Plurality of Worlds. The origins of the Extraterrestrial Life Debate from Democritus to Kant

128 Pages·1982·5.057 MB·English

by  Steven Dick

Plurality of Worlds
The Origins of the Extraterrestrial Life Debate
from Democritus to Kant
STEVEN J. DICK
U.S. Naval Observatory, Washington, D.C.
CAMBRIDGE UNIVERSITY PRESS
Cambridge
London New York New Rochelle
Melbourne Sydney
Published by the Press Syndicate of the University of Cambridge
To my father
The Pitt Building, Trumpington Street, Cambridge CB2 i rp
East 57th Street, New York, ny 10022, USA JAMES E. DICK
296 Beaconsfield Parade, Middle Park, Melbourne 3206, Australia
and
© Cambridge University Press 1982
the memory of my mother
First published 1982
ELIZABETH GRIESHABER DICK
Printed in the United States of America
Library of Congress Cataloging in Publication Data
Dick, Steven J.
Plurality of worlds.
Bibliography: p.
Includes index
1. Plurality of worlds. 2. Life on other
planets. I. Title.
QB54.D5 574-999 81-10165
ISBN O 521 24308 4 AACR2
Passages from Kepler’s Somnium © 1967 by the Board of Regents of the University of
Wisconsin System, used by permission of the University of Wisconsin Press.
Passages from Immanuel Kant’s Universal Natural History and Theory of the Heavens ©
1969 by the University of Michigan Press, used by permission of the University of Michigan
Press.
Standort: rj
Signatur: MJ R 5*589
Akz.-Nr.:
He, who through vast immensity can pierce,
See worlds on worlds compose one universe, CONTENTS
Observe how system into system runs,
What other planets circle other suns,
What varied Being peoples every star,
May tell why Heaven has made us as we are.
Alexander Pope
An Essay on Man, 1734
Preface ix
Introduction 1
1 One World or an Infinity of Worlds?
The Greek Tradition 6
2 Aristotelian Natural Law versus Divine
Omnipotence: the Medieval Tradition 23
3 Infinite Worlds Revisited:
the Revival of Atomism 44
4 The Heliocentric Theory, Scripture,
and the Plurality of Earths 61
5 Cartesian Vortices, the Infinite Universe, and
the Plurality of Solar Systems 106
6 Newton, Natural Theology, and the Triumph
of the Concept of Other Worlds 142
Conclusion: Science and the Plurality of Worlds
Notes 191
Bibliography 222
Index 236
PREFACE
Any work covering such a lengthy period as that embraced by this
study generates many debts, and my debt to a great number of
scholars, past and present, is evident in the notes and bibliog­
raphy. Among present scholars, I must thank in particular the
members of the Department of History and Philosophy of Science
at Indiana University, where this study began as a doctoral disser­
tation almost ten years ago. These include Richard S. Westfall,
Victor Thoren, Frederick B. Churchill, Noretta Koertge, and es­
pecially Edward Grant — teacher, scholar, and friend — with whom
many a pleasant hour was spent poring over medieval Latin works
and discussing the wider implications of this study. Gerald Strauss
of the Department of History at Indiana University also helped to
shape my view of Renaissance history.
I must express my deep appreciation to Professor Michael J.
Crowe of the University of Notre Dame, who, during the course
of my work, exemplified that trait which to me embodies the true
meaning of scholarship, the free and exciting interchange of
knowledge. I also wish to thank Professor Philip P. Wiener, for
many years the able editor of the Journal of the History of Ideas,
for his careful reading of the manuscript, and his many substantive
suggestions.
I owe much to many libraries and many librarians, in particular
the resources of the Indiana University Library, the Library of
Congress, Folger Shakespeare Library, Princeton University Li­
brary, and the British Museum. The Landmarks of Science micro­
fiche series, edited by Duane H. D. Roller, has also proved indis­
pensable.
I have profited much from discussions during seminars and lec­
tures on this subject delivered at Harvard University, St. Louis
University, the University of Notre Dame, and Eisenhower Col­
lege, as well as from a memorable session at the History of Science
Society meeting in Dallas in 1977 in which I was privileged to
participate with Lynn White, Jr. (chairman), Frederic Burnham, INTRODUCTION
Michael J. Crowe, and Stanley L. Jaki.
Finally, I wish to thank my wife, Terry, who helped, and my
three-year-old son, Gregory, who tried to help. They know only
too well the nature of a husband and father whose mind has for
perhaps too many years wandered among a plurality of worlds.
Washington, D.C. Steven J. Dick We are privileged to live at a time when an answer to the age-old
October 1981 question of extraterrestrial life is finally within reach. The last two
decades have seen spacecraft land on the moon and Mars, provid­
ing direct evidence of the absence of life forms on the two celestial
bodies that had previously been the subject of most speculation.
Other spacecraft have returned remarkable photographs of the
planets and their satellites, revealing in detail new worlds — all
apparently uninhabited — previously visible as little more than lu­
minous points. Searches for planets outside our solar system are
being planned and undertaken with a host of promising tech­
niques. And radio astronomy now provides the means for one of
the most intriguing enterprises of all: the search for radio signals
from intelligent civilizations.
As these scientific activities proceed, an examination of their his­
torical antecedents becomes more relevant and increasingly impor­
tant: just how did the startling idea that we might not be alone in
the universe originate? And by what rationale did that revolution­
ary idea finally triumph? It may come as a surprise to most to learn
that the concept of extraterrestrial intelligence did not first appear
in the twentieth century, but that its antecedents stretch back to
two of the most fertile periods of Western science: ancient Greece,
where the seed of this, and so many other germinal ideas, was
implanted, and the seventeenth and eighteenth centuries, which
witnessed the scientific revolution, the fruition of the marriage of
experimental method and mathematics, and - somewhat ironi­
cally — the triumph of the concept of extraterrestrial life. This
study therefore concentrates on that period between barren seed
and hardy blossom, bracketed by the fifth century B.C. and the
eighteenth century of the Christian Era, a time during which the
concept of other worlds and extraterrestrial life was transformed
from heresy to orthodoxy in Western thought. It was during this
INTRODUCTION
period that the question was first posed, the possibility widely ac­
forms beyond the Earth would be a subject for nineteenth- and
cepted, and the framework for an answer developed. It is in this
twentieth-century debate.
period also that the origins of many of the arguments that still
Given these definitions, which confine the plurality of worlds
rebound in the modern debate appear. These must provide the
tradition to specific, though hardly parochial, boundaries, where
foundation for any study of the idea in the nineteenth and twen­
is one to begin such a history? In the history of science, when many
tieth centuries.
believe it has no place in science even today? In the history of
It is important to recognize that most ideas undergo an evolu­
philosophy, where it strains the bounds of a discipline usually cen­
tion and a transformation to such an extent that historical ante­ tered around the problem of the relationship between man and his
cedents often bear little resemblance to their modern counterparts. cosmos? In the history of theology, where again the traditional
This is certainly true of the concept of extraterrestrial life. The concern has been the relationship between man and God? Or in
term “extraterrestrial life” is itself modern, having come into the history of literature, where it has been extolled and condemned
widespread use only in the twentieth century. The historical term in prose and poetry by many a writer normally concerned with
out of which the extraterrestrial life debate grew is “plurality of more mundane problems?
worlds,” which first appeared in ancient Greece in the extreme Although any of these approaches might have been taken, pos­
form of the concept of infinite worlds (aperoi kosmoi), became sibly with divergent and equally interesting results, I have chosen
known in the Latin West as the question of many worlds (plures to follow the thread from the point of view of the history of sci­
mundi), and was translated into the English, French, and German ence. Several considerations justify this choice. First, the tradition
vernacular as “plurality of worlds,” “pluralité des mondes,” and involves, in a substantial way, many of the famous names in the
“vielheit der Welten.” history of science, among them, in the period under consideration,
It is this plurality of worlds tradition, which encompasses a Democritus, Epicurus, Lucretius, Aristotle, Thomas Aquinas, Wil­
larger body of ideas than simply extraterrestrial life, that is the liam of Ockham, Nicole Oresme, Johannes Kepler, John Wilkins,
subject of our study. The tradition was initially concerned not Bernard le Bovier de Fontenelle, Christiaan Huygens, and Imman­
with the existence of Earthlike celestial bodies but with the plural­ uel Kant. This in itself does not place the subject in the realm of
ity of kosmoi - cosmic systems composed of an Earth, planets, and science: scientists throughout history have been known to hold
fixed stars, like the kosmos that the Greeks believed was the home beliefs that would hardly qualify today as science. Many have ar­
of man. It was the multiplication of world as kosmos that occu­ gued that the concept of extraterrestrial life falls in just such a
pied the minds of the Greeks in the fourth and fifth centuries B.C.; category, outside the boundaries of science. The distinguished bi­
extraterrestrial life was only a minor consideration. But it was ologist A. R. Wallace, for one, held in 1903 that the modern belief
with this older concept and its associated arguments clearly in in other worlds, like the earlier belief, was “founded more upon
mind that Renaissance thinkers shifted the focus to celestial bodies religious ideas than upon a scientific and careful examination of
as worlds in themselves, a shift that required the downfall of the the whole of the facts both astronomical, physical, and biological
long-cherished Aristotelian principle that there was a sharp dis­ . . He concluded that “the belief that other planets are inhabited
tinction between the Earth and all other celestial bodies. When has been generally entertained, not in coi^equence of the physical
this obstacle had been overcome, the determination of the physical reasons but in spite of them.”1 Wallace, the cofounder with Dar­
conditions on the planets and of the possible existence of life forms win of the theory of natural selection, may have been a better bi­
adaptable to those conditions became viable questions. During the ologist than he was astronomer or historian. Yet his judgment,
period of our study, “life” beyond the Earth almost always im­ and the very fact of his own keen interest, raises the legitimate
plied intelligent life; the origin and evolution of more primitive life questions of why such eminent men should have discussed the sub-
2 3
ject at all, the nature of their reasoning, and the relationship of the ideas that he notes “were to reappear again and again in the his­
question to the scientific enterprise. tory of Western science and thought in constantly more subtle and
A second reason for focusing on the history of science is that the expressive forms.”2 The concept is here juxtaposed with such
plurality of worlds concept is demonstrably enmeshed in many of ideas as atomism, force, and infinity - all of which have been
the great scientific traditions, notably those centered around Aris­ treated extensively by historians of science. But no detailed histor­
totle, the ancient atomists, Copernicus, Descartes, and Newton. ical explication of the idea of a plurality of worlds as related to
The reader will therefore find the chapters of this book following Western science and culture has yet appeared.
each of these traditions. The first chapter documents the sharp Thomas Kuhn makes many allusions to the concept in his work
contrast between the ancient atomist belief in an infinite number on the Copernican revolution, but does not specifically address
of worlds and Aristotle’s belief in a single world. The medieval himself in detail to the question of the association of heliocentrism
reaction to Aristotle is discussed in the second chapter, and is and the plurality of worlds.3 The majority of the few articles that
based on primary documents, most of which are translated from deal with the historical tradition of the plurality of worlds are
the original Latin for the first time. The subsequent chapters, aimed at showing the widespread acceptance of the doctrine, its
which deal with the revival of atomism and with the Copernican, metaphysical importance, or its literary impact.4 Arthur O. Love-
Cartesian, and Newtonian traditions, seek to understand not only joy devotes a chapter of his classic work The Great Chain of Being
those well-known treatises on the plurality of worlds (along with to an attempt to show the overriding importance of the metaphys­
the lesser-known treatises) but also the role that the concept of ical principle of plenitude as opposed to scientific considerations
other worlds played among other natural philosophers steeped in in the acceptance of the plurality of worlds concept.5 Only the
these scientific traditions. work of the French historian and philosopher of science Pierre
A final reason for adopting the history of science as a central Duhem has treated the question, for a limited period (the Middle
concern in this study is that this discipline, in its fullest and richest Ages), from the point of view of its relation to the history of con­
sense, is historically intertwined with ideas and movements in the current scientific developments.6
history of philosophy, theology, and literature, while the converse It has not been emphasized previously that the scientific revolu­
is not always true. The considerations common to those disciplines tion of the seventeenth century was marked not only by the order­
are therefore interwoven in the discussion wherever necessary. We ing of celestial bodies according to rational law, and by the infin-
examine the literary responses of Spenser, Donne, and Milton, for itization of the universe, but also by the projection of the rational
example; we analyze the arguments over Scriptural interpretation intellect onto celestial bodies. This study charts the implications of
and the role of the growth of natural theology; the importance of that projection of mind into the universe, and is intended to clar­
general philosophical principles is made clear throughout. The ify, with the historian’s perspective, the origins and growth of this
Conclusion examines explicitly the interplay of theory, metaphys­ long-debated subject. If modern science succeeds, in the near or
distant future, in discovering extraterrestrial intelligence, this his­
ics, observation, and imagination in the plurality of worlds tradi­
tory may serve only as a prelude to a more intensive discussion of
tion, and the role of that tradition in the scientific revolution.
the implications of intelligence beyond the Earth for science, phi­
While the focus remains on the history of science, it is hoped that
losophy, theology, and the future of homo sapiens on this planet.
this study will be of interest to those in related fields.
The plurality of worlds tradition has not gone entirely unrec­
ognized by historians; rather, their generalizations indicate the
need for additional research with specific questions in mind. Thus
Marshall Clagett places the idea of a plurality or infinity of worlds
among eight “stock ideas” of the Presocratics and their successors,
this visible world is the all (irav), the universe {o\ov), or whether
ONE WORLD OR AN INFINITY OF
innumerable such worlds (kosmoi) coexist, each with its own
WORLDS?
planets and stars.
THE GREEK TRADITION For a science in the throes of its birth to attempt to embrace
other worlds in this holistic sense when our own world was so
little understood might seem presumptuous. Such was precisely
There are infinite worlds both like and unlike this world of ours. For the
atoms being infinite in number, as was already proved, are borne on far the criticism of the early Greek belief rendered by the seventeenth-
out into space. For those atoms which are of such nature that a world century natural philosopher Walter Charleton, who justifiably
could be created by them or made by them, have not been used up either
questioned why these early thinkers
on one world or a limited number of worlds. ... So that there nowhere
exists an obstacle to the infinite number of worlds. extended their disquisitions beyond the Extremes or
Epicurus (fourth century B.C.)1
Confines of this adspectable World to a multitude of
Either, therefore, the initial assumptions must be rejected, or there must be others without it, as vast, as glorious, as rich in variety
only one center and one circumference; and given this latter fact, it follows of Forms: when, indeed, their Understandings came so
from the same evidence and by the same compulsion, that the world must
much short of conquering all the obvious Difficulties of
be unique. There cannot be several worlds.
this one, that even the grass they trod on, and the small­
Aristotle (fourth century B.C.)2
est of Insects, a Handworm, must put their Curiosity to
a stand.4
The birth of the idea of other worlds in its earliest form is almost Why should other worlds have become the subject of scientific
coincident with the birth of Western science in ancient Greece. discourse, when they were neither among the phenomena demand­
That this should be so is remarkable, especially considering that ing explanation, nor, by definition, could their existence ever be
the claim did not refer to those visible celestial bodies known as confirmed by observation? The answer is to be found in the con­
planets whose movements the Greeks systematically charted, nor text of atomism, a system usually regarded as providing insight
even to the fixed stars, but rather to other universes entirely be­ into the microscopic structure of matter, not a pronouncement on
yond the range of human senses. In the words of the Greek philos­ the structure of the universe. Within this atomism, one of the ear­
opher Epicurus (341-Z70 B.C.): liest scientific traditions, the concept of a plurality of worlds found
a firm foothold.
A world (kosmos) is a circumscribed portion of the sky
Even a cursory study of the system of the early atomists reveals
(ouranos), containing heavenly bodies and an earth and
a consistent concern with both the macroscopic and the micro­
all the heavenly phenomena, whose dissolution will
scopic. Although the adherents to the atomic philosophy were ea­
cause all within it to fall into confusion: it is a piece cut
ger to apply their speculations on the nature of matter to the ex­
off from the infinite (apeiron) and ends in a boundary
plication of everyday phenomena - such explanatory power was
either rare or dense, either revolving or stationary: its
the root inspiration for the atomists’ theory, and was the criterion
outline may be spherical, or three-cornered, or any kind
upon which its vitality depended — their system carried them far
of shape.3
beyond the Earth, into the realms of cosmology and cosmogony.
By this definition, all the visible phenomena as seen from our The belief in the existence of innumerable worlds (aperoi kosmoi),
Earth, including the Earth, sun, moon, planets, and fixed stars, was the central aspect of that cosmology. It did not arise because
were considered part of the single world accessible to human these early philosophers speculated randomly on a wide variety of
senses. The surprising question that the Greeks posed was whether subjects (and therefore incidentally on a plurality of worlds), or by
a simple microcosm-macrocosm analogy. On the contrary, the
Democritus (ca. 460-370 B.C.), the founders of the atomist school,
concept of a plurality of worlds, of which innumerable worlds is
already proposed such a belief the century before Aristotle would
the extreme case, arose in the context for which the atomists are
argue so strenuously for a single highly structured cosmos. Neither
most famous: their atomism. More specifically, it derived from the
of the early atomist works survive, but the third-century a.d . com­
cosmogonic assumption of ancient atomism: the belief that the
piler Diogenes Laertius recorded one of the few references to their
constituent bodies of the cosmos are formed by the chance coa­
beliefs in his Lives of Famous Philosophers: “Leucippus holds that
lescence of moving atoms, the same type of indivisible particles of the whole is infinite . . . part of it is full and part void. . . . Hence
which matter on Earth was composed. arise innumerable worlds, and are resolved again into these ele­
Western science as it developed in Greece from the sixth to the ments.”8 The passage demonstrates the close association of other
fourth centuries B.C. was greatly concerned with the nature of the worlds with the atomist ontology based on atoms (“part full”) and
external world, for in the discussion of the material universe the void. The other quality essential for the formation of worlds is
nature of external reality is the fundamental question. The rudi­ motion, and its pivotal role for Leucippus becomes immediately
ments of ancient atomism arose in reaction to the Parmenidean evident as Diogenes continues his account.
monistic system, in which even the potential existence of many
The worlds come into being as follows: many bodies of
worlds was impossible. According to Parmenides, whatever exists
all sorts and shapes move by abscission from the infinite
“is uncreated and imperishable, for it is entire, immovable and
into a great void; they come together there and produce
without end. It was not in the past, nor shall it be, since it is now,
a single whirl, in which, colliding with one another and
all at once, one, continuous.”5 In short, the Parmenidean view was
revolving in all manner of ways, they begin to separate
antithetical to the generation or existence of other worlds.
like to like.9
In contrast, atomism provided for the existence of atoms and
the existence of void. Furthermore, change pervaded the system; This passage, which describes the details of the formation of one
the atoms were in motion, colliding, sticking together. Given the world, is an expression of that cosmogonic assumption peculiar to
occurrence of these natural processes, and the obvious example of the atomist system, whereby a single cosmos arises from a single
potential stability revealed in our own finite world, it was not un­ whirl merely by the fortuitous coalescence of swarms of invisible
reasonable to suppose the existence of other stable conglomera­ atoms. The details of world formation were elaborated by later
tions. The atomists further employed the principle that when atomists,10 but are not so important to an understanding of other
causes were present, effects must occur.6 Atoms were the agents of worlds as is the question why the atomists should have extended
causality and their number was infinite. The effect was innumera­ this theory, which is not an empirical one even for our own cos­
ble worlds in formation, in collision, and in decay. mos, to the universe as a whole. The passage from Diogenes im­
This striking contrast of atomism with Parmenides’ unchanging plies that such an occurrence is repeated many times in the uni­
being emphasizes a point of fundamental importance: on the most verse, but there is no explicit justification of why this should be so.
basic level, the cosmogony of the atomists was conducive to the Presumably the “abscission from the infinite” that begins the cos­
possibility of other worlds. While the natural philosophy of the mogonic process is not a unique event.
earlier Ionian monists such as Anaximander and Anaximenes may Democritus’s account of the atoms does not clarify this point,
have permitted them to contemplate the problem, the atomists of but reaffirms the view of Leucippus and elaborates on the nature
the fifth century B.C. were most likely the first to espouse a belief and relationship of the worlds after they have been formed. Ac­
in the plurality of coexistent worlds.7 cording to the third-century a .d . theologian Hippolytus, Democri­
An ontology compatible with the formation of worlds does not tus not only believed that atoms in constant motion in the void
require that such a belief be adopted. Nevertheless Leucippus and produced innumerable worlds but also that these worlds differed
in size. Moreover, “in some worlds there is no Sun and Moon, in cosmos and of atoms outside it of the same kind and subject to the
others they are larger than in our world, and in others more nu­ same laws, the uniqueness of our world would require a special
merous.” Democritus also believed that the distribution of the argument. This reasoning is implicit in Epicurus’s statement, and
worlds was unequal, and in a state of flux: “in some parts there is explicit in the De rerum natura [On the Nature of Things] of
are more worlds, in others fewer; some are increasing, some at Lucretius, the chief vehicle through which the atomic philosophy
their height, some decreasing; in some parts they are arising, in eventually spread throughout Europe: “Since there is illimitable
others failing. They are destroyed by collision with one another.” space in every direction, and since seeds innumerable in number
Finally, there was an early allusion to what, millennia later, would and unfathomable in sum are flying about in many ways driven in
become the central point of contention: “There are some worlds everlasting movement,” the existence of other worlds must be ad­
devoid of living creatures or plants or any moisture.”11 mitted, “especially since this world was made by nature. . . .”14 At
Although these vivid details betray a solid commitment by the the heart of this argument is a commitment to the uniformity of
fifth-century atomists to cosmogony and its application to the for­ natural process, which demanded that if order was brought from
mation of an infinite number of kosmoi, it is only in Epicurus and the chaos in our world, so it must have been in others. Cosmos
his faithful Roman follower Lucretius (ca. 99-55 B.C.) that lines and chaos were polar opposites; even given the role of chance in
of inference between atomism and the infinity of worlds are made Epicurean cosmogony, the formation of our cosmos could not
explicit. Epicurus wrote in his “Letter to Herodotus,” also pre­ have been an accident unrepeated throughout the universe.
served in Diogenes: Loyalty to the concept of the uniformity of Nature, both ani­
mate and inanimate, provided Lucretius with another argument
There are infinite worlds both like and unlike this world
for other worlds unrelated to atomism. There is nothing, he ar­
of ours. For the atoms being infinite in number, as was
gued, unique in the universe, but rather everything belongs to a
already proved, are borne on far out into space. For
generic type. So, he noted, there are many examples of each kind
those atoms which are of such nature that a world could
of life on Earth:
be created by them or made by them, have not been used
Wherefore you must in like manner confess for sky and
up either on one world or a limited number of worlds,
earth, for sun, moon, sea and all else that exists, that
nor again on worlds which are alike, or on those which
they are not unique but of number innumerable; since
are different from these. So that there nowhere exists an
there is a deepset limit of life equally awaiting them, and
obstacle to the infinite number of worlds.12
they are as much made of a perishable body as any kind
This passage has led Bailey, one of the most important scholars of here on earth which has so many specimens of its kind.15
ancient atomism, to characterize the infinity of worlds as almost a
As there are many kinds of fish there are many Earths, as there are
“direct deduction” from the infinity of the universe.13 More spe­
many beasts there are many suns, as there are many kinds of life
cifically, such a belief follows closely from the assumption of an
there are many kinds of worlds.
infinite number of atoms (which Epicurus considered proven) and
Finally, Lucretius raised a metaphysical argument that was des­
the finitude of our cosmos, which leaves many atoms to be used in
tined to appear again and again in the tradition of the plurality of
the formation of other worlds. The inference is typically Epicu­
worlds. As Epicurus derived the existence of infinite worlds from
rean: when there is nothing in the phenomena to contradict the
the premise that there nowhere existed any obstacle, so .Lucretius
hypothesis, it may then be assumed to be true until disproven.
professed “when abundant matter is ready, when space is to hand,
The Epicurean argument with its infinite number of invisible
and no thing and no cause hinders, things must assuredly be done
atoms is hardly empirical, but it is strengthened by the empirical
and completed.”16 This argument is a manifestation of what
fact of the stability of our own system. Given the existence of one
z 1