  Typicality arguments attempt to use the Copernican Principle to draw
conclusions about the cosmos and presently unknown conscious beings within it,
including extraterrestrial intelligences (ETI). The most notorious is the
Doomsday Argument, which purports to constrain humanity's future from its
current lifespan alone. These arguments rest on a likelihood calculation that
penalizes models in proportion to the number of distinguishable observers. I
argue that such reasoning leads to solipsism, the belief that one is the only
being in the world, and is therefore unacceptable. Using variants of the
"Sleeping Beauty" thought experiment as a guide, I present a framework for
evaluating observations in a large cosmos: Weighted Fine Graining (WFG). WFG
requires the construction of specific models of physical outcomes and
observations. Valid typicality arguments then emerge from the combinatorial
properties of third-person physical microhypotheses. Indexical
(observer-relative) facts do not directly constrain physical theories, but
instead weight different provisional evaluations of credence. As indexical
knowledge changes, the weights shift. I show that the self-applied Doomsday
Argument fails in WFG, even though it can work for an external observer. I
argue that the Copernican Principle does not let us apply self-observations to
constrain ETIs.
