From Eratosthenes to the Cosmic Background: Unraveling the Universe

The Cosmic Journey: From Eratosthenes to Planck Observatory

In 2023, at the JVP Pune Exhibition of observatories in outer space, I was handed the responsibility for COBE (Cosmic Background Explorer). It felt overwhelming at first—I barely had any idea what cosmic background radiation (CMB) was or why a whole satellite was dedicated to studying it. However, this assignment marked the beginning of a fascinating journey, leading me deep into the mysteries of the universe. As I delved into the CMB and its significance, I realized that this discovery was a pivotal moment in modern astronomy.

The experience made me reflect on how humans, with only a small fraction of knowledge at their disposal, manage to deduce the grandest astronomical phenomena. I couldn’t help but draw parallels to ancient scholars, particularly Eratosthenes, who, with minimal tools, made profound discoveries about our world. His work echoed in my mind, as I considered how modern scientists can uncover the shape of the universe by studying cosmic microwaves. This blog traces my journey from pondering Eratosthenes’ measurements to understanding the Planck Observatory’s role in cosmology—a story of human ingenuity and our relentless pursuit to comprehend the universe.

Eratosthenes and His Remarkable Experiment (240 B.C.)

The story begins in 240 B.C. with Eratosthenes, a brilliant Greek mathematician. He conducted a simple yet profound experiment to measure the Earth’s circumference. By comparing the angle of the sun’s shadow in two different Egyptian cities—Syene (now Aswan) and Alexandria—he was able to make one of the most accurate calculations of his time. Using just basic geometry and the knowledge of the distance between the two cities, Eratosthenes deduced the Earth’s circumference with remarkable precision.

His work was revolutionary. It not only provided a quantitative measurement but also reinforced the idea of empirical evidence in science. In an era devoid of modern instruments, this achievement stands as a testament to human curiosity and creativity. What struck me the most about Eratosthenes’ approach was how, with limited technology, he could uncover such profound truths—much like scientists who study the CMB today to explore the vast cosmos.

The Cosmic Microwave Background: The Echoes of the Big Bang

Fast-forwarding to the 20th century, the discovery of the CMB became one of the most critical pieces of evidence supporting the Big Bang theory. The CMB is essentially the afterglow of the Big Bang, permeating the universe and offering insights into its early moments.

One of the most astonishing revelations from studying the CMB is the flatness of the universe. This conclusion comes from measuring temperature fluctuations across the CMB, which appear uniform with slight variations. These fluctuations serve as a window into the geometry of the universe, and their angular size allows scientists to infer whether the universe is curved or flat.

The data collected by missions like the Wilkinson Microwave Anisotropy Probe (WMAP) and later the Planck Observatory showed that the CMB fluctuations correspond to predictions for a flat universe. This implies that, on large scales, the universe follows Euclidean geometry. What’s remarkable is that early scientists, armed with much less advanced instruments, could glean so much from this faint cosmic signal.

George Gamow and Theorizing the CMB (1940s)

The theoretical groundwork for the CMB was laid in the 1940s by George Gamow, along with his collaborators Ralph Alpher and Robert Herman. They predicted that the early universe was in a hot, dense state, leading to the formation of light elements—a process known as Big Bang nucleosynthesis.

Gamow and his team hypothesized that this hot universe would leave behind a residual radiation as it cooled down, which they estimated to have a temperature of about 5 K (Kelvin). This prediction was astonishingly close to the later measured temperature of around 2.7 K for the CMB. Although their model didn’t explain the formation of heavier elements, their work laid the foundation for future discoveries.

The Accidental Discovery of the CMB (1964)

The story of the CMB took an unexpected turn in 1964 when two radio astronomers, Arno Penzias and Robert Wilson, accidentally discovered it while working at Bell Labs. They were trying to eliminate a persistent noise from their radio antenna, only to realize that this noise was actually the faint remnants of the Big Bang—the CMB.

Meanwhile, a team led by Robert Dicke at Princeton University was theoretically searching for the CMB. When they learned about Penzias and Wilson’s findings, they recognized it as the evidence they had been seeking. In 1978, Penzias and Wilson were awarded the Nobel Prize in Physics for their discovery, solidifying the CMB’s place as a cornerstone of cosmology.

Planck Observatory and Modern Cosmology

The most recent chapter in this cosmic journey involves the Planck Observatory, which launched in 2009 and is currently orbiting at Lagrange Point 2 (L2). The Planck satellite provided the most detailed map of the CMB to date, refining our understanding of the universe’s age, composition, and structure. It confirmed the flatness of the universe with unprecedented precision and offered insights into dark matter, dark energy, and the inflationary phase of the early universe.

The study of the CMB continues to offer tantalizing clues about the universe’s birth, evolution, and ultimate fate. Even today, with all our advanced technology, we are still piecing together the puzzle, much like Eratosthenes did millennia ago with the Earth’s circumference.

Conclusion

From Eratosthenes’ early experiments in ancient Egypt to the groundbreaking discoveries of the Planck Observatory, this journey through cosmic discovery highlights humanity's incredible ability to deduce the nature of the universe with limited information. The CMB stands as a testament to how far we’ve come, from measuring shadows to detecting the faintest echoes of the Big Bang. Our curiosity drives us to keep exploring, and who knows what more we might discover as we continue to unravel the universe’s mysteries?

 References:

- Smithsonian Magazine: "Galileo's Revolutionary Vision Helped Usher In Modern Astronomy."

- BBC Sky at Night Magazine: "How Galileo Changed the Way We Look at the Universe."

- Encyclopedia Britannica: "Cosmic Microwave Background."

- Scientific Lib: "Biography of George Gamow."

- NASA Science: "Discovering the Runaway Universe."

- Springer: "Fermilab Center for Astrophysics."