When people think of scientific genius, two names immediately come to mind: Einstein and Newton. While it is still widely debated which was actually the more ingenius of the two (as if it really mattered), scientists agree on one thing: it's purely a two-man race. The intellects and achievements of all the other great scientists can hardly be considered mediocre, but none can measure up to the impossible brilliance of these two. Einstein and Newton were to the other guys what ordinary geniuses are to us.
The differences between Einsteinian and Newtonian physics all boil down to two basic concepts: space and time. Newton's space and time were absolue, that is, unchangable. Space was boundless, static, and completely empty save for the universal medium, the ether, and time had flowed inexoribly since Creation. Einstein's space and time, however, wound and twisted about one another into one absolute concept, spacetime. In Einstein's universe, space and time were continually being warped and shaped according to the motions of energy and matter.
Before Newton's time, people were utter mystifyed by the motion of the stars in the heavens, inventing elaborate explainations involving gods and imbedded spheres and the such. But Newton found that his theory of gravity explained their motions almost perfectly. Only such a superb mind as his could have equated the force that acts on an apple falling from a tree to that which keeps the Earth in orbit around the sun. Newton's gravity was a force carried in a universal medium called the luminous ether by which every object in the universe affects every other. Although a few scattered objections persisted, Newton's laws were so successful in explaining the motions of the planets that his concepts were universally accepted.
Einstein, however, abolished all that, saying that gravity was not a force at all, but merely the observed effect of the warping of space and time by matter. He examined two situations: resting on the surface of a massive body and accelerating in empty space. If the rate of acceleration was adjusted correctly, a person would feel the same downward pull of gravity. Einstein asserted that these effects were actually the same. A far cry from Newton's view of gravity as a force acting at a distance!
We have already observed the slowdown of time and the redshifting of light due to gravity. In Einstein's universe, these two phenomena naturally occur together. The newtonian physicist, however, would not also predict that time flows slower with stronger gravity, because Newton's time did not change.
For many centuries, astronomers have noticed a small discrepancy in Mercury's observed orbit around the sun and that predicted by Newton's laws. Because it is so close to the Sun, the Sun's mass distorts Mercury's path, so that with each revolution, its perihelion (closest point to the Sun) gets a closer to the Sun. OnNewton's theory had predicted a shift only half as large as the actual one, but Einstein's predictions perfectly matched observations.
The difference between Newton's and Einstein's laws at ordinary speeds is negligably small, and Newton's laws are much simpler to use, so depite their inaccuracies, Newton's laws are still used for calculating in everday situations. However, many keys to understanding the universe lie not in ordinary experience, but in extraodinary phenomena such as supernovae and black holes. In the realms of the very big and very small, Newton's laws simply did not suffice.
"Cosmic religiousness is the strongest and most noble driving force of scientific research."
American Institute of Physics-- Great overall view of Einstein that chronicles his personal and professional life. Includes pictures and an essay by Einstein.