Centrifugal forces

摘要

"In the second century of the Chris-tian era," Edward Gibbon began his "Decline and Fall of the Roman Empire", "the empire of Rome comprehended the fairest part of the earth and the most civilised portion of mankind." America could lay claim to a modern equivalent. At the start of the 21st century, the empire of the United States has created the most open and dynamic society in the world. One indicator of social dynamism is population growth. In the 20th century, America's population increased by 250%, whereas France's and Britain's rose by less than 60%. In the past ten years, the number of Americans has risen from 263m to almost 30om, the fastest growth for 40 years. America's population is rising more than twice as fast as the European Union's, and two-thirds of that growth comes from natural increase, whereas almost all the modest rise in the EU'S population recently has come from immigration.