  As observers of the universe we are quantum physical systems within it. If
the universe is very large in space and/or time, the probability becomes
significant that the data on which we base predictions is replicated at other
locations in spacetime. The physical conditions at these locations that are not
specified by the data may differ. Predictions of our future observations
therefore require an assumed probability distribution (the xerographic
distribution) for our location among the possible ones. It is the combination
of basic theory plus the xerographic distribution that can be predictive and
testable by further observations.
