On March 20, 1916, Albert Einstein submitted to the German scientific journal Annalen der Physik the final version of an article outlining his answer to the scientific problem he had been wrestling with for nearly a decade. He called his solution a “General Theory of Relativity.”
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The General Theory deals with the relationships between space, time, matter, energy and gravity, and changes Newtonian physics’ understanding of them.
As a consequence of Einstein’s equations, whose validity has been confirmed experimentally, it became clear (well, clear to some scientists, at least) that time and space comprise a single continuum, whose shape can be bent or warped by gravitation.
In 1905, Einstein had published his so-called Special Theory of Relativity,” in which he explained mathematically how the speed of light is absolute and constant, even in situations when it appears to be variable. What also derived from the Special Theory was the well-known equation E=MC2, which defines the interchangeable relationship between matter and energy, and gave rise to the idea that if the energy holding together the nucleus of an atom could be released, it would yield an explosive power unlike anything ever seen by humanity. Much to Einstein’s later regret, this understanding gave birth to the atomic bomb.
The problem with the Special Theory was that it only applied to objects traveling in a straight line and at a fixed velocity. Thus, for much of the next 10 years, Einstein worked to figure out a “general theory” to described the relationship between the same variables.
By November 1915, he had worked out most of details, having presented an incomplete version of the general theory in lecture form the preceding summer at the University of Goettingen.
One of his hosts in Goettingen was the mathematician David Hilbert, a friend and colleague, who took the incomplete formulas presented by Einstein and attempted to complete the work on his own.
Hilbert shared what he was doing with Einstein, and when he finally published an article, he credited Einstein for the initial work he had done. Still, Einstein was irritated when he learned that Hilbert was working away on “his baby,” and hurried to complete and publish his own version.
In the end, the two men worked out their differences, and, while Hilbert gets credit for being co-author of the equations, it is Einstein who is remembered by history for conceptualizing the general theory.
The first experimental confirmation of the formula posited in the General Theory came in 1919. Einstein himself had suggested that a full solar eclipse would offer such an opportunity, and predicted that light from distant stars passing the sun on its way to earth would be bent by the gravity of the sun, such that it would appear to be in a different position in the sky from where it should be.
(Trying to carry out such an experiment when the sun is not covered by a full moon, as is the case in a total eclipse, is not possible because the light of the sun would make the light from the distant star invisible.)
Einstein’s theory predicted the precise degree by which the starlight would shift, and when the measurements taken during the eclipse confirmed the accuracy of his calculations, it was a front-page story worldwide.
(Two years later, in 1921, Einstein earned the Nobel Prize for Physics, but it was awarded not for his theories of relativity, but rather for his work on the photoelectric effect, by which certain metals release electrons when they are hit by light, an important concept in the development of quantum mechanics.)
Additional proof that Einstein was right about the general theory of relativity came earlier this year, when scientists announced that they had detected extraordinarily faint gravitational waves transmitted through space, a remnant of the collision of two black holes about 1.3 billion light years away from Earth, somewhere between 600 million years ago and 1.8 billion years ago.
The gravitational waves were measured by two enormous and incredibly sensitive Laser Interferometer Gravitational-wave Observatory) facilities, whose construction and testing had been completed only during the past year.