The success of Einstein's 1905 papers established him as an accomplished physicist. Upon request, he wrote several review articles explaining Special Relativity; in the process he realized that "all natural phenomena could be discussed in terms of special relativity except for the law of gravitation." Einstein struggled to define gravitation in his spare time—after long hours at the patent office and even when he became a professor at the University of Zurich.
By 1911, gravity had finally lured Einstein from other topics, and his thoughts culminated in 1916 with his masterpiece, General Theory of Relativity. Many scientists did not accept Einstein's ideas at first. But confirmation of his theory came in 1919 when astronomers documented the deflection of starlight by the Sun's gravity. Einstein had predicted this phenomenon, but he could not foresee the fame that would follow.
Seeing Is Believing
Sir Arthur Eddington led a 1919 expedition that captured the eclipse images needed to confirm what General Relativity predicted: The Sun's gravity deflects light.
Sir Isaac Newton wondered in 1704: "Do not Bodies act upon Light at a distance, and by their action bend its Rays; and is not this action strongest at the least distance?"
Gravity's Growing Pains
Einstein began his quest to expand the Special Theory of Relativity in 1907 when he realized he couldn't "represent gravitation in the framework of this theory." This inkling led Einstein to his "equivalence principle," the cornerstone of his new theory that stated gravity and acceleration are equivalent. Troubled by the mathematics, Einstein ruminated on this idea for nine years. He called Special Relativity "child's play" compared to his new problem.
School chum and mathematician Marcel Grossmann helped Einstein find the mathematical tools needed to describe the universe. Einstein used those tools to formulate General Relativity, and he expected mixed reactions from other physicists. "Gravitation elicits just as much respect among my colleagues as skepticism," he wrote in 1914. Einstein staked his theory on a series of astronomical observations—all of which were later confirmed, launching him into the spotlight.
Behind the Scenes
"Grossmann, you've got to help me, or I'll go crazy," Einstein wrote to his good friend Marcel Grossmann when General Relativity hit a mathematical roadblock. Grossmann had twice before come to the rescue; this time he identified the mathematics Einstein needed to complete the new theory.