If you look over all possible worlds, then asking “did the coin come up Heads or Tails” as if there’s only one answer is incoherent. If you look over all possible worlds, there’s a ~100% chance the coin comes up as Heads in at least one world, and a ~100% chance the coin comes up as Tails in at least one world.
But from the perspective of a particular observer, the question they’re trying to answer is a question of indexical uncertainty—out of all the observers in their situation, how many of them are in Heads-worlds, and how many of them are in Tails-worlds? It’s true that there are equally as many Heads-worlds as Tails-worlds—but 2⁄3 of observers are in the latter worlds.
Or to put it another way—suppose you put 10 people in one house, and 20 people in another house. A given person should estimate a 1⁄3 chance that they’re in the first house—and the fact that 1 house is half of 2 houses is completely irrelevant. Why should this reasoning be any different just because we’re talking about possible universes rather than houses?
If you look over all possible worlds, then asking “did the coin come up Heads or Tails” as if there’s only one answer is incoherent. If you look over all possible worlds, there’s a ~100% chance the coin comes up as Heads in at least one world, and a ~100% chance the coin comes up as Tails in at least one world.
But from the perspective of a particular observer, the question they’re trying to answer is a question of indexical uncertainty—out of all the observers in their situation, how many of them are in Heads-worlds, and how many of them are in Tails-worlds? It’s true that there are equally as many Heads-worlds as Tails-worlds—but 2⁄3 of observers are in the latter worlds.
Or to put it another way—suppose you put 10 people in one house, and 20 people in another house. A given person should estimate a 1⁄3 chance that they’re in the first house—and the fact that 1 house is half of 2 houses is completely irrelevant. Why should this reasoning be any different just because we’re talking about possible universes rather than houses?