Why is SETI Important?

Science, having spent centuries doing its humble and arduous homework, has finally become competent to address itself to the most fundamental questions of all, the questions asked by children and philosophers: How did it all begin? What am I? Quo vadimus?

All stars are suns. Some are larger and some smaller than the star that warms this Earth; some are younger, but most are older. Stars are not distributed uniformly or randomly throughout space, but instead occur in huge aggregations called galaxies; some of which show a spiral form, others an ellipsoidal shape. Our Galaxy, the Milky Way, is a spiral galaxy containing several hundred billion stars. The universe contains over a billion galaxies, or, in all, more stars than there are grains of sand on all the beaches of Earth.

Out of the findings of the sciences that have converged to give us our present picture of cosmic evolution we draw certain conclusions that are the premises of a plausibility argument for the prevalence of technologically advanced extraterrestrial life.

• Planetary systems are the rule rather than the exception. Our understanding of the process of star formation leads us to expect planetary systems around most stars, and to expect a favorably situated planet in most systems. There are therefore probably on the order of 10**10 potential life sites in the Galaxy.
• The origin and early evolution of life on Earth is apparently explicable in terms of the basic laws of physics and chemistry operating in the primitive terrestrial environment.
• The laws of physics and chemistry apply throughout the universe. Moreover, the composition of the primordial material, from which life on Earth arose in accordance with these laws, is commonly repeated elsewhere.
• The factors causing natural selection, which led to the evolution of more complex species and ultimately to intelligent life on Earth, may reasonably be expected to be present on any planet on which life originated.
• Intelligence, if it develops, is generally believed to confer survival value and therefore to be favored in natural selection. On Earth, intelligence led to attempts to modify and utilize the environment, which were the beginnings of technology. This course of development seems a highly probable one on any earthlike planet.

In their totality these premises argue that the Galaxy contains a tremendous number of planets on which life could start, and evolve, and that there is nothing special about Earth to favor it over the others. Sagan refers to this as the "assumption of mediocrity". It is important to note that the assumption of mediocrity does not imply that living systems elsewhere will have compositions and forms identical to those of Earth. Indeed, such a coincidence would be too improbable to expect. Nor does it imply that life began on every suitable planet, or that it evolved inevitably to possess intelligence and technological prowess. It does imply that the basic processes of stellar, chemical, biological, and cultural evolution are universal and, when carried to fruition, lead to technologies that must have close similarities to ours today and in the future.

It is not important that the particular sequence of events leading to intelligent life on Earth be repeated elsewhere, but only that some sequence occur that leads to a similar end result. Thus, the key question is not whether the precise conditions causing a particular sequence are replicated elsewhere, but whether the forcing functions are present and whether enough alternate routes exist.

The origin and evolution of life would appear to be favored if a planet provides a wide variety of environments -- that is, a range of values for every important parameter. Since all planets will have a range of climate from poles to equator, most will have tilted axes and therefore seasons, and many will have both seas and land and therefore solar tides, we can expect the variety of environments found on Earth to be common. For all we know, life on Earth may have had serious setbacks and been forced to re-evolve. If this be true, the genesis time on many planets may have been much shorter than four billion years.

We can, of course, continue to probe the universe, the atom, and ourselves. But so long as our cosmology is limited to unraveling the evolution of the physical universe and our molecular biology to unraveling the complex chemistry of Earth-based life alone, so long as we are limited to physical cosmology and to geocentric biology, many enormously exciting and very fundamental questions will remain unanswered; these include:

• Are we alone? Is Earth unique not only in the solar system but in the universe? Failure to discover other life could never answer this question in the affirmative, but the discovery of only one other race would provide the needed counterexample and supply at least partial answers to questions that follow.
• How prevalent is life in the universe? Over what range of environmental conditions can it occur?
• Is it the result of independent starts, or are planets "seeded"?
• Is the biochemistry of life unique or are there alternatives to DNA?
• What is the typical longevity of planetary cultures?
• Are evolving life forms very sensitive chemically and morphologically to small differences in environmental factors, or does there tend to be an optimum design for a highly evolved species? In other words is evolution highly divergent or convergent?
• Is interworld communication common or exceptional; does a galactic community of cultures exist?
• Is there interstellar space travel, or merely intercommunication?
• Does life itself serve a role in the evolution of the physical universe, perhaps modifying it in some way; or does it exist completely at the mercy of the latter?
• What is our destiny? Do cultures survive the death of their primary stars? Of a collapsing universe?

These are only a few of the many questions that might be answered by, and perhaps only by, establishing contact with another race. The day this happens will be the birth date for us of a new science, which we might call biocosmology.

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