  Models of quantum gravity imply a fundamental revision of our description of
position and momentum that manifests in modifications of the canonical
commutation relations. Experimental tests of such modifications remain an
outstanding challenge. These corrections scale with the mass of test particles,
which motivates experiments using macroscopic composite particles. Here we
consider a challenge to such tests, namely that quantum gravity corrections of
canonical commutation relations are expected to be suppressed with increasing
number of constituent particles. Since the precise scaling of this suppression
is unknown, it needs to be bounded experimentally and explicitly incorporated
into rigorous analyses of quantum gravity tests. We analyse this scaling based
on concrete experiments involving macroscopic pendula and provide tight bounds
that exceed those of current experiments based on quantum mechanical
oscillators. Furthermore, we discuss possible experiments that promise even
stronger bounds thus bringing rigorous and well-controlled tests of quantum
gravity closer to reality.
