Rock2011$ingh1Contention One is ImpactsExtinction is inevitable in the short term absent space colonizationNew York Times ‘7(John Tierney, “A Survival Imperative for Space Colonization” July 17, )In 1993, J. Richard Gott III computed with scientific certainty that humanity would survive at least 5,100 more years. At the time, I took that as reason to relax, but Dr. Gotthas now convinced me I was wrong. He has issued a wake-up call: To ensure our long-term survival, we need to get a colony up and running on Mars within 46 years. If you’re not awakened yet, I understand. It’s only prudent to be skeptical of people who make scientific forecasts about the end of humanity. Dr. Gott, a professor of astrophysics at Princeton, got plenty of grief after he made his original prediction in 1993.But in the ensuing 14 years, his prophetic credentials have strengthened, and not merely because humanity is still around. Dr. Gott has used his technique to successfully forecast the longevity of Broadway plays, newspapers, dogs and, most recently, the tenurein office of hundreds of political leadersaround the world. He bases predictions onjust onebit of data, how long something has lasted already; andon one assumption, that there is nothing special about the particular momentthat you’re observing this phenomenon.This assumption is called the Copernican Principle, after the astronomer who assumed he wasn’t seeing the universe from a special spot in the center. Suppose you want to forecast the political longevity of the leader of a foreign country, and you know nothing about her country except that she has just finished her 39th week in power. What are the odds that she’ll leave office in her 40th week? According to the Copernican Principle, there’s nothing special about this week, so there’s only a 1-in-40 chance, or 2.5 percent, that she’s now in the final week of her tenure. It’s equally unlikely that she’s still at the very beginning of her tenure. If she were just completing the first 2.5 percent of her time in power, that would mean her remaining time would be 39 times as long as the period she’s already served — 1,521 more weeks (a little more than 29 years). So you can now confidently forecast that she will stay in power at least one more week but not as long as 1,521 weeks. The odds of your being wrong are 2.5 percent on the short end and 2.5 percent on the long end — a total of just 5 percent, which means that your forecast has anexpected accuracy of 95 percent, the scientific standard for statistical significance. And you can apply this Copernican formula to lots of other phenomena by assuming they’re neither in the first 2.5 percent nor the final 2.5 percent of their life spans. Now, that range is so broad it may not seem terribly useful to you, and Dr. Gott readily concedes that his Copernican formula often is not the ideal method.