the stupid questions thread is very full

Might be worth having those more often too; the last one was very popular, and had lots of questions that open threads don't typically attract.

Because Turing machines are deterministic, AIXI cannot make hypotheses involving randomness. To model the fair coin, AIXI would come up with increasingly convoluted Turing machines, attempting to compress a bitstring that approaches Kolmogorov randomness as its length approaches infinity. Meanwhile, AIXI would be punished and rewarded randomly.

Just a naïve thought, but maybe it would come up with MWI fairly quickly because of this. (I can imagine this being a beisutsukai challenge – show a student radioactive decay, and see how long it takes them to come up with MWI.) A probabilistic one is probably better for the other reasons brought up, though.