Almost forty years ago, the Space Science board of the US National Academy of Sciences considered it appropriate to sponsor a preliminary examination of the problem of extraterrestrial intelligent life in the universe. An informal conference was held in November 1961, at the National Radio Astronomy Observatory at Green Bank, West Virginia. The purpose of the discussions was to examine the prospects for the existence of other societies in the galaxy with whom communications might be possible; to attempt an estimate of their number; to consider some of the technical problems involved in the establishment of communication; and to examine ways in which our understanding of the problem might be improved. To facilitate orderly discussion, one of host organizers, Frank Drake, sought to formulate the conference's central problem as an equation. The expression presented for this purpose was:
N = R.fpneflfifcL
In this equation N is the estimated number of communicative societies in the galaxy at any time, R. is the rate of star formation, fp the fraction of stars forming planets, ne the number of planets per star with environments suitable for life, fl the fraction of suitable planets on which life appears, fi the fraction of these planets where life evolves into intelligence, fc the number of intelligent cultures which are communicative in an interstellar sense, and L the mean lifetime of such civilizations. Sagan* considered an estimate of one million technological civilizations in the galaxy to be conservative. Others are less optimistic.
I believe it really is impossible to realistically estimate those odds because with only a slight difference in the interpretation of the statistics, you can get numbers that are very large, very small, or anywhere in between. Presentations arguing for all of these positions have been delivered at meetings of professional astronomers, which simply reinforces the impossibility of making good a priori estimations about the likelihood of intelligent life in our galaxy. The only way to determine this value is by performing a comprehensive observational program.
We can say, that over the years, the Drake Equation was taken as the dominant paradigm that justifies the SETI (Search for Extraterrestrial Intelligence) research programs. In this way, SETI proponents operate under a two-pronged hypothesis. The first assumption, known as the Principle of Mediocrity, is that the development of life is a basic, unexceptional consequence of physical processes taking place in appropriate environments—in this case on Earth-like planets. The idea is that if these processes occur on Earth, they will occur in the same way anywhere else with the same conditions. Because our galaxy has hundreds of billions of stars, and the Universe has billions of galaxies, there should be many "elsewheres," habitable Earth-like planets, and life should be common in the cosmic realm. Of course, the diversity of living systems elsewhere would surpass the imagination, and we cannot even begin to speculate about the abundance of other types of life that might evolve in environments much different from Earth, and which would be based on radically different types of biology.
The second assumption is that on some planets which shelter broods of living creatures, at least one species will develop intelligence and a technological culture that will have an interest in communicating with other sentient creatures elsewhere in the cosmos, and will beam signals out into space with that goal. If these cultures would, like us, use electromagnetic signals to communicate, and that the signals they produced would have an artificial signature we could recognize, it should be possible to detect these electromagnetic waves, establish contact with these civilizations, and exchange information across interstellar distances.
Under all these assumptions, we may expect a logical progression: the presence of planets with suitable environments will lead to the emergence of life, which will lead to the emergence of intelligence, which will give rise to interstellar communication technology. Viewed from one angle, it may be said that SETI programs are simply attempts to test this theory.
Another basic assumption of SETI researchers is that the physical laws governing the universe are the same everywhere in the cosmos. If this is true, then the basic principles of our science and the science of extraterrestrial beings should be fundamentally the same, and we should be able to communicate with them by referring to those things we share in common: the principles of mathematics, physics, chemistry and so on.
Rescher* argues that despite sharing universal laws with us, extraterrestrials are extremely unlikely to have any type of science we would recognize. He contends that they will be very different organisms, with different needs, senses, and behaviors, and that, as Mayr* suggests, they may inhabit environments in which neither science nor technology may needed for survival. Even if they do have technology, Rescher argues, the science of an alien civilization would reflect the way they perceive nature, as funneled through the course of their particular evolutionary adjustment to their specific environment, and that will make it impossible for us to distinguish any of their possible intelligent manifestations.
All intelligent problem-solvers are subject to the same ultimate constraints: limitations on space, time and resources. In order for life to evolve powerful ways to deal with such constraints, they must be able to represent the situations they face, and they must have processes for manipulating those representations. Minsky* proposes two basic principles for every intelligence:
ECONOMICS: every intelligence must develop symbol-systems for representing objects, causes and goals, and for formulating and remembering the procedures it develops for achieving those goals.
SPARSENESS: every evolving intelligence will eventually encounter certain very special ideas — e.g. about arithmetic, casual reasoning and economics — because these particular ideas are very much simpler than other ideas with similar uses.
Minsky believes that because we and they will have had to develop these principles in order to survive and develop technology, aliens will have evolved thought processes and communication strategies that will match our own to a degree that will enable us to comprehend them. SETI proponents largely agree with him, and go farther to assume that all galactic civilizations will converge in their interpretations of the physical laws. It is likely, they believe, that we will be able to communicate with extraterrestrials about scientific principles, and especially about mathematics.
According to this hypothesis, aliens will have evolved thought processes and languages that will match our own somewhat that will enable us to comprehend them. SETI proponents have the implicit assumption that there is some sort of "convergence" in all the different interpretations of the physical laws, among the galactic civilizations.
Another consideration is that technological civilizations must survive long enough to be discovered. There are obvious advantages to intelligence and technology: once, a mere 100,000 or so hominids dwelt in Africa's Rift; now nearly six billion of their descendants live the world around, an increase in number of nearly five orders of magnitude, a population growth that few other organisms have matched. However, these advantages are counterbalanced by threats when civilizations reach our evolutionary stage—what the late Carl Sagan called "technological adolescence"—when technology brings the potentially civilization-ending threats of ecological catastrophe, the exhaustion of natural resources, and nuclear war. Barring such disasters, the physical environment of the Earth will remain stable for several billion years, because intelligence and technology have developed here about halfway through the stable eight billion-year life-period of the sun.
The only significant test of the existence of extraterrestrial intelligence is an experimental one. No a priori arguments on this subject can be compelling or should be used as a substitute for an observational program.
The acronym SETI is in some sense misnomer. As of now, we have no means for directly detecting intelligence over interstellar distances. What we can do is to attempt to detect any manifestation of a technological activity, produced by that intelligence. Imagine that we find, in the middle of the ocean, a message inside a bottle. We may be unable to understand the message, but surely we can make the abduction that an intelligent being created the bottle. Abductive reasoning accepts a conclusion on the grounds that it explains the available evidence. It addresses a wide range of issues concerning the logic of discovery and the economics of research.
Contrary to the traditional statement that the scientific grounds of the SETI project is based on the possible numbers of the Drake Equation, here we have proposed a different epistemological approach. Using the hypothetico-deductive method, we just make the hypothesis that there should be other intelligent beings in the Universe. We just do not make any kind of hypothesis about the different evolutionary paths and planetary or other cosmic environments that would let the intelligence to appear. In order to test this hypothesis or more appropriately to falsify it, we must developed a comprehensive search for extraterrestrial technological activities (SETTA). The laws of nature will always place limits to any possible technological manifestation.
It is much simpler to distinguish the artificial origin of a technological activity than to establish a universal criterion to determine how to recognize the signature of life on other worlds. Based in our understanding of the laws of nature, we can systematically explore all the possible artificial signatures. Harwit and Tarter* determined how to estimate, in a first approach, the limits of our space of configuration. Our cosmic haystack has 1029 different "cells". Until now, just a mere fraction of 1013 to 1014 has been explored and we are still unable to verify or falsify our hypothesis that there are other intelligent beings in the Universe.
* all references omitted
Detectability of Intelligent Life in the Universe: A Search Based in our Knowledge of the Laws of Nature, Guillermo A. Lemarchand, in Astrobiology By Julián Chela Flores, Guillermo A. Lemarchand, J. Oró
No comments:
Post a Comment