Oh, that's very much encapsulated in the concept of space and time. Alternate realities are generally believed, and can most certainly be created by, different decisions and actions taken at crucial points in time. With each individual making countless potentially reality-altering choices in any given moment, there are believed to be innumerable realities that bear very little resemblance to one another ultimately, but could possibly be traced to crucial moments which led to their deviance, provided enough information were available.