Timo said:
It does seem to boil down to metaphysics. Is a difference that makes no difference still a difference?
It's impossible to tell whether atoms A and B of a given element are "same" or "different", in any practical sense. Indeed, if we get so impractical as to discover differences between A and B, we have to admit that A is going to be different from A most of the time, too. The atoms making up "me" now are not the same as the ones that made up "me" when I started typing this. Even the molecules or cells, vast structures when compared to atoms, come and go in and out of my body during my so-called life.
Add to this that there is no good consensus on the line separating life from death today, and that the issue is becoming more muddled by the day. Certainly the issue of defining one's physical identity begins to look less and less relevant here, with the question of one's soul relegated to even greater insignificance in the process.
Timo Saloniemi