Big Bang

From Myths to Early Measurements of the Cosmos The history of our understanding of the universe is a journey from supernatural storytelling to rigorous logical inquiry. For millennia, humans relied on creation myths—from Chinese legends of giants carving the landscape to West African tales of gods forming solid ground—to explain the world's origins. These stories invoked supernatural beings to explain natural phenomena and were considered absolute truths, with any questioning often seen as heresy. A fundamental shift occurred in the sixth century BC when Greek philosophers began seeking explanations for the natural world without resorting to deities. Figures like Anaximander and Xenophanes proposed that the sun and stars were physical objects, like fire-filled rings or burning gases, rather than gods in chariots. While their specific theories were often incorrect, their approach was revolutionary because it invited criticism, refinement, and logical debate, marking the birth of cosmology.

Pythagoras furthered this rationalist movement by demonstrating that mathematics could describe reality. His discovery that musical harmony was governed by simple numerical ratios established the principle that the universe follows mathematical rules, which led to the scientific requirement that theories must be testable and compatible with observed reality. The Greeks used this logic to determine that the Earth was a sphere, observing how ships disappeared over the horizon and noting the round shadow the Earth cast on the moon during eclipses. In the third century BC, Eratosthenes achieved a milestone by scientifically measuring the Earth's circumference. By observing the difference in the sun's angle at noon between Alexandria and Syene, he used simple geometry to calculate the planet's size with remarkable accuracy. This discovery acted as a stepping stone, allowing thinkers like Aristarchus to estimate the sizes of the moon and sun and the distances between them, proving that the universe could be measured through intellect and simple tools.

Despite these breakthroughs, the Greek model of the universe remained Earth-centered for nearly two millennia. While Aristarchus had correctly proposed that the Earth orbits the sun and rotates on its axis, his peers rejected this view. It seemed to defy common sense; they argued that if the Earth moved, we would feel a constant wind, and they could not detect the slight shift in star positions known as stellar parallax. Consequently, the complex Ptolemaic system, with its intricate "circles within circles" to explain planetary paths, became the dominant authority. The Renaissance brought a direct challenge to this view through Nicholas Copernicus, who in the early sixteenth century formulated a model where the sun sat at the center of the universe. He argued that the apparent retrograde motion of planets was merely an optical illusion caused by our vantage point on a moving Earth. Fearing persecution, Copernicus delayed publishing his work until he was on his deathbed, and even then it was undermined by an unauthorized preface suggesting the model was just a mathematical convenience.

The Copernican model was initially less accurate than the Ptolemaic system because it assumed all orbits were perfect circles. It took the collaboration of Tycho Brahe, who provided the most accurate naked-eye observations in history, and Johannes Kepler, who used that data to discover that planets move in ellipses, to resolve this. This adjustment allowed the sun-centered model to predict planetary motions with unprecedented precision, satisfying the principle of Occam’s razor—that the simplest explanation is usually correct. Galileo Galilei provided the final evidentiary blow using the newly invented telescope. He discovered moons orbiting Jupiter, proving not everything revolved around Earth, and observed the phases of Venus, which could only occur if it orbited the sun. Despite being found guilty of heresy by the Inquisition, Galileo’s work established that the laws of physics, not religious dogma, dictate the movement of the heavens. By the nineteenth century, as geologists realized the Earth was billions of years old, many scientists assumed the universe was eternal, setting the stage for twentieth-century cosmologists to seek a definitive answer to how it all began.