. Our universe is nearly flat and current observations can't tell us if it is finite or infinite. However, that postulate sounds very reasonable for me for the reasons of mathematical beauty, also described by Max Tegmark in his work.

So I think it is much easier to accept the 'Infinite Universe' and to derive the Born Rule postulate than postulate to the Born Rule explicitly.

Do you know if Wallace or Zeh have any motivation for not accepting the derivation by Max Tegmark?

Well then atleast you admit that it is a additional postulate and then we can agree, that maybe indeed Tegmark can succesfully derive the Born Rule within that model.

I'm not sure about Wallace, but seeing as he has been working on the decision-theoretic approach the last decade I think he is pretty much convinced that approach is the right one.
As for Zeh I don't think it would be right to publish his personal correspondence on a public forum like this, but mainly he objected to it due to the fact that it rests on the assumption of infinity.

 

[Hurkyl]

I have seen NOONE else endorse this approach and everyone I have asked (even prominent MWI'ers) say that the approach is flawed.

The specific section on the confusion operators and deriving the frequentist limit is a good one. When I figured it out on my own a few years back, I was given the impression that the argument was already old hat then. It's the rest of the paper that's 'weird', trying to recast QM as an ensemble over repetitions in an infinite universe.

 

[Ken G]

This is true for any interpretation except MWI. MWI is NULL interpretation, all wordy stuff in it is just an explanation (for humans) that no extra stuff is needed and pure QM math is enough.

MWI is only a null interpretation if you adopt a rationalist perspective, that is what I keep pointing out. The rationalists on this thread just don't seem to get emiricism, to the extent they don't even recognize the other possibility so make claims like "MWI is a null interpretation." I can only repeat: in empiricism, the purpose of an observation is not to check a theory, but to establish what is true. Thus, it is the purpose of a theory to make sense of the observation. If the theory has to postulate "other worlds" that are not observed to make sense of the observations, it has overstepped its authority and is now asserting what is true. Observations do that, only.

This is the only interpretation compatible with MUH.

In my view, MUH completely removes any importance in MWI. MUH asserts the existence of any world that is describable mathematically, so the "many worlds" of MWI are now completely superfluous, as they are "just more" worlds that can be described mathematically, and have no more connection to our observations than mathematical theories which clearly don't agree with our observations (but exist in "some other world"). MUH is where MWI goes to die.

 

[Hurkyl]

If the theory has to postulate "other worlds" that are not observed to make sense of the observations, it has overstepped its authority and is now asserting what is true. Observations do that, only.

Wonderful. I just flipped a coin, and my observation was parm -- I saw heads.

What? My observation was not parm? What did you observe to tell you that? Oh, there wasn't an observation that told you that?

If a theory has to postulate repeated collapses to make sense of observations, it has overstepped its authority and is now asserting what is true. Observations do that, only.

 

[Fyzix]

Hurkyl: do you really believe in MWI or are you playing "Devil's Advocate" ?

 

[Hurkyl]

By the way, have you yet encountered the paradox of grue and bleen? (the following story is mine)While out for a walk on the morning of December 22, 2013, you notice a large congregation of space aliens in the park. Curious, you go to investigate and ask one what's going on.

Alien: "Oh, your planet is about to experience an interesting phenomenon! The sky and ground are going to swap colors! Aren't you excited?"

You: "Swap colors? What do you mean?"

Alien: "It's the darnedest thing! Your sky is bleen and your grass is grue, but at noon today they'll swap -- your sky will be grue and your grass will be bleen! You have such wonders on your planet."

You: "Grue? Bleen?"

Alien: "Oh, that's right. I heard you have some weird colors... blue and green, I think. I heard your blue color is normally our bleen, but at until noon today, your blue color switches to grue. And conversely for green. Where did you ever get such a strange notion of color anyways? Weird coincidence that your colors switch the same time the sky and ground swap colors. Oh well, I've got to get a good spot to watch the change!"

 

[Hurkyl]

Hurkyl: do you really believe in MWI or are you playing "Devil's Advocate" ?

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