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  __Theory of Relativity __ 

The term theory of relativity was named by Max Planck in 1908. It normally refers to the two theory of Albert Einstein but is sometimes used to relate to the Galilean relativity. Einstein's theories explain why matter, energy and even space and time react how they do. They are what most of modern physics is built on.

__Principle of Relativity__

The principle of relativity is related to Newton's theory of gravity and is related to his concept of space and time (Safko). Newton considered space and time to be absolute concepts which were separate from the material universe. He also created the concept of the inertial frame or inertial coordinate system. He concluded that space was like a stage that the planets and stars existed on. A coordinate system is a grid of rods and clocks at rest with respect to each other that exists throughout space. Newton's first law is that in the absence of outside forces any body moves with constant velocity. Any coordinate system moving with constant velocity with respect to an inertial system is also an inertial system (Safko). Untill the late 1800's most scientist thought that all natural events could be explained by Newton's laws ( Dine). This all changed when Maxwell's theory came about. Maxwell's theory of electricity and magnitism had only a single value for the speed of light. He beleived that the speed of light would be the same for all inertial observers. The way Newton thought of it would require the speed of light to change if you changed the inertial frames. Albert Einstein looked at all the research and concluded that Maxwell was correct.

__Special Relativity__

Special relativity is a subcategory of the Theory of Relativity. It describes the motion of particles moving at close to the speed of light, it gives the correct laws of motion for any particle (SLAC). This principle has two parts. The first, There is no ether, and the speed of light is the same for all observers, whatever their relative motion. The second, The laws of nature are the same in all inertial frames, where the laws are understood to include those described by Maxwell. Einstein based his special theory of relativity on this principle. The theory solved the puzzle of the Michelson-Morley experiment and also made dramatic new predictions which were later proved (Dine). Special relativity use equations knows as Lorentz transformations. Theses are used to describe how an event occurring in one inertial frame would appear so someone in another inertial frame. The equations are named after Hendrik A. Lorentz, a Dutch physicist. He first wrote them down in 1895. He developed them in an attempt to understand the Michelson-Morley experiment. The Michelson-Morley experiment was conducted to measure the expected differences in the speed of light relative to their laboratory. Throught their experiment they found no differenced at all. This caused many problems and physicists tried without success to determin if and how light could act in ways consistant with both Galiean relativity and the Michelson-Morley experiment (Dine). Through all of this, special relativity became an excepted explenation for theses happenings.

__General Relativity__

General relativity came about as a way to make everything work. It modified Newton's law of gravitaion so that it would agree with special relativity. The main disagreement was in the descriptions of how objects exert forces on one another. In special relativity, nothing can travel faster than the speed of light. This principle also applies to forces as well as rays of light (Dine). Einstein realized that many of the effects of non-uniform motion are sumilar to the effects of gravity. He thought that any theory of general relativity would also have to have to include gravity. After more than ten years, his new theory was ready. According to general relativity, a large concentration of mass, such as the Earth, significantly distorts space-time in its vicinity. Objects moving throught a region of distorted space-time would move differently than if it was moving through an undistorted space-time (physical world). General relativity could be described as a field theory of gravity. It is based off of a set of equations called the Einstein field equations.

__Work Cited__

Dine, Michael. "NASA - Relativity ." __NASA - Home__. 27 Jan. 2009 .

This site has large amounts of good information. It is from NASA so it is trustworthy. It has information all about the theory of relativity and all the sub categories.

"Max Planck and Einstein." __Astrophysik an der Universit__. 29 Jan. 2009 <[|http://www.astro.physik.uni-potsdam.de/~afeld/]>.

This is a German site with good information and a good picture of Max Planck and Einstein both of which helped with the theory of relativity.

Safko, J. L.. "Unit 56." __University of South Carolina Astronomy Center__. 27 Jan. 2009 .

This is a great site created by the university of south carolina. it is part of their Astronomy center. it is a very reliable source will with great information.

"The intangible Universe - Relativity,space,time and gravity - part 1 of 4." __Welcome to The Physical World__. 27 Jan. 2009 .

This site is a great resource. It has loads of information that is helpful when learning about the theory of relativity. it also has some great graphics that help you learn about the theory of relativity and make it easier to understand the complex equations.

"Theory: Special Relativity (SLAC VVC)." __SLAC Public Website Server__. 31 Oct. 2008. 27 Jan. 2009 .

This site is a good credible site. It is by SLAC National Accelerator Laboratory and is helped by the U.S department of energy. It has information on the Theory of Relativity.It talks about energy, mass and momentum. It was last updated on 10/31/08.