My original source was unfortunately a combination of conversations and a book I don’t remember the title of, so I can’t take you back to the original source.
But, I found something here. (†)
Thanks! It looks like the reference equates the number of worlds with the number of microstates, since it calculates it as exp(S/k), not as the number of eigenstates of some interaction Hamiltonian, which is the standard lore. From this point of view, it is not clear how many worlds you get in, say, a single-particle Stern-Gerlach experiment: 2 or exponent of the entropy change of the detector after it’s triggered. Of course, one can say that we can coarse-grain them the usual way we construct macrostates from microstates, but then why introduce many worlds instead of simply doing quantum stat mech or even classical thermodynamics?
Anyway, I could not find this essential point (how many worlds?) in the QM sequence, but maybe I missed it. All I remember is the worlds of different “thickness”, which is sort of like coarse-graining microstates into macrostates, I suppose.
Thanks! It looks like the reference equates the number of worlds with the number of microstates, since it calculates it as exp(S/k), not as the number of eigenstates of some interaction Hamiltonian, which is the standard lore. From this point of view, it is not clear how many worlds you get in, say, a single-particle Stern-Gerlach experiment: 2 or exponent of the entropy change of the detector after it’s triggered. Of course, one can say that we can coarse-grain them the usual way we construct macrostates from microstates, but then why introduce many worlds instead of simply doing quantum stat mech or even classical thermodynamics?
Anyway, I could not find this essential point (how many worlds?) in the QM sequence, but maybe I missed it. All I remember is the worlds of different “thickness”, which is sort of like coarse-graining microstates into macrostates, I suppose.
It is coarse-graining them into macrostates. Each macrostate is a bundle of a thermodynamically numerous effectively-mutually-independent worlds.