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General Theory of Relativity
Although Einstein had changed the face of modern physics with the release of his 1905 paper on Special Relativity, he was not satisfied with the theory. He wanted to build a more general theory that would include and explain gravity.
The Falling Man
Albert Einstein in 1921
Source: Nobel Prize in Physics photograph
One of Einstein's first thought experiments on the subject involved a falling man. He realized that a person falling in freefall would not feel their own weight. If the person was in an enclosed chamber while falling, they would have the same experience as someone floating weightless in outer space (at least until they hit the ground). What this meant to Einstein was that gravitation did not exist to the observer.
The Equivalence Principle
Einstein used his "falling man" thought experiment to develop the equivalence principle. This principle said that the affects of gravity and the affects of acceleration were both produced by the same structure. He published his ideas at the end of a 1907 article published by the Yearbook of Radioactivity and Electronics. Although it would take several more years, the concept of the equivalence principle would serve as an important step in the road to general relativity.
In addition to coming up with the equivalence principle, Einstein used this idea to make some important real world predictions. First, he demonstrated that clocks would actually run slower the more intense the gravitational field. In other words, clocks on Jupiter would run more slowly than clocks on Earth. This is now known as gravitational time dilation. Einstein also predicted that gravity would cause light to curve, a prediction that could be proven through experiment.
This picture shows one of Einstein's thought experiments
where he compares a ball falling to the floor in an accelerating rocket
(left) and one on Earth (right).
The effect is identical in both situations.
Source: Markus Poessel (Mapos), CC BY-SA 3.0,
Over the next several years Einstein would pursue a solution to general relativity using two different strategies: a mathematical strategy and a physical strategy. His early attempts in 1912 at the mathematical solution can be seen in a notebook called the Zurich Notebook. However, Einstein abandoned the mathematical strategy after a year feeling that his final equations did not meet the necessary conditions. He then turned his effort fully to the physical strategy and released a paper that became known as the Entwurf on the subject.
Success and the General Theory of Relativity
Einstein was only somewhat satisfied with the Entwurf paper and, by 1915, he had come to the realization that the Entwurf theory was flawed. Ever persistent, Einstein returned to a mathematical strategy. By the end of 1915, Einstein had begun to form equations that would explain his idea of general relativity. His first major success came when he successfully calculated the correct results for the shift in Mercury's orbit. This event has been described as one of the most emotional days in Einstein's life. It was the result of years of hard work. He then refined his equations and presented them in a lecture at the Prussian Academy called "The Field Equations of Gravitation." Einstein would consider his theory of general relativity the crowning achievement of his career.
Einstein's new equations were not as simple as his earlier E=mc2, but they were just as profound. The most famous of Einstein's field equations looks like this:
Solar Eclipse and Experimental Verification
Einstein's theory was not widely accepted or used by the scientific world at first. In 1919, his theory was confirmed when it correctly predicted the deflection of starlight by the sun during a solar eclipse. The confirmation of his theory brought Einstein worldwide fame. One British newspaper proclaimed "Revolution in Science - New Theory of the Universe - Newtonian Ideas Overthrown." Although this experiment brought significant attention and acceptance to the theory, the theory wasn't widely used by physicists until the 1960s and 1970s.
A picture of the eclipse of 1919
Author: F. W. Dyson, A. S. Eddington, and C. Davidson
When discussing his success at finding a solution to general relativity Einstein said "My boldest dreams have now come true."
Einstein worked with mathematician David Hilbert on the theory of general relativity including attending Hilbert's lectures and sharing ideas in letters.
Albert Einstein Biography Contents
Back to Biographies >> Inventors and Scientists
- Growing up Einstein
- Education, the Patent Office, and Marriage
- The Miracle Year
- Theory of General Relativity
- Academic Career and Nobel Prize
- Leaving Germany and World War II
- More Discoveries
- Later Life and Death
- Albert Einstein Quotes and Bibliography
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