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Before committing resources to searching for evidence of extraterrestrial intelligence, many scientists would ask: is it worth searching for? It seems fashionable to argue these days that life on Earth is a special case, a result of a unique set of circumstances, unlikely to be repeated elsewhere in the universe. Ashpole repeats the assertion that if the Earth were just a little nearer the sun it would have suffered a runaway greenhouse effect, like Venus, where the surface is hot enough to melt lead, or be a frozen desert, like Mars.
However, the question is not a simple one of solar energy and planetary orbits. Astronomers generally agree that the sun was considerably cooler a few billion years ago, when life first evolved on Earth. Yet the Earth was obviously not frozen then. Pictures from Mars indicate that at some time in the distant past (when the sun was cooler) water flowed on its surface. Yet it has obviously got colder, rather than warmer. Also, Venus actually absorbs less energy from the sun than does the Earth, as the Verusian clouds reflect most of it back into space.
Ashpole does discuss the models on which modem theories of the evolution of the terrestrial planets are based, but the problem is that they tend to say what presumably happened in the past. based on very little direct evidence of actual conditions. The available evidence does indicate, though, as Ashpole states, that planets on which advanced life-forms can evolve must be rather rare, and thus likely to be located at very great distances from us, in time as well as in space.
There is an interesting discussion of the techniques used to detect possible intelligent radio signals, which would be improved if more details had been given. Searching for such signals is obviously very tedious, but the process is becoming increasingly automated, so that observers are alerted only when unusual signals are received and recorded by the apparatus.
In discussing 'ancient astronaut' theories, Ashpole points to the unlikelihood that aliens would have visited Earth only in the last few thousand years when they could have done so at any time in the past few billion. This sort of argument does not impress me. Either we have or have not been visited. The main argument against such visitations is the lack of any reliable evidence of them. In order to evaluate the possibility of extraterrestrials travelling to Earth, we have to consider the possibilities in terms of what seems plausible in the light of our present scientific and technological achievements. In order to do this, Ashpole postulates that there may be a 'ceiling' on our possible progress, so that we now know nearly all there is to know about such matters.
This may seem like the attitude held by many 19th century scientists, who were quickly proved to have been mistaken, but if we assume there are no limits to progress in this sphere, then we must assume that complex extraterrestrials would employ methods completely beyond our powers of imagination. Even when discussions of technological interstellar travel are based on known technological possibilities, discussions of their practicality cause much heated argument. Recommended for those unfamiliar with this topic.
- John Harney, from Magonia 37, October 1990
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