Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Demographic gravitation is a concept of social physics", introduced by Princeton University astrophysicist John Quincy Stewart in 1947. It is an attempt to use equations and notions of classical physics - such as gravity - to seek simplified insights and even laws of demographic behaviour for large numbers of human beings. A basic conception within it is that large numbers of people, in a city for example, actually behave as an attractive force for other people to migrate there, hence the notion of demographic gravitation. It has been related to W. J. Reilly''s law of retail gravitation, George Kingsley Zipf''s Demographic Energy, and to the theory of Trip distribution through gravity models Trip distribution#Gravity model."