The problem with making predictions about a complex system (nonlinear system) like human civilization is that there are so many factors and variables that can affect the trajectory that accurate prediction is virtually impossible. You would think that, of all people, a physicist would appreciate that and thus refrain from making strong claims about the future trajectory of such a system.

http://en.wikipedia.org/wiki/Butterfly_effect

http://necsi.edu/research/overview/prediction.html