This volume is about "Structure". The search for "structure", always the
pursuit of sciences within their specific areas and perspectives, is
witnessing these days a dra- matic revolution. The coexistence and
interaction of so many structures (atoms, hu- mans, cosmos and all that
there is in between) would be unconceivable according to many experts,
if there were not, behind it all, some gen- eral organizational
principle. s that (at least in some asymptotic way) make possible so
many equilibria among species and natural objects, fan- tastically tuned
to an extremely high degree of precision. The evidence accumulates to an
increasingly impressive degree; a concrete example comes from physics,
whose constant aim always was and is that of searching for "ultimate
laws", out of which everything should follow, from quarks to the cosmos.
Our notions and philosophy have un- dergone major revolutions, whenever
the "unthinkable" has been changed by its wonderful endeavours into
"fact". Well, it is just from physics that evidence comes: even if the
"ultimate" could be reached, it would not in any way be a terminal
point. When "complexity" comes into the game, entirely new notions have
to be invented; they all have to do with "structure", though this time
in a much wider sense than would have been understood a decade or so
ago.