The End of Average: How We Succeed in a World That Values Sameness

by Todd Rose

They wanted to know if they could use the average behavior of a group of gas molecules to predict the average behavior of a single gas molecule. To answer this question, physicists worked out a set of mathematical principles known as ergodic theory that specified exactly when you could use information about a group to draw conclusions about individual members of the group.9 The rules are fairly straightforward. According to ergodic theory, you are allowed to use a group average to make predictions about individuals if two conditions are true: (1) every member of the group is identical, and (2) every member of the group will remain the same in the future.10 If a particular group of entities fulfills these two conditions, the group is considered to be “ergodic,” in which case it is fine to use the average behavior of the group to make predictions about an individual. Unfortunately for nineteenth-century physicists, it turned out that the majority of gas molecules, despite their apparent simplicity, are not actually ergodic.11