## "How to Predict Everything"

by Timothy Ferris, The New Yorker, 12 July 1999, pp. 35-39.

Princeton physicist J. Richard Gott III has an all-purpose method for estimating how long things will last. In particular, he has estimated that, with 95% confidence, humans are going to be around at least fifty-one hundred years, but less than 7.8 million years. Gott calls his procedure the Copernican method, a reference to Copernicus' observation that there is nothing special about the place of the earth in the universe. Not being special plays a key role in Gott's method. In this interview with The New Yorker, Gott explains how he developed the method, and gives some of its many other applications.

In 1969, just after graduating from Harvard, Gott was traveling in Europe. While touring Berlin, he wondered how long the Berlin Wall would remain there. He realized that there was nothing special about his being at the Wall at that time. Thus if the time from the construction of the Wall until its removal were divided into four equal parts, there was a 50% chance that he was in one of the middle two parts. If his visit was at the beginning of this middle 50%, then the Wall would be there three times as long as it had so far; if his visit was at the end of the middle 50%, then the Wall would last 1/3 as long as it had so far. Since the Wall was 8 years old when he visited, Gott estimated that there was a 50% chance that it would last between 2.67 and 24 years. As it turned out, it was 20 more years until the Wall came down in 1989. This success of this prediction spurred Gott to write up his method for publication. (It appeared in the journal Nature in 1993.)

The New Yorker has a special interest in knowing how long various theater productions will run. On May 27, 1993, Gott looked up all the shows listed in The New Yorker, including Broadway and off-Broadway plays and musicals. He called each theater to find when the shows had opened. He then used his method to compute 95% prediction intervals for the time they would close. Forty-four shows were running at the time, and so far thirty-six have closed, all at times within his confidence intervals. Since the others are all still within the range he predicted, Gott remarks that he is "batting a thousand" so far!

Gott describes a number of other amusing applications of the Copernican method. For example, the reason that you so often find yourself in the longest line at the supermarket is that there is nothing special about you. You are just a random person waiting to check out. When you choose a random person from those waiting to check out you are more likely to get one from a long line. You can find much of this discussion on-line in an article Gott wrote for The New Scientist: A Grim Reckoning.