Critical Mass: How one thing leads to another by Philip Ball

Recently I read a piece by Michael Shermer on hard science, in which he contends that if sciences should be ranked (which they shouldn't) the social sciences are much harder than the physical sciences.

This book tells a story of how physics helps the social sciences. By using techniques from physics, social sciences gets insight into how markets work, how crowds behave, how traffic jams, without needing to go into the messy details of motive and behaviour. Simple rules suffice to produce complex behaviour.

The book has some interesting and hopeful commentary on what we can learn and how we should handle what we get to know from this science.