  We explain how the disparate kinematics of quantum mechanics
(finite-dimensional Hilbert space of QM) and special relativity (Minkowski
spacetime from the Lorentz transformations of SR) can both be based on one
principle (relativity principle). This is made possible by the axiomatic
reconstruction of QM via information-theoretic principles, which has
successfully recast QM as a principle theory a la SR. That is, in the quantum
reconstruction program (QRP) and SR, the formalisms (Hilbert space and Lorentz
transformations, respectively) are derived from empirically discovered facts
(Information Invariance & Continuity and light postulate, respectively), so QM
and SR are "principle theories" as defined by Einstein. While SR has a
compelling fundamental principle to justify its empirically discovered fact
(relativity principle), QRP has not produced a compelling fundamental principle
or causal mechanism to account for its empirically discovered fact. To unify
these disparate kinematics, we show how the relativity principle ("no preferred
reference frame" NPRF) can also be used to justify Information Invariance &
Continuity. We do this by showing that when QRP's operational notion of
measurement is spatialized, Information Invariance & Continuity entails the
empirically discovered fact that everyone measures the same value for Planck's
constant h, regardless of their relative spatial orientations or locations
(Planck postulate). Since Poincare transformations relate inertial reference
frames via spatial rotations and translations as well as boosts, the relativity
principle justifies the Planck postulate just like it justifies the light
postulate. Essentially, NPRF + c is an adynamical global constraint over the
spacetime configuration of worldtubes for bodily objects while NPRF + h is an
adynamical global constraint over the distribution of quanta among those bodily
objects.
