[Side question: Does anyone happen to know whether the many-worlds interpretation of q.m. posits infinitely many worlds—or only a very, very large number?]
A “world” is not an ontologically fundamental concept in MWI. The fundamental thing is the wave function of the universe. We colloquially speak of “worlds” to refer to clumps of probability amplitude within the wave function.
A “world” is not an ontologically fundamental concept in MWI. The fundamental thing is the wave function of the universe. We colloquially speak of “worlds” to refer to clumps of probability amplitude within the wave function.