This article below is excerpted from her six-volume series The Story of Science  ©2004 Smithsonian Books

There is something I want to be sure you understand before you finish this article. It’s this: Science is not about certainty; it’s about uncertainty. Does that sound weird? Well, it’s true. Science is all about trying ideas, discarding those that don’t work, and building on those that do. It never stops.

As you know, scientifically minded serious thinkers once “proved” that the Earth was flat. They walked around and observed carefully and made that judgment. It helped them plan their lives. Then someone came along and “proved” the Earth is a globe in the center of the universe. And that worked. And then someone else came along and “proved” that the Sun is in the center of the universe, and that worked, until someone else came along and “proved” that the universe has no center, and….

Well, you get the point. Those people in the past who had wrong ideas weren’t dummies. They were doing the best they could, given the knowledge of their times. We do the same thing today. And you can be sure that people in the future will look back and wonder why we believe some of the things we do. Good scientists know that. They learn to be humble. Does that make science unimportant? After all, if some of our scientific theories are going to be proved false, why bother studying them?

Because uncertainty is the most interesting of all places to be. If you believe something is an absolute truth, you can just memorize it and get on with your life. There’s nothing to discuss.

Science isn’t like that at all. Scientists—the good ones—are always questioning and questing. Yes, there are scientific ideas, often called principles or theories that have proved themselves over time. Then they get called facts, or laws. By using those laws, modern science has achieved incredible things. But nothing is beyond question to the scientific mind—even those laws. So no good scientist will laugh at you for asking questions—because sometimes the silliest seeming questions have led to the most profound answers.

To better understand how science progresses, let’s begin with the Sumerians’ thoughts on the Earth and then take a look at the roughly 2,000 years in which scholars debated whether the Earth is round or flat, big or little.

The universe was called an-ki, which meant “sky-earth.” The wise ones, who were deep thinkers and observers, said the sky was like an upside-down soup dish—solid and bowl shaped. Some called it a heavenly vault. Perhaps it was fashioned of tin, although more than a few thought it was made of the beautiful blue gemstone lapis lazuli. Others said there were three layers of translucent crystal. Stars, which were celestial fires, shone through holes in that glorious roof. Water was stored between the layers, they said. When a hole got unplugged, it rained.

And the Earth? It was a flat disk set in a surrounding ocean. Below Earth was the vast underworld. Each night it was visited by the Sun. Once a month, the Moon made the same journey to the lower region.

From where did life come? From the ocean—which was eternal; out of it had come everything living.
These were the thoughts of the Sumerians, who, 5,000 years ago, created what may have been the world’s first great civilization. Their ancient myths were important, they were part of a process that would stretch minds. But science was still an infant, just taking baby steps out of the cradle. It would take another 2,000 years for stargazers to start trying to answer the big questions of the universe in a scientific way.

*   *   *

Along the Aegean Sea, Mother Earth is no shy flower. There, though spectacularly beautiful, she is also boisterous and hard to tame. Crops grow poorly. Earthquakes and volcanoes terrify and leave scars. The sea swallows its victims. The Greek-speaking people, who settled sea-washed Turkey, Greece, and the islands between, needed sharp minds to survive, and they developed them. About 3,000 years ago, some of them began using their minds in new ways. It was a time when superstition and fear still guided most thought and action. Rulers who claimed godly powers told subjects what to think. But in Ionia, on the Turkish coast, there were no god-kings. There, cities thrived. Traders and travelers brought new ideas. Ordinary people were free to think for themselves. A few, who examined the world with clear, unfrightened minds, drew conclusions from what they observed.

“But,” writes astronomer Carl Sagan, “in Ionia, a new concept developed, one of the great ideas of the human species. The universe is knowable, the ancient Ionians argued… There are regularities in Nature that permit its secrets to be uncovered. Nature is not entirely unpredictable; there are rules even she must obey.”

Thales (THAY-leez), a sixth-century b.c.e. Ionian living in the prosperous port of Miletus, is said to be the world’s first philosopher-scientist-mathematician; the first to look for explanations in observed facts, not myths; the first scientist to leave his name on his ideas.

A road went from Thales’ home in Miletus to the fabled city of Babylon, where the savvy ruler Nebuchadnezzar (neb-uh-kuhd-NEZ-uhr) had a stable of astronomers at work. (Babylonia had succeeded Sumer as the leading culture in Mesopotamia.) From Babylon, traders and scholars went to India and Mongolia and China, learned of those cultures, and brought home goods that dazzled. Back in Ionia, they were joined by soldiers, returned from the Persian Wars. The soldiers bragged of their army’s engineers, who had built marvels. Some were now working in the Ionian ports.

Given all this intellectual ferment, Thales may have been exasperated by the fickle gods worshiped by most people of his time. Perhaps he realized the importance of a fresh start that turned away from myths toward observation and thought. He would use no gods to explain nature. Rather, he would use his senses and his intelligence and teach others to do the same. It was the beginning of the scientific approach.

Is the Earth Flat or Round?
Thales did a new kind of thinking, but it might not have gone anywhere if he hadn’t been a teacher.  Anaximander (ca. 611-ca. 547 b.c.e.), who was a pupil of Thales, is often called the Founder of Astronomy. That’s not quite true. People had been looking at the stars from the earliest of times. But Anaximander did do something new. He tried to picture the whole Earth and understand its place in the cosmos. He figured out that the Earth’s surface must be curved (that explains the changing position of stars when one travels). And, in a breakthrough thought, he described the sky as a transparent sphere that moves and carries the Sun and stars; it was not just an arch over the Earth.

But Anaximander’s Earth wasn’t a sphere. It was a kind of pudgy cylinder with a top that had a north-south curve. Earth stood all day by itself in the middle of the universe. Nothing was holding it, said Anaximander. That idea of an unsupported Earth was hard for most people to imagine; it took a big intellectual leap. Once it was made, it wasn’t difficult to go from a freestanding cylinder to a free-floating globe, as Pythagoras (pi-THAG-uh-ruhs) did just a few decades later.

Pythagoras, who was born in ca. 582 b.c.e., is often called the world’s first great mathematician. He was lucky in the time and place of his growing up. His home was on the island of Samos, just a mile’s swim in the Aegean Sea from the coast of Turkey.

When Pythagoras was a boy, Samos was a big-time prosperous port. Ships carrying new ideas seemed to blow in on almost every breeze. The Greek historian Herodotus tells us that the people of Samos “are responsible for three of the greatest building and engineering feats in the Greek world.” If we take ourselves to Samos in the sixth century b.c.e., you can see those engineering marvels: a spectacular tunnel channeling water pipes through a big hill, a man-made harbor, and the largest of all known Greek temples.

It is an age of ferment—and genius. Besides Thales and Anaximander in Ionia, there are Confucius (kuhn-FYOO-shuhs) and Lao-tzu (rhymes with “now-duh”) in China, the Pharaoh Necho (NEE-ko) in Egypt, Zoroaster (ZOR-oh-as-ter) in Persia, the Jewish prophets in Israel, and Gautama Buddha in India. Pythagoras has a mind that can hold its own with any of them.

Samos was part of Ionia, but no one considers Pythagoras as an Ionian because he didn’t think like the other Ionian scientists. He stands alone.

How do you make sense of the universe? Do you do it by considering mountains of information—observing this, observing that—adding one block of knowledge to another? Believe that, and you’re an Ionian-style scientist.

Or, is it an orderly, perfect creation that can be understood through mathematical formulas and headwork? Believe that, and you’re thinking like Pythagoras.

Actually, today’s scientific method combines approaches, pure thinking along with observation, as well as something essential to modern science—experimentation that leads to proofs. But it took a long time to get that method working. The Greeks didn’t do much experimenting.

For Pythagoras, the way to understand the universe was by searching for things that are absolutely true, and numbers seemed perfect for that quest. “All is number,” he said. And he meant it. Everything in the world, he believed, could be explained through mathematics. He went still further: He thought numbers were divine, an expression of God’s mind.

We don’t have any books or papers or words that Pythagoras actually wrote. All of his work has been lost. But we know enough from the writings of others, who tell of him and his achievements, to realize he was one of the most influential people of all time.

There is an exactness to the world, an orderliness, and it follows rules that can be understood with numbers: that’s what Pythagoras told us, and it has been confirmed again and again.

If all this isn’t enough, Pythagoras is thought to be the first person to teach that the Earth is a sphere. (He took the next step after Anaximander’s squatty cylinder.)

What an astonishing feat, to understand that Earth is a big ball (a slightly out-of-shape ball, as we now know). Would you have figured out its spherical shape if you hadn’t been told? And that still isn’t all: Pythagoras understood that Earth moves!

Anaximander had explained the motion of the Sun and stars by saying that they are all attached to a heavenly sphere that rotates, carrying them in its grip. Pythagoras accepted that idea, but in his cosmology, the Earth, the Sun, and the planets are not attached to the same heavenly sphere as the stars: they follow different paths; some, like Earth, are circling a great celestial fireball. Take note of that fireball—Earth is not in the center in this universe.

Something else: Pythagoras introduced the idea of multiple spheres. For way more than 1,000 years afterward, astronomers would worry about separate spheres for the Sun and planets. (Finally, modern science came up with gravity, smashing those crystal spheres.)

This astonishing thinker and observer understood that the structure and relationships of the universe can be described with mathematical formulas. He made mathematics the language of Western science. No one has done more.

 

 

 

Within 200 years after Pythagoras, Greek thinkers seem to have agreed that the Earth is round. Sky gazers had figured out that the round shape on the Moon during a lunar eclipse is our planet’s shadow. Since those sky gazers were apt to be the wisest of scholars, it was a heavy nail in the flat-Earth coffin.

There were others. The Greeks traveled widely in the Mediterranean lands. They knew that the North Star is lower in the sky in southern Egypt than it is in northern Greece. A round Earth explains that. And they also knew that the first one sees of a ship coming over the horizon is its sail; only later does the hull come into view. That seemed to confirm the round-world theory. But knowing the shape of the Earth wasn’t enough. Scholars also wanted to know how big the Earth is.  That was a question for Eratosthenes.

Is the Earth Big or Small?
Eratosthenes (ca. 275-ca 195 b.c.e.), who was born in coastal North Africa (now Libya), went to school in Athens and then was called to Egypt by Ptolemy III, who asked him to become director of the library/museum/university at Alexandria. He was the perfect person for that job. Eratosthenes (er-uh-TOS-thuh-neez) was a great scholar himself, and he energized others. His nickname was “Beta,” which is the second letter in the Greek alphabet. Some people thought him second only to Aristotle in broad talent. Today Eratosthenes is remembered mostly because of some measuring he did.

Eratosthenes discovered that at noon on the summer solstice (the longest day of the year), at Syene (an Egyptian city near modern Aswân on the southern Nile), the Sun’s rays lit the very bottom of a deep well, and a stick cast no shadow at all.

That wasn’t true at Alexandria, on the northern mouth of the Nile, where at the same time on the same day, the Sun’s rays did cast a shadow.

Eratosthenes must have asked himself, “Why a shadow at Alexandria and no shadow at Syene?” Then he figured out that the Sun might be right overhead at Syene but not quite overhead at Alexandria, and he realized that he had hit upon valuable information. He saw it as yet another indication that the Earth is curved and as an opportunity to find out the circumference of the Earth.

Eratosthenes is said to have put a stick in the ground in Alexandria and measured the angle of its shadow. It was 7.2°, which is Z\b/ of a circle. If the Earth is truly a globe—as he believed—then the distance between Alexandria and Syene is Z\b/ of that globe. To find the size of the whole globe, all he had to do was measure the distance between the two cities. So he paid someone to walk from Alexandria to Syene, counting his steps, and then he multiplied that distance by 50. The answer was very close to the best modern measurements of the circumference of the Earth. That was more than two millennia ago, and the only equipment Eratosthenes used was a stick in the ground, his brain, and a hired walker.

Given what he found to be the large size of the Earth and the small size of the known land, Eratosthenes surmised that there was a huge interconnected ocean. (That would be verified by the voyage of Magellan 18 centuries later.)

Most of Eratosthenes’ works, like those of most of the ancient thinkers, have been lost. Much of what we know of him and his accomplishments comes from the written comments of others. And they tell us that he was a geographer, historian, and literary critic, as well as an astronomer. He was the first man, of whom we know, who was concerned with accurate dating. He set up a chronology that began history with the Trojan War. But it was when he came up with that close-to-accurate measurement of the Earth that he demonstrated that the universe is understandable. Given some brainpower, we can figure out how it works. What would his contemporaries and future generations do with that insight? For a long time they just forgot all about it.

 

 

 

 

 

 

 

 

 

 

 

Darkness Descends
After some impressive centuries of rule and a time of peace and harmony unusual in human history, the vast and mighty Roman Empire was in trouble. Historians will give you a whole lot of reasons for its decline:

• poor leadership
• economic woes
• urban (city) problems connected to size and rapid growth
• nasty political fighting
• crime

Whatever the cause, when wild, uncivilized, barbaric tribes began attacking, the empire started to collapse. It did not happen overnight; it was a long process. Those barbarians—bands of warring hoodlums—came from the north, and kept coming. They were being pushed out of their lands by still fiercer hordes who had fought on horseback all the way across Asia from Mongolia. Wherever they went, these barbarian tribes brought disaster, destruction, energy, and change.

While the Roman Empire was tumbling, a new religion was spreading like a grass fire (which means fast). The new religion was Christianity. It preached love and brotherhood and brought a vision of a world to come. It was a message of hope. And it spoke to those who were facing confusion, violence, and wrenching change in what had once been civilized, secure communities. Christianity led believers inward, to a quiet, spiritual life. At a time when the known world was often unbearably brutal, Christians focused on the world of the soul and the promise of eternal life.

In 313 c.e., Emperor Constantine made Christianity a tolerated and lawful religion of the Roman Empire. Christians, who had been struggling outcasts, began to hold political as well as spiritual power. Their ideas on science now mattered. Should priests and bishops encourage Christians to study the natural world? Or should they urge Christians to concentrate on saving their souls? Studying science and mathematics meant studying the Greeks. But the Greeks were being called pagans. If the Greeks were wrong about religion, as the Christians believed, could they be right about scientific matters? This was a serious, troubling dilemma.

Greek scientists had taught that the Earth is round. But if the world is round, then some people must be hanging upside down, said the priests. “Can anyone be so foolish as to believe that there are men whose feet are higher than their heads, or places where things may be hanging downwards, trees growing backwards, or rain falling upwards?” wrote the much-loved African priest and author Lactantius. (He was tutor to Emperor Constantine’s son.) The side of the Earth opposite Europe (and below the equator) was called the antipodes (an-TIP-uh-deez). How could anyone live on the antipodes? The Bible’s stories seem to make it an impossibility. Belief in a habitable round Earth was often seen as proof of heresy. (Almost no one understood that there is no top and bottom nor up and down in space.)

What happened to that round-Earth idea the Greeks had developed? A sixth-century monk named Cosmas wrote a 12-volume Topographia Christiana, which was meant to replace it. The first volume of his work has this title: Against those who, while wishing to profess Christianity, think and imagine like the pagans that the heaven is spherical. The Earth, said Cosmas, is rectangular—twice as long as it is wide—and surrounded by an ocean, which is surrounded by a second Earth: Adam’s Paradise. The sky is like the roof of a tent with stars and planets pushed by angels.

Did people believe Cosmas? Yes, most did. But it didn’t seem to matter much. Hardly anyone was concerned with the science of the universe. Its moment had passed. No other culture anywhere had done what the Greeks had done; but now Alexandria was becoming a forgotten town. Science and question-asking were out of fashion.

The Sumerian idea of a flat Earth returned—this time richly embroidered with descriptions of sea monsters and bizarre land creatures. It stayed around for almost 1,000 years. (To give yourself an idea of 1,000 years, it’s twice as long ago as Columbus’s voyage to America.)

Historians call the time between the fall of the Roman Empire (476) and the beginning of the Renaissance (early 15th century) the Middle Ages. Some divide that medieval era and call the first of it (from 476 to about 1000) the Dark Ages. Some call those years the Great Interruption. Whatever name you choose, it describes a time when most of Europe took a big step backward. Life became coarse and primitive, not just in comparison to our life today, but in contrast to other world civilizations of the time, such as the T’ang and Sung dynasties in China, the Eastern Orthodox Byzantine Empire centered in Constantinople (now Istanbul, Turkey), and the Islamic Empire (led by the culture-loving Abbasid rulers).

The tradition of scientific question-asking shifted to Arab lands, where it stayed alive for some five or six centuries and helped create a golden age of Islam.

In China, technology was making enormous strides. Astronomers and mapmakers there were way ahead of those left in Europe. They were charting regions of the Earth exactly, although they still hadn’t figured out that Earth was round. Ships’ rudders, the compass, wheelbarrows, canals with locks, paper, printing, gunpowder, stirrups, and harnesses—those were just a few of the ideas and inventions that were eventually carried across the Silk Road from the East to the West. But neither the Chinese nor the Japanese nor the Mayans nor any other culture anywhere matched the Greeks when it came to asking questions about the universe. Without the right questions, you don’t get the right answers. You don’t even get energetic discussions. These were dark ages for science and dreadful years for most Europeans—especially for those with intelligence and imagination.

If anyone, then, had suggested that Europe was going to develop a science-based culture that would be a beacon to most of the world—well, that hardly seemed possible. By the year 1000, the once-famous Roman Forum had become a pasture for cattle. Squatters were living in Rome’s Coliseum and hanging laundry from its windows. Alexandria? You could ask anyone: Its glory days were in the mostly forgotten past.

Light Prevails
Pope Sylvester II, who reigned during the millennial year 1000, was sometimes called the Magician Pope, for he was a versatile thinker with many talents.

As a young man, Sylvester—whose name then was Gerbert of Aurillac—went to Islamic Spain, where he studied Arabic math and science. While he was there, he read the ancient Greeks—in Arabic! When he was 39, Gerbert was the star of an all-day public debate sponsored by the German King Otto II. Scholars and students traveled from all over Europe for these events. Gerbert argued that physics is a branch of mathematics, won the debate, and was soon court mathematician and advisor to the powerful Otto. So, along with a high-powered mind, he now had political influence.

He was already a controversial figure. When he came home from Spain, he told friends and colleagues about Arabic mathematics and about Greek thinkers. A few other Christian scholars set off for Spain—although outsiders weren’t welcomed. They were more likely to bring trouble than anything else. Most Spaniards thought they had little to learn from other European peoples.

Around 1110, an English philosopher named Adelard of Bath disguises himself as a Muslim student and heads for Spain. Adelard has studied and taught in France and traveled to Italy, Syria, and Palestine. He speaks Arabic, so he has no problem pretending to be a Muslim. He is anxious to learn all he can in Spain’s great schools. One of the first books he encounters is Euclid’s comprehensive treatment of geometry called The Elements.

In a world where hardly anyone can multiply or divide big numbers, Euclid is astonishing. Adelard is swept away by The Elements; it makes numbers clear and useful.

Adelard translates Euclid from Arabic into Latin, giving Europe an enormous gift. He helps make it the most influential book on mathematics ever. (It will be the basis of almost all thinking about geometry until the 19th century.)

Thanks to the influential Roman philosopher Boethius, Aristotle’s writings on logic have been known for centuries. Now, with the Dark Ages receding, his works on science get translated and begin to be studied by a few Christian scholars. At the same time, three philosophers from the Arabic world write commentaries on Aristotle—clarifying and extending his thinking. They are Maimonides, who is Jewish; Avicenna, who is Persian; and Averroës, who is Spanish. Their observations give thinkers much to discuss. After centuries of intellectual stagnation, this is all astonishing. Imagine living in the dark and suddenly lights are turned on.

Some say much of the ferment can be traced to the new schools and universities. One of the first of them is built in the 12th century at Chartres (SHAR-truh), France. The great cathedral houses a school where professors begin to teach about nature and science. Universities are soon founded in most large towns across Europe.

Professors need books to teach, which leads to a demand for scholarly works. Scribes are put to work copying the new translations of the ancient works. Some scholars actually begin thinking for themselves. Still, ideas change slowly.

When it comes to geography, European maps show Earth with three continents: Africa, Europe, Asia. All the world’s known land—those three continents—is surrounded by the “Ocean Sea.” That ocean is terrifying because no one has sailed across it and told the tale; sea monsters are thought to abound.

Aristotle’s round world is being taken seriously at most of the universities, but no one with a ship is dealing with the idea. Around the year 1000, Leif Eriksson, a Viking explorer, sailed west from Greenland and discovered a new land that he thought promising for growing grapes. He called it Vinland. But, even a century later, hardly anyone elsewhere knows of that voyage, and no one understands its significance.

Proof: A Grueling, Three-Year “Experiment” at Sea
On September 4, 1522, a battered, worm-infested ship is sighted heading for Seville on Spain’s Guadalquivir (gwah-thuhl-kee-VEER) River. No one has expected it; it is as if a ghost ship has appeared.

The ship’s crew—a pitiful band of 18 Europeans and four East Indians—are living skeletons. The 18 Europeans are all that remain of a hopeful expedition of 270 that set sail three years earlier. The families of the men think them dead.

The ship limps slowly up the river, but word of its appearance spreads rapidly. By September 6, when it reaches Seville, the whole city is consumed with curiosity. Where has this ship been?

The story begins on this same river with an armada of five ships. The ships are not particularly impressive, but the capitán-general is. His name is Ferdinand Magellan, and he has checked, rechecked, and strengthened every timber, every sail, every length of rope.

Magellan is preparing for a two-year expedition. His food supplies include several tons of pickled pork, almost as much honey, and 200 barrels of anchovies. In case they must fight, there are thousands of lances, shields, and helmets. To keep the ships in repair, they pack 40 loads of lumber, pitch, and tar. And there are mirrors, scissors, colored glass beads, and kerchiefs to trade with unknown natives. (Later he will discover that he has been cheated; much that he ordered and paid for is stolen on the docks and not loaded on the ships.)

Some people say Magellan is a fanatic or, at best, a dreamer. Actually, he is a bit of both, as achievers must be. Short and muscular with a bushy black beard and a limp—a battle wound—he has an idea; and it consumes him. He believes he can do what Columbus has not done—reach Asia and its fabled Moluccas (Spice Islands) by sailing west. He expects to find the Moluccas, load his ships with cloves and other spices, and then turn around and sail back, thus pioneering a new trading route. Spices, especially cloves, nutmeg, mace, cinnamon, and ginger, are worth their weight in gold and sometimes more than gold.