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Even to scientists of the day, these theories seemed patchwork: they dealt with nagging questions, but in an artificial and contrived way. Yet they contained seeds of truth. Science was groping toward the answer to the ether dilemma and the limitations of Newtonian physics. And even without Einstein, someone eventually would have solved the puzzle.
Still, the intuitive flash did not occur to any of the scientific greats of the day, but to the 26-year-old patent examiner on the fringes of physics. That insight was shown in two remarkable papers that appeared during 1905 in the German scientific journal Annalen der Physik. The title of the first — "On the Electrodynamics of Moving Bodies" — did not begin to reflect its eventual significance. Later it would become known as Einstein's special theory of relativity.
Einstein boldly disregarded the notion of the ether. Then he went on to state two postulates: 1) An experiment can detect only relative motion, that is, the motion of one observer with respect to an other. 2) Regardless of the motion of its source, light always moves through emp ty space at a constant speed (this seems to violate common sense, which suggests that light projected forward from a moving spacecraft, like a bullet fired from a plane, would travel at a speed equal to its velocity plus that of the craft). From these statements, using thought experiments and simple mathematics, Einstein made deductions that shook the central ideas of Newtonian physics.
In demolishing New ton's basic assumption that time is absolute, that it is universally the same, and that it flows steadily from the past toward the future, Einstein used the following thought experiment: an observer standing next to a railroad embankment sees two bolts of lightning strike the tracks at the same time and thus concludes that they occurred simultaneously, one far to the east, the other an equal distance to the west. Just as the bolts hit, a second observer passes directly 'in front of him on a train moving at high speed from east to west.
To the second observer, the bolts do not seem to strike simultaneously. Rea son: because he is moving away from the bolt in the east, its light takes slightly longer to reach him. Similarly, because he is moving toward the bolt in the west, its light reaches him earlier. Thus what the stationary observer sees as simultaneous lightning strikes, the moving observer sees as a flash in the west followed by one in the east. If, on the other hand, the bolts had struck at different times, it could well have been the moving observer who saw them simultaneously and the man along the tracks who thought that they did not occur at the same time.
In any case, the question remains:
Which of these views is wrong? Nei ther, said Einstein. Measurements of time depend on the choice of the reference frame — in this case, the train or the point along the tracks.
By similar reasoning, Einstein also showed that the Newtonian concept of ab solute length was obsolete.
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