JulieS

 Theory of Relativity  In 1905, Albert Einstein developed the theory of special relativity, and in 1915, he published a theory of general relativity. Einstein's theories of relativity are one of the most significant scientific advances and changed the face of physics forever. It continues to explain new scientific developments, such as the existence of black holes.
 * Background Information**

The theory of special relativity is a theory concerning the relations between space and time. It proposes that distance and time are not absolute (Lightman).
 * Special Relativity**

Einstein's theory of general relativity was published in 1915, and relates to gravity. The idea of general relativity is that gravity pulling in a certain direction is exactly equivalent to an acceleration in the opposite direction. General relativity proposed that gravity, as well as moition, can affect the intervals of time and space (Lightman). Before Einstein's theory of general relativity, Newton's law of universal gravitation was accepted for over 200 years. Many of the predictions of general relativity have been quantitatively confirmed by experiment (Lightman).
 * General Relativity**

The theory of relativity has contributed to society in several ways, including Global Positioning Systems. GPS was developed by the United States Department of Defense for the U.S. military. The current GPS system consists of a network of 24 satellites in orbit around the Earth. Each of those satellites carries with it an atomic clock that "ticks" with an accuracy of one nanosecond (Pogge). A GPS receiver in an airplane determines its current position by comparing the time signals that it receives from a number of the GPS satellites (usually six to twelve) and triangulating on the known positions of each satellite. Even a simple hand-held GPS can determine your absolute position on the Earth's surface to within five to ten meters in just a few seconds. To achieve such a level of precision, the GPS satellites must have an accuracy of twenty to thirty nanoseconds (Pogge). Because an observer on the ground sees the satellites in motion relative to them, special relativity predicts that we should see their clocks ticking more slowly, and it predicts that the on-board atomic clocks on the satellites should fall behind clocks on the ground by about seven microseconds per day because of the slower ticking rate due to time dilation effect of their relative motion (Pogge). Einstein's theory of relativity also contributes to nuclear power. Nuclear energy has help to alleviate a portion of our reliance on non-renewable resources for our energy needs.
 * Applications of Relativity**

Works Cited:

Pogge, Richard. "GPS and Relativity." __The Ohio State University Department of Astronomy__.9 Feb. 2009 http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html>.

Lightman, Alan. "Nova: Einstein's Big Idea: Relativity (Lightman Essay): PBS." __PBS__.9 Feb. 2009 http://www.pbs.org/wgbh/nova/einstein/relativity>.

Arora, Hans. "Einstein's Theory of Relativity: Implications Beyond Science?" __Northwestern University__. 9 Feb. 2009. [|http://http://209.85.173.132/search?q=cache:CCqSPZuVJ3kJ:scienceinsociety.northwestern.edu/content/articles/2008/research-digest/student-papers/einstein/einstein2019s-theory-of-relativity-implications-beyond-science%20theory%20of%20relativity%20%].

