One of the main tools for the evaluation of the possible number N of technological civilizations with which we could enter in touch via radio-waves is the famous Drake Equation: N = R x Fp x ne x Fl x Fi x Fc x L Only R has a reasonably certain value (that is, more or less, 10 per year), while we can only make suppositions about all the other terms, because we have neither, at present, a deep enough knowledge of the laws of nature involved in the related processes, nor the possibility to observe them directly (even if the most recent discoveries of extra-solar planets, although only indirect, allow us to suppose that Fp should be very high, maybe near 1). Anyway, progress both theoretical and technological should provide, in the next future, an increasing amount of data about these subjects as far as Fi, so that our assessments about the first five terms of the Equation should be improved more and more in time. On the contrary, this task sounds particularly difficult with reference to the sixth and seventh terms, Fc and L, because in these cases we seem not to have any law of nature at all to base on, in order to carry out our estimations. The development and the longevity of a technological civilization able to communicate with us, indeed (as well as the decision of actually communicating), seems to depend only on the intelligence, the enterprise and the free choices of its members, which, obviously, cannot be possible objects for science. Anyway, it is possible to find some constraints on this process, which, on the contrary, can be scientifically evaluated. One of them (maybe the main one) is, in my opinion, the problem of energy sources. The starting point is the consideration that any technological civilization needs, for its development, a large amount of free energy. Obviously, we cannot know what kind of energy sources could be used by another, more advanced civilization. However, it is possible to make some reliable considerations basing on what we can deduce about this subject looking at our own history, because we are able to communicate via radio-waves, consequently our present degree of technological development, as primitive as it could be, is a good touchstone for our purposes. If we consider carefully the energy sources we know, we’ll find a surprising circumstance: they are all strictly related with life. This implies that many of the “cosmic coincidences” related with life in the so-called “Anthropic Principle” hold for the energy sources, too. But there are also others, more specific. So, we could even speak about a “Techno-Anthropic” Principle, meaning by this that: “Our universe is shaped in such a way that its laws allow the birth of technological civilizations”. But, from another point of view, just from a very rough observation we can easily see that, while the total amount of fuel needed to develop a given amount of energy tends to decrease with the development of technology, on the contrary the size and complexity of the “match” needed for it tend to increase. This relation seems to hold universally, because it is based on the laws of nature. So, it is very unlikely that a technological civilization could ever arise without needing to use, at least for a while, the simplest energy sources, among which a crucial role is played by fossil fuels. Thus, on one side we should admit that every intelligent species in the universe should have a very high a priori probability (very likely equal to 1) to develop technology. On the other, some precise constraints are implied by what we have said, both on the rising and the duration of a technological civilization. One of these is that intelligent life must evolve on dry land, otherwise it would be unable to use fossil fuels (which must be burnt to provide energy). Now, this may be a very restrictive condition, because, as recently pointed out by Peter D. Ward and Donald Brownlee (see Rare Earth, Copernicus Springer-Verlag, New York, 2000), for the existence of dry land plate tectonics and a very precise amount of liquid water are needed, which may be both very rare. So, even if intelligent life were very widespread in our universe, technological life may be very rare. Should it be the case, this would a very bad new for SETI. But, from another point of view, it would also disclose a new horizon, because it would mean that our search should be directed towards a very little number of very peculiar stars, which scientific progress will identify better and better in the future.
|Titolo:||On the last terms of Drake Equation: the problem of energy sources and the “Rare Earth hypothesis”|
|Data di pubblicazione:||2001|
|Appare nelle tipologie:||Relazione (in Volume)|