  Forgetfulness is a common feature of nature. Moreover, without forgetfulness,
repeatability would be impossible. Despite this, small systems constantly leak
information about their state to their surroundings, and quantum mechanics
tells us that this information cannot be deleted, invariably returning to
influence their future behaviour. How can physical nature be forgetful if it is
forbidden to forget? The results within this thesis bridge this gap between
what we see in the real world and what idealised physical theories say,
explaining the emergence of forgetful processes from closed quantum dynamics
and allowing to quantify the rate at which memory effects become relevant.
