The Living Cosmos: Our Search for Life in the Universe

Book by Impey Chris

Chapter 1.

THE UNFINISHED REVOLUTION

There are infinite worlds both like and unlike this world of ours. . . . [W]e must believe that in all other worlds there are living creatures and plants and other things we see in this world.

-Epicurus (341-270 B.C.E.), letter to Herodotus
The young scholar clutches the book to his chest as he works his way through the crowd. Campo dei Fiori is packed; it's a jubilee year, and Rome teems with pilgrims, beggars, and pickpockets. He edges forward, brushing aside the vendors who tug at his sleeve. Days earlier, a small item in a local broadsheet caught his eye. A Dominican monk from Nola was to be put to death, having exhausted the patience and goodwill of the authorities. The scholar sighs. His heart is heavy at the prospect. It is not yet a century since the death of Leonardo, but enlightenment has dimmed so much that it seems like eons.

With difficulty, the scholar climbs scaffolding behind a merchant stall so he can see over the heads of the mob. Yelling at the far side of the square tells him that Bruno has arrived, having been paraded naked through the streets of Rome. He is bound to the stake with thick rope while a local functionary reads the charges. The scholar can only catch fragments: "impenitent heretic . . . failure to recant . . . persistent follies."

A soldier drives a nail through Bruno's tongue and into his jaw to stop him from speaking. As a token of mercy, the soldier hangs a bag of gunpowder around his neck to speed the end of his suffering. Bruno shakes his head as the crucifix is offered to him. Shouts fill the air; lit torches are raised and then lowered. The scholar cannot bear to watch; he pushes his way out of the square.

···

The book in the hand of the young scholar was On the Infinite Universe and Worlds, written by Giordano Bruno in 1584. Bruno was a mystic and a philosopher. He had no formal training in science, and he never made astronomical observations. Yet his vision of the universe was strikingly modern and, for its time, dangerously bold.

Bruno was condemned for heresy-violation of the teachings of the Catholic Church. He wasn't put to death specifically for his astronomical ideas, but they were audacious. Decades before Galileo turned his simple telescope to the stars, Bruno was dreaming of other worlds. He thought it ludicrous that the Earth should be the center of the universe. The stars, he imagined, were huge balls of glowing gas just like the Sun, appearing faint only because they were so far away. He speculated that those stars would also have planets orbiting them. With a multitude of planets flung through space, surely there were some that hosted living creatures.

Bruno could only imagine, but we're on the verge of being able to know. You're about to read a survey of the frontiers of astrobiology: the study of the origin, nature, and evolution of life on Earth and beyond. In the past twenty years, we've pieced together important aspects of the origins of life on Earth and discovered a dizzying array of microbes. We've sent spacecraft to all of the major planets and moons in the Solar System. We've found more than 250 planets orbiting other stars. So far, we know of life on only one planet: Earth. But we live in a time of tumultuous scientific and technological change. If we find that terrestrial biology is not unique-that this is a living cosmos-it will be a discovery as profound as any in human history.

This book is framed by three questions. Each begins by looking inward but then turns outward to ask about our place in the universe. Is the Earth special? Astrobiology turns this into the question, How many habitable worlds are there? Is life special? In astrobiology, this becomes, Is biology unique to the Earth? Are we alone? That last question may be the most profound, and astrobiology frames it this way: Are there any intelligent, communicable civilizations out there? In this chapter, we'll see that these questions were considered by the first scientists over two millennia ago, and we'll see how the science of astrobiology emerged.

THE AUDACITY OF THE GREEKS

The journey that brings us to this point began 2,500 years ago on the coast of Asia Minor. For thousands of years, large and complex civilizations had existed in Egypt and Mesopotamia without developing the means to investigate what lay beyond the edge of the sky. When later scholars decoded the artifacts from these civilizations, they found mostly long lists of land and property: the bureaucratic baggage of everyday living. They left us no theories of the universe. The Greeks were different. As members of a small maritime culture, they lived by trade and their wits. They were open to ideas and to new ways of looking at the natural world.

THINKING DEEPLY ABOUT NATURE

In the age before science, people had no mental constructs for interpreting nature, so they generally accepted the world as they found it. A rock was a rock, a flower was a flower, and a star was a star. Each had its own immutable nature. Humans were clearly special, the preeminent inhabitants of the world. The dawn of science meant that simple acceptance could give way to inquiry. Science accepts the challenge of looking below the surface for deeper meanings. Its goal is to answer the question of why things are the way they are.

Starting in the sixth century B.C.E., a series of philosophers made bold speculations about the natural world. Thales supposed that the source of the universe was water, the substance from which all materials emerged. His student Anaximander extended this idea, but in his version the primal element was an infinite substance called apeiron. Since everything formed from one material and would return to it, constant recycling allowed for the possibility that other worlds might have existed at other times.

Meanwhile, Pythagoras and his followers were experimenting with numbers and inventing the foundations of geometry. Pythagoras saw mathematics as a powerful tool to understand music-harmony resulted from the ratio of lengths of a plucked string or of air columns in an open flute. He extended this idea of mathematical perfection to the heavens. The Sun, Moon, planets, and stars were carried overhead on crystalline spheres, and an enlightened person might even be able to hear their "harmony." Pythagoras knew that the Moon shone by reflected light, and its phases could be explained only if it was a sphere. The arcing motions of the stars overhead, and the fact that new stars appeared as one traveled south, meant that the Earth, too, was a sphere. We can understand why Plato inscribed "Let Only Geometers Enter Here" above the entrance when he founded the world's first university in an olive grove outside Athens.1

FROM ATOMS TO WORLDS

Another Greek idea with profound implications was atomism. Initially proposed by Leucippus, the idea was developed more fully by his student Democritus. Suppose you cut a stone in half with a sharp knife, then in half and in half again. Eventually, it'll be reduced to a grain of sand and then become too small to see or too small to cut. Democritus found it implausible that this process could continue infinitely, so he proposed tiny, indivisible units of matter called atoms. It's a moniker that survives today: everything is made of atoms, and the atoms are in constant motion. All the familiar aspects of matter-color, smell, taste, texture-are secondary properties of collections of atoms; the atoms themselves have none of these attributes.2

Atomism gave new impetus to speculations about life beyond Earth. In the theory, everything on Earth and in the heavens was made of indivisible atoms, and there were an enormous number of them. The Greek idea of elements was rudimentary; there were only four: earth, air, fire, and water. Anaxagoras thought celestial bodies were made of the same elements as the Earth and suggested that the Sun was a flaming rock as large as Greece. This was brave indeed, to suggest that the world was not unique.

Democritus went even further, speculating that the Moon had mountains and valleys and that the Milky Way was an aggregation of stars. He postulated space as infinite and occupied by atoms with pure void in between. This is strikingly close to modern cosmological views. He had no trouble imagining the variety of worlds that an infinite number of atoms might provide: "On some worlds there is no Sun and Moon, others are larger than our world, in some places they are more numerous. . . . There are some worlds devoid of living creatures or plants or even moisture." Democritus was known as the laughing philosopher, content to think about puzzles of matter and space. He said, "I would rather discover a single cause than become king of the Persians."3

This is the birth of the "many worlds" concept, which holds that the Earth isn't special. It sits in opposition to the geocentric view. The Earth is just one world among many-perhaps an infinite number- scattered through space. And if the Earth is littered with diverse forms of life, why should other worlds be barren?

Radical ideas are risky-or, rather, the act of questioning everything is radical because it threatens the social order, as Socrates had found out. Pythagoras and his followers were hounded from the Greek mainland for operating a cult with mathematics as its secret language, and Anaxagoras was banished for impiety in daring to suggest that the Sun was as large as a country. Hypatia the geometer engaged in political intrigue and was torn apart by a mob in Alexandria. It would be recasting history to present Giordano Bruno as an archetype of science in conflict with religion; his writings had no coherent explanatory framework. But he collided with authority over ideas that are uncontroversial today and paid the ultimate price.

THE MAN WHO DISPLACED THE EARTH

Viewed through the mists of time, the Greek philosophers are enigmatic. We know very little about the man who ...