The Shift in Understanding

On May 29, 1919, a pivotal moment in science occurred. For centuries, Isaac Newton's laws of gravity had stood firm, consistently aligning with observations and measurements. However, discrepancies began to emerge in the mid-19th century regarding Mercury's orbit, prompting scientists to reconsider Newton's framework. The advent of special relativity added fuel to the fire, revealing that absolute distance was a flawed concept and suggesting that Newton's instantaneous force contradicted relativity.

In 1915, Albert Einstein introduced a revolutionary theory of gravity: General Relativity. The ultimate test of this new theory awaited a total solar eclipse. A century ago, Einstein's predictions were confirmed, altering our understanding of the universe.

During a total solar eclipse, the light from distant stars bends as it passes close to the Sun, allowing astronomers to observe this phenomenon from Earth. This observation provided the first significant evidence supporting Einstein's theory. (NASA'S SCIENTIFIC VISUALIZATION STUDIO)

The Legacy of General Relativity

Today, Einstein's General Relativity is heralded as one of the most successful scientific theories, explaining a wide array of phenomena from GPS technology to the behavior of black holes. Its predictions have never failed to hold true.

When General Relativity was first proposed, it sought to replace Newton's gravitation. While it successfully replicated Newton's earlier predictions, it also introduced a new understanding of gravity's nature. The theory asserts that mass and energy curve the fabric of space and time, influencing how objects move within that curved space.

When light passes near a massive object, such as the Sun, it bends due to this curvature. In Newton's view, mass attracts mass; however, light, being massless, was thought to be unaffected. Yet, through the equation E = mc², light can be assigned an effective mass, leading to predictable bending. Newton predicted a deflection of just under 1 arc-second, but Einstein's theory anticipated a deflection closer to 2 arc-seconds.

The Prelude to General Relativity

The development of General Relativity stemmed from the inconsistencies in Newton's gravitational model. Introduced in 1687, Newton's laws had successfully explained everything from the motion of cannonballs to the orbits of celestial bodies. However, the peculiarities of Mercury's orbit posed a challenge that led to Einstein's breakthrough.

Mercury's orbit exhibited precession, meaning its elliptical path slowly rotated over time. While Newton predicted a precession of 5,557 arc-seconds per century, observations indicated it was actually 5,600 arc-seconds per century—a discrepancy of 43 arc-seconds that Newton's model could not account for. This inconsistency spurred further investigation, ultimately guiding scientists toward General Relativity.

The Eclipses of Discovery

Einstein's framework posited that gravity results from the curvature of spacetime rather than a direct attraction between masses. This allowed for predictions that aligned with observed anomalies, such as Mercury's orbit. Yet to truly validate General Relativity, a definitive test was necessary—one that would set it apart from Newton's theories.

The opportunity arose during a total solar eclipse when stars would appear displaced due to the bending of light around the Sun. This effect could be measured and compared against the predictions of both Einstein and Newton.

Eddington's Expedition

In 1919, Arthur Eddington led an expedition to measure the deflection of starlight during an eclipse, with teams positioned in Brazil and Africa. This historic event lasted nearly 7 minutes, providing the perfect conditions to observe the bending of light.

The results were groundbreaking. Einstein's predictions were confirmed, while Newton's framework faltered. Despite some initial controversy surrounding the validity of the data, subsequent observations reinforced the accuracy of General Relativity, further establishing its credibility.

Celebrating a Century of Understanding

As we commemorate the 100th anniversary of this monumental achievement, it's clear that while Newton's laws remain useful, they serve as approximations within the broader context of Einstein's theory. General Relativity continues to thrive, successfully predicting phenomena such as gravitational waves and frame-dragging, without encountering contradictions.

Although many mysteries of the universe remain unsolved, today is a celebration of what we have learned. A century after the initial validation of General Relativity, our understanding of gravity remains robust and continues to evolve.