Extraterrestrial Civilizations Read online

  Also by Isaac Asimov:

  EARTH: OUR CROWDED SPACESHIP

  REALM OF NUMBERS

  EXTRATERRESTRIAL CIVILIZATIONS

  THIS BOOK CONTAINS THE COMPLETE TEXT OF THE

  ORIGINAL HARDCOVER EDITION.

  Published by Fawcett Columbine Books, a unit of

  CBS Publications, the Consumer Publishing Division of

  CBS Inc., by arrangement with Crown Publishers, Inc.

  Copyright ©1979 by Isaac Asimov

  ALL RIGHTS RESERVED

  eISBN: 978-0-307-79230-3

  v3.1

  To the memory of Paul Nadan (1929-1978)

  for whom I should have

  started the book sooner.

  Contents

  Cover

  Other Book by This Author

  Title Page

  Dedication

  Copyright

  1 ·The Earth

  Spirits

  Animals

  Primates

  Brains

  Fire

  Civilization

  2 · The Moon

  Phases

  Another World

  Waterlessness

  Moon Hoax

  Airlessness

  3 · The Inner Solar System

  Nearby Worlds

  Venus

  Martian Canals

  Mars Probes

  4 · The Outer Solar System

  Planetary Chemistry

  Titan

  Jupiter

  5 · The Stars

  Substars

  The Milky Way

  The Galaxy

  The Other Galaxies

  6 · Planetary Systems

  Nebular Hypothesis

  Stellar Collisions

  Nebular Hypothesis Again

  The Rotating Stars

  The Wobbling Stars

  7 · Sunlike Stars

  Giant Stars

  Midget Stars

  Just Right

  8 · Earthlike Planets

  Binary Stars

  Star Populations

  The Ecosphere

  Habitability

  9 · Life

  Spontaneous Generation

  Origin of Life?

  The Primordial Earth

  Meteorites

  Dust Clouds

  When Life Started

  Multicellular Life

  Land Life

  Intelligence

  10 · Civilizations Elsewhere

  Our Giant Satellite

  Our Captured Satellite?

  Intelligence

  Extinction

  Cooperation

  Exploration

  Visits

  11 · Space Exploration

  The Next Targets

  Space Settlements

  Space Mariners

  Stepping Stone

  12 · Interstellar Flight

  The Speed of Light

  Beyond the Speed of Light

  Time Dilatation

  Coasting

  Worlds Adrift

  13 · Messages

  Sending

  Receiving

  Photons

  Microwaves

  Where?

  Why?

  CHAPTER 1

  The Earth

  The question is: Are we alone?

  Are human beings the only possessors of eyes that probe the depths of the Universe? The only builders of devices to extend the natural senses? The only owners of minds that strive to understand and interpret what is seen and sensed?

  And the answer is, just possibly: We are not alone! There are other kinds that seek and wonder, and do so perhaps even more effectively than we.

  Many astronomers believe this is so, and I believe this is so.

  We don’t know where those other minds are, but they are somewhere. We don’t know what they do, but they do much. We don’t know what they’re like, but they are intelligent.

  Will they find us if they are somewhere out there? Or have they found us already?

  If they have not found us, can we find them? Better yet, should we find them? Is it safe?

  These are the questions that must be asked once we agree that we are not alone, and astronomers are asking them.

  The whole matter of the search for extraterrestrial intelligence has now become so common, in fact, that it has been abbreviated to save trouble in referring to it. Astronomers now refer to it as SETI, from the initials of the phrase “the search for extraterrestrial intelligence.”

  The first scientific discussion of SETI that offered a hope of carrying through the search successfully came only in 1959. It is natural to suppose, then, that the question of intelligence other than our own is of recent vintage. It would seem to be entirely a twentieth-century phenomenon arising out of the advance of astronomy in recent decades. It would seem to be the child of rocketry and of manned flight in outer space.

  Perhaps you may feel that prior to the last few decades, human beings took it for granted that we were alone, and that the new view of other-intelligence is coming as a great shock to people and is forcing them willy-nilly to undergo an internal revolution of outlook.

  Nothing could be farther from the truth!

  It has been taken for granted by almost all people through almost all of history that we are not alone. The existence of other intelligences has been accepted as a matter of course.

  Such beliefs have not arisen through the advance of science. Quite the contrary. What science has done has been to remove the supports from under the early casual assumptions as to the existence of other-intelligence. Science has created a new view of the world around us in which, by the old standards, humanity stands alone.

  Let us start with that establishment of aloneness before we can go on to a new view of a new kind of other-intelligence.

  SPIRITS

  To go back to the beginning, we will have to recognize that the phrase extraterrestrial intelligence is already sophisticated. It refers, after all, to intelligence found on worlds other than Earth and for it to have meaning there must be some recognition that worlds other than Earth exist.

  To the vast majority of human beings, however, through almost all of history, there were no worlds other than Earth. Earth was the world, the home of living things. The sky, to early observers, was exactly what it appeared to be: a canopy overhanging the world, blue by day and punctuated by the round glare of the Sun; black by night and pin-pricked with the brightness of the stars.

  Under those conditions, the phrase extraterrestrial intelligence has no significance. Let us talk, instead, of nonhuman intelligence.

  As soon as we do that, we can see at once that human beings of the prescientific age always assumed that humanity was not alone; that the one world they thought of as filling the universe contained a variety of nonhuman intelligences. Not only was human intelligence one of very many, but it was very likely to be the weakest and least advanced of all.

  To the prescientific mind, after all, events in the world seemed whimsical and willful. Nothing followed natural and inexorable “law” because law was not recognized as part of the Universe. If something happened unpredictably, it was not because not enough was known to predict it, but because every part of the Universe was behaving with free will and doing things through some uncomprehended motivation—through even, perhaps, an incomprehensible motivation.

  Free will is inevitably associated with intelligence. To do something willful, after all, you have to understand the existence of alternatives and choose among them, and these are attributes of intelligence. It seemed to make sense, therefore, to consider intelligence a universal aspect of nature.

  To the early Greeks (whose myths we know best), every aspect of nature had its spirits. Every mountain, every rock, every stream, every pool, every tree, had its nymph, marked not only by intelligence but even by a more or less human shape.

  The ocean had its deity, as did the sky and the underworld; they were given human attributes such as childbirth and sleep, and various levels of abstraction such as art, beauty, and chance.

  As time went on, Greek thinkers grew sophisticated enough to view all these spirits and deities as symbols, and to strive to withdraw them from human associations.

  Thus, Zeus and his fellow gods were thought to live on Mount Olympus in northern Greece to begin with, but were later transferred to a vague “Heaven” in the sky.* The same transfer took place in the case of the God of the Israelites, who originally lived on Mt. Sinai or in the Ark of the Covenant, but who was eventually relocated to Heaven.

  In the same way, the world of the spirits of the dead could be thought of at first as sharing the one world with the living. Thus, in the Odyssey, Odysseus visits Hades in some vague spot in the far West, and it is somewhere in the West that the Elysian Fields, the Greek Paradise, may also have existed. The spirits of the dead were eventually transferred to a semimystical underground Hell.

  Nevertheless, this process of sophisticated abstraction is a purely intellectual phenomenon intended to save the thinker the embarrassment of unsophisticated opinions. They rarely affected the common person.

  Thus, whatever the Greek philosopher may have thought as to the cause of rain, the common uneducated farmer may have thought of rain (as Aristophanes jokingly says in one of his plays) as “Zeus pissing through a sieve.”

  In the contemporary United States, meteorology is a complex study, and the changes in weather are treated as natural phenomena that follow l
aws so complex, alas, that even yet we do not thoroughly understand them and can predict with only moderate accuracy. To many Americans, however, a drought, for instance, is the will of God, and they flock to the churches to pray for rain under the impression that the plans God has made are so trivial and unimportant that He will change them if asked to do so.

  We are used to thinking of all the gods and demons of mythology as “supernatural,” but that is not really a proper use of the term. Any culture in its myth-making stage does not yet have the concept of natural law in the modern sense, so that nothing is really supernatural. The gods and demons are merely superhuman. They can do things that human beings cannot.

  It is only modern science that introduced the concept of natural laws that cannot be broken under any circumstances—the various laws of conservation, the laws of thermodynamics, Maxwell’s laws, quantum theory, relativity, the uncertainty principle, causal relationships.

  To be superhuman is perfectly permissible, for cases of it are common. The horse is superhuman in speed; the elephant in strength; the tortoise in longevity; the camel in endurance; the dolphin in swimming. It is even conceivable that some nonhuman entity might be of superhuman intelligence.

  To transcend the laws of nature, be “supernatural” is, however, impermissible in the Universe as interpreted by science, in the “Scientific Universe,” which is the only one dealt with in this book.

  It might easily be argued that human beings have no right to say that this or that is “impermissible”; that something that is called supernatural receives its name by arbitrary definition out of knowledge that is finite and incomplete. Every scientist must admit that we do not know all the laws of nature that may exist, and that we do not thoroughly understand all the implications and limitations of the laws of nature that we think do exist. Beyond what little we know there may be much that seems “supernatural” to our puny understanding, but that nevertheless exists.

  Quite right, but consider this—

  When we lead from ignorance, we can come to no conclusions. When we say, “Anything can happen, and anything can be, because we know so little that we have no right to say ‘This is’ or ‘This isn’t,’ ” then all reasoning comes to a halt right there. We can eliminate nothing; we can assert nothing. All we can do is put words and thoughts together on the basis of intuition or faith or revelation and, unfortunately, no two people seem to share the same intuition or faith or revelation.

  What we must do is set rules and place limits, however arbitrary these may seem to be. We then discover what we can say within these rules and limits.

  The scientific view of the Universe is such as to admit only those phenomena that can, in one way or another, be observed in a fashion accessible to all, and to admit those generalizations (which we call laws of nature) that can be induced from those observations.

  Thus, there are exactly four force fields that control all the interactions of subatomic particles and therefore, in the long run, all phenomena. These are, in order of discovery, the gravitational, the electromagnetic, the strong nuclear, and the weak nuclear interactions. No phenomenon that has been observed fails to be explained by one or another of these forces. No phenomenon is as yet so puzzling that scientists must conclude that some fifth force other than the four I’ve listed must exist.

  It is perfectly possible to say that there is a fifth type of interaction that exists, but cannot be observed, or a sixth, or any number. If it cannot be observed, if it cannot make itself evident in any way, nothing is gained by talking about it—except, perhaps, for the amusement of inventing a fantasy.* It is also perfectly possible to say that there is a fifth interaction (or a sixth or any number) that can indeed be observed, but only by certain people and only under certain unpredictable conditions.

  That may conceivably be so, but it doesn’t fall within the purview of science since under those conditions, anything can be said. I can say that the Rocky Mountains are made out of emeralds that have the property of looking like ordinary rock to everyone else but me. You can’t disprove that statement but of what value is it? (Far from being of value, such statements are so annoying to people generally that anyone who insists on making them is liable to be treated as insane.)

  Science deals only with phenomena that can be reproduced; observations that, under certain fixed conditions, can be made by anybody of normal intelligence; observations upon which reasonable men† can agree.

  It may well be argued, in fact, that science is the only field of human intellectual endeavor on which reasonable men can very often agree, and in which reasonable men can sometimes change their minds as new evidence comes in. In politics, art, literature, music, philosophy, religion, economics, history—carry on the list as long as you wish—otherwise reasonable men can not only disagree, but invariably do, and sometimes with the utmost passion; and never change their minds, either, it would appear.

  Of course, the scientific world view has not been handed down intact from time immemorial. It was discovered and worked out little by little. It is not complete now, and it may never be entirely complete. New refinements, modifications, additions may seem fantasy at first (quantum theory and relativity certainly did), but there are well-known ways of testing such things carefully; and if the theories pass, they are accepted. The testing method is not always simple and easy, and in the course of the testing disputations may arise* and verification may be unnecessarily delayed.

  Acceptance will come in the end, though, for scientific thought is self-correcting as long as there is reasonable freedom of research and publication. (Without infinite money and infinite space, it is hard to be sure of absolute freedom, of course.)

  All this is my justification for having this book deal with the supernormal whenever necessary, but never with the supernatural. In the discussion of nonhuman intelligence that will occupy us in this book, we will consider neither angels nor demons, neither God nor Devil, nor anything that is not accessible to observation and experiment and reason.