Dear Seth Shostak
27th April 2000
It is 400 years since Giordano Bruno was burnt at the stake for heresy. He believed that the earth was not at the centre of the universe and that life on Earth was not unique. He was right about the former, but what about the latter?
Asked the question “are we alone in the Universe?” most people believe that the answer is “no,” even when the question specifies that life elsewhere must be able to communicate with us in an intelligible form. Supporters of the “life is unique” brigade have a big hill to climb. Let me start the ascent.
The argument of those who believe that we are not alone runs as follows. There are many stars in the galaxy (many more in the Universe) and many have planets. A large fraction of these will have the conditions necessary for our kind of life: oxygen, water, and so on. It is then only one step to the evolution of intelligent life, et voilà: “Life is common.” End of problem.
True, planets are quite common around other stars, and their presence has been demonstrated by a number of scientists using the techniques of optical astronomy; it should not be long before planets with the ingredients of life are detected. Moreover, the recent work on the Mars meteorite, with the possible detection of bacteria-style fossils, is intriguing. Although there is considerable argument about the accuracy of these findings, free water was found on the early Martian surface and there may well be elementary life beneath the surface now. It would not be surprising if elementary life-Martian-style-were common.
It is the next step-a step which took 3 billion years on Earth-which worries me: the transition from elementary biological systems (perhaps extending as far as lower animals) to the polished intelligent beings who now inhabit Earth. My worries are twofold.
The first concerns the factors which can snuff out life before it reaches the intelligent category. Setting aside naturally occurring problems of climate, fertility and so on, there are astronomical hazards associated with the impact of extraterrestrial bodies, enhanced emissions from the Sun, and effects from other stars. This problem is arousing considerable interest, not least because the US military has found a new enemy to replace the Russians. Although it looks as though Earth could last a billion years before the doomsday comet arrives,…