advanced technology, then the probability is high that civilizations more advanced than ours have either visited the solar system or left a beacon nearby. Accordingly, the only way to account for the silence is to adopt a value of 1 for N. Supporters of N = 1 also appeal to the element of chance in the stability of the Earth’s climate, stressing its uniqueness as a condition for sustained life. But this view might be offset by appeal to the Gaia hypothesis (Lovelock, 1979) which argues that stability necessary for life is maintained in terms of open system interaction between the atmosphere, hydrosphere and the Earth’s crust, and that certain feedback mechanisms – the evolution of microbes and marine organisms – contribute to the maintenance of a geothermal steady state. On such principles it is held to be probable that other biosystems are maintaining similar eco-systems.
There are various biologically based objections to the N = 1 school, which appeal to the ability of life to adapt to a wide range of habitats and claim that the emergence of creatures with mammalian intelligence is a repeatable phenomenon among numerous phyletic lines on Earth and is likely to emerge elsewhere.
What is the methodological status of the Drake equation? It is frequently said that it is more a way of organizing ignorance than a defining scientific methodology. According to Jakosky (1998: 285) Drake’s equation is ‘just a mathematical way of saying “who knows?” ’ But he adds: ‘It does allow us to focus on those issues that have the largest uncertainties: Does life occur on every planet where it is possible? Does intelligent life evolve as an imperative? How long can a civilization last?’ It poses questions rather than answers; it does not provide proof, but it gives a structure to hypothesis generation which is based on falsifiable empirical developments in major branches of science including astrophysics and biology. Drake’s structure conveys plausibility, which is not destroyed by the failure of any particular search; yet the component theories and empirical statements in Drake’s structure are subject to either corroboration or falsification as knowledge develops. As long as this structure remains intact, it is possible to employ it when hypothesizing about intelligent civilizations. Yet it does not tell us where to look, and no extraterrestrial civilization can be deduced from it. It does not provide an indication of how many technological civilizations may exist; it is not an instrument that will tell us how to find them, but rather it brings together a series of problems to be solved by means of a fusion of many disciplines.
SETI, as Timothy Ferris (1992: 25) argues, is not so much a science as ‘a campaign for exploration’. It has a broad emotional and metaphysical appeal, which accounts for its attractiveness, but it captures the excitement of the explorer rather than the investigative scientist. The difference between science and exploration is very fine, but basically science survives by making accurate predictions. Exploration does not: many of the great explorers have failed to provide even the remotest sign of an accurate prediction. The ancient Chinese navigated the Pacific in search of the elixir of life; Columbus predicted that he
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could sail west all the way to the Indies, which was impossible, especially as he believed that the Earth was merely one-third of its true size. We search for extraterrestrial intelligence, not because we have any hard knowledge of its existence, or know that we can find it, but because we think we might. Yet campaigns for exploration are an integral feature of frontier science, where the generation of untested hypotheses, new theories and experimental instruments are simultaneous with techniques of persuasion and appeals to future rewards.
The belief in the possibility of extraterrestrial intelligence as well as the Copernican principle, which displaces the idea of a unique Earth, functions like other metaphysical regulators in science. These beliefs, which are akin to what Sir Karl Popper describes as non-falsifiable conjectures about the world, have stimulated and directed scientific inquiry. They include some of the great scientific theories, such as the Cartesian theory of matter as a continuum, Democritus’ atomic theory and Einstein’s General Relativity Theory. What matters most is that the hypotheses derived from them are testable and conform to established scientific knowledge.
The authors of the Cyclops Report envisaged a search that would take centuries and spoke of the need for faith and perseverance as well as the latest technology.
To undertake so enduring a program not only requires that the search be highly automated, it requires a long-term funding commitment. This in turn requires faith. Faith that the quest is worth the effort, faith that man will survive to reap the benefits of success, and faith that other races are, and have been equally curious and determined to expand their horizons. We are almost certainly the first intelligent species to un-dertake the search. The first races to do so undoubtedly followed their listening phase with long transmission epochs, and so have later races to enter the search. Their perseverance will be our greatest asset in our beginning listening phase.
(Oliver and Billingham, 1973: 171)
Nevertheless, as a call for exploration the Drake equation appeals to many branches of science. R* is the province of geophysics and astrophysics; f p involves geophysics and atmospheric physics and ne is to be examined in the boundary between astronomy and biology; f l involves organic chemistry and biochemistry; f i involves neurophysiology; f c is bound up with anthropology, archaeology and history, while L is inescapably linked to politics, sociology and psychology. Although SETI is not taught in universities as a scientific subject and does not have its own scientific journal, it is very much in the field of the interdisciplinary empirical sciences bringing together work in astronomy, physics, engineering, biology and the social sciences.
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