Space Book

The History of Cosmology

Humans have been pondering the beginnings of life and the universe for thousands of years. Each culture has its own creation story to explain how it all began. Chinese traditions, Babylonian stories, Native American traditions and many others have different ways of describing the beginning and meaning of the universe. It is only recently, with modern telescopes and computer modeling, that we are getting closer to an understanding of the structure, origin and evolution of the universe.

In ancient Greece as long ago as 600 BCE, Anaximander was studying the universe which the Greeks believed could be described in geometric or mathematical terms. By the second century CE, Ptolemy, based on the work of Plato and Aristotle, described the universe as spherical, with the Earth at its center and thought all of the stars and planets revolved around it in circles. Each planet’s motion was described individually by a different mathematical formula, and the planets’ motion appeared quite complex.

The work of Aristotle (not Ptolemy) became the basis of European beliefs about the Earth’s place in the universe. During the Dark Ages in Europe, Islamic societies continued to further the study of science, astronomy and cosmology. It was not until Nicolaus Copernicus in the 1500s that progress beyond Ptolemy’s work was made in Europe. Copernicus wanted to derive a single theory about the universe, where everything worked on the same principle. He was uncomfortable with the models that required each planet to have its own set of complicated equations to describe it. He demonstrated that the Sun, not the Earth, was the center of the Solar System, which greatly simplified the mathematics needed to describe the system. However, the planets’ motion was not completely simplified by this development. He left his writings on this topic to be published after his death because he didn’t want to face the backlash he knew his ideas would provoke.

One hundred years later, Johannes Kepler was the first to uncover the mystery of the planets’ strange motions. Working from accurate astronomical observations obtained by Tycho Brahe, he realized that the orbits of the planets are elliptical.

Early scientists like Newton thought that the universe must be infinitely big and infinitely old, and evenly distributed. Otherwise, they reasoned, gravity would have long ago caused the universe to collapse on itself. Newton showed that the elliptical orbits described by Kepler were the natural consequence of a universal law of gravitation. Newton believed that the universe was infinite and behaved as a giant machine, and that it followed laws put in place by an omnipresent God.

Newton’s model dominated scientific thinking for the next 200 years although some questioned the plausibility of an infinite universe, and the growing understanding of thermodynamics made scientists theorize that a machine like the universe can’t continue forever without eventually running out of energy.

In 1823 a German astronomer named Heinrich Olbers asked why, if the universe is infinite, is the sky dark at night? If the universe is infinitely large, old, and evenly distributed, then every direction you look in the night sky should line up precisely with a star. If that were the case, the day and night skies should be as bright as the sun. Scientists began to realize that the universe could not really be infinite.