StephanieW

** In the early 1900's, Albert Einstein proposed two theories that brought the physics community to its knees. These theories challenged previous research, building on its credibility while adding new concepts to explain how the universe works as a whole. His concepts were not influenced by current research of his time but experiments by Galileo and Michelson and Morley. It is hard to believe Einstein would have expected his research to become the foundation of modern physics. Based on current research, Einstein's theory of relativity is true based on previous research on relativity, the theory of special relativity, and the theory of general relativity. ** Early Research ** Einstein was not the first scientist to develop the theory of relativity. In 1632, Galileo completed his work //Dialogue Concerning the Two Chief World Systems// which described two situations within a ship's cabin (Dine). His book suggested that by observing the motion in the ship, neither of the two friends inside the cabin could determine whether the ship was at rest or moving. Both scenarios involved two friends, butterflies and other small flying animals, fish swimming in a bowl, a bottle from which drops of water fall into another container, and a ball (Dine). The first experiment had the ship at rest while the animals move freely about the environment and the two friends inside the cabin throw a ball to each other. The second experiment has the ship traveling at a constant velocity with all the events of the first experiment still applying to this situation. The book explained that all the objects in the cabin, including the living things, share the moton of the ship (Dine).
 * [[image:einstein2.jpg align="right" caption="Albert Einstein"]]The Theory of Relativity: Fact or Fiction

Galileo's experiment led to the development of the term inertial frame. The term comes from the evidence that inertia would apply relative to the ship's cabin. In the example provided in Galileo's book, the fishbowl, due to inertia, would tend to stay at rest relative to the cabin (Dine). If the boat was gaining speed, it would no longer be able to be called an inertial frame because the cabin would not have a constant speed. The basis for this phenomena comes from Issac Newton's laws of motion published in 1687 (Dine). In conclusion, Galilean relativity can be stated as "The laws of nature are the same in all inertial frames," where the laws of nature were understood to be Newton's laws of motion and any laws based on them (Dine). This theory led to calculations known as Galilean transformations. These equations show how an event in one inertial frame would appear to an observer in another inertial frame; the prinicple which is the foundation for this theory is Newton's first law: Any frame of reference that is moving at a constant velocity relative to an inertial frame is also an inertial frame (Dine).

In 1887, two American physicists, Albert A. Michelson and Edward W. Morley, conducted an experiment on light rays to show what was wrong about Galileo's principle of relativity (Dine). Maxwell, a Scottish physicist, developed a theory in 1864 that suggested a relationship between electric and magnetic fields. In his research, Maxwell developed equations to show that electric and magnetic fields can combine to create waves, and the electromagnetic waves created travel at the speed of light (Dine). He also said that light consisted of electromagnetic waves. The equations indicated that light moved at a particular speed, //c//, and Maxwell assumed that //c// was the speed of light relative to ether (Dine). Michelson and Morley's experiment, based on this finding, measured the expected differences in the speed of light in relation to their laboratory. They discovered through the measurements, with small differences in the speed, that no differences could be found at all. Physicists were unsure how light could act in a manner consistent with both Galilean relativity and the Michelson-Morley experiment (Dine).  ** Special Relativity  ** The theory of special relativity was published by Einstein in 1905. The theory results from two basic postulates: (1) the speed of light is the same for all observers, no matter what their relative speeds, (2) the laws of physics are the same in any inertial (that is, non-accelerated) frame of reference ("Theory: Special Relativity (SLAC VVC)"). With these statements, Einstein demonstrated that the equations for momentum and energy must be revised and how quantities such as length and time changes from one observer to the other to get consistent results for physical quantities like a particle's half-life.

The first postulate helped Einstein develop his theory. A quantity can be defined as c, the speed of light, which is a fundamental constant in nature ("Theory: Special Relativity (SLAC VVC)"). This postulate led to the concept of time dilation, which is directly developed from the Lorentz transformation. The Lorentz transformation uses equations by Dutch physicist Hendrik A. Lorentz to understand the Michelson-Morley experiment; the equations describe how an event occuring in one inertial frame would appear to an observer in another inertial frame (Dine). Time and space are not separate entities, but an entity made up of a combination of the dimension of time and three dimensions of space - length, width and height (Dine). With time dilation, the time on a clock of two spaceships traveling at the speed of light relative to each other will have different times displayed on their clocks. Spaceship A will observe that the clock in Spaceship B is running more slowly than the clock in Spaceship A, but people in Spaceship B will observe the clock in Spaceship A running slower than the clock in Spaceship B (Dine). Time dilaltion is not detectible as people go about their daily lives. This concept is mainly importatnt to studies of high-enery particles.

Einstein's second postulate is the basic assumption in all sciences - the idea that we can formulate rules of nature which do not depend on our particular observing situation. This means that the effect of the force on an object is the same independent of what causes the force and also where the object is or what its speed is ("Theory: Special Relativity (SLAV VVC)"). This theory relates greatly to the concepts of momentum and gamma. Momentum (p) is the product of velocity and mass, but "when speed becomes realitivistic," momentum equals gamma ("Theory: Special Relativity (SLAC VVC)".) If the particle has a non-zero mass, the momentum eventually becomes larger and larger and reaches the speed of light. It takes too much force, however, to accelerate a particle to infinite momentum so it is concluded that a massive particle always travels at speeds less than the speed of light ("Theory: Special Relativity (SLAC VVC)"). Gamma is what relativisitc effects are based on. Gamma depends on the speed of a particle.

The most important finding of his second theory of relativity is the mass energy equation: E=MC^2. Einstein also showed that the correct relativistic expression for the energy of a particle of mass m with momentum p is E2 = m2c4 + p2c2. This is a key equation for any real particle, giving the relationship between its energy (E), momentum (p), and its rest mass (m) ("Theory: Special Relativity (SLAC VVC)"). The equation givess the total energy for a freely moving particle. It tells us as well that energy and mass can be interchanged ("Theory: Special Relativity (SLAC VVC)"). The equation displays how to convert between energy units and mass units.

**

General Relativity ** Einstein's later theory of general relativity emerged 10 years after his theory of special relativity in 1915. This theory states that gravity, as well as motion, can affect intervals of time and space (Lightman). The important idea of general relativity is the equivalence principle which states that gravity pulling in one direction is completely equivalent to an acceleration in the opposite direction. Since gravity and acceleration are equivalents, gravity can affect motion just like motion affects time and space. The gravity of a mass can warp the space and time around it (Lightman). These statements have been proven by the existence of black holes and the effect of gravity on the universe. Black holes have a gravitational force that is so intense that nothing can escape it. They are believed to have formed from the collapse of old stars. With Einstein's theory of general relativity, if a burned-out star has a mass larger than about three times the mass of our sun, no amount of additional pressure can stave off total gravitional collapse and the star collapses to form a black hole (Lightman). This possiblity was discoered initally by J. Robert Oppenheimer and Harland Snyder in 1939. Thse scieintists were manipulating Einstein's general relativity equations when they obtained their resuts (Lightman). The first black hole, Cygnus X-1, was discovered in 1970 with many others identified over time. Astronomers and astrophysicists believe massive black holes are in the centers of energetic galaxies and release massive energy amounts. Einstein did not believe in black holes but his theory helped to predict their existence (Lightman).

Cosmology is the other concept that proves the existence of general relativity. The big bang theory was the leading cosmologic theory in 1922 developed by Alexander Friedmann (Lightman). Friedmann used Einstein's equations of general relativity and discovered a solution to the equations that the universe was formed in a state of extemely high density and temperature. The big bang theory is continued to be researched currently throught the use of telescopes to measure the density of matter versus the rate of expansion (Lightman). The universe may expand forever due to inward gravity tha is not sufficiently strong enough to counterbalance the outward motion of galaxies or the universe will reach a maximum expanion point and start collapsing. It is suggested that the universe will keep expanding forever (Lightman).

Einstein's theory of relativity was questionable when it was first published because it expanded ideas founded by earlier scientists and shattered their ideas by providing more scientific research. The theory is true and the previous research of physicist, the theory of special relativity, and the theory of general relativity helps to solidify this fact. //By keeping out for more current research, Einstein's theory will continue to be proven valid. His theory is the basis for physics and the reason why every concept taught is applicable to the real world.//
 * In Conclusion**

**Annotated Works Cited** Dine, Michael. "NASA - Relativity." __NASA - Home__. 4 Feb. 2009 . NASA's article on relativity describes both theories that Einstein developed in the 1900's: general relativity and special relativity. The history of previous theories which Einstein founded his own theory on is given as well explanations for the concepts which the theories encompass respectively. Dr. Michael Dine, the author of the article, is a reliable writer because his credentials include holding a position as Professor of Physics at the University of California in Santa Cruz, CA. This article is credible because it is hosted by NASA from World Book, meaning America's top scientific organization is checking the validity of said information.

Greig, Lori. "The Theory of Relativty." Photograph. 9 June 2007. __Flickr Photo Download: The Theory of Relativity__. 8 Feb. 2008 . This photograph taken by Lori Greig shows the E=MC^2 sculpture from "The Walk of Ideas" in Berlin, Germany. A resource from Creative Commons, this photography can be used with the author's permission as long as the image is credited to the photgrapher and is not altered in any way.

Lightman, John. "NOVA | Einstein's Big Idea | Relativity (Lightman Essay) | PBS." __PBS__. June 2005. 3 Feb. 2009  John Lightman, the current Adjunct Professor of Humanties at MIT, describes Einstein's theory of general relativity, mainly gravity's effect on the universe. The article talks in depth how general relativity laid the groundwork for other experiments and research that could only be possible with Einstein's theory. Lightman's research on the topic is accurate based on his background as a physicist. The site is credible because the article is an essay on NOVA's educational website for the program, "Einstein's Big Idea," which was broadcasted on PBS. The article is factual and unbiased because it supports currently known research on the topic and provides reasons why the theory is excepted in the science community.

"Theory: Special Relativity (SLAC VVC)." __SLAC Public Website Server__. 31 Oct. 2008. SLAC National Accelerator Laboratory. 3 Feb. 2009 . SLAC National Accelerator Laboratroy's research on Einstein's theory of special relativity looks at both postulates and explains in detail the research proving their validity. The breakdown of each postulate is accompanied by data and concepts relative to its statement. The research presented was conducted at their own facilities and supported by the U.S. Department of Energy. As a result, this website is credible because the government is monitoring the authenticity of the research. As of three months ago, the website was updated, detailing any new findings.