![]() In the latter, the light source is INSIDE the moving system. In the former, the light source is OUTSIDE the moving system. The light-from-rear-going-past-car experiment and the Michelson-Morley experiment are by no means analogous. The most famous of these experiments is one performed by Michelson and Morley in 1887." What could it be?.As mentioned above, attempts were made to determine the absolute velocity of the earth through the hypothetical "ether" that was supposed to pervade all space. We shall discuss one of these experiments in detail, to show exactly what was done and what was the matter something was the matter, of course, something was wrong with the equations of physics. A number of experiments based on this general idea were performed to determine the velocity of the earth, but they all failed - they gave no velocity at all. In any case, by measuring the speed of the light going past the car (if the Galilean transformation is correct for light), one could determine the speed of the car. For instance, if the car is going 100,000 mi/sec, and the light is going 186,000 mi/sec, then apparently the light going past the car should go 86,000 mi/sec. Differentiating the first equation in (15.2) gives dx'/dt=dx/dt-u, which means that according to the Galilean transformation the apparent speed of the passing light, as we measure it in the car, should not be c but should be c-u. This independence of the motion of the source, in the case of light, brings up an interesting problem: Suppose we are riding in a car that is going at a speed u, and light from the rear is going past the car with speed c. This is analogous to the case of sound, the speed of sound waves being likewise independent of the motion of the source. Richard Feynman: "Another consequence of the equations is that if the source of the disturbance is moving, the light emitted goes through space at the same speed c. ![]()
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