Albert Einstein developed the two parts of the theory of relativity between 1905 and 1915.
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Courtesy of Tracey Keifer. Emilio Segre Visual Archives. American Institute of Physics.
The Theory of Relativity
Albert Einstein developed one of the most famous theories in the history of science, the theory of relativity. This theory actually has two parts: the special theory of relativity and the general theory of relativity. These two theories introduced some very new, different, and strange ideas about the basic nature of the Universe.
According to special relativity, very odd things happen when an object moves at nearly the speed of light. Time slows down, the length of an object becomes shorter, and the mass of the moving object increases. If two observers are moving relative to each other, they may disagree as to whether two events happen at the same time. Mass and energy can be converted back and forth according to Einstein's famous equation, E = mc2. Einstein introduced the special theory of relativity in 1905.
The general theory of relativity claims that the "shape" of space itself can be curved near large objects that have a lot of gravity. In fact, according to relativity, gravity isn't so much a force as a curvature of space. Even rays of light curve when they pass through the space near a massive object. This is why black holes can "suck up" light that passes near them. Einstein developed the general theory of relativity between the years of 1907 through 1915.
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