Cosmology in Ancient Greece

Cosmology in ancient Greece was connected with both religion and science. While other ancient societies viewed the universe as part of their religious life, in which the gods controlled humans, the Greeks attempted to go farther. While astronomy helped explain the physical world of the cosmos, cosmology attempted to discover how and why the cosmos exists.

The Greeks could observe the movements of the stars and planets, but they needed to create a system to explain them. According to the early Greeks, the origins of the heavens rested with the gods. This idea was consistent with other early religions, which saw the cosmos as the realm of the gods, where they interacted with humanity. But eventually the Greeks began to move away from the idea that the gods, who could be fickle, controlled the cosmos.

In their early religion, the Greeks based their creation story upon their mythology. They believed that chaos existed first, and out of this void emerged Night and Erebus, the unknown where death existed. From this dark and empty place, Eros (Love) arose, bringing order; and from it, Light and Day became and then Gaea (Earth) appeared. From Erebus and Night came Aether, the heavenly light, and Day, the earthly light. But Night also produced Doom, Fate, Death, Sleep, Dreams, Nemesis, and all those dark worlds of humans.

In the Greek mythology, it followed that Gaea (Earth) produced Uranus (the heavens), and the two mated to produce several Titan offspring. Uranus hated the Titans and tried to do away with them. The early Greeks saw the Earth as surrounded, with air above, water around, and Hades below. Gaea convinced the youngest Titan, Cronus, to attack Uranus, and he castrated him and threw his genitals into the ocean. In response, Uranus cursed Cronus and the Titans. From his genitals in the ocean came Aphrodite.

Both Gaea and Uranus had prophesized that Cronus would be overthrown by his son, so Cronus swallowed each child, both boys and girls, except the last, Zeus, who was exchanged for a stone by his mother, Rhea. Zeus was later accepted by Cronus and allowed to live on Mount Olympus. There, he gave Cronus a drink that forced him to vomit up his five children; these became the gods who made Zeus their leader as they fought Cronus and the other Titans.

Zeus successfully exiled the Titans to Tartarus except for Atlas, who was punished by having to hold the Earth on his shoulders for eternity. Involved in the whole process of Greek mythology were the Three Fates, goddesses who weave a rug that depicts all the mortals’ and gods’ affairs, and nothing can stop this, not even the gods. In other words, there is the idea of a force that rules everything, even the divine.

While some Greeks understood the idea of the Moon reflecting light from the Sun and the concept of lunar and solar eclipses, most still hewed to an idea based on mythology. For instance, Thales of Miletus (624-548) argued that the Earth floated on water. This explained earthquakes as waves in the cosmic ocean with stars floating in the upper waters. Anaxagoras, observing that meteors fall to Earth and are composed of the same material, theorized that these were really remnants of earlier parts of the planet that were thrown out due to its rapid rotation, and then as they slow down, they fall back to Earth. Anaximander stated that the Earth was in the middle of several spheres of mist, and in turn was surrounded by a big fire shining through the mist, which includes the Sun, the Moon, and the stars.

These ideas and others were people’s attempts to account for what they were observing. The cosmos allowed for other phenomena as well, such as navigation. The early Greeks soon learned the positions of the stars and figured out how to use their regular movements to guide their journeys. This in turn allowed them to move beyond the ideas that the cosmos was just random.

For many Greek philosophers, there was an attempt to construct a view of the universe that did not rely on the existence of gods. In particular, they wished to create a model that explained the movements of various objects in the sky. The most important of these thinkers was Plato, who viewed the creation of the cosmos through the Demiurge, whose name was derived from demos, meaning “people,” and ourgos, meaning “work.”

The Demiurge, the most highly placed of the gods, worked for the public good. He was the creator of all that was seen on Earth and in the sky. In his work Timaeus, Plato said that the Demiurge created the cosmos out of chaos that already existed as random parts of matter. He organized it into the four parts of matter, or elements: earth, water, air, and fire. Within these elements existed the cosmos, with its soul the most important part since it was eternal and brought about the circular motion of the heavens.

These were part of another universe, which was good, and our realm was a copy of these ideas or forms. From these elements, the Demiurge created the lower gods, the soul, and the stars. Plato went on to explain that the lower gods created mortals, whose souls created by the Demiurge were immortal and went through the process of reincarnation. Those men who were wicked would have their souls reincarnated as women, and if they were still wicked, they would become animals in the next reincarnation. In this system, Plato probably saw the Earth as the center of the universe, although he does not explicitly state that.

Plato’s pupil Aristotle continued to develop this concept through his own observations. He argued that the stars are placed in a semicircular fashion above the Earth. He postulated that since the Sun rises and sets each day, and we have the sensation of movement, then clearly the Earth is the center of the universe. He further argued that the Earth does not move, but rather the rest of the cosmos moves around it.

This geocentric version would last for the next 2,000 years. Plato had viewed the cosmos as a two-dimensional system of circular motion, while Aristotle now argued for a three-dimensional version. He further refined Plato’s concepts of the elements by limiting them to the area ranging from the Earth to the Moon; beyond the Moon lay the perfect celestial realm, composed of a mysterious and unexplained fifth element. All the elements moved toward the natural center of the universe (i.e., Earth), and as such, there could be no other worlds.

Some ideas had other practical applications. Thales of Miletus (624-546) used information from Babylon to predict a solar eclipse in 585, showing that it was not just a sudden apparition from the gods but a physical event. He was the teacher of Anaximander of Miletus (610-546) who had argued that all matter was made of the four elements (earth, water, air, and fire). He argued that the element earth resulted from the condensation of air and fire. Democritus (460-370) argued against the idea of the four elements and proposed the concept of atoms (whose name came from the Greek a-tome, meaning “unable to cut”) the indestructible building blocks of matter.

He argued that the universe obeyed the laws of mechanics, and these atoms moved about and collided with each other to produce larger objects. He also stipulated that infinite atoms made up the universe, and that between atoms, there is a void; therefore, the universe is infinite and eternal. His theories are the closest to the modern concepts of the universe.

Around 400, the Pythagoreans on Samos argued that everything in the universe could be explained in whole numbers. Music, math, and astronomy followed this pattern, such as the idea that vibrating strings could produce tones when the ratios of their lengths are whole numbers. As their concept goes, the number is sacred and derived from a point equaling 1, a line being 2, a two-dimensional surface being 3, and a solid or cube being 4, and when added together, this produced 10.

The mathematician Pythagoras then developed a theory of cosmology in which the Earth was a perfect sphere, as were other celestial bodies that moved around a celestial fire (but this was not the Sun, as it too moved around this fire), which was invisible to the eye. Since 10 was a sacred number, he believed that there were 10 objects around this central fire, some moving in opposing directions to create eclipses.

All of these theories attempted to create an understanding of how the universe worked, beginning with mythology and religion, and finally creating sophisticated theories to explain observable data.