Physics has come a long way since the days when people believed the Earth was flat and that it was the center of the universe. In 1543, Nicholas Copernicus proposed that the Earth really wasn't the center of the universe, it wasn't even the center of our little corner of the universe. He wasn't, of course, the first to think this, but the first to publish it. Later, a man named Johannes Kepler theorized that the planets actually orbit in ellipses, not perfect circles. Around the same time, an Italian astronomer named Galileo Galilei, discovered that some of the planets had their own moons, but more importantly that two objects of unequal mass fall at the same speed toward the Earth. All of these discoveries made the idea that the Earth wasn't the center of the universe more and more believable. Finally, in 1687, Sir Isaac Newton published Philosophiae naturalis principia mathematica, in which he finally explained how it was possible that the Earth wasn't the center of the universe. Newton's discovery was that all objects exert a force on one another, and this force is proportional to the product of the masses of the two objects and inversely proportional to the square of the distance between them. Newton also came up with his three laws, which are the basis of classical mechanics.

One of Newton's beliefs was that there was a point in space that was at absolute rest - that is, that point was at rest, and all other objects in the universe were in motion relative to that point. Any other object that was not moving relative to that point was said to be at absolute rest.

Newton also believed that light was made up of particles, which were known as corpuscles of light. With these particles of light, Newton could describe the laws of relection and refraction. In 1678, Christian Huygens showed that light would behave similarly if it were a wave. It wasn't until 1803, however, when Thomas Young showed that light could interfere destructively, that the idea of light as a wave was widely accepted. This, however, left physicists with a problem: if light is made up of waves and not particles, what medium does it move through? The ether theory tried to solve this problem. Ether was to be a medium through which light propagated, which was at absolute rest, meaning it was at rest with respect to the center of the universe. The luminiferous ether, as it was called, was to be massless and rigid, and would have no effect on the motion of planets or other celestial bodies. Ether seemed to be a good answer to the question. Some physicists had shown that the ether worked in accordance with Maxwell's equations, and the question seemed to be settled. As the 20th century approached, it was beginning to appear that everything in physics had been discovered.

Only a few small problems remained that could not be explained by current theories. Maxwell's equations predicted the universal constant for the speed of light, c. However, if a source of light was moving in the same direction that it was emitting light, according to Newton's laws, the velocity of the source should be added to the velocity of the light. This would result in a beam of light moving faster than the speed of light. Also, if the light were moving through the ether, which is at absolute rest, as observers in motion we should be able to detect our movement relative to the ether. Another problem was that Maxwell's equations should only be exact when used in a reference frame at absolute rest. Since electric and magnetic fields were supposedly manifested in the ether, as the Earth moved through the ether, the electric and magnetic fields would remain at absolute rest. This could be compensated for if the absolute motion of the Earth could be found, that is, the motion of the Earth relative to the ether.

Many experiments were carried out to determine the Earth's movement through the ether. Probably the most famous of these experiments is the Michaelson-Morley experiment. Albert Michaelson and Edward Morley set up an experiment to measure the "ether drift", the drifting of a light wave as it moved through the resting ether, with respect to an observer on Earth. In theory, as a light beam was originated on Earth and travelled through the ether, the light would travel in a straight path through the ether, while the Earth drifted through. The light, then, should have been lagging behind in the ether as the Earth drifted by, causing the light to interfere with itself. No interference in the light was detected. This experiment did not completely disprove the ether theory, but it was a blow to the theory of absolute space.

George Fitzgerald came up with an explanation of how the Michaelson and Morley experiment could still be correct and still work with the theory of ether. He suggested that objects moving through the ether would experience a contraction in the direction of their movement. A meter stick moving forwards lengthwise would therefore experience a contaction and would be slightly shorter than a meter stick at absolute rest. This proposition could not be tested, however, because any attempt to measure a shortened meter stick would have to be made with a meter stick, and in order to make the measurement, that meter stick would have to be moving as well, and experience the same length contraction. Fitzgerald's theory could not be tested, and was not taken very seriously for a period of a few years.

Hendrik Lorentz looked at Fitzgerald's problem, and came up with a new explanation. The contraction could be explained by electromagnetic forces produced in the object as it moved through the ether. Lorentz developed a set of equations that could transform measurements made in one reference frame to another. These equations were developed a full decade before Einstein derived the same equations in his special theory of relativity. Einstein, however, was trying to disprove the idea of ether, while Lorentz and Fitzgerald were trying to explain the negative results of the Michaelson-Morley experiment in accordance with ether theory.

While Fitzgerald and Lorentz were trying to reconcile the physical consequences of turn of the century experiments, Henri Poincaré was taking a more philosophical approach. Poincaré put forth this thought: "Suppose that in one night all the dimensions of the universe became a thousand times larger. The world would remain similar to itself, if we give the word similitude the meaning it has in the third book of Euclid. ...Have we any right, therefore, to say we know the distance between two points?" Poincaré said no, that space was relative to the frame of reference inside of which distances were measured. In his speech at the International Congress of Arts and Sciences in 1904, Poincaré proposed that the speed of light is an impassable limit, and also that at speeds much less than the speed of light, normal mechanics would still apply, but be approximations of "a whole new mechanics." This statement turned out to be almost equivalent to Einstein's theory, but it was Einstein, only one year later, who put all of the parts together to postulate the Special Theory of Relativity. The stage was set for a new theory which would solve these problems. The special theory of relativity...