Professor Adrian Kent:
"One world versus many: the inadequacy of Everettian accounts of evolution, probability, and scientific confirmation":
"Copenhagen quantum theory is a one-world version of quantum theory: any given experiment or quantum event has a number of possible outcomes, but only one actual outcome. Some other non-Everettian variants and modifications of quantum theory, such as de Broglie-Bohm theory and dynamical collapse models, similarly randomly select from many possible physical evolutions, and can be (and usually are) interpreted as defining a unique quasiclassical world. The consistent histories approach , if combined with an (alas unknown) suitable set selection rule, would also lead naturally to a one-world interpretation, in which reality is described by one randomly chosen history from the selected set. And these by now venerable contenders certainly don’t exhaust the possible options: a new covariant one-world
version of standard quantum theory applicable to closed systems, plausibly able to select a unique quasiclassical world from realistic cosmological models, was recently proposed. My aim here is not to advocate a specific one-world
version or variant of quantum theory, or to assess the current state of the art, but rather to compare and contrast one-world and many-world accounts of probability. For that purpose, let us suppose, for the sake of argument, that we
have to hand a particular one-world theory that implies that, while the universe could have evolved in a (presumably very large) number of different ways, one quasiclassically evolving world – the one we observe – was randomly selected.
One-world versions of quantum theory, together with hypotheses about the initial conditions and unitary evolution, predict the probabilities of our experimental results and observations. We test the theory and these hypotheses by
checking whether the results are of a form we would typically expect given the predicted probabilities. In practice, pretty much everyone agrees on the methodology of theory confirmation, at least sufficiently so that, for example,
everyone agrees that, within the domain of validity of Copenhagen quantum theory, the Born rule is very well confirmed statistically. However, there is much less agreement on how, or even whether, we can make sense of fundamentally
probabilistic physical theories. What exactly, if anything, does it mean to say that the probability of the universe turning out the way it did was 0.00038?
Everettian authors have stressed this last point lately. We should not, they argue, apply different standards to one-world and many-worlds quantum theory. If our account of standard probability applied to one-world quantum theory is suspect, or incomplete, or involves ad hoc postulates, we cannot reasonably reject an alternative many-worlds account on the grounds that it runs into difficulties that mi ght, on close analysis, turn out to be precisely analogous.
There are several possible responses for one-worlders here. One response is to try to defend or buttress or further develop frequentism, or another standard account of standard probability. A second is to try to point out some
insuperable problems with many-worlds accounts of probability, and thus make the case that, whatever difficulties one-world quantum theory might run into, many-worlds quantum theory cannot possibly be satisfactory. A third is
to argue that the difficulties that many-worlders face in dealing with probability are worse than – not, as claimed, precisely analogous to – those faced by one-worlders.
As Professor Kent points out, a central debate between the classical, realist, one-world views and the
The sober, non-mystical one-world views of Dr. Kent (and there are others, see here:Dr Streater: There is nothing to the many-worlds theory. There are no theorems, conjectures, experimental predictions or results of any sort, other than those of Hilbert space. It is not a cogent idea.""") should serve as a reminder of how shallow pop-science readings of quantum mechanics and relativity often mislead and befuddle the masses. The newest hucksters now chant string theory, or a "multiverse": in effect they mistake possible outcomes for actual places. When someone throws dice at a crap table, there are many possible outcomes (though finite). Those outcomes that did not occur do not exist--there's no alternative "world" where you won, though lost in this world. There's only one world, with a specific event (really, merely stones with some number-marks falling--in theory predictable, ala Laplace). In effect, that is frequentism--which suffices for nearly all conceivable situations involving randomness, or apparent randomness. Lack of computability (ie knowing all the parameters involved in a toss of the dice, and thus de facto unpredictability) does not in itself defeat determinism. Some scientists don't care for frequentist theory, claiming it is merely data collection, and alternatives are offered, such as the Kolmogorov axioms, but in a sense anytime the entire sample space cannot be defined (ie known, initial conditions) then one is left with something like frequentism (and David Hume's points contra- induction--though the physics of suspension bridges should not be mistaken for atmospheric physics).
Belgian physicist,Jean Bricmont also takes issue with the pop-mystical and indeterministic readings of quantum mechanics. As he points out, Einstein considered quantum theory an incomplete description: "Einstein wrote in 1949: I am, in fact, firmly convinced that the essentially statistical character of contemporary quantum theory is solely to be ascribed to the fact that this (theory) operates with an incomplete description of physical systems...[In] a complete physical description, the statistical quantum theory would... take an approximately analogous position to the statistical mechanics within the framework of classical mechanics."
Of course, a deterministic one-world realism is not sufficiently mysterious or sexy enough for a quack. A quack wants great mysteries, he wants to chant super-strings, and toss up a page of differential equations or mayan calendars to impress some gullible and/or bourgeois hipsters. Mysticism, even the science-based has a political context. The scientist-mystic (or quack-nazis quoting their favorite pseudo-scientists) craves power of a sort, and a science-based mystic ideology--and futurism itself-- furthers that power; and not surprisingly, much of the multiverse-hype comes out of big private, right-wing universities like Stanford. In effect, the pop-science mystic circumvents economic reality and real world problems (like say energy issues, water issues, poverty) by means of his gaseous dreams, and futurist salespitch. The mystic has no solutions to say depleted oil reserves, or droughts, poverty, or war, and bloated defense budgets. In fact, his "quantum escapism" is part of the problem.