Sir

In the issue of 30 September 1993, Landsberg, Dewynne and Please1 used a formula of mine2 to predict how long the Conservative government in Britain would continue its rule. My formula, based on the Copernican principle, stated that, if your location is not special, there is a 95 per cent chance that the future observed longevity of whatever you are observing now will be at least 1/39th as long as its past observed longevity but less than 39 times as long as its past observed longevity. Since the Conservative party had been in power for 14 years in 1993, Landsberg et al. estimated with 95 per cent confidence that it would remain in power for at least 4.3 more months but less than 546 more years.

The Conservative party lost power 3.6 years later, on 2 May 1997, in agreement with the prediction. This was a reasonable application of the formula, because it was prompted by the publication of my paper, whose publication date had no relation to British politics (unlike this letter). Indeed the claim of my paper is that its date of publication, 27 May 1993, is not special (except relative to itself, of course). The Copernican hypothesis can be tested: take an ensemble of things observable on my paper's date of publication and ask whether their future observability is correctly predicted by the formula 95 per cent of the time (see ref. 3 for some examples, from Broadway and off-Broadway plays and musicals to world leaders' terms of office).

There have been other successful predictions. My paper used the above (95 per cent confidence) formula explicitly to predict that the human spaceflight programme would last at least 32/39ths of a year more — it has — and that Nature would continue publication for at least 3.15 more years — it has. The upper limits for these, 1,248 years and 4,800 years respectively, can be checked in the future. If the formula works well in all these applications, we may well take seriously my paper's (95 per cent confidence) prediction for the (200,000-year-old) human race as well: that its future longevity will be at least 5,100 years but less than 7.8 million years.