Comments on: Foundational Questions in the Azores II: Limiting frequency arguments for the Born rule in Many Worlds http://winephysicssong.com/2009/09/02/foundational-questions-in-the-azores-ii-limiting-frequency-arguments-for-the-born-rule-in-many-worlds/ Howard Barnum's blog on art, music, culture, science, public affairs, philosophy, and life Mon, 07 May 2012 17:33:51 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: howard http://winephysicssong.com/2009/09/02/foundational-questions-in-the-azores-ii-limiting-frequency-arguments-for-the-born-rule-in-many-worlds/comment-page-1/#comment-1634 howard Fri, 06 Jan 2012 17:55:19 +0000 http://winephysicssong.com/?p=83#comment-1634 David, I think I'm about as close to a decision on the viability of the MWI now as I was when I wrote that post---I'm strongly inclined to believe it's not viable. The difficulty of using it as a guide to action, because of the difficulty of introducing probabilities, is still my main technical objection. However, and relatedly, I have doubts about the viability of notions like "the wavefunction of the universe". But this is partly because I view the wavefunction, or density matrix, as a description of probabilities of observations, and don't necessarily see room for an observer outside the universe, whose potential observations the wavefunction of the universe would ascribe probabilities to. That's hardly a knockdown independent argument against many-worlders, who won't share its premise. Some of my more general thoughts on this can be found in <a href="http://pirsa.org/09100091/" rel="nofollow">this rather informal lecture</a> from a conference on the quantum state at Perimeter Institute a couple of years back (note that the abstract is misleading, though). I've been meaning for many years to write up my views on the current versions of the David Wallace / David Deutsch type "quantum decision-theoretic" arguments for probability assignment in many worlds, which are the strongest ones, in my view, although I am not convinced by them. But I haven't yet done so. <a href="http://arxiv.org/abs/1003.4555" rel="nofollow">A paper of mine</a> (also rather informal, and not submitted anywhere else) that took off from this lecture, though with even less focus on many worlds, has some more of my thoughts on the nature of the quantum state. David, I think I'm about as close to a decision on the viability of the MWI now as I was when I wrote that post---I'm strongly inclined to believe it's not viable. The difficulty of using it as a guide to action, because of the difficulty of introducing probabilities, is still my main technical objection. However, and relatedly, I have doubts about the viability of notions like "the wavefunction of the universe". But this is partly because I view the wavefunction, or density matrix, as a description of probabilities of observations, and don't necessarily see room for an observer outside the universe, whose potential observations the wavefunction of the universe would ascribe probabilities to. That's hardly a knockdown independent argument against many-worlders, who won't share its premise. Some of my more general thoughts on this can be found in this rather informal lecture from a conference on the quantum state at Perimeter Institute a couple of years back (note that the abstract is misleading, though). I've been meaning for many years to write up my views on the current versions of the David Wallace / David Deutsch type "quantum decision-theoretic" arguments for probability assignment in many worlds, which are the strongest ones, in my view, although I am not convinced by them. But I haven't yet done so. A paper of mine (also rather informal, and not submitted anywhere else) that took off from this lecture, though with even less focus on many worlds, has some more of my thoughts on the nature of the quantum state.

]]> By: David http://winephysicssong.com/2009/09/02/foundational-questions-in-the-azores-ii-limiting-frequency-arguments-for-the-born-rule-in-many-worlds/comment-page-1/#comment-1601 David Mon, 12 Dec 2011 08:28:27 +0000 http://winephysicssong.com/?p=83#comment-1601 Hello, A very interesting post! Too bad you haven't written any continuation of this subject. Have you come any closer to a decision on wheter you think MWI is viable or not? Also do you feel that the probability/Born rule issue is the *only* issue of MWI or do you find any of the other aspects technically problematic? Hello,

A very interesting post!
Too bad you haven't written any continuation of this subject.

Have you come any closer to a decision on wheter you think MWI is viable or not?
Also do you feel that the probability/Born rule issue is the *only* issue of MWI or do you find any of the other aspects technically problematic?

]]> By: howard http://winephysicssong.com/2009/09/02/foundational-questions-in-the-azores-ii-limiting-frequency-arguments-for-the-born-rule-in-many-worlds/comment-page-1/#comment-1009 howard Fri, 20 Aug 2010 17:33:46 +0000 http://winephysicssong.com/?p=83#comment-1009 Peter, sorry for the delay in replying. I do think there is a problem with just taking the Born rule as an axiom in the MWI, because in the MWI there aren't definite outcomes to ascribe probabilities to. At least, most of the things we usually view as definite measurement results, and ascribe probabilities to, when we use quantum theory, aren't events according to the MWI---they are, roughly, components of the wavevector in some decomposition of the Hilbert space into orthogonal subspaces. From my point of view, the only way to reasonably interpret an axiom about what the probabilities are is that it is making a statement about *how we should choose* between alternatives. I suppose one could take the point of view that the MWI is something like the statement that "reality is the statevector, and when confronted with a choice between two different superpositions, you should choose between them as if you were choosing between lotteries with these probabilities (i.e., norms of the components of psi in the subspaces in which things differ in ways we care about). But for me, much of the meaning of a physical theory's account of "how reality is" is in how it provides a guide to action. So on this account of the MWI, the "reality" is more than just the statevector: both the statevector, and the Born-rule prescription for deciding between superpositions, get into the nature of reality. In which case I have serious trouble distinguishing it from a more "Quantum Bayesian" view of QM---in which what it has to say about reality is encompassed by the decision rule, but with a view that the definite outcomes become real---the superposition is not the reality. There does seem to be a stated distinction: MWI'ers, "the statevector is real", QBists, "the outcomes are real, the statevector isn't". But it almost seems to be a distinction with no practical implications. That's a bit too short of a reply, I know, but my thoughts on this aren't completely settled. Peter, sorry for the delay in replying. I do think there is a problem with just taking the Born rule as an axiom in the MWI, because in the MWI there aren't definite outcomes to ascribe probabilities to. At least, most of the things we usually view as definite measurement results, and ascribe probabilities to, when we use quantum theory, aren't events according to the MWI---they are, roughly, components of the wavevector in some decomposition of the Hilbert space into orthogonal subspaces. From my point of view, the only way to reasonably interpret an axiom about what the probabilities are is that it is making a statement about *how we should choose* between alternatives. I suppose one could take the point of view that the MWI is something like the statement that "reality is the statevector, and when confronted with a choice between two different superpositions, you should choose between them as if you were choosing between lotteries with these probabilities (i.e., norms of the components of psi in the subspaces in which things differ in ways we care about). But for me, much of the meaning of a physical theory's account of "how reality is" is in how it provides a guide to action. So on this account of the MWI, the "reality" is more than just the statevector: both the statevector, and the Born-rule prescription for deciding between superpositions, get into the nature of reality. In which case I have serious trouble distinguishing it from a more "Quantum Bayesian" view of QM---in which what it has to say about reality is encompassed by the decision rule, but with a view that the definite outcomes become real---the superposition is not the reality. There does seem to be a stated distinction: MWI'ers, "the statevector is real", QBists, "the outcomes are real, the statevector isn't". But it almost seems to be a distinction with no practical implications. That's a bit too short of a reply, I know, but my thoughts on this aren't completely settled.

]]> By: Peter http://winephysicssong.com/2009/09/02/foundational-questions-in-the-azores-ii-limiting-frequency-arguments-for-the-born-rule-in-many-worlds/comment-page-1/#comment-977 Peter Thu, 08 Jul 2010 19:33:04 +0000 http://winephysicssong.com/?p=83#comment-977 If one view Born Rule as a axiom rather than trying to derive it, are you still left with these problems? Because that seems to be the way most MWI proponents are going nowadays... If one view Born Rule as a axiom rather than trying to derive it, are you still left with these problems?
Because that seems to be the way most MWI proponents are going nowadays...

]]> By: howard http://winephysicssong.com/2009/09/02/foundational-questions-in-the-azores-ii-limiting-frequency-arguments-for-the-born-rule-in-many-worlds/comment-page-1/#comment-33 howard Fri, 18 Sep 2009 16:46:17 +0000 http://winephysicssong.com/?p=83#comment-33 Hi Alex--- Well, personally I'd say not much. But I'm pretty Bayesian---or more accurately, I believe that much of the meaning of probability statements as used in scientific theories is a committment to, or recommendation of, certain decisionmaking ("betting") behavior. In this situation, though, it's important to note that I'm paraphrasing my recollection of what Alan said, and he may not have used the word "predicting". Maybe understanding, explaining, or maybe just something like "I'm interested in the frequencies with which things occur, not in betting". I think this is the tip of an iceberg of philosophical difference about the role of probability in scientific theories, between me and those physicists attracted to the idea that quantum probability is about frequencies. There do seem to be a lot of people who think, to put it in a relatively plausible-sounding way, that probability in science is about an attempt to describe, in a compact way, the frequencies with which various properties are associated with each other, given that we can't do so with deterministic laws of invariable association. They just want to describe, at a somewhat coarse-grained level, features of the block universe such as what fraction of portions of the universe with property A also have property B. Hi Alex---

Well, personally I'd say not much. But I'm pretty Bayesian---or more accurately, I believe that much of the meaning of probability statements as used in scientific theories is a committment to, or recommendation of, certain decisionmaking ("betting") behavior.

In this situation, though, it's important to note that I'm paraphrasing my recollection of what Alan said, and he may not have used the word "predicting". Maybe understanding, explaining, or maybe just something like "I'm interested in the frequencies with which things occur, not in betting". I think this is the tip of an iceberg of philosophical difference about the role of probability in scientific theories, between me and those physicists attracted to the idea that quantum probability is about frequencies. There do seem to be a lot of people who think, to put it in a relatively plausible-sounding way, that probability in science is about an attempt to describe, in a compact way, the frequencies with which various properties are associated with each other, given that we can't do so with deterministic laws of invariable association. They just want to describe, at a somewhat coarse-grained level, features of the block universe such as what fraction of portions of the universe with property A also have property B.

]]> By: Alex Wilce http://winephysicssong.com/2009/09/02/foundational-questions-in-the-azores-ii-limiting-frequency-arguments-for-the-born-rule-in-many-worlds/comment-page-1/#comment-7 Alex Wilce Fri, 11 Sep 2009 18:31:23 +0000 http://winephysicssong.com/?p=83#comment-7 "... he said he was interested in predicting the frequencies with which things occur, not in betting." What's the difference? "... he said he was interested in predicting the frequencies with which things occur, not in betting."

What's the difference?

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