  The real area of contact of a frictional interface changes rapidly when the
normal load is altered, and evolves slowly when normal load is held constant,
aging over time. Traditionally, the total area of contact is considered a proxy
for the frictional strength of the interface. Here we show that the state of a
frictional interface is not entirely defined by the total real area of contact
but depends on the geometrical nature of that contact as well. We directly
visualize an interface between rough elastomers and smooth glass and identify
that normal loading and frictional aging evolve the interface differently, even
at a single contact level. We introduce a protocol wherein the real area of
contact is held constant in time. Under these conditions, the interface is
continually evolving; small contacts shrink and large contacts coarsen.

Soft Condensed Matter;Geophysics