THE WORD

Upper Paleolithic cave art in Europe demonstrates that humans of forty thousand years ago were already thinking abstractly and expressing creativity by projecting their mental images of animals onto the rock environment. During the Neolithic era, stone megaliths sprang up across Europe, most famously Stonehenge, which was erected in 2,300 BCE and was used for royal burials as well as charting the course of the sun and hosting solstice festivals for pilgrims. This suggests that humans had begun relating to their outside environment in an entirely new way—a way that has been exclusive to Homo sapiens ever since.

Earlier, around 3,500 BCE, writing, called cuneiform, had been invented in Mesopotamia in the form of wedge-shaped characters carved into clay, and for the first time information could be accurately preserved and transferred without depending on the memory of a human messenger. When the ancient Sumerians first took wedge to clay tablet, they couldn't have known that they were writing the first chapter of humankind's journal. But they were. And that story begins roughly six thousand years ago, which is why some still cling to the belief that planet Earth is only six thousand years old—despite conclusive scientific evidence that it is 4.5 billion years old and that our universe goes back 13.8 billion years.

Indeed, our world is six thousand years old. Our Story began when we started to write about it, 3000–4000 BCE. Everything that happened before then we call “prehistory.” In a way, it is a prologue because we don't know the names of any Neolithic people. They speak to us only in images, structures, and artifacts. In the early Bronze Age, humans start using words and so that's when individuals emerge and Our Story begins. “In the beginning was the Word.”

With the development of civilized culture and writing, we have on record the fact that Bronze Age humans thought in terms of myths (from Greek muthos, meaning “story”), sacred tales that served as explanations for what they observed in the world around them. And the words that they used to describe these myths had power, which gave them a magical quality. Written cosmologies were more systematic than prehistoric, animistic attempts to describe the world, but the supernatural was still a major component.

In Egypt, cosmological myths were woven into the religion with the heavenly bodies being associated with gods. Creation stories with differing details depending on city have been deciphered from various texts and tomb-wall decorations; I will just mention their common elements.

In most Egyptian creation myths, the world arose out of a watery chaos called Nu, an obvious allusion to the river Nile so central to Egyptian life. A pyramid-shaped mound emerged from the waters. The sun god Ra, or in some cases Khephri, appeared out of the mound—a self-created god who then created other gods and eventually humans.

Since it was imperative that priests could anticipate the appearance of gods in the sky and, more important, predict the Nile flood, they developed a calendar with twelve thirty-day months within a year of 365 days based on astronomical observations. And so ancient astronomy made the first step toward applied science.

Science involves two activities, which are today largely carried out by separate groups of professionals—observers or experimentalists who gather the data and theorists who develop models, usually mathematical, to describe what is observed. While the observational side of ancient astronomy was remarkably accomplished, the theory side remained heavily magical and mythological.1

The Egyptian theory of creation is an example. According to the most common Egyptian creation myth, the sky goddess Nut gives birth to the sun god Ra once a year, thus describing a universe that is self-creating and eternal.

The Egyptian cosmos was composed of a flat, rectangular Earth with the Nile at its center. In the south, in the sky supported by mountains, there was a river, and on this river the sun god made his daily trip. The sky was a roof placed over the world, supported by columns placed at the four cardinal points. The stars were suspended from the heavens by strong cables, but no apparent explanation was given for their movements.²

The civilizations of Mesopotamia and Canaan all had similar concepts of the cosmos and humanity's place in it.³ Earth was a disk with the firmament, or vault of heaven, resting on its edge. Beneath Earth were the waters of the abyss.⁴ Once again, we note the role of water, obviously derived from the fact that the civilization developed along the Tigris and Euphrates Rivers.

Babylonian astronomy was remarkable, with records going back to 800 BCE that are the oldest scientific documents in existence. Babylonian astronomers discovered the 18.6-year cycle of the rising and setting of the moon. They made the earliest recorded sighting of Halley's Comet in 164 BCE, making possible accurate calculations of its orbit by Halley and other astronomers centuries later. Babylonians produced the first almanacs of the movements of the sun, moon, and planets. Although primarily intended for astrological forecasting, the techniques they developed enabled accurate predictions of planetary motion and eclipses.

Curiously, Babylonian scientific astronomy did not lead them to a scientific cosmology; their cosmology remained highly mythological. However, the Greeks would utilize Babylonian astronomy to produce the first cosmology that could be clearly identified as natural rather than magical or mythological.⁵

As in Egypt, Mesopotamian cosmology was integrated into religious belief and a cosmogony, a myth of creation. That myth is described in a poem known as the Enûma Elish dating from a little before 1000 BCE. It describes a clash among the gods in which Marduk (or Assur) defeats the ocean goddess Tiamat and rips her body into two halves that become the heavens and earth. He then organizes the sun, moon, stars, planets, and the weather. He creates humans from the blood of Tiamat's husband, Kingu, so they can do the work of the gods.

The Christian faith, the biggest in the world today, emerged two thousand years ago out of the older faith of a tiny tribe of desert dwellers in Canaan called the Hebrews. The Hebrews divided the universe up into heaven, earth, sea, and the underworld, as shown in figure 1.1. Earth is a more-or-less flat disk floating on water with the vault of heaven resting on foundations on the edge of the sea. Beneath earth were the waters of the abyss. God sits at the apex of a series of heavens above the vault of the sky.⁶

Of course Christians today, even those who insist that the Bible is infallible, know that there is more to the universe than what is depicted in figure 1.1. Furthermore, God is now generally imagined to be either everywhere in space and time or outside both (depending on theologian), rather than at one special place. Nevertheless, it must be kept in mind that Christianity was built on the superstitions of very simple people for whom the model in figure 1.1 represented the best knowledge available at the time—based on their own observations of the land, sea, and sky. It was easy for them to conceive of God as a great king watching everything that happens and making sure events proceed according to his divine plan.

There are actually two contradictory creation myths in the Hebrew Bible. For example, in Genesis 1, vegetation is made before animals and animals are made before Adam and Eve. In Genesis 2 Adam is made first, then vegetation, then animals, then Eve.⁷ Chapter 1 was composed in the sixth century BCE when the Jews were in exile in Babylon, and it is clearly descended from the ancient Babylonian Enûma Elish. The creation myth in chapter 2 of Genesis came from Canaan a few centuries earlier.

Figure 1.1. The ancient Hebrew conception of the universe. Image © Michael Paukner.

The biblical creation myth familiar to us today, based on Genesis 1, needs little elaboration: God creates the world in six days, resting on the seventh. On the first day, he starts by creating heaven and earth. But they are in darkness and he (using the power of the Word) says, “Let there be light.” On the second day, he makes a firmament to divide the waters above, which he called heaven, from the waters below. On the third day, God demands dry land to appear in the waters below, and he calls it earth and the waters seas. Then he tells earth to bring forth vegetation yielding seed and trees bearing fruit.

On day four, God adds the sun, moon, and stars to the firmament of the heavens. On the fifth day, he orders the waters to bring forth fish and birds and blesses them, saying, “Be fruitful and multiply.” On the sixth day, God has earth bring forth cattle, beasts, and creepy things. And finally, God makes man in his image and gives him dominion over all Earth and its living things. And then he saw it was good and took a day off to recover from his labors.

Genesis, of course, also tells the story of the first humans that God kicked out of Eden because they ate from the tree of knowledge of good and evil. In Christianity, this became the original sin that Christ died for.

Since the late nineteenth century, most scholars have concluded that Moses did not write the book of Genesis, as tradition claims, but it most likely arose during the Jewish captivity in Babylon. This is primarily based on the discovery in 1872 of Babylonian cuneiform tablets containing a deluge story closely resembling the biblical flood.8 It has even been argued by some that the Hebrew Bible and Judaism itself derives directly from Mesopotamian mythology, although how much remains in dispute.⁹

CREATION EX NIHILO

Today's prominent Christian apologists, such as William Lane Craig and Dinesh D’Souza, argue that Genesis is the only ancient creation story that is consistent with modern cosmology in featuring a transcendent deity that created the universe out of nothing, the doctrine known as creation ex nihilo.¹⁰ However, it is to be noted that Genesis does not speak of any creation ex nihilo, which was a doctrine that developed much later.

The first words of the Bible are, “In the beginning, God created the heavens and the earth.” But, as biblical scholar Tim Callahan points out, this is not the only translation of the original Hebrew.11 The word bara can be translated not only as “create” but also as “chose,” “divide,” and other meanings depending on context. And Hebrew translations depend very much on context.

Old Testament scholar Ellen van Wolde says that in the context of Genesis, the first sentence should be translated, “In the beginning, God separated the heavens and the earth.”¹² This is more consistent with the other “separations” that are then described: light from darkness, waters above from waters below, and land from water. Furthermore, this interpretation is more in line with the Babylonian creation myth, on which the Hebrew myth was surely based. In the Enûma Elish mentioned above, Marduk slices Tiamat's body into the heavens above and earth below.

But even if creation ex nihilo is the correct interpretation, it is not unique to the Bible. Callahan observes that, before being killed by Marduk, Tiamat ruled over a chaotic, formless void.¹³ As we will see, formless chaos is about as nihilo as nihilo can be. Neither have any information or structure that you can use to define them as something other than nothing.

The late keeper of the Egyptian and Assyrian antiquities at the British Museum, Sir Wallis Budge, lists a series of what he oddly calls “epithets” collected by the nineteenth-century German Egyptologist Heinrich Brugsch (1827–1894) from hieroglyphs. Here is a sample:

God is from the beginning, and He hath been from the beginning; He hath existed from of old and was when nothing else had being. He existed when nothing else existed, and what existeth he created after He had come into being….

God is the eternal One, He is eternal and infinite; and endureth forever and aye; He hath endureth for countless ages, and He shall endure to all eternity….

God hath made the universe, and He hath created all that therein is: He is the Creator of what is in this world, and it was He Who fashioned it with His hands before there was any beginning.14

Budge says these epithets, which “are applied to the gods, from texts of all periods,” show that “the ideas and beliefs of the Egyptians concerning God were almost identical to the Hebrews and Mohammadans at later periods.”¹⁵

However, no actual texts are cited. It makes one wonder if we have a bit of apologetics going on here, designed to show that Judeo-Christian-Islamic beliefs are universal. Ironically, these claims contradict those of the apologists mentioned above who want to make us think that the Christian creation myth is unique and original.

In Budge's own translation of the Papyrus of Nesi Amsu in the museum (No. 10,188), the god Neb-er-tcher identifies himself as Ausares (Osiris) and says, “I developed myself out of the primeval matter which has evolved multitudes of evolutions from the beginning of time.” This sounds more like creation from already-existing matter. Incidentally, the god does this by word alone: “I uttered my own name, as a word of power, from my own mouth, and I straightway evolved myself.”¹⁶ Again we see how much stock the ancients put in the power of words by themselves.

Moving to India, in his Creation Myths of the World, David Leeming gives the following quotation from the Hindu Rig Veda, which goes back at least to 1000 BCE:

In the beginning there was neither Being nor Non-Being, neither air nor sky. What was there? Who or what oversaw it? What was it when there was no darkness, light, life or death? We can only say that there was the One that which breathed of itself deep on the void, that which was heat and became desire and the germ of the spirit.¹⁷

In any case, according to Leeming, creation ex nihilo myths are as common as creation from a preexisting watery chaos. And, as I will often remark, complete chaos is indistinguishable from nothing.

OTHER CULTURES

It is not my purpose here to give a comprehensive survey of the many rich creation myths and cosmologies that can be found in the oral and written traditions of ancient cultures. While differing greatly in details, most early cosmogonies, as mentioned, attempted to explain the origin of the world in human terms with anthropomorphic gods bringing order out of chaos or out of nothing (ex nihilo).

Of course, many complex traditions can be found in ancient India and China. It would take me far afield to do justice to them. In any case, they have little bearing on my topic, which is the development of scientific cosmology to the present day and its clash with the religions of yesterday and today. Modern science emerged exclusively in Europe, with its origins in the great river civilizations of the Middle East and Greece where the religions it most clashes with also arose.

Still, it is worth mentioning that Hindu thinking envisaged a world that passed endlessly between phases of creation and destruction. The concept of a cyclical universe, which differs markedly from the Judeo-Christian-Islamic view of a created universe finite in time, has raised its head in some scientific cosmologies of today.18

In astronomy, the Hindu astronomical work called the Surys Siddhanta, written about 400 CE by an unknown author, gave the average length of the sidereal year that is only 1.4 seconds longer than the modern value, and it stood for over a thousand years as the most accurate measurement of that quantity made anywhere in the world.

A common picture of the cosmos is found across most ancient cultures, probably because it described what people observed: a flat, central Earth surrounded by water, celestial bodies rotating above, and a dark, forbidding underground associated with death.

Ancient astronomers did remarkable work in measuring the motions of the sun, moon, planets, and stars. This enabled them to produce calendars from which they could predict the seasons and repetitive events, such as the annual Nile flood. Indeed, these motions behaved so predictably compared to events on Earth, such as storms, earthquakes, and floods (other than the Nile flood), that the heavens were viewed as a divine province that controlled the lives of humans and the world around them. And so, in addition to predicting the seasons, astronomers took on a second role as astrologers to be consulted on virtually every decision.

GREEK PHYSICAL COSMOLOGY

Starting in the sixth century BCE, a group of thinkers residing in the Greek cities of Ionia on the western coast of Asia Minor began to remove gods and the supernatural from any major role in the world. Together with several philosophical schools in Greek colonies in Italy, they are called the Presocratics, although some of the later ones were contemporaneous with Socrates (ca. 469–399 BCE). The designation was introduced in the nineteenth century to distinguish this group of philosophers from Socrates, who was more concerned with human problems while the Ionian Presocratics, at least, dealt with cosmology and physics where the role of humanity is minimal.19

It should be kept in mind that few of the writings of the Presocratics have survived and most of what we know about them comes from later sources, in particular, Aristotle (384 –322 BCE), who was not all that sympathetic to their teachings and was in strong disagreement with some. Aristotle named the Ionians physikoi or physiologoi, from their concern with physis or nature.²⁰ Today we call them physicists. As we will see, by contrast the Italian Presocratics were mostly mystical so they really should not be grouped with the Ionians.

The Ionians began a movement described by the term Kosmos, which denoted an ordered world in contrast to Chaos, the unpredictable, capricious world of divine intervention described in the epic poems of Homer (ca. 700–800 BCE) and Hesiod (ca. 650–750 BCE).

Thales

Thales of Miletus (ca. 624–546 BCE) is generally regarded as the first physicist. He sought natural explanations for phenomena that made no reference to mythology. For example, he explained earthquakes as a result of Earth resting on water and being rocked by waves. Thales is famous for supposedly predicting the eclipse of the sun that modern astronomers calculate occurred over Asia Minor on May 28, 585 BCE (current calendar). However, most historians today doubt the truth of this tale.

Thales's most significant contribution was to propose that all material substances are composed of a single elementary constituent, namely, water. While he was (not unreasonably) wrong about water being elementary, Thales's proposal represents the first recorded attempt to explain the nature of matter without the invocation of invisible spirits.

Thales and the other Ionian philosophers that followed espoused a view of reality now called material monism in which everything is matter and nothing else.

Anaximander

Anaximander (ca. 610–546 BCE) was the second master of Thales's school in Miletus. He proposed that the universe is boundless and has no origin. Furthermore, boundlessness or apeiron was the source of all things:

The first principle of existing things is the Boundless for from this all things come into being and into it all perishes. Wherefore innumerable worlds are brought to birth and again dissolved into that out of which they came.21

Despite an unlimited number of worlds, Earth still floats at its center. Anaximander's cosmos is shown in Figure 1.2.²²

Figure 1.2. Anaximander's cosmology. Image from Mary Ackworth Orr, Dante and the Early Astronomers (Port Washington, NY: Kennikat, 1969).

Anaximenes

Anaximenes (585–528 BCE) was a student or at least a younger colleague of Anaximander. He proposed that everything is made of air, which in ancient times was widely regarded as the breath of life. In Anaximenes's cosmology, Earth is formed by a condensing or felting of air and rests on a cushion of air. The heavens are like a felt cap with the heavenly bodies fixed to its surface that turns around the head. Interestingly, the sun does not circle Earth as in most geocentric cosmologies but is hidden behind mountains at night. (In chapter 13 we will see how this theory is falsified by a photograph of the sun taken at night with neutrinos passing through Earth).

The Atomists

Leucippus and Democritus were the founders of atomism. In my previous book God and the Atom, I told the story of how their notion that everything is composed of elementary particles of matter has been triumphantly corroborated by modern physics.²³

According to Orr, Leucippus and Democritus, along with the Pythagoreans we will discuss below, made a great step forward in cosmology when they realized that the sky is not a hemisphere ending at the horizon but surrounds Earth like a sphere.24 She attributes the diagram shown in figure 1.3 to Democritus. In a similar diagram she ascribes to Leucippus, Earth covers the whole lower hemisphere, which is air in the Democritus version.

Figure 1.3. Cosmology of Democritus. The cosmology of Leucippus is the same except Earth extends down in the lower hemisphere shown here as air. Image from Mary Ackworth Orr, Dante and the Early Astronomers (Port Washington, NY: Kennikat, 1969).

Epicurus (341–270 BCE) transformed the atomism and cosmology of Leucippus and Democritus into a major philosophical school.²⁵ Three hundred and fifty years later, the Roman poet Titus Lucretius Carus (ca. 99–55 BCE) immortalized the teachings of Epicurus and the earlier atomists in his epic work De rerum natura (The Nature of Things). What follows is Lucretius's presentation of atomist cosmology:

Since empty space is limitless on all sides and the amount

Of atoms meandering in the measureless universe, past count,

All flitting about in many different ways, endlessly hurled

In restless motion, it is most unlikely that the world,

This sky and rondure of the earth, was made the only one,

And all those atoms outside of our world get nothing done;

Especially since this world is the product of Nature, the happenstance

Of the seeds of things colliding into each other by pure chance

In every possible way, no aim in view, at random, blind,

Till sooner or later certain atoms suddenly combined

So that they lay the warp to weave the cloth of mighty things:

Of earth, of sea, of sky, of all the species of living beings,

That's why I say you must admit that there are other cases

Of congregations of matter that exist in other places

Like this one here of ours the aether ardently embraces.26

In short, the universe of the atomists, like that of Anaximander, is unbounded, eternal, uncreated, and composed of many worlds.

Furthermore, according to atomism, the universe is in large measure the product of random chance. As with atoms, the atomists got this one right, too–long before anyone else did.

Some historians dispute that the atomists’ universe was eternal.²⁷ While it is true that the stuff made of atoms decayed, the atoms themselves are eternal, as Lucretius explains:

If atoms are solid, therefore, and without void, as I've taught,

Then they must be eternal. And what's more, if they were not,

Everything would have met with its demise,

And any objects that we see here, now, before our eyes

Would have been born again from nothingness. But since I've taught

That nothing's made of nothing, and the nothing can be brought

To nothingness once it is made, then there must be first bodies

Made of stuff that last forever—atoms—and it is these

That everything is broken down to in its final hour

So there is a supply of matter on hand to re-power

The world. These atoms thus are pure and solid through an through;

How else could they survive infinite time to make things new?²⁸

Pythagoras and Philolaus

Pythagoras (ca. 570–495 BCE) is probably the best known of the Presocratics and so unlike the Ionians that it is incongruous to lump them together as historians do. He was the founder of a religious and political community in Croton, Sicily, where he achieved wide fame as a mystic, a wonder-worker, and the purveyor of the doctrine of an immortal soul able to transmigrate into animals. It is to be noted that the notion of an immortal soul, so widespread today, was not prevalent in Greece or Italy at that time.

Pythagoras's modern image as a master mathematician, geometer, and scientist is less secure. Neither Plato nor Aristotle attributes the “Pythagorean theorem” to Pythagoras.

According to historian John North, Pythagoras taught that the universe was produced by heaven inhaling infinity to produce numbers.29 Orr presents the diagram in figure 1.4 as the “earliest form” of the universe of the Pythagoreans, although there is no record of Pythagoras himself having held this picture.³⁰ It may be the earliest cosmology in which Earth is a sphere. The region labeled “Cosmos” contains the five planets, the sun, and the moon. “Olympos” contains the stars. “Ouranos” refers to the sky. The whole is surrounded by the celestial fires and beyond that by Apeiron, the infinite space from which the world draws its breath.

This model was modified by Philolaus (ca. 470–385 BCE) of the Pythagorean school in the dramatic way illustrated in figure 1.5.³¹ Philolaus proposed that Earth is not the center of the universe. But neither is the sun. Rather, Earth, the sun, and the seven planets visible to the naked eye revolve around a central fire. The stars are fixed and at a great distance. Earth rotates every twenty-four hours about the central fire, the sun once a year. In addition, another planet, a counter-Earth called Antichthon exists that also revolves every twenty-four hours and is always on the other side of the central fire from Earth. The reason we do not see either the central fire or Antichthon is that only the side of Earth turned away from each is inhabited.

Figure 1.4. The early Pythagorean cosmos. Image from Mary Ackworth Orr, Dante and the Early Astronomers (Port Washington, NY: Kennikat, 1969).

Compared to the Ionians, I think it can be safely said that the Pythagoreans, even if they were great mathematicians, were not scientists. Their ideas were based on mystical arguments rather than observations. The five planets visible to the naked eye plus the sun and moon numbered seven, a sacred number since it was the number of notes on the musical scale that the Pythagoreans had discovered. Adding Earth and the central fire made nine, so Philolaus introduced Antichthon to bring the total to ten, another sacred number (presumably because we have ten fingers and toes). According to Orr, the Pythagoreans regarded the central fire as the Watch Tower of Zeus, the Hearth of the Universe, where was placed the purest element, fire.32

Figure 1.5. The system of Philolaus. Earth, the sun, and the counter-Earth, Antichthon, revolve around a central fire. Only the side of Earth opposite the central fire and Antichthon is occupied, so both the central fire and Antichthon are unseen. The top diagram illustrates night on Earth and the lower diagram illustrates day. Not shown, the moon's orbit is inside that of the sun, and the planets’ orbits are all outside. Image from Mary Ackworth Orr, Dante and the Early Astronomers (Port Washington, NY: Kennikat, 1969).

Curiously, despite their obsession with numbers, it never occurred to the Pythagoreans to make quantitative measurements of the heavenly bodies, which would have quickly disproved Philolaus's cosmology. But it was a bold guess nonetheless and the earliest record of a cosmology that was not centered on Earth. As Orr writes,

It was the braver of the Pythagoreans to shake the steady earth from her centre, and set her whirling in the depths of space, that they realized, as no one had done before, how large she must be; for Greece and the surrounding lands, the Middle and the other seas, instead of making the whole of the earth, were now understood to be only a portion of a great globe.

Here, then, is a conception of the universe widely different from Homer's. The little flat disc has become a round ball swiftly moving through space; the crystal dome that tenderly covered it like a bell-glass over some fragile flower, has lifted and the vast sphere is seen, infinitely distant and studded with enormous stars. Man himself is now a tiny creature on a great earth, and his world but one of many, but if he is humiliated by his insignificance, is he not elevated by the vastness of his outlook?33

Empedocles

Empedocles (490–430 BCE) was a citizen of Agrigentum in Sicily and was closer to the Ionian physicists than he was to the Pythagorean mystics. Empedocles was the first to propose that matter is composed of the four elements: earth, water, air, and fire. Since Aristotle adopted this picture, it became the “standard model” for millennia until it was replaced in the nineteenth century by the chemical elements of the periodic table, and then in the late twentieth century by the quarks, leptons, and bosons of what we now call the standard model of elementary particles.

Empedocles's cosmos contained a number of insights, such as the moon shines by reflected light from the sun and a solar eclipse is the result of the moon blocking off the sun.

More mystically, Empedocles proposed that two opposing forces called “Love” and “Strife” (or, perhaps, attraction and repulsion) governed the elements, resulting in cyclical patterns as the two competed with one another. In Empedocles we find a thinker deeply suspicious that matter has many different fundamental forms. Also, Empedocles believed the behavior of matter was controlled by intangible but real natural forces that came in multiple forms as well. This philosophical breakthrough laid the foundations of all future study of matter, and survives to this day.

Plato

Eventually, the Presocratics in Ionia and Italy gave way to the Socratics in Athens. We know about Socrates mainly from the writings of Plato (429–347 BCE), which indicate Plato was no scientist, believing that true knowledge of reality can only be obtained by pure reason without the help of the senses.

According to Plato, Socrates tried to move philosophical interest from physics and cosmology to human concerns such as ethics and politics. But he did not totally succeed. Greek philosophers in Athens and elsewhere continued to think about the universe, although most were not quite willing to adopt the naturalist views of the Ionians, especially the atomic theory.

In Plato's Timaeus, the character by that name is introduced as an astronomer and student of the universe. He describes a creation out of chaos, “where there is no order, and no matter which can be distinguished by name, but all is confused and seething with random restless motions.”34 That was a good guess, but the rest was not. The heavenly bodies, according to Timaeus, are divine, intelligent beings. They all are perfect spheres composed of fire. Earth is also a perfect sphere at the center.

In Timaeus, Plato clearly rejects the notion of multiple universes: “The Maker made neither two, nor yet an infinite number of worlds. On the contrary, our universe came to be as the one and only thing of its kind, is so now and will continue to be so in the future.”³⁵

Plato was certainly not a material monist—someone who believes the world is matter and nothing more. He argued that what we humans detect with our eyes and other senses are but shadows of a true, more perfect reality. Plato taught that a divine craftsman called the Demiurge constructed the cosmos according to a sacred plan. There are two realms of reality: a realm of forms or ideas that is perfect and a material realm in which these forms or ideas are imperfectly replicated.³⁶

Plato's creation is to be contrasted, however, with the notion that the universe was created ex nihilo—from nothing—while the Demiurge used already-existing materials.

For example, the heavenly bodies are perfect spheres rotating in perfect circles around the sun. The fact that the planets appear to wander about the sky (planet means “wandering star” in Greek) is explained as a distortion of the senses, the way a lens distorts what we see.

Since far more writings of Plato and Aristotle have survived than those of their predecessors, or immediate successors for that matter, they have tended to have the greatest influence of any ancients on human thinking throughout the ages. Not to take anything away from their enormous contributions, but the often-unquestioned authority of Plato and Aristotle has not always been to the benefit of human progress.

Plato's importance to history may have been his reintroduction of divinity into the scheme of things after it had been dismissed by the Ionians. Not only did the Demiurge create the universe, but the planets and stars hosted the celestial gods. According to historian David Lindberg, “Plato restored the gods in order to account for precisely those features of the cosmos that, in the view of the physikoi, required the banishing of the gods.”37

Aristotle

Unlike his mentor, Plato, Aristotle was a legitimate scientist who made observations and performed experiments, although he still trusted his reason over his data. It was not until Galileo that the priority of reason over observation was reversed and observation became the final arbiter of knowledge—at which point, coincidentally and not accidentally, science began its great climb to where it resides today, joining other advances at the pinnacle of human accomplishments.

Aristotle, like almost all the other post-Pythagoreans, put Earth back at the center of the cosmos. He said the form of the universe had to be a sphere because it is the most perfect solid. For Aristotle, the universe had no beginning and will have no end (a teaching Christianity would ignore). Here the reason he gives is that the gods are immortal, and since they live in the highest heaven of the universe, so too must the universe be immortal.

As mentioned, Aristotle adopted Empedocles's model in which earth, water, air, and fire are the basic elements from which all of matter is composed. This led to its adoption as the “standard model” of matter until the rise of modern chemistry and physics. Aristotle added a fifth element, a quintessence called aether, as the stuff of the heavens.

Aristotle declared that there are three forms of natural movement, exemplified by the motions of five elements: (1) earth and water move in a straight line toward the center of Earth; (2) air and fire move in a straight line away from the center; (3) celestial bodies move in circles around the center. The last provided an explanation for the ancient question of why the heavenly bodies never fall to the ground.

Figure 1.6. Aristotle's cosmology. Image courtesy of NASA/StarChild.

Aristotle's cosmology is illustrated in figure 1.6.³⁸ He made a major advance in proposing that the planets and stars were actual physical bodies, although still perfect spheres. This contrasted with Plato's image of the celestial bodies as divine beings. Moreover, Aristotle disagreed with Plato's claim the universe was created. He said it was eternal, but not infinite.

Note the “Sphere of the Prime Mover” in the figure. Aristotle's physics required that all motion have a cause, and the ultimate cause, the Prime Mover, was the “First Cause Uncaused.” This entity was interpreted by Christian theologians in the Middle Ages, notably Thomas Aquinas, to be the creator God. However, Aristotle introduced the unmoved mover in Physics not as the creator but as a spiritual something located at the outermost part of the universe that is the source of all celestial motion.³⁹

Aristotle disagreed with the atomists. In their view, earth, water, air, and fire are not elementary but are composed of atoms that are more elementary. Aristotle claimed to prove that the atomists’ void was impossible, while the key principle of atomism is that everything is atoms and the void. The atomists agreed that the universe was eternal but disagreed that it was finite. They also claimed that there were multiple worlds.

Aristotle's teachings on physics and cosmology were not totally accepted in pre-Christian Greece and Rome. Not only the atomists, led by Epicurus, but also the Stoics, led by Zeno of Citium (ca. 334–262 BCE), claimed that the universe was infinite as well as eternal.

Nevertheless, Christian theology adopted Aristotle as an ancient authority on many subjects, especially the idea of First Cause. As a result, the great European universities built by the Catholic Church in the Middle Ages became so deeply entrenched in what is called Aristotelian scholasticism that the scientific revolution, which repudiated much of Aristotle's science—especially his physics—occurred outside these institutions.

Aristarchus

Aristarchus of Samos (310–230 BCE) is the first recorded astronomer to place the sun at the center of the universe. The Babylonian astronomer Seleucus (ca. 190 BCE) is said to have made the same proposal a bit later. Aristarchus also located the planets in their correct distance-order from the sun. Although he used proper geometrical arguments, his distance estimates were too low because of faulty data.40 He did recognize, however, that the stars had to be far away because of their absence of measurable parallax.

Hipparchus

Hipparchus (ca. 190–120 BCE) was born in Nicaea in Bithynia but lived most of his life in Rhodes. He made the first accurate models of motions of sun and moon, based on Babylonian tables. Hipparchus also discovered the precession of the equinoxes, calculated the length of the year to within six and a half minutes, compiled the first known star catalog, and made an early formulation of trigonometry. As such, he is regarded as the first to apply numerical data from observations to geometrical models. Hipparchus laid the foundation for the work of Ptolemy three centuries later, and he has been called “the greatest astronomer in antiquity.”⁴¹

Ptolemy

Claudius Ptolemy (ca. 90–168 CE) resided in Alexandria, where he had available to him the immense store of the writings of the Greeks and Romans that had been gathered in the Library of Alexandria, the greatest library of the ancient world. In 48 BCE, Julius Caesar (100–44 BCE) accidentally burned a large number of books stored near the docks when he set fire to the ship in the harbor. However, two other collections in the city were spared. These were largely destroyed during Christian riots in 390 CE, but Alexandria continued to be a center of Greek learning.

Ptolemy also was able to utilize excellent astronomical instruments in the observatory associated with the library. With these facilities, he combined astronomical data accumulated over centuries, including those of Hipparchus, with his own observations to frame a system that mathematically described all celestial motions observed to that day. He published his system in a set of thirteen books originally named the “Mathematical System of Astronomy,” which was renamed by others as Magiste Syntaxis (Great System), and later by the Arabs as the Almagest (The Great System or just The Majestic), by which it has since been known. This work remained the definitive treatise on astronomy until Copernicus's De revolutionibus orbium celestium (On the Revolutions of the Heavenly Spheres) appeared in 1543.42

Ptolemy maintained the Earth-centered system of almost all his predecessors, although Earth is slightly off-center. He described his physical premises as follows:

The heaven is spherical in shape, and moves as a sphere; the Earth too is sensibly spherical in shape, when taken as a whole; in position it lies in the middle of the heavens very much like its centre; in size and distance it has the ratio of a point to the sphere of the fixed stars; and it has no motion from place to place.⁴³

In order to maintain Earth near the center of his system and still accurately describe planetary motions, which are far from circular about Earth, Ptolemy constructed a model of enormous complexity, illustrated in simplified form in figure 1.7.⁴⁴

In Ptolemy's system, the planets move in circles called epicycles whose centers themselves move in circles about a point called the equant that is not exactly centered on Earth. In some cases, the epicycles themselves move in epicycles.

The Almagest is primarily a technical work that enabled trained astronomers to predict planetary motions. Ptolemy's cosmology is presented in another work, Planetary Hypotheses, which is known mainly from Arabic sources. It is essentially the same as Aristotle's cosmology. Earth is composed of the four elements earth, water, fire, and air. It does not rotate about its axis. The heavens are composed of ten concentric spheres composed of the transparent fifth element, quintessence or aether, proposed by Aristotle, which rotate in circles around Earth. There is no void, no empty space, between the spheres, in agreement with Aristotle's insistence that a void cannot exist. They are filled with quintessence.

Figure 1.7. The Ptolemaic model of the solar system. The planets move in circles on the surfaces of concentric spheres that revolve in circles around a point not precisely at the center of Earth. The spheres are not empty but are composed of Aristotle's quintessence or aether. Image by the author.

In order of distance from Earth are the spheres containing (1) the moon, (2) Mercury, (3) Venus, (4) the sun, (5) Mars, (6) Jupiter, (7) Saturn, and (8)–(10) the “fixed stars,” which are fixed in the sense that they do not move with respect to one another as their spheres rotate. Of course, everything rotates with a period of twenty-four hours. Ptolemy's model does not provide the distance to the objects.

Ptolemy counted 1,022 stars in forty-eight constellations and listed the fifteen brightest stars.45 As well as solar, lunar, and planetary motion, his system enabled one to predict the rising and setting of stars.

The Ptolemaic system marked the end of the advance of Greek astronomy. As the Greek language gave way to Latin in the Roman Empire, few could read Ptolemy's books. The Romans themselves made no significant contributions to the science of astronomy but typically found value in its practical use for measuring time. By the time of Julius Caesar, the calendar had gotten all out of kilter, so he called upon the Alexandrian astronomer Sosigenes (first century BCE) to provide a new one. The so-called Julian calendar that Sosigenes provided is still in use with only small corrections made over the centuries since. Note, however, that it was still Greek astronomy that provided the mechanism.⁴⁶