  Glasses and disordered materials are known to display anomalous features in
the density of states, in the specific heat and in thermal transport.
Nevertheless, in recent years, the question whether these properties are really
anomalous (and peculiar of disordered systems) or rather more universal than
previously thought, has emerged. New experimental and theoretical observations
have questioned the origin of the boson peak and the linear in T specific heat
exclusively from disorder and TLS. The same properties have been indeed
observed in ordered or minimally disordered compounds and in incommensurate
structures for which the standard explanations are not applicable. Using the
formal analogy between phason modes (e.g. in quasicrystals and incommensurate
lattices) and diffusons, and between amplitude modes and optical phonons, we
suggest the existence of a more universal physics behind these properties. In
particular, we strengthen the idea that linear in T specific heat is linked to
low energy diffusive modes and that a BP excess can be simply induced by gapped
optical-like modes.
