SECTION || COLLOQUIES 1. COSMIC EVOLUTION 2. CULTURAL EVOLUTION 3. DETECTION OF OTHER PLANETARY SYSTEMS 4. THE RATIONALE FOR A PREFERRED FREQUENCY BAND: 5. SEARCH STRATEGIES 6. THE SCIENCE OF SETI (These colloquies are general discussions on matters of central importance to SETI. Much of the discussion has been abstracted from the minutes of the meetings of the Science Workshops.) COSMIC EVOLUTION Through the centuries, man has continually searched the sky for clues to his destiny. His imagination has been captivated by the stars, his mind challenged by the mystery of their origin and extent, and his spirit imbued with a thirst for some understanding of his role in the cosmos. Scientific discoveries in fields as diverse as astronomy and molecular biology have brought us, in the course of only the last 15 years, closer to solving three timeless riddles which many cultures have attempted to explain: How did the Universe begin and develop? How did life originate and evolve? What is our place and destiny in the Universe? This burst of interdisciplinary discoveries has given rise to new concepts of the origin of life from inanimate material on the primitive Earth, of the formation of planets and stars, of the synthesis of fundamental particles of matter, and of the beginnings of the Universe itself: all seem to be founded on the same basic laws of chemistry and physics. The conclusion that the origin and evolution of life is inextricably interwoven with the origin and evolution of the cosmos seems inescapable. Taken in its totality, this pathway, from fundamental particles to advanced civilizations, forms the essence of the concept of cosmic evolution. To be sure, the sequence from primordial fireball to matter to stars to planets to prebiotic chemistry to life and to intelligence, is incomplete and even controversial in some of its details. However, a broad picture is emerging, a picture that is both imaginative and illuminating. The Universe appears to have begun as an awesome primordial fireball of pure radiation, commonly referred to as the "big bang," some 15 billion years ago. The totality of matter in the Universe, probably in the form of the most fundamental particles in nature, namely electrons, protons and neutrons, was flung apart with tremendous speed. As the fireball expanded and cooled, thermonuclear reactions produced helium nuclei. Still further expansion dropped the temperature to the point where hydrogen and helium atoms formed by combination of the electrons with the protons and helium nuclei, but elements heavier than helium were not produced in appreciable quantities. During later phases of the expansion, gravitational forces probably acted to enhance any nonuniformities of density that may have existed, and thus began the hierarchy of condensations that resulted in galaxies, stars, and, ultimately, planets. Galaxies apparently had their origin in roughly spherical, slowly rotating, pregalactic clouds of hydrogen and helium which collapsed under their own gravity. When the contraction had proceeded sufficiently, stars began to form, and their rate of formation increased rapidly. The observed distribution of stellar populations agrees qualitatively with this general picture of contraction of the evolving galactic gas cloud. Stars, like living organisms, are not immutable. They are born, evolve, and die. A star begins as a globular fraction of a larger gas cloud. The globule contracts under its own gravity, compressing and heating the gas to incandescence. The luminosity steadily increases as gravitational potential energy is converted into heat. When the internal temperature becomes high enough |