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[Show Me the Wire]

Originally Posted by Actor

Newtonian mechanics (A.K.A. Galilean mechanics) seems almost intuitive. An observer standing on a railroad platform see two trains approaching, one from the east and one from the west. By some means the observer measures the approaching velocity of both trains and finds that the east train is approaching at 100 km/hr and the west train is approaching at 80 km/hr. He himself is standing still.

The engineer of the east train sees the west train approaching at 180 km/hr while the platform is approaching at 100 km/hr. The engineer of the west train sees the east train approaching at 180 km/hr while the platform is approaching at 80 km/hr. All these numbers add up: 100 + 80 = 180. Of course each observer assigns these numbers to different things, east train, west train, platform, but the numbers always add up.

This also works if we measure the speed of sound waves, with one proviso. Whereas the observer on the platform and the two engineers in the previous example each had their own frame of reference, with sound waves there is a “privileged frame of reference,” namely the medium, i.e., the atmosphere, through which sound travels. Within this privileged frame of reference the speed of sound is always the same. (+ or – slight variations due to barometric pressure and humidity.)

Sound is a wave and so is light (according to the wave model). This lead 19th century scientists to speculate that there was a privileged frame of reference for light, some sort of medium in which light was waving. They named this medium the aether. If this model was true then the earth must be moving through the aether, changing direction during the year. In 1887 two physicists, Michelson and Morley, tried to detect the aether (using a rather ingenious device) and failed.

In 1905 Einstein explained this failure with his Special Theory of Relativity. Einstein’s model states that (1)there is no aether and (2)the speed of light is constant for all observers in any frame of reference. I.e., there is no privileged frame of reference, all frames of reference are equal. This has implications for our perceptions of both time and space. Two observers in different frames of reference, frames that are moving with respect to one another, will observe different time intervals between the same two events. Furthermore, each will observe a different size and shape of the same object. These phenomena have been experimentally verified. If you own a GPS the computer program within it takes these phenomena into account and corrects for them.

More on time and space later.

Really Hey PA I have an idea. Since both Actor and boxcar want to give lectures that nobody is interested in reading, why don't you charge them $ and dedicate a thread to each, in which they post their lectures to their hearts' content.