  Classical and quantum measurement theories are usually held to be different
because the algebra of classical measurements is commutative, however the
Poisson bracket allows noncommutativity to be added naturally. After we
introduce noncommutativity into classical measurement theory, we can also add
quantum noise, differentiated from thermal noise by Poincar\'e invariance. With
these two changes, the extended classical and quantum measurement theories are
equally capable, so we may speak of a single "measurement theory". The
reconciliation of general relativity and quantum theory has been long delayed
because classical and quantum systems have been thought to be very different,
however this unification allows us to discuss a unified measurement theory for
geometry in physics.
