On 2/24/2025 6:09 PM, Quentin Anciaux wrote:
Bruce,
Your response assumes that unitary evolution inherently produces "one
observer per branch" in a discrete way, but that’s not what follows
from the wavefunction’s continuous structure. Everett’s relative state
formulation does not propose discrete worlds but rather an evolving
superposition where decoherence prevents interference. The fact that
we describe macroscopic branches as "splitting" is a convenient
approximation, not a fundamental aspect of the theory.
The key point you keep ignoring is that amplitudes are not just
"carried along" without meaning—they define the structure of the
wavefunction, and decoherence prevents low-amplitude branches from
significantly contributing to observer experiences. Your claim that
"one observer per branch" follows directly from unitary evolution is
an assumption, not a derivation.
If you insist that unitary evolution cannot produce probability
weights, then your argument applies equally to any interpretation of
quantum mechanics. The Born rule is a fact of experiment, and any
valid interpretation must explain it. If you believe MWI cannot do so,
you must show why—not just assert that it "hasn’t been done" while
dismissing attempts to derive it. Assume your pride, publish and get
the glory.
A measurement in QM conforms to the Born rule, but it's not unitary,
it's a projection operator. That's how it produces probabilities, it
projects the unitarily evolved state vector onto the basis eigenvectors
of the operator. That's pretty much the problem MWI wants to solve:
"How can we replace that projection operation with some unitary
evolution." And it comes up with "self-locating uncertainty" which
postulates the Born rule for "selfs".
Brent
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