Why Were the luminiferous aether theories, of the nineteenth century, unsuccessful at explaining the behaviour of light? THE AETHER IS THE PERSONIFICATION OF THE CLEAR UPPER AIR OF THE SKY THAT THE GODS BREATHE Introduction WHY THE LUMINIFEROUS AETHER? Four years ago, I wrote an essay titled “My Theory of Everything”; the theme of this essay was to try and explain a personal vision of a theory of unified fields. Two years later, after some research, I realized that my concept resembled some of the original ideas from the classical aether theories. After reading “Nineteenth-Century Aether Theories” [1] I came to the conclusion that most of the focus and interest of the nineteenth century theoretical physics community was based around the development and explanation of the luminiferous characteristics of the aether. It will be these same theories that later inspired Einstein’s theory of Special relativity. For that reason, I decided to base my IPQ on the luminiferous aether theories because it will allow me to understand the base from which the, more complex, theory of Special relativity parts from and will also allow me to study an aspect of the aether in depth. For this dissertation I used various sources of information. Mainly secondary sources of information like historical literature and scientific papers; however, I did entend in carring out primary research by recreating the Michelson-Morley interferometer. I already had a solid background from my previous independent research of the aether theory therefore most of my secondary research comes from scientific papers. I used a paper titled: The History of the Aether Theory and the previously mentioned Nineteenth-Century Aether Theories” as a guide to structure this dissertation. This project is divided into three main chapters: in the first sections I begin by giving a brief overview of the history (prior to the 19th century) of the aether theory. In this same chapter I continue by explaining the three main aether theory of the nineteenth century, which are: Fresnels aether theory, Stokes aberration theory and Lorentz ether theory. I will go into great depth to show the rationalism and theoretical assumptions made in each theory and explain the mathematical support that each scientist provides for these assumptions. The second section related to the most important experiment in the history of the aether theory, which is commonly known as the Michelson-Morley interferometer. These sections are divided into two main parts which discourse: firstly, the logic and premise of the experiment and its theoretical background and secondly instructions to setup the primary source of this dissertation, a recreation of the original Michelson- Morley interferometer. Finally, the third chapter will be a conclusion which includes; my personal opinion on the aether theory after the research done and the impact that the aether theory had in modern physics. History The aether originated during the pre-scientific ancient Greek era, were philosophers of the time coined the term æther for the first time. This ancient physics model described the universe to be formed of four primordial elements: fire, water, air and earth. The aether, in this model, was described by Aristotle to be the air of the gods: “The heavens (that region beyond the sphere of the Moon) are made of a fifth substance called aether. Unlike the other four substances, which can be transformed into one another, aether is unchanging and indestructible.”[1] More modern scientist that contributed to the development of the aether theory come from the enlightenment era such as the scientist, mathematician and philosopher René Descartes, who said to be the founding father of modern philosophy and inheritor of the scientific renaissance revolution. Descartes believed in a fluid Plenum aether that filled all of the universe, which was responsible for gravity. Sir Isaac Newton proposed an aether model, that provided a medium in which light waves could move through the vacuum of space. Here we can see one of the main divisions within the aether theories. The mechanical aethers, in charge of explaining the forces between charges and masses and the luminiferous aether, responsible for the propagation of light through the universe. The Nineteenth century were pivotal years for the luminiferous aether theory. This century saw, the biggest development in the theoretical explanations of the ethereal behaviour of light and groundbreaking experimental discoveries like the Michelson-Morley interferometer. The three aether theories that had the greatest impact in the scientific community during the nineteenth century were: Fresnel’s static aether theory; Stoke’s aberration theory which competed with Fresnel's theory and Lorentz ether theory, that attempted to solve the flaws of from both theories. Before starting, we should ask: what was the purpose of this theories? The purpose of this theories, as stated previously, was to explain certain physical phenomena of light. For example, both Stokes and Fresnel described with different mechanisms why stellar aberration and diffraction occur. Fresnel’s theory also attempted to offer a mechanism to explain: double refraction; polarization and partial-dragging. Both Stoke’s and Fresnel’s theories had a common feature called “Aether Drag” or “Aether Winds”, these concepts will be further explained in chapter II. LIGHT PHENOMENA Stellar aberration is the partial effect that a moving observer sees when looking at a stationary object. The effect in question is described as the partial movement of static objects due to the observers own velocity. First noticed by Bradley in the 1727-8, while trying to measure the annual parallax effect of the "fixt stars". After observing this "aberration" phenomena from his results he formulated a mathematical expression to explain this event. We know (Using Fig.I [1]) and the sine laws that sin a/CB = sin b/AC. Using "similar triangles" we know that triangle of velocities in this case would be CB : AC : : v : c, in this case v is the orbital speed of the earth and c is the speed of light because c>>v therefore a<< therefore approximately tan a = v/c where v/c is referred as the aberration constant. Stellar Parallax, not to be confused with stellar aberration, is the effect in which the same stationary star appears to be in different locations depending in the observer's position relative to said object. This differs from stellar aberration as the first one describes an observed movement of the start while parallax describes a change in position between a maximum and a minimum. Diffraction is a more well know light phenomena, the term light diffraction is described as: "the phenomenon exhibited by wave fronts that, passing the edge of an opaque body, are modulated, thereby causing a redistribution of energy within the front: it is detectable in light waves by the presence of a pattern of closely spaced dark and light bands (diffraction pattern) at the edge of a shadow."[3] Polarization is the physical process in which light waves that pass through a specific material or filter will leave the material with a fixed oscillation axes (See Fig.II [10]). STOKES ABERRATION THEORY Stokes aberration theory was one of the most influential aether developments during the 19th century. Stokes aberration theory, published in 1845, gave an explanation to stellar aberration based on the wave theory of light and the total drag of the Earth over the aether. Stokes assumption was that the Earth totally dragged the aether when moving through it (orbiting around the sun), however this total dragged only influenced a relatively small area of aether above the Earth's surface. The velocity of this dragged aether was equal to the absolute velocity of the Earth in the universe. He also assumed that at a relatively small distance away from the Earth surface the dragging effect will not be present and thus the aether would be considered at rest. In his work Stokes notes that the direction of propagation of the wave incident from the star should be proportional to the velocity of propagation (speed of light) on the aether and the velocity of the dragged aether, which is considered to be equal to the velocity of the Earth. Strokes aberration theory together with Fresnels aether theory were both used to account and explain aberration phenomena until 1886; when after the confirmation of Fresnel's partial drag coefficient by the Michelson Morley experiment and criticism from Lorentz, Stokes theorem lost most of the support from the scientific community. FRESNEL AETHER THEORY Before working on the aberration theory of the luminiferous aether Fresnel, following from Christiaan Huygens work, had previously made great advancement in the field of wave propagation. This work known as the "Huygens-Fresnel principle" gave a method of analysis that could be applied to extreme limits of diffraction and reflection. Fresnels involvement with the aether theory began after the French physicist, Dominique François Jean Arago wrote a letter to Fresnel talking about the results of his experiments on light aberration. In his letter Aragos stated that a strange phenomenon in the behaviour of light going through prisms was observed dependent in the direction of the incident start light used. The observations showed that the light behaved differently when it moved against or in the direction of the Earth orbital movement. He continued to explain that he had attempted to carry out experiments to draw a conclusion based on the corpuscular theory, but his experiment gave a null result. Argos finally asked for help from Fresnel, as he thought his wave propagation theory could explain the concept. In reply Fresnel wrote a letter to Aragos in which he formulated an extremely elegant explanation based on a wave theory of light. This letter was published in the Annales de Chemie in 1818 and this theory not only accounted for aberration effect but was also confirmed in a series of experiments during the 19th century.