  Among the challenges in discriminating between theoretical approaches to the
glass transition is obtaining suitable data. In particular, particle--resolved
data in liquids supercooled past the mode--coupling crossover has until
recently been hard to obtain. Here we combine nano-particle resolved
experiments and GPU simulation data which addresses this and investigate the
predictions of differing theoretical approaches. We find support for both
dynamic facilitation and thermodynamic approaches. In particular, excitations,
the elementary units of relaxation in dynamic facilitation theory follow the
predicted scaling behaviour and the properties of cooperatively rearranging
regions (CRRs) are consistent with RFOT theory. At weak supercooling there is
limited correlation between particles identified in excitations and CRRs, but
this increases very substantially at deep supercooling. We identify a timescale
related to the CRRs which is coupled to the structural relaxation time and thus
decoupled from the excitation timescale, which remains microscopic.
