  In the mid-19th century, both the laws of mechanics and thermodynamics were
known, and both appeared fundamental. This was changed by Boltzmann and Gibbs,
who showed that thermodynamics can be *derived*, by applying mechanics to very
large systems, and making simple statistical assumptions about their behavior.
Similarly, when Quantum Mechanics (QM) was first discovered, it appeared to
require two sets of postulates: one about the deterministic evolution of
wavefunctions, and another about the probabilistic measurement process. Here
again, the latter is derivable from the former: by applying unitary evolution
to large systems (apparatuses, observers and environment), and making simple
assumptions about their behavior, one can derive all the features of quantum
measurement. We set out to demonstrate this claim, using a simple and explicit
model of a quantum experiment, which we hope will be clear and compelling to
the average physicist.
