I think Eliezer recognizes the the vagueness of “world” but sees it as a problem for single-worlders. This is what he seems to be saying here:
We have specific reasons to be highly suspicious of the notion of only one world. The notion of “one world” exists on a higher level of organization, like the location of Earth in space; on the quantum level there are no firm boundaries (though brains that differ by entire neurons firing are certainly decoherent). How would a fundamental physical law identify one high-level world?
mitchell,
I think Eliezer recognizes the the vagueness of “world” but sees it as a problem for single-worlders. This is what he seems to be saying here: