The next 500 years
Stuart Brand's Clock of the Long Now (10,000) sets the timeframe for thinking about human survival and planetary habitability.
The temporal unit of 500 years, however, is one in which we have to learn from the past about how to redesign our future.
This is the lifetime of cultures.
It is also the lifetime of the Turchin Principle (reviewed in White 2009): The Empires of today are those who were conquered in the past. From the perspective of a timeless present: Beware of conquest for no purpose. Those whom you conquer will be those who destroy you.
Social physics: Networks and causal chains - Trade, war, and global warming
White, Douglas R. 2009 (forthcoming) Dynamics of Human Behavior (Cohesion and Resistance). To appear in Encyclopedia of Complexity and Systems Science. Berlin, Heidelberg: Springer-Verlag. http://intersci.ss.uci.edu/wiki/pub/Dynamics_of_Human_Behavior3_Cut1f.pdf Roadmap to the paper (Abstract)