Faint Echoes, Distant Stars_The Science and Politics of Finding Life Beyond Earth

by Ben Bova

  Those early hunting/gathering tribes saw no difference between the animate and inanimate. To them, everything was alive: trees, rocks, clouds, animals—especially the animals they hunted for food and the predators who hunted them. Each and all had their own individual spirit.

  They did not feel alone in a cold and uncaring universe. If anything, there were too many other creatures, real and imagined, sharing the world with them. They must have felt overwhelmed by spirits that were much more powerful than themselves. On the walls of their caves they drew hauntingly beautiful pictures of the animals they lived among, probably in an effort to gain some sort of mystical control over those wild beasts, or at least to ease some of the fear they felt when facing the animals’ fangs and antlers with nothing more than primitive weapons of wood and bone.

  And they watched the night sky. Paleontologists have discovered a bone with the phases of the Moon carved into it, dating back 30,000 years.

  Eventually, our ancestors invented agriculture.

  FROM AKHENATON TO ZEUS

  Farmers depend on the weather. So much so that the earliest farmers believed that the forces of the weather—wind, rain, sun—were gods who needed to be propitiated by prayers, sacrifices, and fertility rites. The idea that there were beings who were more than human, beings much more powerful than themselves, was well-entrenched in them by the time agriculture began to irrevocably change human society some 12,000 years ago.

  In ancient Egypt the Sun was worshiped as a god. One of the earliest prayers we know of is attributed to the Pharaoh Akhenaton (circa 1370 B.C.), a prayer to the Sun that gave life to the world, which he called Aton:

  Thy dawning is beautiful in the horizon of the sky,

  O living Aton, beginning of life.

  When thou risest in the eastern horizon,

  Thou fillest every land with thy beauty.

  Even wild nomadic tribes such as the Achaeans, who invaded and conquered the land we now call Greece, worshiped gods of the sky and the weather. Zeus, the chief god of their pantheon, was originally a storm god. The thunderbolt was his sign and his weapon.

  Farming also depends on the seasons, and farming societies began to study the stars in an effort to predict when they should plant their crops. In ancient Egypt, where the Nile’s annual flood brought fresh, fertile silt to the parched land, it was vital to know when the Nile would rise. The Egyptians learned that when the bright star Sirius rose just before dawn, the river’s flood was only a matter of days away. In cloudy, dank, chilly Britain, Stone Age farmers somehow managed to build gigantic megalithic circles such as Stonehenge, which served as astronomical computers that predicted the seasons, most importantly the spring equinox, the time to plant the summer’s crops.1

  FROM ASTROLOGY TO LUCRETIUS

  It was only natural for people to believe that the heavens had an important influence on their lives. They did! Curious thinkers wondered why this was so and how these influences could be predicted, interpreted, and used for practical everyday affairs.

  Thus was born the ancient art of astrology, which attempts to predict the events of an individual’s life by considering the positions of the stars and planets. It doesn’t really work, but to this day most newspapers and many Internet sites carry a daily horoscope column based on ideas that were hoary with age in Julius Caesar’s time.

  The ancients also came to believe that the realm of the stars must be very different from the Earth on which we live. A mental separation between Earth and sky arose, a separation that would have seemed strange to the Ice Age hunting tribes. To the average citizen of ancient Athens or Rome, this world of ours was an imperfect place, filled with pain and unhappiness. The heavens, however, they thought to be very different. As they watched the stars moving serenely across the night sky, it must have seemed obvious to them that this celestial domain was the abode of creatures far removed from ordinary, fallible humans.

  They saw that the stars marched across the sky in perfect order, night after night, year after year, generation after generation. There was a certainty and predictability about the stars. Even the Moon’s ever-changing face was predictable: For millennia people have been counting time by watching the Moon go through its monthly phases from full to new to full again. They realized that women’s menstrual cycles were roughly equal to the Moon’s phases; obviously, the heavens exerted some form of control over human lives.

  By the time ancient Greek civilization produced the great philosophers Socrates, Plato, and Aristotle (470–322 B.C.), most men believed that the Earth was the fixed and immovable center of the universe and the stars were flecks of fire on the vast bowl of the sky that hung over us. The stars and the bowl of the sky revolved around the Earth, they believed. Although the Earth was the center of the universe, it was a dull and dirty place, the abode of sinful, changeable, mortal humans; the heavens were considered to be perfect and everlasting, the fitting abode of the immortal gods.

  In the clear, dark night skies of the ancient world, long before industrial smog and pollution, it was easy to see the stars and make out the groupings that we now call constellations: the Great and Little Bears, the lopsided W of Cassiopeia, the Big Dog, Orion the Hunter, Perseus the Hero, the Bull, the Twins, the Lion, the Scorpion, and many others.

  There were five stars, however, that refused to stay put. They meandered across the sky, constantly changing their positions. The Greeks called them planetos, meaning “wanderers.” Today we call them planets. Clearly such powerful stars must be very special. Ancient societies named them after their gods, and we know them by their Roman names: Mercury, Venus, Mars, Jupiter, and Saturn.2

  Claudius Ptolemaeus (better known to us as Ptolemy) lived in Alexandria, Egypt, in the second century A.D. Using the observations of earlier Greek astronomers such as Hipparchus of Nicaea (circa 190–120 B.C.), Ptolemy wrote a book that described the prevailing ideas on “the state of the universe.” His book is known to us today by the name Arabic astronomers gave it: Almagest, which means, roughly, “the greatest.”

  Ptolemy’s Almagest laid out the details for the geocentric concept of the universe: the idea that the Earth is at the center of it all, and the Moon, Sun, planets, and stars all revolve around us. This Ptolemaic system held sway for more than a thousand years.

  There were a few thinkers who believed that the Earth was a sphere, not flat. Aristarchus of Samos (circa 310–230 B.C.) even suggested that the Earth goes around the Sun, not vice versa. The Alexandrian Greek astronomer Eratosthenes (276–195 B.C.) actually measured the circumference of the Earth and came up with a figure that was within 1 percent of our planet’s actual girth. But these ideas were in the minority; the geocentric system ruled supreme.

  Astronomy In A Well

  If you had nothing but your naked eyes and a few simple instruments for measuring the angles between stars, you would be hard-pressed to prove that the Earth is not at the center of the universe. Just go out and look! The heavens obviously pinwheel around us.

  The first-century B.C. Roman writer and philosopher Titus Lucretius Carus was among the earliest thinkers to propose that there are other worlds like the Earth out there in the depths of space—and other creatures like men living on them. Lucretius was an atomist: He believed that all matter was composed of invisibly small units (atomos was the Greek word for it). He wrote:

  It is in the highest degree unlikely that this earth and sky is the only one to have been created and that all those particles of matter outside [the Earth] are accomplishing nothing. This follows from the fact that our world has been made by nature from the spontaneous and casual collision . . . of atoms whose suddenly formed combinations could serve on each occasion as the starting point of substantial fabrics—earth and sea and sky and the races of living creatures.

  THE TIMID CLERIC AND THE HOT-HEADED MONK

  The Roman Empire collapsed in the fifth century A.D., and Europe entered an era of ignorance that lasted nearly one thousand years. New ideas were discouraged. Th
e Roman Catholic Church held a considerable amount of political power as well as religious authority, and it actively suppressed ideas that contradicted its own position in every field of thought, from theology to cosmology, from economics to art.

  Ptolemy’s geocentric system explained the heavens perfectly well as far as the Church was concerned. Even though there were a few nagging problems about it (for example, the planets were not exactly where the system predicted they should be), the prevailing view was that the Earth was the center of the universe and the stars were very different from our world.

  Moreover, the Church believed that the Earth had been made specifically to be the abode of human beings, who had been created by God and given dominion over all other forms of life in the world.

  Enter a timid Polish cleric, a man who earned a living as an official of the Church but whose real interests were in mathematics and astronomy. We know him by the Anglicized version of his name, Nicholas Copernicus (1473–1543). Dissatisfied with the shortcomings of the geocentric theory of the universe, Copernicus worked out a heliocentric system in which the Sun was at the center of it all and the Earth revolved around it, together with the other planets.

  He wrote in Latin, and his book was titled De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres). Familiar as he was with the workings of the Church, Copernicus had no desire to be a rebel. He actually finished De Revolutionibus in the early 1530s but did not have it published until the month of his death in 1543. Even so, he presented his heliocentric system not as an actual description of the way the heavens really worked, but as a mathematical proposition, something to think about and speculate over. No flaming revolutionary, he!

  In earlier ages, new ideas were slow to propagate and could even be stifled because books were rare and had to be copied by hand. The printing press changed all that; Copernicus’ ideas were quickly disseminated throughout Europe.

  One of the men who was “turned on” by Copernicus’ heliocentric theory was a Dominican monk named Giordano Bruno. Bruno was basically a philosopher who happened to be an eloquent public speaker and excellent writer. In a way, he was rather like the Carl Sagan of his era. Bruno immediately saw implications in Copernicus’ ideas that would have petrified the modest Polish cleric.

  Above all else, Bruno broadcast the concept that the universe was infinite in extent and that it must contain untold numbers of worlds like our Earth—worlds peopled by intelligent creatures. He was the first to make the point that the stars must be other suns; the reason that they appear as pinpoints of light is that they are immensely far away.

  If the stars are suns, he reasoned, “innumerable Earths must revolve around those suns in a manner similar to the way the . . . planets revolve around our Sun. Living beings inhabit those worlds. No reasonable mind can assume that heavenly bodies which may be far more magnificent than ours would not bear upon them creatures similar or even superior to those upon our human earth.” [Italics added.]

  Such ideas seriously challenged the long-held geocentric theory. Gone was the familiar and comfortable concept that the Earth had been specially created just for us and that we were the center of the universe. Gone with it was the belief that a kind and loving God had created all this solely for our benefit. If there are other worlds and other intelligent beings on them, did God create them, too? If they exist, how can we consider ourselves to be the focal point of creation, the center and reason for the universe’s existence?

  The Church would not tolerate such a challenge. Bruno would not give up his views or even ameliorate them. He became a hunted man. After wandering across half of Europe and even changing his name to avoid capture, Bruno was arrested in Venice in 1592. The Inquisition charged him with heresy. He refused to compromise or abandon his ideas. Eventually he was found guilty; in 1600, he was burned at the stake in Rome, in the Campo dei Fiori (the Field of Flowers).

  THE FEISTY ITALIAN

  While Bruno was basically a philosopher, Galileo Galilei (1564–1642) was the first true scientist, in the modern sense of the word. Copernicus could suggest his heliocentric theory as an intellectual exercise; Galileo produced the evidence that proved it to be right.

  Galileo realized that keen observations and careful measurements could reveal much about the way the world worked. His first experiments were on the motions of pendulums—inspired, according to legend, by watching lamps in church swaying on their long chains. Where most philosophers believed that a heavy object falls faster than a light one, Galileo took two unequal weights to the top of a church tower and dropped them. They hit the ground at the same time, and they always do. Centuries of philosophical argument were ended by an experiment that took only a few seconds.3

  In 1609, Galileo learned that a Dutch maker of lenses had invented a device that made distant objects appear close. With nothing more than that bit of gossip, Galileo ground a pair of lenses and (again, according to legend) sawed off a length of pipe from a church organ to produce his own telescope.

  Then, instead of spying on his neighbors or offering his device to the military, he turned his newly fashioned telescope to the heavens.

  Galileo provided the observational evidence that showed Copernicus was right. He saw that the planet Venus goes through phases, like the Moon, waxing and waning as it travels in its yearly orbit. That could only happen if Venus circled the Sun and not the Earth. The geocentric view claimed that the heavens were perfect and heavenly objects were without blemish. Yet Galileo’s telescope revealed that the Moon is pockmarked with craters and rough with rugged mountains. He saw that the Sun is speckled with dark sunspots, which so upset some academics and Church officials that they refused to look through his telescope to see for themselves.

  Even more startling, Galileo saw that the planet Jupiter is accompanied by four moons. They obviously revolved around Jupiter, clear proof that not everything in the universe revolves around the Earth. Although we know today that Jupiter has at least forty satellites, most of them only a few kilometers across, the four moons that Galileo discovered are big, larger than our own Moon, with two of them as large as the planet Mercury. They are called Jupiter’s Galilean satellites to this day.

  These discoveries greatly disturbed the Roman Catholic Church, for two reasons. If Copernicus was right, they fretted, then perhaps Bruno was right, too. The idea that the Earth is not the center of the universe, that it was not specially created by God for us and placed in a unique position, was literally anathema to the Church.

  The second reason was that Galileo did not sit quietly on his observational evidence; he trumpeted the information as widely as he could, especially in his book, Dialogue Concerning the Two Chief World Systems: Ptolemaic and Copernican, published in 1632.

  In 1633, the Holy Office of the Inquisition arrested Galileo and threatened him with torture if he did not abandon his views. Nearly seventy, plagued by painful arthritis, deserted by his friends within the Church hierarchy, Galileo relented. Undoubtedly he recalled what Bruno’s defiance had earned that rebel thirty-three years earlier.

  Wearing the white robes of a penitent and made to kneel before his accusers, Galileo recanted:

  [H]aving been admonished by this Holy Office entirely to abandon the false opinion that the Sun is the center of the world and immovable, and that the Earth is not the center of the same and that it moves . . . I curse and detest the said errors and heresies, and generally all and every error and sect contrary to the Holy Catholic Church.

  He spent the final nine years of his life under house arrest, going blind, confined to his home near Florence. It took the Church 359 years to relent. In 1992, Pope John Paul II publicly endorsed Galileo’s philosophy, tacitly admitting that the Church had wrongly accused and punished him.

  Legend has it that when he finally “confessed” to his inquisitors that the Earth was the fixed and immovable center of the universe, Galileo muttered under his breath, “Eppur si muove.” Yet it does move.

 
And so it does.

  THE RISE OF SCIENCE

  In the four centuries since Bruno’s execution, scientists from Galileo to Stephen Hawking have immensely expanded our knowledge and understanding of the universe. We know that the Earth does indeed revolve around the Sun, and the other planets of our solar system are truly other worlds—although none of them is very much like Earth. We have learned that the universe is mind-staggeringly immense. The Sun is but one of more than a hundred billion stars that comprise the vast pinwheel of the Milky Way galaxy, and the Milky Way is only one of many billions of galaxies.

  In the past ten years, new discoveries have come flooding in, discoveries that would make Lucretius smile with pleasure and Bruno shout, “I told you so!”

  Astronomers have detected planets orbiting other stars, planets that are even less Earth-like than any in our own solar system. Yet most astronomers believe that Earth-like planets are out there; they are too small and dim for us to detect with existing instruments. This will change, though, as our technical capabilities grow.

  Geologists and biologists have found forms of life on our own planet that live under conditions of extreme temperatures and pressures that were thought, only a few years ago, to be too harsh for life to exist. Even the bedrock idea that sunlight is essential for all life on Earth has been shown to be wrong: There is a deep, hot biosphere kilometers belowground that never sees the Sun. And it probably holds as much living matter as all the organisms living on the surface of Earth.