It’s like selecting a random observer from all possible universes taken as a single bag. E.g. if there are 2 possible universes with equal initial probability, and one has twice the population of the other, then if you select a random person across universes, you end up in the higher population one with higher probability. The doomsday argument motivates one reason why this might make sense. Also, if you imagine these alternative universes as actually existing due to some kind of big universe theory (just being very large, or many-worlds, or multiversal), then SSA and SIA will tend to agree.
SIA doesn’t handle cases with infinite universes in a well-defined manner. For that you might need some modification like selecting a universe with higher probability if it has more observers per unit computation, or similar. In general, the presumptuous philosopher problem is a counterintuitive implication of SIA.
It’s like selecting a random observer from all possible universes taken as a single bag. E.g. if there are 2 possible universes with equal initial probability, and one has twice the population of the other, then if you select a random person across universes, you end up in the higher population one with higher probability. The doomsday argument motivates one reason why this might make sense. Also, if you imagine these alternative universes as actually existing due to some kind of big universe theory (just being very large, or many-worlds, or multiversal), then SSA and SIA will tend to agree.
SIA doesn’t handle cases with infinite universes in a well-defined manner. For that you might need some modification like selecting a universe with higher probability if it has more observers per unit computation, or similar. In general, the presumptuous philosopher problem is a counterintuitive implication of SIA.