garden which contains the greatest variety of productions in different
flourishing beds . . . is it not almost the same thing whether we live suc-
cessively to witness the germination, blooming, foliage, fecundity, fad-
ing, withering and corruption of a plant, or whether a vast number of
specimens, selected from every stage through which the plant passes in
the course of its existence, be brought at once to our view?” This insight
set the stage for our modern evolutionary view of cosmic phenomena.
Plurality of Worlds
31
William was obsessed with building the largest telescopes in order to
see farther than anyone ever had.* Many of his instruments were more
impressive in size than optical quality, but at the age of forty-three he
stumbled upon the planet Uranus, the first “new” planet ever discov-
ered by humans. Like the first discoveries, in our own time, of new
planets beyond our solar system, Herschel’s new world encouraged plu-
ralist speculation. Up until that moment, for all we actually knew, there
might be only six planets in the whole universe. Finding Uranus con-
firmed the widespread conjectures that other planets were out there,
beyond the ones we can see with the unaided eye. Herschel capitalized
skillfully on the naming rights to his new planet, calling it the Georgian
planet. King George III rewarded him with an annual pension of two
hundred pounds, which allowed him to quit his day job as a musician
and devote himself full-time to his astronomical passion.†
Herschel’s zeal for bigger scopes and better views was driven by a
lifelong belief in the existence of life elsewhere. He once wrote that if he
had a choice, he’d prefer to live on the Moon. Herschel was determined
to find definite evidence of life on Earth’s nearby companion. He made
drawings detailing his observations of lunar forests and cities. Some of
Herschel’s reports of lunar vegetation, turnpikes, canals, and even pyra-
mids read like today’s tabloid headlines you might find yourself reading
furtively in the checkout line at the grocery. An amateur astronomer
hoping to be accepted as a professional, William refrained from pub-
lishing these spectacular findings out of concern for his reputation, but
to Herschel the discovery of Uranus was important chiefly because it
provided the financial means to support his more important studies of
lunar civilization.
Today, Herschel’s interpretations of planetary observations seem
clearly biased by wishful thinking. He played up similarities between
Earth and Mars and ignored obvious differences to support his belief
that “its inhabitants probably enjoy a situation in many respects similar
to ours.” But his insights into stellar evolution and his discoveries—
especially of the planet Uranus—serve as lasting reminders that investi-
*Freud would not be born for another century.
†I’m surprised that modern planet discoverers haven’t resorted to hitting up modern roy-alty for naming rights. “Planet Bill Gates” would be easier to remember than “the planet orbiting HR3522.”
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L o n e l y P l a n e t s
gations driven by fervid beliefs can sometimes produce spectacular and
lasting scientific results.
S Y S T E M O F T H E W O R L D
The most important mathematician of the late eighteenth century was
Pierre-Simon Laplace. Math tutor and confidant of Napoléon—who
dubbed him “the Newton of France”—Laplace made lasting contribu-
tions to probability theory, calculus, electricity and magnetism, and
especially celestial mechanics—the theory of the motions of heavenly
bodies. In his System of the World, published in 1796, he developed his
“nebular hypothesis,” which explained the origin of the solar system
from a contracting, flattened, rotating disk of gas. Kant had painted a
similar picture forty-one years earlier, but Laplace put mathematical
flesh on the bones of Kant’s idea, presenting a masterful derivation
showing that such a spinning disk would inevitably result from a cloud
collapsing in space.
Today, the physics we use to describe solar system formation is
directly descended from Laplace. One important implication of the
nebular hypothesis is that all stars, if they form in the way that ours
did, should be born with planets. For nearly two hundred years plural-
ists had been saying that other stars must have planets. This, however,
was based only on a metaphysical principle: the argument by analogy.
Laplace came along and showed how this belief is supported by a
sophisticated scientific theory. His nebular hypothesis was a major shot
in the arm for pluralism.
Like most scientists of his day, Laplace believed in a plurality of
inhabited worlds. Of the planet Jupiter he wrote, “It is not natural to
suppose that matter . . . should be sterile upon a planet so large.”
Laplace described the startling insignificance of humanity and the Earth
in the vastness of space, but he urged his contemporaries to rejoice in
the power of the human intellect, rather than despair at our pathetically
diminished stature:
“Man appears upon a small planet, almost imperceptible in the vast
extent of the solar system, itself only an insensible point in the immen-
sity of space. The sublime results to which this discovery has led may
console him for the limited place assigned him in the universe.”
The success of mathematics and physics in explaining so much of the
material world emboldened men like Laplace to believe that there was a
Plurality of Worlds
33
physical, mechanical explanation for everything, and to question the
role of God in creating and maintaining the cosmic dance. When
Napoléon, after having read System of the World, asked Laplace why
there was no mention of God in his work, he replied, “Citizen First
Consul, I have no need of that hypothesis.”
By 1800, the international scientific community was nearly unani-
mous in holding pluralist beliefs. Religion was also finally adapting to
the new consensus reality. It became more common to use theological
arguments to argue for pluralism than against it!
Among Enlightenment intellectuals, belief in extraterrestrial life
became a major source of doubt in Christianity. The plurality of worlds
was used to argue against the reality of the Incarnation of Christ.
American revolutionary hero Thomas Paine made this point without
pulling his punches in Age of Reason (1794):
“From whence then could arise the solitary and strange conceit, that
the Almighty, who had millions of worlds equally dependent on his
protection, should quit the care of all the rest, and come to die in our
world, because they say one man and one woman had eaten an apple!
and, on the other hand, are we to suppose that every world in the
boundless creation had an Eve, an apple, a serpent, and redeemer? In
this case, the person who is irreverently called the Son of God, and
sometimes God himself, would have nothing else to do than to travel
from world to world
, in an endless succession of death, with scarcely a
momentary interval of life.”
In the obvious conflict between pluralism and certain aspects of
Christian doctrine, the tables had been turned.
A Wobbly Ladder
3 to the Stars
The discussions in which we are engaged belong to
the very boundary regions of science, to the frontier
Image unavailable for
where knowledge ends and ignorance begins.
electronic edition
—WILLIAM WHEWELL, 1853
No shortage of explanations for life’s mysteries.
Image unavailable for
Explanations are two a penny these days. The truth,
electronic edition
however, is altogether harder to find.
—SALMAN RUSHDIE, The Ground Beneath
Her Feet
N O T H I N G F R O M W H I C H T O R E A S O N
Over the course of the seventeenth and eighteenth centuries, belief
in extraterrestrial life traveled from the fringes to the mainstream.
Pluralism went, in the words of science historian Michael Crowe,
“from being a belief of a few to a dogma taught in scientific textbooks
and preached from pulpits.” A backlash was inevitable. In 1853,
William Whewell, the master of Trinity College, Cambridge, wrote one
of the first polemics against life elsewhere that was based on scientific
evidence. He was the first to use a line of argument that has since been
offered many times and that has most recently been resurrected as the
Rare Earth Hypothesis. Whewell’s arguments against the existence of
intelligent life elsewhere were based on the following:
1. Empirical evidence indicates that the other planets in our solar
system have conditions so different from Earth’s that they must be
uninhabitable by any life we can imagine.
A Wobbly Ladder to the Stars
35
2. There was no evidence of Earth-like planets orbiting other stars.
Therefore Earth may be completely unique in the universe.
3. The history of life on Earth, as revealed by geology, shows that
intelligent life is only a recent phenomenon here. During most of
cosmic history, complex life did not exist even on this planet.
Therefore, arguments by analogy are weakened.
Whewell concluded, “The belief that other planets, as well as our
own, are the seats of habitation of living things, has been entertained,
in general, not in consequence of physical reasons, but in spite of phys-
ical reasons; and because there were conceived to be other reasons, of
another kind, theological or philosophical, for such a belief.”
Whewell’s book provoked outrage, as belief in extraterrestrial intelli-
gence was deeply entrenched in scholarly and popular culture through-
out the nineteenth century. He became an antipluralist lightning rod.
Mocking the perceived arrogance of Whewell and his hypothesis, the
renowned American astronomer Maria Mitchell wrote, “They say in
Cambridge that Dr. Whewell’s book, Plurality of Worlds, reasons to
this end: The planets were created for this world; this world for man;
man for England; England for Cambridge; and Cambridge for Dr.
Whewell!”
Mitchell’s mid-nineteenth-century scientific judgment was that “there is
nothing from which to reason. The planets may or may not be inhabited.”
T H E E V O L U T I O N R E V O L U T I O N *
In 1859, six years after Whewell’s book reignited the pluralism debate,
another book touched off an even greater firestorm—one that smolders
still. Charles Darwin’s On the Origin of Species permanently changed
our view of the relationship between Earth and its life and, ultimately,
between life and the cosmos. Darwin was a pluralist, and his theory of
evolution did for our species what the Copernican revolution had done
for our planet: it knocked us off our pedestal. Darwin and his followers
showed that we are part of a continuum of life in which all species are
descended from common ancestors. Evolutionary theory gave us a new
answer to the question of why the Earth seems so ideally suitable for
*With a tip of the hat to Lancelot Link, Secret Chimp.
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L o n e l y P l a n e t s
life. Our planet only seems to have been created as the perfect environ-
ment for man, Darwin suggested, because we have evolved by natural
selection to best take advantage of conditions found here.
The implications for the “plurality of worlds” debate were both
obvious and profound. Pluralists saw in the theory of evolution by nat-
ural selection the seeds of a universal process of life-making and evolv-
ing. Teleological arguments, long a mainstay of pluralist belief, were
abandoned and replaced by evolutionary arguments. No longer were
the other worlds clearly made for someone else, as this world was made
for us. The new rationale was that other planets must be inhabited
because natural selection would fashion living beings to take advantage
of local conditions throughout the cosmos.
Darwin’s radical theory generated ripples that were felt in all areas of
natural science. What started as a new idea about Earth and its inhabi-
tants was soon being applied to life elsewhere, and even the life of the
cosmos as a whole. Astronomers began to think in terms of cosmic evo-
lution: Did the universe itself evolve through distinct phases, perhaps
culminating in the evolution of life?
Biology and astronomy were not the only fields in rapid transition.
During this same period, advances in chemistry showed the stuff of life
to be less mysterious, less distinct from the rest of nature. “Organic”
matter was found to be composed of complex compounds of the ele-
ment carbon.
In the 1860s, it finally became possible to investigate experimentally
another of the metaphysical pillars on which belief in plurality had
rested: the assumption of the uniformity of the cosmos. This became
subject to test by the new methods of spectroscopy: precise measure-
ments of the intensity of light at each separate color, or wavelength.
Viewed in this carefully dissected light, each chemical compound has its
own specific signature, and we can determine what something is made
of by examining the light it shines or reflects. Stick a spectroscope on
the end of a telescope and voilà: you’ve got a probe for studying the
composition of distant planets and stars. When Sir William Huggins
reported his pioneering spectroscopic work showing that distant stars
are made of the same stuff as the Sun, he wrote that this provided “an
experimental basis on which a conclusion, hitherto but a pure specula-
tion, may rest—viz. that at least the brighter stars are, like our sun,
upholding and energizing centres of systems of worlds adapted to be
the abode of living beings.”
A Wobbly Ladder to the Stars
37
As the nineteenth century drew to a close, these advances in biology,
chemistry, and physics had removed several barriers to belief in life on
other worlds. If life here is a natural consequence of universal physical
processes, and our solar system is nothing special, then why shouldn’t
the universe be crawling with all kinds of creatures?
L O W E L L ’ S M A R T I A N S
Into this atmosphere of great scientific receptivity to pluralism strode
Percival Lowell, a brash, wealthy Bostonian on a mission. His scientifi-
cally informed fantasy of a Martian civilization would capture the
world’s imagination, temporarily advancing the pluralist cause but ulti-
mately setting it back for most of the century.
Upon graduating with honors from Harvard in 1876, Lowell gave a
commencement address on Laplace’s nebular hypothesis. Before turn-
ing to astronomy full-time in his forties, he traveled repeatedly to Asia
in pursuit of arcane knowledge of Eastern religion. From these journeys
he gained a mystical belief in the unity of the cosmos that influenced his
devout pluralism. “Each body,” he concluded, “under the same laws,
conditioned only by size and position, inevitably evolves upon itself
organic forms.”
Shortly after returning to Boston in 1893, Lowell learned of the tele-
scopic observations of the Italian astronomer Giovanni Schiaparelli,
who, in 1877, had drawn maps of Mars with unprecedented detail,
showing a network of straight lines that he called canals. Schiaparelli’s
canals sparked the imagination of Percival Lowell, who began to con-
ceive a way of confirming his cosmic vision of abundant life and intelli-
gence. It did not take him long to throw together a well-financed (with
Lowell family money) expedition of Harvard astronomers to Arizona in
search of an ideal high-altitude site to build a new observatory. He chose
a forested hill at seven thousand feet on the outskirts of Flagstaff, where
today the Lowell Observatory remains one of the premier American
institutes of planetary research. Charismatic, and fabulously wealthy,
Lowell had the means to build an observatory, but he lacked the patience
and objectivity of a great observer. He arrived in Flagstaff to begin his
observations in May 1894. Less than a year later he was already popu-
larizing incredible discoveries and a radical new view of Mars.
Lowell confirmed the presence of a geometric pattern of Martian
canals covering the entire globe. The dark areas, however, were not
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watery seas as Schiaparelli and others had concluded. Rather, he deter-
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