As I understand, it’s less of a problem for a hardline Copenhagen interpretation because no definite ontological status is assigned to the wavefunction, or indeed the collapse of the wavefunction. CI can roughly be paraphrased as
“Consider this set of rules for predicting experimental outcomes. Look how well it works! Of course, we’re not asserting anything about actual reality here”.
One of those rules is the Born rule. Another is the fact that physical transformations correspond to unitary maps on the Hilbert space. All of them are postulated, and their correctness is a matter of experimental falsification/verification.
Conversely, MWI assigns definite reality to the wavefunction, but denies that collapse is a real process, and does not postulate any rules about predictions of experimental outcomes. Instead, the claim that a process of measurement inevitably results in a single result being recorded—with probability given by the square amplitude of the wavefunction—must be derived from the pre-existing structure of the theory (possibly with some reasonable assumptions about gambling commitments).
A conceivable alternative to MWI might have the Born rule as an additional postulate, supported only by experiment rather than following from the structure of the theory. I feel that this would be much less appealing to many of its advocates.
As I understand, it’s less of a problem for a hardline Copenhagen interpretation because no definite ontological status is assigned to the wavefunction, or indeed the collapse of the wavefunction. CI can roughly be paraphrased as
“Consider this set of rules for predicting experimental outcomes. Look how well it works! Of course, we’re not asserting anything about actual reality here”.
One of those rules is the Born rule. Another is the fact that physical transformations correspond to unitary maps on the Hilbert space. All of them are postulated, and their correctness is a matter of experimental falsification/verification.
Conversely, MWI assigns definite reality to the wavefunction, but denies that collapse is a real process, and does not postulate any rules about predictions of experimental outcomes. Instead, the claim that a process of measurement inevitably results in a single result being recorded—with probability given by the square amplitude of the wavefunction—must be derived from the pre-existing structure of the theory (possibly with some reasonable assumptions about gambling commitments).
A conceivable alternative to MWI might have the Born rule as an additional postulate, supported only by experiment rather than following from the structure of the theory. I feel that this would be much less appealing to many of its advocates.