A Universe from Nothing

Discovering the Expanding Universe

The journey to understanding the cosmos began with a fundamental mystery: how the universe itself evolves. In 1916, Albert Einstein completed his general theory of relativity, which redefined gravity not as a force but as a property of space and time. Unlike previous models, this theory could describe the evolution of the entire universe. However, Einstein faced an immediate problem: his equations suggested a dynamic cosmos, yet the scientific consensus of 1917 held that the universe was static, eternal, and consisted solely of the Milky Way galaxy. Because gravity is always attractive, a static collection of stars should eventually collapse inward.

Einstein was deeply guided by observation. His confidence in relativity was cemented when his equations perfectly predicted a slight shift in Mercury’s orbit that Newtonian physics could not explain. This success made the apparent conflict with a static universe particularly troubling, leading him to temporarily modify his equations—a move he later regretted. The tension between theory and observation was eventually broken not by philosophical debate, but by better tools for measuring the heavens.

In the early 20th century, astronomers debated whether fuzzy patches in the sky, known as nebulae, were part of our galaxy or distant "island universes." This mystery was solved by Henrietta Swan Leavitt and Edwin Hubble. Leavitt, working as a calculator at Harvard, discovered a relationship between the brightness and pulse timing of Cepheid variable stars. This provided a cosmic yardstick: by measuring a star's pulse, astronomers could determine its true brightness and, by extension, its distance. Using this method, Hubble proved in 1925 that the Andromeda nebula was a separate galaxy far beyond our own.

Hubble’s next breakthrough changed our understanding of time itself. By comparing the distances of galaxies to the light they emitted, he noticed a startling pattern. Light waves from distant objects are stretched as they move away, making them appear redder—a phenomenon known as redshift. Hubble found that almost all galaxies are moving away from us, and the farther away they are, the faster they recede. This linear relationship, known as Hubble’s Law, demonstrated that the universe is expanding.

While some interpreted this expansion as evidence of a divine beginning, the scientific reality was first mapped out by Georges Lemaître, a priest and physicist. Lemaître used Einstein’s equations to propose that the universe began as a single point, which he called the primeval atom. He argued that the physical validity of this "Big Bang" model was a scientific question, independent of religious interpretation. The model suggested that if we play the cosmic movie backward, everything in the observable universe was once concentrated in an incredibly hot, dense state.

Evidence for this hot beginning is found in the very atoms that make up the world. Calculations show that the intense heat of the early universe could only produce the lightest elements, such as hydrogen, helium, and lithium, and the observed amounts of these elements in space match these predictions with incredible precision. Heavier elements, like the carbon and oxygen essential for life, were forged in the hearts of stars and scattered across the cosmos when those stars exploded as supernovae. Every atom in the human body was once part of a star that died billions of years ago. Modern astronomy uses a specific type of explosion, the Type Ia supernova, as a "standard candle" to refine our map of the universe. By observing these distant fireworks, scientists have determined that the universe is approximately 13.7 billion years old, confirming we live in a vast, ancient, and continuously growing cosmos.