Whilst the BBC may lean towards the left and be a powerful organisation, I doubt that the effect it had was anywhere near as great as the combined forces of the Daily Mail, The Sun, the Daily Telegraph, and The Times. These newspapers, which account for a huge percentage of the UK's circulation, conducted what I can justifiably describe as a co-ordinated campaign of vitriolic rhetoric against the Labour party and Ed Miliband's character. It's telling that 2 of the 4 are owned by Rupert Murdoch, who has a lot to gain from a continued Conservative government.

There is simply no way the BBC would be able to pull the same kind of trick, as their reputation rests on them at least appearing politically neutral. It can't have been that hard to come up with some derisive slogan regarding the welfare cuts Cameron is inevitably going to try and make, but the country (both left and right) would be up in arms if it was seen to be the opinion of the BBC. The only left-leaning newspaper with a comparable circulation is the Daily Mirror, which ran the headline "Keep Cameron Out". I haven't seen this article myself, but I doubt it has the same attacks on character as the right-wing papers.

Yes, in the UK this is called the "Shy Tory" effect. I don't think all the media here is biased against the Conservative Party (some are pro, some are con) but you are quite right that the BBC (which is easily the largest and most powerful media organisation) is hostile. It's possible this is (part of) the cause of this effect, and it's notable that the three general elections where the polls messed up all did so by underestimating the Conservatives and overestimating Labour.

But I don't know that this is a case of the polls getting it wrong. If this was a case of the "Shy Tory" effect, why did the exit poll (and the unpublished Survation poll) get it right? By comparison, in 1992 the exit poll was wrong.

Probabilities aren't ontological; they're epistemological. I agree with everything that Eliezer writes about that, probabilities are in the map, etc.

But remove that word; there is something ontological that assigns measurement outcomes when I make a measurement. Or to keep it simpler: when I make a measurement, the measurement outcome is ontological.

I happened upon the website of a Norwegian physicist named Kim Øyhus who independently came to the many-worlds conclusion in 1990. The page strikes me as an unusually good example of epistemic rationality. He starts from a premise ("if the math of quantum mechanics is true,") and moves onto four hypotheses (which cover all possible states of reality, since the fourth hypothesis is, "something else"), figures out testable predictions of each hypothesis, and comes to the conclusion that the Many-Worlds Interpretation is correct.

Sorry, I forgot to answer you about PBR. I agree with Matt Leifer's analysis. Briefly: it's a fine theorem, and it's good that they proved it, but it shouldn't surprise anybody, and it doesn't rule out any of the interpretations that people actually advocate.

As for my interpretation, I don't have any problems with Caves, Fuchs, and Schack's comprehensive 2001 paper on the subject (this is not their first 2001 paper, which was more about a technical result and vaguer on the interpretation). This paper writes extensively about states of knowledge. But since then, Fuchs has criticized that phrasing as insufficiently Bayesian (by which he really means insufficiently subjectivist). Quantum States: What the Hell Are They? at his website covers this, although it's hard to read. As you can see from the dates, he had these thoughts pretty early on. Anyway, if the original 2001 papers define the orthodoxy for the Bayesian interpretation, then I am an orthodox quantum Bayesian, and Fuchs is the heretic.

Knowledge of what? Fuchs says knowledge of (or beliefs about, etc) the conesequences of one's interventions in a system; one can also say (which may be same thing) knowledge of the outcomes of further measurements. I would use more realist language: knowledge of the physical observables. If you try to build an ontological model in which each observable has an associated actual value and the results of measurements are determined by these values, then you'll have a hard time with that; but that's not what I want to do. An observable O does not (necessarily) have an actual value, but it has potential values (comprising its spectrum), and I have knowledge about O that can be summarized as a probability distribution over these potential values.

I meant the second. If that is the point of the papers, then I guess that's fair enough, but, well, I don't anticipate that their argument is going to be valid. I'll go and read it; no need to summarize.

First paper,

The trouble with all these interpretations [Bohm, spontaneous collapse, WMI] as quick fixes for Bell’s hard-edged remark is that they look to be just that, really quick fixes.

I recognize that this is subjective and fuzzy, but... no? Bohm looks like an incredibly... well, I won't get into that, but it doesn't seem to me like a quick fix. Spontaneous collapse, okay, I grant that one. MWI doesn't seem like a quick fix in any sense either.

Their world purports to have no observers, but then it has no probabilities ei- ther. What are we then to do with the Born Rule for calculating quantum probabilities? Throw it away and say it never mattered?

No, that's silly.

It is true that quite an effort has been made by the Everettians to rederive the rule from decision theory.

Yes, that was silly. But that's hardly the strongest argument that could or has been made. You don't get to pick your opponents' arguments like that. The way Decision theory is used when I've seen it is: any structure which is formally equivalent to a decider is a decider, and QM has such structures.

No amount of sophistry can make “decision” anything other than a hollow concept in a predetermined world.

... No, that's stupid. No amount of sophistry can make predetermination relevant to the meaningfulness of 'decision'. And of course the relevance of this argument is dependent on taking the argument for probability-in-MWI to be strictly dependent on the applicability of decision theory in a particular way which is not the way it's actually being used. In particular, by the time you ascend the level of abstraction enough for decision theory to be relevant, you're past the point at which predetermination has fallen away and you're dealing with an effectively non-predetermined system.

And then he just goes off and makes an argument that the theory is information about the state, not the state itself. But... ... ... if it successfully models your information about a thing, then the thing acts consistently with the model, which means you're also modeling the thing. There are theorems that constrain the ontology given these observations, and it basically boils down to 'QM is super legit'.

First, condescending snark? Seriously?

Second, now I'm really confused. In what way can't QM be the fundamental ontology of the universe?

My own brief summary of the subject is in an nLab article. (This is a math/physics wiki, and I assumed that the reader already knows quantum mechanics, at least up to the point of knowing what a density matrix is and what it's good for.) There are references there, but you'll notice that they're all linked from the History section. (Part of the point of that section is to make it clear that the idea predates Caves, Fuchs, et al, although they certainly deserve credit for making it prominent.) I don't know any over-all exposition that I really like, although I will always like the one cited as Baez 1993, which is where I learnt about it (and in fact where I first learnt about density matrices). That article doesn't say ‘Bayesian’, but as I was already a Bayesian when I read it, and since I knew Baez to be a Bayesian, I naturally interpreted it so. If you interpret the probabilities in a different way, then you'll get a very different interpretation of quantum mechanics as a result!

Someday I want to write something for beginners, at the level of Eliezer's essays here (and in fact probably post it here too), but I haven't done that yet! Until then, Baez's piece is at the right level, but it doesn't address the things that LessWrongers specifically would want to see.

I'm also a fan of the Bayesian interpretation of quantum mechanics (and I've said so here a couple of times). I try not to say ‘Quantum Bayesianism’, because it seems to me that Fuchs has run with that term in directions that I don't necessarily want to go. (I'm an objective Bayesian, while Fuchs is a subjective Bayesian, and that's just the start.) Some fans of Everett avoid the term ‘many worlds’ and cringe at some of the writings of David Deutsch, for similar reasons.

All of which is to say that if a hard-headed rationalist thinks that Fuchs is saying crazy things, run it against your model of a classical Bayesian saying similar things, and see if maybe it's the interpretation of Bayesianism that you object to rather than the interpretation of quantum mechanics, and adjust accordingly. (Of course, this doesn't help if you're not a Bayesian in the first place, but Bayes is more sacred here than Everett.)

Just from reading the abstract, I'm not interested in an egocentric model of the universe. Ontology doesn't follow the same rules as epistemology.