LeslieS


 * The theory of relativity, or simply relativity, generally refers specifically to two theories Albert Einstein created; special relativity and general relativity.
 * Special relativity is a theory of the structure of spacetime.
 * It was first introduced in Albert Einstein's 1905 paper, "On the Electrodynamics of Moving Bodies".
 * General relativity is a theory of gravitation developed by Einstein in the years 1907–1915.
 * The development of general relativity began with the equivalence principle, which states that accelerated motion and being at rest in a gravitational field (for example when standing on the surface of the Earth) are physically identical.
 * This is that because free fall is inertial motion: in other words an object in free fall is falling because it is how objects move when there is no force being exerted on them.
 * This is incompatible with classical mechanics and special relativity because in both of those theories, inertially moving objects cannot accelerate with respect to each other, but objects in free fall do.
 * Einstein first proposed that spacetime is curved, in 1915. He devised the Einstein field equations which relate the curvature of spacetime with the mass, energy, and momentum within it.
 * With general relativity... time goes more slowly in higher gravitational fields, this is called gravitational time dilation; orbits process in a way unexpected in Newton's theory of gravity; rays of light bend in the presence of a gravitational field; and frame-dragging, which means a rotating mass "drags along" the space time around it.


 * Einstein came up with the theory that small masses travel towards larger masses. However, this is not because the smaller masses are "attracted" to the larger masses by a mysterious force, but because the smaller masses travel through space which is warped by the larger mass. Physicists can illustrate Einstein's theory by using embedding diagrams. Although embedding diagrams do not depict the three-dimensional "space" of our everyday experience, it demonstrates how a two-dimensional split through the familiar three-dimensional space looks. A curve downwards when embedded in a flattened hyperspace, is the appearence of this image. Fully invisioning this hyperspace is difficult, though, since it does contain seven dimensions, including one for time.


 * "Time does not flow at a fixed rate," this is what Einstein's Special Theory of Relativity predicts. Meaning, moving clocks appear to tick more slowly relative to its stationary counterparts. However, this prediction only becomes really significant at very high velocities approaching the speed of light.
 * When this is "generalized" to include gravitation, relativity predicts that gravity, not only stretches or shrinks distances (depending on their position in respect to the gravitiationl field) but it can also appear to slow down or "dilate" the flow of time.
 * Time dilation is miniscule in most circumstance in the universe. However, when spactime is curved by a massive object, for example a black hole, the difference can become very significant. Let's say an astronaut is falling into a black hole, an observer far from this black hole would see the time for the astonaut as passing extremely slowly. In fact, the distand observer would never actually see the helpless astronaut fall into the black hole. The time measured by the observer would appear to "stand still."