Tom Jonard's What Einstein Did Not Do Page1) Einstein did not "discover" or "invent" relativity. Galileo (and perhaps others before him) did that.Galileo (1564-1642) described the basics of Relativity of Motion -- the idea that bodies and persons in uniform motion have no idea and no way of knowing they are in motion lest they communicate with the world outside that does not share their motion. Galileo proposed a thought experiment: That a heavy object dropped from the top of the mast of a moving ship lands at the base of the mast. The ship does not because of its motion move out from underneath the free-falling object. Therefore the object shares some of the ships motion, i.e., it is relative.2) Einstein did not "discover" or "invent" the Speed of Light. A number of observations and one grand theory predating Einstein led to determining the Speed of Light.
There is no experiment or observation than one can make in the enclosed cabin of a boat drifting on a swift-moving but placid stream that would show you to be in motion. We only know we are in uniform motion by observing the surrounding countryside pass. This is as true with modern transportation but our modern experience is marred by vibration and noise associated more with our machinery than with the motion. In fact automobiles that are able to shield us from this vibration and noise command a high price for their quality. And one is always amazed while driving or riding in one of these how they never seem to be going as fast as they are at high speed.
I am always amazed when flying the amount of deceleration that occurs when landing without the plane falling out of they sky -- no doubt I have been fooled by the relativity of motion into thinking that I am not moving at all (despite the noise and vibration)!
The astronomer Olaus Roemer in the 1670's provided the first evidence that light traveled at a definite speed (as opposed to instantaneously). He studied the occultations and eclipses of the Jupiter's Galilean moons and found that actually observed times of these events differed from times calculated from orbital mechanics but not always by the same amount. Sometimes the event occurred several minutes early; sometimes several minutes late. He concluded that the differences were due to the places Jupiter and Earth occupied in their orbits at the times of the observations resulting in different distances between the two. The longer the distance, the longer it took the light to travel from the Jovian system to Earth. These facts allowed a simple calculation of the speed of light. In 1728, another astronomer, James Bradley, used the aberration of starlight to perform a similar calculation. Aberration of starlight is itself an interesting if little known phenomenon. The best way to understand the aberration of starlight is by analogy: Think of a rainstorm in which the rain is falling straight down. If you were out walking in such a storm you would think that the rain was slanting from whatever direction you were moving -- your front would get wet and your back remain dry. If you had one you would angle your umbrella as though the rain were falling at an angle. But it is not. Rather your motion combined with the straight fall of the rain drops makes it seem the rain slants in this way. The same thing happens to light from stars near the poles of the Earth's orbit. The combined motion of their "straight falling" light and the Earth in it's orbit makes them appear to be displaced from their true positions in the direction the Earth is moving. Since the Earth goes around the Sun the polar stars appear to go around in tiny ellipses in the sky. Measuring the size of this displacement and knowing the speed of the Earth in its orbit allowed Bradley to calculate the speed of light. The Speed of Light was first measured on earth ("in a laboratory" would not be quite accurate since the apparatus used was located on two hill tops) by physicist Armand Hippolyte Louis Fizeau in 1849. Fizeau used a rotating disk which chopped a beam of light into segments and reflected it off a distant mirror so that it passed back through the rotating disk. By adjusting the speed of this disk he could determine the round trip travel time of the segments. Interestingly this experiment was not as accurate as the astronomical methods that preceded it. But it served to confirm the astronomical observations for the skeptical. One of the curious observations that resulted was that while the rotation of the earth changed the orientation of the experiment with respect to the earth's orbital motion no variation of the velocity of light was observed. This led to other experiments and theories regarding the unvarying speed of light culminating with Einstein.
The grand theory belongs to James Clerk Maxwell and was published in 1873. Maxwell studied electrical and magnetic phenomena and formulated a revolutionary theory that combined the two phenomenon into one -- electromagnetism. Maxell's theory described the propagation of electromagnetic waves in a vacuum at what was already known by experiment to be the Speed of Light. He proposed these electro-magnetic waves and light were in fact the same thing. The interesting part about this is that his theory specifies the Speed of Light based only on theory, albeit a theory which incorporates other easily observed electrical and magnetic properties. Specifically the Speed of Light (c) is given by:c = 1/(m0e0)1/2where m0 is the permitivity and e0 is the permeability of the vacuum.
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Created December 28, 2001,
© 2001, Thomas A. Jonard