Experimental evidences of universal relaxation and diffusion properties
in complex materials and systems are presented. The materials discussed
include liquids, colloids, polymers, rubbers, plastic crystals,
biomolecules, ceramics, electrolytes, fuel cell materials, molten salts,
inorganic, organic, polymeric and metallic glass-formers. The origin of
the universal properties is traced to the relaxation dynamic of
interacting many-body systems, rigorous theory of which does not exist
as this time. However taking advantage of some insight and guides by
solutions of much simplified models, predictions of the properties have
been generated. The predictions can explain qualitative as well as
quantitative in many cases the experimentally observed properties of
different complex materials, essentially from the strength of the
many-body interaction. The success provides some measure of
understanding the relaxation properties of complex interacting systems
and also paves the way for the construction of rigorous theories in the
future. Change of relaxation dynamics when dimensions are reduced to
nanometer scale are also considered and discussed.