Some interesting stuff about our conceptions of the world might fall apart if you adopt the mathematical universe. If you think that the entirety of mathematical structures exists in the same way, than it is hard to think what happens when you decide to do good to someone with the entire structure. The whole thing just “is there”. Your decision could be thought of as a computational process that takes place in many different subsets. But the exact opposite decision still takes place where it takes place. Then you get something complicated in which your decision ends up conflates with self location in the near future. As if you deciding something doesn’t change the whole, but only where in the whole are things of the “you” kind to be found.
And then, citing Lewis becomes helpful to find out about the minimal levels of complexity we are dealing with:
As suggested above, let us call an individual which is wholly part of
one world a possible individual.” If a possible individual X is part of
a trans-world individual Y, and X is not a proper part of any other possible
individual that is part of Y, let us call X a stage of Y. The stages of a
trans-world individual are its maximal possible parts; they are the
intersections of it with the worlds which it overlaps. It has at most one
stage per world, and it is the mereological sum of its stages. Sometimes
one stage of a trans-world individual will be a counterpart of another.
If all stages of a trans-world individual Y are counterparts of one another,
let us call Y counterpart-interrelated. If Y is counterpart-interrelated, and
not a proper part of any other counterpart-interrelated trans-world
individual (that is, if Y is maximal counterpart-interrelated), then let us
call Y a -possible individual.
Given any predicate that applies to possible individuals, we can define
a corresponding starred predicate that applies to -possible individuals
relative to worlds. A -possible individual is a -man at W iff it has a
stage at W that is a man; it -wins the presidency at W iff it has a stage
at W that wins the presidency; it is a -ordinary individual at W iff it
has a stage at W that is an ordinary individual. It -exists at world W
iff it has a stage at W that exists; likewise it -exists in its entirety at world
W iff it has a stage at W that exists its entirety, so—since any stage at
any world does exist in its entirety—a -possible individual -exists in
its entirety at any world where it -exists at all. (Even though it does not
exist in its entirety at any world.) It -is not a trans-world individual at
W iff it has a stage at W that is not a trans-world individual, so every
-possible individual (although it is a trans-world individual) also -is not
a trans-world individual at any world. It is a -possible individual at W iff
it has a stage at W that is a possible individual, so something is a -possible
individual simpliciter iff it is a -possible individual at every world where
it -exists. Likewise for relations. One -possible individual -kicks another
at world W iff a stage at W of the first kicks a stage at W of the second;
two -possible individuals are -identical at W iff a stage at W of the
first is identical to a stage at W of the second; and so on.
Some interesting stuff about our conceptions of the world might fall apart if you adopt the mathematical universe. If you think that the entirety of mathematical structures exists in the same way, than it is hard to think what happens when you decide to do good to someone with the entire structure. The whole thing just “is there”. Your decision could be thought of as a computational process that takes place in many different subsets. But the exact opposite decision still takes place where it takes place. Then you get something complicated in which your decision ends up conflates with self location in the near future. As if you deciding something doesn’t change the whole, but only where in the whole are things of the “you” kind to be found.
And then, citing Lewis becomes helpful to find out about the minimal levels of complexity we are dealing with: As suggested above, let us call an individual which is wholly part of one world a possible individual.” If a possible individual X is part of a trans-world individual Y, and X is not a proper part of any other possible individual that is part of Y, let us call X a stage of Y. The stages of a trans-world individual are its maximal possible parts; they are the intersections of it with the worlds which it overlaps. It has at most one stage per world, and it is the mereological sum of its stages. Sometimes one stage of a trans-world individual will be a counterpart of another. If all stages of a trans-world individual Y are counterparts of one another, let us call Y counterpart-interrelated. If Y is counterpart-interrelated, and not a proper part of any other counterpart-interrelated trans-world individual (that is, if Y is maximal counterpart-interrelated), then let us call Y a -possible individual. Given any predicate that applies to possible individuals, we can define a corresponding starred predicate that applies to -possible individuals relative to worlds. A -possible individual is a -man at W iff it has a stage at W that is a man; it -wins the presidency at W iff it has a stage at W that wins the presidency; it is a -ordinary individual at W iff it has a stage at W that is an ordinary individual. It -exists at world W iff it has a stage at W that exists; likewise it -exists in its entirety at world W iff it has a stage at W that exists its entirety, so—since any stage at any world does exist in its entirety—a -possible individual -exists in its entirety at any world where it -exists at all. (Even though it does not exist in its entirety at any world.) It -is not a trans-world individual at W iff it has a stage at W that is not a trans-world individual, so every -possible individual (although it is a trans-world individual) also -is not a trans-world individual at any world. It is a -possible individual at W iff it has a stage at W that is a possible individual, so something is a -possible individual simpliciter iff it is a -possible individual at every world where it -exists. Likewise for relations. One -possible individual -kicks another at world W iff a stage at W of the first kicks a stage at W of the second; two -possible individuals are -identical at W iff a stage at W of the first is identical to a stage at W of the second; and so on.