It has been well over a year since I first read Permutation City and relating writings on the internet on Greg Egan's dust theory. It still haunts me. The theory has been discussed tangentially in this community, but I haven't found an article that directly addresses the rationality of Egan's own dismissal of the theory.
In the FAQ, Egan says things like:
I wrote the ending as a way of dramatising[sic] a dissatisfaction I had with the “pure” Dust Theory that I never could (and still haven't) made precise (see Q5): the universe we live in is more coherent than the Dust Theory demands, so there must be something else going on.
and:
I have yet to hear a convincing refutation of it on purely logical grounds...
However, I think the universe we live in provides strong empirical evidence against the “pure” Dust Theory, because it is far too orderly and obeys far simpler and more homogeneous physical laws than it would need to, merely in order to contain observers with an enduring sense of their own existence. If every arrangement of the dust that contained such observers was realised, then there would be billions of times more arrangements in which the observers were surrounded by chaotic events, than arrangements in which there were uniform physical laws.
Isn't this, along with so many other problems, a candidate for our sometime friend the anthropic principle? That is: only in a conscious configuration field which has memories of perceptions of an orderly universe is the dust theory controversial or doubted? In the vastly more numerous conscious configuration fields with memories of perceptions of a chaotic and disorderly universe lacking a rational way to support the observer the dust theory could be accepted a priori or at least be a favored theory.
It is fine to dismiss dust theory because it simply isn't very helpful and because it has no predictions, testable or otherwise. I suppose it is also fine never to question the nature of consciousness as the answers don't seem to lead anywhere helpful either; though the question of it will continue to vex some instances of these configuration states.
Well, I agree we need to base theory on observable facts. Dust theory is more of a thought experiment or problem related to the nature of consciousness, which is not something we've been able to attack empirically. Nonetheless, Egan dismisses it with this "orderly universe" business. I'm arguing that there is a selection bias - if dust theory were true then only in an "orderly universe" do we argue about dust theory.
But I'm starting to come around to the position I think most of you are taking, which is that this is just a "pink unicorn" what-if proposition that isn't worth contemplating - since we do in fact have an orderly universe which seems to account for things the way they are.
My problem is that once I accept the information state theory of consciousness, "dust based" conscious entities seems like an inevitable result, unless the actual universe is sufficiently bounded in time and space that the statistical likliehood of this is prohibitive.
But for anyone that adopts a many-worlds interpretation of QM or any variant of cosmology theory that yields an unbounded configuration space then I don't see a way around this problem.
That's just the Boltzmann's brain problem, right? It goes away if you assume our universe started with very low entropy for some reason other than pure Boltzmann-style chance. (I believe some theories, like String theories, provide this feature?) It seems to be an open problem in physics/cosmology.
I don't understand QM. But intuitively I would expect that even in many-worlds, with an unbounded configuration space, the sum of probability over all configurations is (should be?) constant. Is that so, and would it solve the Boltzmann problem by reducing it to another (unsolved) problem, namely the origin and meaning of the Born probabilities?