  The 2022 Tel Aviv conference on the Many Worlds interpretation of quantum
mechanics highlighted many differences between theorists. A very significant
dichotomy is between Everettian fission (splitting) and Saunders-Wallace-Wilson
divergence. For fission, an observer may have multiple futures, whereas for
divergence they always have a single future. Divergence was explicitly
introduced to resolve the problem of pre-measurement uncertainty for Everettian
theory, which is universally believed to be absent for fission. Here, I
maintain that there is indeed uncertainty about future observations prior to
fission, so long as objective probability is a property of Everettian branches.
This is made possible if the universe is a set and branches are subsets with
probability measure. A universe which is a set of universes which are
macroscopically isomorphic and span all possible configurations of microscopic
local be\"ables fulfils that role. If objective probability is a property of
branches, a successful Deutsch-Wallace decision-theoretic argument would
justify the Principal Principle and be part of probability theory rather than
being specific to Many Worlds. Any macroscopic object in our environment
becomes a set of isomorphs with different microscopic configurations, each in
an elemental universe (elemental in the set-theoretic sense). This is similar
to Many Interacting Worlds theory but the observer inhabits the set of worlds,
not an individual world. An observer has many elemental bodies.
