I've recently finished reading Time Travel in Einstein's Universe by J. Richard Gott III, a highly readable treatise on the origins of our universe by an award-winning scholar, professor and writer eminently qualified to author such a book. The last chapter of the book, Report from the Future, is a delightful treatise on the implications of the Copernican principle.

You'll recall that Copernicus created quite a stir by claiming (c. 1530) that the earth was not the central point in the universe about which everything else revolved. The key insight that allowed Copernicus to see this basic fact was his realization that there was nothing special about his location, his point of observation. To quote Gott:

The Copernican principle works because, by definition, out of all the places for intelligent observers to live, only a few special places and many more non-special places exist. You are simply likely to be at one of the many nonspecial places. Christiaan Huygens (Newton's clever contemporaty, who developed the wave theory of light and the most accurate clock of his day) used this principle to correctly predict the distances to the stars. He reasoned, Why should the Sun be special, the brightest light in the universe? He noted that if Sirius, the brightest star seen in the sky, was intrinsically as bright as the Sun, he could figure out its distance simply by estimating how far away you would have to move the Sun to make it look as dim as Sirius. Later investigators found that Huygens had gotten the distance to sirius right to within a factor of 20, a remarkable accomplishment for that day.

Gott realized the Copernican principle can be used to make all kinds of predictions. For example,

Our species, Homo sapiens, has been around for about 200,000 years. If there is nothing special about our time of observation now, we have a 95 percent chance of living sometime in the middle 95 percent of human history. Thus, we can set 95 percent confidence level limits on the future longevity of out species. It should be more than 5,100 years but less than 7.8 million years. The average, or mean, duration of all species lies between 1 million and 11 million years.

Gott goes on to predict future longevity for a number of things including the good old U.S. of A. He states, with 95 percent accuracy, that the USA is likely to last for more than 5.7 years but less than 8,736 years. This is a large span to be sure, no country has ever lasted that long, so the prediction could be improved with the addition of other data, still it means many of us could actually witness the end of the USA and still be within Gott's estimate.

      - Mark