Tuesday, January 31, 2012

Some recommended reading

Robert Wald reviews the 2010 book Many Worlds?: Everett, Quantum Theory, and Reality, based on meetings at Oxford and at the Perimeter Institute, commemorating the 50th anniversary of Everett's paper.

A central issue in the Everett interpretation is the status of the `Born rule', which asserts that, for state ψ, the probability of obtaining a particular outcome of a measurement is ||Pψ||2, where P is the projection operator onto the eigensubspace associated with the measurement outcome. In traditional interpretations, the Born rule is simply postulated as part of the collapse hypothesis. In the Everett interpretation, it is far from obvious that the Born rule even has any meaning—if all outcomes occur, how can one talk about the probability of a particular outcome? Given the importance of this issue, it is highly appropriate that four chapters of the book (by Saunders, Papineau, Wallace, and Greaves and Myrvold) are devoted to addressing probability and the Born rule from the Everett viewpoint, and three chapters (by Kent, Albert, and Price) are devoted to criticising these views.

... In any case, if the conclusion of a mathematically correct argument is that rational decision strategies require the Born rule, then there must be quite a bit lying in the assumptions. The articles by Kent, Albert, and Price do a good job of fleshing out these assumptions and pointing out the weaknesses and flaws in the probability and decision theory discussions within the Everett framework. ...

See here for my thoughts on this.

The origin of the Everettian heresy (see also Byrne's excellent biography of Everett).

... These efforts gave rise to a lively debate with the Copenhagen group, the existence and content of which have been only recently disclosed by the discovery of unpublished documents. The analysis of such documents opens a window on the conceptual background of Everett’s proposal, and illuminates at the same time some crucial aspects of the Copenhagen view of the measurement problem. Also, it provides an original insight into the interplay between philosophical and social factors which underlay the postwar controversies on the interpretation of quantum mechanics.

... Here is a tentative chronology of the thesis versions and of the related papers:

(1a) Objective vs Subjective probability, short manuscript (first half of 1955).
(1b) Quantitative Measure of Correlation, short manuscript (summer 1955).
(1c) Probability in Wave Mechanics, short manuscript (summer 1955).

(2) Wave Mechanics Without Probability, second version of the dissertation (the long thesis) (winter 1955–1956), published as The Theory of the Universal Wave Function (1973).

(3) On the Foundations of Quantum Mechanics, final dissertation (winter 1956–1957), published as ‘‘Relative State’’ Formulation of Quantum Mechanics (July 1957).

A Commentary on ‘Common SNPs Explain a Large Proportion of the Heritability for Human Height’ by Yang et al. (2010). (Ungated pdf.) Why do Visscher and company have to speak so slowly and enunciate so carefully in order to be understood?

During the refereeing process (the paper was rejected by two other journals before publication in Nature Genetics) and following the publication of Yang et al. (2010) it became clear to us that the methodology we applied, the interpretation of the results and the consequences of the findings on the genetic architecture of human height and that for other traits such as complex disease are not well understood or appreciated ...

Well before reading the Yang et al. paper, but after hearing much about "missing" heritability, I asked impatiently why GWAS researchers had not tried to make a global fit of total heritability, as opposed to searching for individual alleles. See also Heritability 2.0.

Turkheimer on heritability: Still Missing.

A century of familial studies of twins, siblings, parents and children, adoptees, and whole pedigrees has established beyond a shadow of a doubt that genes play a crucial role in the explanation of all human differences, from the medical to the normal, the biological to the behavioral ...

As a social scientist and twin researcher, I had to struggle with the biological and statistical genetics underlying the Yang et al. analyses, but the analysis of variance, the acausal “capturing” and “tracking” of one domain of variance with another came naturally to me. The situation was reversed for the geneticists who were the target audience of the paper: biologically based scientists, accustomed to genes that have an actual causal pathway to their outcomes. Over and above its technical brilliance, the real contribution of the Yang et al. article is to bring into focus this conceptual chasm between biological and quantitative genetics, and thus between the physical sciences and social science. Genomics is only now learning a hard lesson that social scientists had to learn a long time ago: sometimes prediction is just prediction. That is what the missing heritability problem is really about, and why it has not yet been solved

For more Turkheimer, see here. Note that although he emphasizes the difficulty of teasing out causality in a complex system, for some "engineering" applications (such as genetic engineering), prediction may be enough, as long as the correlations between genetic variant and phenotype are confirmed to be robust across a variety of environments. The specific causal mechanism is not as important as the ability to modify and control ;-)


Henry Harpending said...

Steve your link "A commentary" is broken.

There is some kind of lesson about our current system of peer review in the fact that Visscher's crew had to shop their paper around.

steve hsu said...

Thanks! I think it is fixed now...

Henry Harpending said...

The full paper is available at http://homepages.ed.ac.uk/qgjc/2010_2011/CommentaryOnYang.pdf


RKU1 said...

Decades ago, Niven published an interesting SF speculation on the psychological Heisenberg impact of Many Worlds becoming universally accepted as factually correct among the public.  Essentially, people would start saying that if all their personal decisions were just being made along different simultaneous forks, they might as well just do whatever they felt like doing since that's exactly what would anyway happen along some branch.  Hence a large increase in seemingly random killings, rapes, and suicides.

On the other hand, I suppose the same psychological argument can be advanced for the belief that all decisions are determined by fate or divine will, which has been pretty common among many religions.

Richard Seiter said...

RKU1 are you talking about "All the Myriad Ways"?  There is a post about it here: 
http://vusf.wordpress.com/2011/09/16/cause-and-effect-in-a-probabilistic-multiverse/  I don't have that one among my 19 Niven books.  Is it worth chasing down?

RKU1 said...

Yes, it's a pretty good story and one of the few not set in Known Space or one of Niven's other two or three "universes".  It's found in several of his different collections, so you should be able to find it pretty easily in a well-stocked used book store, or on-line

Richard Seiter said...

Thanks RKU1.  I'll be looking for it the next time I'm in a used book store.  In case anyone is interested there is a PDF of the story here: 

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