Excellent post.
There are a few examples of non-emergence. For example, if we tessellate many small equilateral triangles to create a larger equilateral triangle, the resulting figure will not show any emergent properties.
Outside of mathematics, though, the concept is vague and I can't see much use for it as applied to specific phenomena.
Eliezer, whatever it is you were getting at in your comment, it was waaay over my head. When I searched on Wikipedia for Big World, I got an album by Joe Jackson. When I looked for Everett branches, I found an intriguing article about the Piscataquog River. Could you point me to some further reading? I hate to feel left out of the loop here.
Conchis and Nick, I should have explained my position more clearly. As an atheist myself, I have come to the conclusion that my children will find the ability to think more useful than an arbitrary set of rules that they have been conditioned to follow. The virtue of Santa is that it is a belief they will inevitably question and learn from, while an outspoken conscience will only cloud their ability to reason when they have to make important choices that will determine their future levels of happiness. While you might be able to convince me empirically that children with an internalized sense of morality are happier, you would be making an argument for something preferable, but not for something truthful (though I would certainly raise my children in the way you prescribed).
Eliezer, I will concede that parents only have a finite amount of time with which to maximize their children's sense of wonder, and it is also plausible that the number of alternative ways to do so is infinite. However, my argument was that there need not be a choice between Santa and the alternatives. If we consider that there is diminishing marginal wonder for any activity we select, then the choice among alternatives becomes similar to the choice a firm with a finite amount of capital makes between alternative factors of production. Like a firm maximizing the return to its investments, we will want to allocate time towards the activities with the highest marginal wonder, and it is plausible that Santa will be one of those choices before the highest marginal wonder is less than the cost to our time. It becomes even more likely once we consider the transaction costs of using the "market" of available alternatives--we must discover them and make use of them in the most efficient manner possible (e.g., driving the kids to a museum once a week). Santa, in comparison, is the cultural default and requires little time or energy to reinforce. Most of the work is done by the children's peers, and to discourage the belief would use valuable time that could have been allocated towards activities with a higher marginal rate of return. Since you seem to accept that there is some limited benefit to Santa, the opportunity cost of the time spent convincing our children of a truth that they will come to realize anyway will only add to the deadweight loss of wonder.
In effect, we may have to choose how much time to allocate towards lying about Santa, but it seems unlikely that there will be a strict choice between Santa and the alternatives, given the diminishing marginal wonder of the different activities in our choice set.
Perhaps the status quo bias you pointed out later in your post has its roots in an unconscious (but rational) cost-benefit analysis. In addition, as we would say of a firm trying to maximize its returns, there is a good deal of uncertainty that alternatives will provide the same wonder that we know Santa has provided and will continue to provide (in addition to the other benefits you enumerated). In this case, it makes quite a bit of sense to avoid the alternatives altogether, assuming that the opportunity cost of our time is high and our information about the alternatives is scarce. In conclusion, you may be demonstrating an unusual bias in opposition to the status quo, and have justified it with a false dilemma between the "best" and the "good."
Sorry for the long comment. I could provide a dozen caveats to this analysis, but I sense the highest marginal return to my time lies elsewhere.
When the stakes are high enough I one-box, while gritting my teeth. Otherwise, I'm more interested in demonstrating my "rationality" (Eliezer has convinced me to use those quotes).
Perhaps we could just specify an agent that uses reverse causation in only particular situations, as it seems that humans are capable of doing.