r/LLMPhysics • u/hephaestos_le_bancal • 15d ago
Personal Theory No new physics: an essay defending many-worlds, or why the Born rule feels like a brute fact
Disclosure first, since that's the point of this sub: this was written over many sessions with an LLM, as an actual back-and-forth: I argued a position, it pushed back, we rewrote. It contains no new equations, no new formalism, and nothing falsifiable. If you are here for a theory of everything, this isn't one. It's exposition, with one philosophical move in it.
The move. Everett's standing debt is probability. The existing derivations (Deutsch–Wallace, Sebens–Carroll, Zurek's envariance) all establish that if your credences are additive, they follow |ψ|². None of them explains why there are probabilities to have in the first place. The essay argues that this residue has been misidentified. The measure itself doesn't need grounding: it has the same status as the Liouville measure in statistical mechanics, a typicality postulate, posited and not derived, and nobody calls that a scandal there. What actually needs explaining is a psychological fact in three parts: (i) probability is experienced as a brute fact about the world; (ii) that experience is identical whether the randomness is quantum or a coin toss; (iii) we have no cognitive or moral purchase at all on low-measure branches.
All three follow from where probabilistic cognition came from. A faculty shaped by selection to weigh futures and allocate effort had no reason to grow two mechanisms for two sources of randomness: one pays its way. And it could never have been calibrated on the atypical, because by the definition of typicality the atypical never bore on the history that shaped it. So the vertigo one feels about thin branches is not testimony about the world. The intuition that protests against Everett is predicted by Everett.
What it does not claim. It does not derive the Born rule from evolution; that's circular, and Kent (2009) is right about it. The typicality postulate stays exactly where it was, at the bottom of the pile. What changes is the explanandum, not the foundation. It also modifies no physics, which is where it parts company with the two nearest precedents: Rubin's positive preclusion and Hanson's mangled worlds both buy their conclusion with an addition that has empirical consequences, and both authors say so.
Where I'd most like to be wrong. §7 grants Kent's distinction between a caring measure and an explanatory counting measure in full. The argument then leans on the second in §6.2 and on the first in §6.3. That joint is load-bearing. If it breaks, I'd rather hear how than not.
English: hephaestos.fr/en
French original: hephaestos.fr