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Theory of Relativity Albert Einstein first discovered the theory of relativity in 1915, and it was the first new theory of gravity since Isaac Newton’s theories that were discovered more than 250 years earlier (Lightman). The new idea proposed that gravity as well as motion could affect the intervals of time and space, and Einstein believed that astronomers could make certain obse rvations to test the general theory of relativity. Proving Einstein’s calculation that the theory of relativity would be displayed through the bending of light during a solar eclipse, British astronomer Arthur S. Eddington made Einstein famous in 1919 after observing that an eclipse matched Einstein’s predictions (NASA). Since then, the theory of relativity has evolved into a building block of modern physics. The theory of relativity has yet to be proven wrong, and, throughout scientific history, Albert Einstein has contributed numerous explanations and theories regarding the earth and solar system. His proven general theory of relativity has been used since its discovery to explain phenomena that has impacted our society.  The theory of relativity has been used to explain the equivalence principle and expand knowledge on gravity. The equivalence principle, also known as the key idea of the theory of relativity, is that gravity pulling in one direction is completely equivalent to acceleration in the opposite direction. For example, a car accelerating forwards feels just like sideways gravity pushing you back against your seat, and an elevator accelerating upwards feels just like gravity pushing you into the floor (Lightman). Using the equivalence principle, a lot of information on gravity has been able to become exposed. After the discovery of the theory of relativity, it was, and still is believed that the gravity of any mass, such as our sun, has the effect of warping the space and time around it. For exam ple, the angles of a triangle no longer add up to 180 degrees, and clocks tick more slowly the closer they are to a gravitational mass like the sun (Lightman). Using this information led to the discovery of black holes, curvatures and orbits, and inquiries about the speed of light.  J. Robert Oppenheimer and Hartland Snyder, who were manipulating the equations of Einstein's general relativity, discovered the possibility that stars could collapse to form black holes in 1939. A black hole is a region of space whose attractive gravitational force is so intense that no matter, light, or communication of any kind can escape (Lightman). Black holes are forms of light cones. When these light cones are very near the black hole, they are so strongly bent that a light beam that is shined directly outwards can not escape from the gravitational field of the object. If you are close enough to the black hole you can only move closer to the center of the black hole. The light cone emanating from a particular point in space time also defines the region to which one can send a signal (Felder). Light cones are also related to the speed of light. The basic idea behind light cones is the fact that nothing can travel faster than the speed of light. Also, in special relativity, nothing can travel between two points faster than the speed of light. This principle applies to forces as well as rays of light. General relativity also explains curvature and orbits. In Ge neral Relativity, a massive body like the sun causes the space time around it to curve, and this curvature in turn affects the motion of the planets, causing them to orbit around the sun (Felder). Curvature is very important, because the curvature created by the Earth keeps the moon in orbit, but at the same time the curvature created by the moon is enough to affect the tides (Jones). In General Relativity, "gravitational field" refers to the space time curvature induced by a set of objects, so the theory explains what space and time are like near the sun (Felder). Beginning in 1917, Einstein and others applied general relativity to the structure and evolution of the universe as a whole. Soon after Einstein developed the theory of relativity, he began applying it to cosmology, which is the study of the large scale structure of the universe. The equations that Einstein developed have no solutions that are static on large scales. In fact, the equations of the theory of relativity predict that the universe must either be expanding or contracting because of the force of gravity. For example, if you were to have a universe where all the stars were at rest relative to each other, their mutua l gravity would cause them to start moving towards each other. Isaac Newton’s form of physics, however, assumed that the universe went on forever and the attraction felt by any given star would be equally balanced on all sides. The theory of relativity shows, however, that even in such a case the space as a whole will contract and the distances between the stars will shrink. The universe could start out expanding, and depending on how fast it was expanding it might continue to do so or it might eventually stop and start contracting. However, it could never stay still (Felder). Eventually the leading cosmological theory, called the big bang theory, was formulated in 1922 by the Russian mathematician and meteorologist Alexander Friedmann, who began with Einstein's equations of general relativity as a starting point in his developmental theory (Lightman). <span style="font-family: Times New Roman, serif;">Throughout his lifetime, Albert Einstein was able to successfully prove the general theory of relativity. Not only was his discovery helpful throughout his time, but it has also become a major part of how physics is studied today. Einstein's general theory of relativity is currently proven to be true, and the research completed by scientists throughout history has been able to conclude that the theory is beneficial in predicting the outcome of various scientific phenomena throughout the universe. By accepting the theory of relativity, scientists and researchers have been able to draw numerous conclusions and explanations that have led to the overall advancement of science. Works Cited "Cosmology." __Kheper__. 27 Jan. 2009 <www.kheper.net/topics/cosmology/Rosicr-1.gif>. This website had little information that could be found beneficial, however, the image of the cosmological model was something I had not seen on any other website. My use of the image is the only reason it is cited, and I did not get any information from this website.

Dine, Michael. "NASA - Relativity." __NASA - Home__. 27 Jan. 2009 <http://www.nasa.gov/worldbook/relativity_worldbook.html>. This website greatly impacted my knowledge of the theory of relativity in relation to the universe. It offered a lot of useful and detailed information, as well as specific examples of research that NASA discovered. This website is written for the general public and is easy to read and get information from. I believe that this website had the most impact on the reader, because NASA used their own experiments and findings as a primary resource. This website is very valid, easy to follow, and helpful tool in finding information regarding the theory of relativity.

Felder, Gary. "General Relativity: Einstein: Physics." __NC State: WWW4 Server__. 27 Jan. 2009 <http://www4.ncsu.edu/unity/lockers/users/f/felder/public/kenny/papers/gr1.html>. This website explains the theory of relativity as well as the effects it has on the universe. This website uses mathematical equations and diagrams in order for the reader to follow along about relativity and cosmology. The author could tend to use vocabulary or references that the general public may not recognize, so the general audience is for people who already have preexisting knowledge of the theory of relativity. Although some sections of the essay were somewhat lengthy or hard to follow, I believe this website significantly helped add to my research because of all the information it provided.

Jones, Andrew. "General Relativity - an overview of Einstein's theory of general relativity." __Physics__. 27 Jan. 2009 <http://physics.about.com/od/relativisticmechanics/a/relativity_4.htm>. This website helped support the information I found on other websites about the theory of relativity. Although it did not provide any new information, it had a few interesting facts that helped improve my paper. This website is definitely written for readers who have little or no background knowledge on the theory of relativity. I thought its basic, easy to follow layout helped start my research in a helpful way.

Lightman, Alan. "NOVA | Einstein's Big Idea | Relativity (Lightman Essay) | PBS." __PBS__. 27 Jan. 2009 <http://www.pbs.org/wgbh/nova/einstein/relativity/>. This website relates to Einstein's work on the theory of relativity. The webpage is written in the form of an essay, and the information is directed toward students or people with at least a light background in physics. It explains the theory of relativity and how it was discovered and what current scientists are able to draw from Einstein's conclusions. The author wrote very concise statements supporting the research done by Einstein and the validity of what he found. Overall, it is a very detailed and helpful site.