2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/94035Contrary to an oft-made claim, there can be observational distinctions (say for the expansion of the universe or the cosmological constant) between "single-history" quantum theories and "many-worlds" quantum theories. The distinctions occur when the number of observers is not uniquely predicted by the theory. In single-history theories, each history is weighted simply by its quantum-mechanical probability, but in many-worlds theories in which random observations are considered, there should also be the weighting by the numbers or amounts of observations occurring in each history.8 pages, no figures, LaTeX. Messages from Jerry Finkelstein and Jacques Mallah have led me to realize that, although I stand by my prediction that in a many-worlds theory you will be alive in the year 2100 in some worlds, paradoxically the evidence you will have then will not support many-worlds quantum theory over single-history quantum theory, since in either theory it will be evidence of very low measure and likelihood for a random observation. Therefore, I deleted this part of the paper (and shortened other parts)Quantum PhysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext