Einstein and his theory of Special Relativity (1905) General relativity came later and deals more with gravity (1915) 07 relativity.

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1 Einstein and his theory of Special Relativity (1905) General relativity came later and deals more with gravity (1915) Groundwork for Einstein's theory was laid out my Michelson and Morley with their interferometer and their search for aether. The experiments null result led Einstein to his 1st postulate the speed of light is absolute to all observers regardless of their FRAME OF REFERENCE. Or, RELATIVE to their FRAME OF REFERENCE. The 2nd postulate is Newton's laws of motion apply to all inertial frames (non accelerating frames. (textbook example pg. 635 ) Simply put Einstein's famous theory states that we need to be aware of our frame when we measure an event especially when we are moving relative to the events frame. Our measurements will be relative. But, in full complexity, when one couples the simple notion of the theory with the 1st postulate, confusion about our imagined concrete world erupts. Special Relativity Newton's laws of motion give us a complete description of the behavior moving objects at low speeds. The laws are differen speeds reached by the particles at SLAC. Einstein's Special Theory of Relativity describes the motion of particles moving at close to the speed of light. In fact, it give correct laws of motion for any particle. This doesn't mean Newton was wrong, his equations are contained within the relativ equations. Newton's "laws" provide a very good approximate form, valid when v is much less than c. For particles moving at slow speeds (very much less than the speed of light), the differences between Einstein's laws of motion and those derived by New tiny. That's why relativity doesn't play a large role in everyday life. Einstein's theory supersedes Newton's, but Newton's theo provides a very good approximation for objects moving at everyday speeds. Einstein's theory is now very well established as the correct description of motion of relativistic objects, that is those travelin significant fraction of the speed of light. Because most of us have little experience with objects moving at speeds near the speed of light, Einstein's predictions may s strange. However, many years of high energy physics experiments have thoroughly tested Einstein's theory and shown that i results to date. Theoretical Basis for Special Relativity Einstein's theory of special relativity results from two statements the two basic postulates of special relativity: The speed of light is the same for all observers, no matter what their relative speeds. The laws of physics are the same in any inertial (that is, non accelerated) frame of reference. This means that the laws of phy observed by a hypothetical observer traveling with a relativistic particle must be the same as those observed by an observer w stationary in the laboratory. Given these two statements, Einstein showed how definitions of momentum and energy must be refined and how quantities length and time must change from one observer to another in order to get consistent results for physical quantities such as pa half life. To decide whether his postulates are a correct theory of nature, physicists test whether the predictions of Einstein's match observations. Indeed many such tests have been made and the answers Einstein gave are right every time! The Speed of Light is the same for all observers. The first postulate the speed of light will be seen to be the same relative to any observer, independent of the motion of the observer is the crucial idea that led Einstein to formulate his theory. It means we can define a quantity c, the speed of light, which a fundamental constant of nature. Note that this is quite different from the motion of ordinary, massive objects. If I am driving down the freeway at 50 miles p relative to the road, a car traveling in the same direction at 55 mph has a speed of only 5 mph relative to me, while a car com the opposite direction at 55 mph approaches me at a rate of 105 mph. Their speed relative to me depends on my motion as w on theirs. Physics is the same for all inertial observers. This second postulate is really a basic though unspoken assumption in all of science the idea that we can formulate rules o which do not depend on our particular observing situation. This does not mean that things behave in the same way on the ea space, e.g. an observer at the surface of the earth is affected by the earth's gravity, but it does mean that the effect of a force object is the same independent of what causes the force and also of where the object is or what its speed is. Einstein developed a theory of motion that could consistently contain both the same speed of light for any observer and the f addition of velocities described above for slow moving objects. This is called special the theory of relativity, since it deals with the relative motions of objects. Note that Einstein's General Theory of Relativity is a separate theory about a very different topic the effects of gravity. 1

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3 Consequences Your measurement of space and time vary depending upon your frame Time dilation (moves slower for faster moving objects) Length contraction (objects shrink measured from an outside observer) Mass increase (objects mass increased when measured from an outside observer) t = t o 1 v2 L = L o m = 1 v2 m o 1 v2 Simultaneity no two events occur at the same time measured by different observers Note t o, m o, L o are proper measures beginning and end of the experiment occur at the same point in space. t, m, L are relative measures the experiment occurs at different points in space For a detailed explanation follow the following link. t length contraction demo variety of physic animations Hamstra's powerpoint tuebingen.de/~kobras/ibsrt/index.html 3

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5 Δt = 2 L/c L 5