...is not as time-consuming as one might think. Humans could begin the process by sending colonists to two nearby stars, a trip that might take 100 years with foreseeable technology. After 400 years to dig in, each colony sends out two of its own, and so on. Within 10,000 years our descendants could inhabit every star system within 200 light-years. Settling the entire galaxy would take 3.75 million years--a split second in cosmic terms.