Why Were the 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 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 . 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 . 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 .

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 proposed an aether model, that provided a medium in which light waves could move through the vacuum of . 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 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. In his reply Fresnel began by saying that the corpuscular theory was an unlikely explanation as it required for any radiating object to supply an almost infinite number of corpuscular bodies at different velocities and for the eye to only be able to interact with one part of this velocities. Fresnel theory also discarded the idea of total aether drag, Fresnel accepted Young´s idea that the aether should be able to pass freely through the Earth, if light phenomena were to be explained using the wave theory of light. Instead of total drag Fresnel suggested a partial drag of the aether. Fresnels partial dragging coefficient is derived from the wave theory as such:

c / cb = nb / n = nb / 1 = √ Δb / √Δ

Where c is the speed of light in vacuum, n is the refractive index of vacuum=1 and Δ is the aether density in the material. the subscript b represents the same values but inside the diffractive material. Fresnel supposes that only the aether density above the density of free space is dragged by a moving object. Therefore Δb - Δ thus: 2 Δb(1-1/nb )

2 Where the factor (1-1/nb ) is known as the partial dragging coefficient. Fresnel says that his theory is capable of explaining Argos results and also predicted that if an experiment were to be carried out, in which you fill a telescope with water it will have to effect on the observing a stellar aberration. In 1871 scientist Airy carried out this experiment and the results supported Fresnels views. LORENTZ THEORY In his work Lorentz starts talking about the failure from both main aether theories to successfully explain all-natural light phenomena, both Stokes and Fresnel's theory were incomplete theories. Lorentz supported Fresnels assumption of a partial drag on the aether by the Earth's movement through it and he was quite critical with respect to Stokes aberration theory quoting: "his assumptions about the movement of the ether taking place in the neighbourhood of the earth contradict themselves" [2, pg. 247]. Lorentz, together with most of the scientific community, became very skeptic of Fresnels idea after the null result of the Michelson-Morley experiment and Mr, Des Coudres experiment of mutual induction of two circuits. Lorentz gives the rational approach that anybody that does not contain a gas behaves mechanically identical to a vacuum. Lorentz reasoning states that the compression of liquids and solids (high density ether structures) requires a force and they resist the compression. Therefore, the aether in the vacuum of space should also, when compressed, offer some form of resistance. Based on Fizeau´s interference experiment, an experimental setup to measure the speed of light in moving water using an interferometer, which show that transparent substances do not add their velocity to light when moving. Based on this Lorentz makes two assumptions: I. The property of the aether from Fizeau's experiment can necessarily not be a property of individual atoms, however in large lattices it does occur if the space between the atoms is much greater than the radius of the atom; II. Atoms can be considered as alteration of the ether in a point of space; therefore, all matter can be considered permeable relative to the aether flow.

Aether Winds

“…QUITE TOO SMALL TO BE OBSERVED”- JAMES C. MAXWELL ON THE AETHER WINDS.[2 PG. 80]

MICHELSON-MORLEY EXPERIMENT Perhaps one of the most important experiments from the nineteenth century; was the one carried out by Albert A. Michelson and Edward W. Morley, in 1887. Previously in 1880 Michelson had designed the first version of this experiment in Berlin’s Hermann von Helmholtz laboratory, which will later be known as the Michelson interferometer. However, the results of his first experiment were viewed by the scientific community as too inaccurate and thus were ignored. After abandoning this experiment for seven years Michelson met Morley, who shared the same strong interested for the study of the aether. Together they designed an improved version of the original interferometer, the Michelson-Morley experiment. The Michelson-Morley experiment wanted to measure the optic effect that a fast- moving object, like the earth, would cause in the existence of a static aether. During the nineteenth century the leading aether theory was the one described by Fresnel; he believed that the aether was static (v=0ms-1). Fresnel's views are relatively simple to understand, he believed that if the aether was static and the earth was moving through the aether at high speeds. It would not matter the density of the aether, light rays should experience some sort of drag effect due to the earth's high speed. In the same way you experience drag when moving at high speeds through the atmosphere despite there being no wind. This relative drag caused by the earth’s movement was known as the aether winds. The Michelson-Morley experiment wanted to test for this aether winds. The premise of the experiment was simple. One single laser pointed at a semi-reflecting semi-transparent lens, placed at 45º relative to the laser beam, will create two equal perpendicular beams of light. At the end of each beam was a reflective mirror at equal distance from the central lens. When the beams joined back together, the existence of the aether winds will theoretically cause a phase difference and therefore an interference pattern.

IMAGES FROM: [4] For a phase difference to occur with two equally fast rays the distance traveled must be slightly different from each other; reaching the central lens at different times and therefore causing the waves to super pose each other. This slide difference in path length is caused by the aether drag. For simplicity I have decided to use the following diagrams for a visual explanation: When the experiment was carried out in 1887 the results from it were very disappointing for the aether supporting scientific community. When the results were processed by Michelson the calculated aether wind drag was significantly lower than the theoretical value calculated by Fresnel.

PRIMARY SOURCE I want to reproduce the Michelson-Morley results by carrying out the same procedure in my school's laboratory. The equipment used in the original Michelson-Morley are: i. Semi-reflecting / semi-transparent optic lens; ii. Two mirrors; iii. Laser; iv. Ruler and Vernier Caliper; v. Protractor; vi. Screen; vii. Optics bench. [4] Note: The semi-reflecting/ semi-transparent optic lens was very difficult to find. However, doing some further research I found out that some vinyl used in car windows to allow only people from the inside to see though the window share the same properties as the required lens. Therefore, I used this car vinyl and an empty slide-show to recreate the optic lens. When tested the slide-show behaved in the way as a semi-reflecting/ semi-transparent optic lens would. IDENTIFYING THE VARIABLES i. Dependent: The separation of the fringes in the interference pattern projected in the screen. ii. Independent: The separation of the mirrors from the central slideshow; and the time at which the experiment is carried out. iii. Constants: The intensity of the laser; the distance of the screen to the slide-show; the orientations of the system with respect to the earth's rotation.

SETUP The original interferometer had several different features that increased precision of measurement and helped make the calculations more precise. This experimental setup meets most of this original features. However, one feature that this setup does not share with the original is the ability to move the entire interferometer three dimensionally. This setup unlike Michelson-Morley´s original setup is only capable of moving in a single plane parallel to the floor; not three dimensionally. The interferometer consists of two superposed optical beams at ½π radians of each other. To ensure that both beams are exactly perpendicular and that the setup is oriented north, like the original interferometer; place two compasses at the end of the optical beams and align the y-beam with the magnetic north and the x-beam with the relative east. This setup must be placed in a totally dark room away from external vibrations (e.g. traffic) to increase image quality and precision; based on the one of the problems that the original experiment had when carried out in a laboratory in Berlin. Using two bubble levels and right angles make sure that the two beams are parallel to the x-y plane (at the same distance from the floor at all positions). Using one of the optical beams place the slide-show in the point of intersection and using a protractor rotate ¼π radians clockwise. Using a clamp and a stand position the laser at a suitable height so it hits the vinyl exactly at the center point. Place the mirrors in optical bench supports and place one at the end of each optical beam. Note: due to imperfections of the vinyl used the laser beams that was reflected from the slide-show suffered some image quality loss; going from a laser point to a smudgy line. Therefore, the mirror that reflects this beam is position much closer to the slide-show to increase image sharpness. On the remaining optical beam end place, using a support, a white screen. i. After turning the laser on, the setup must be calibrated first, this is done by carrying out the following procedure: ii. Regulating the height and inclination of the laser so both beams move in a single plane parallel to the floor, using the clamp. iii. Rotating the mirrors in the z-axis so both perpendicular lasers meet in the same point, both in the vinyl and projection screen. iv. Rotating the vinyl by its z-axis so both lasers meet in the same point.

Note: This experiment takes a different approach to the M-M original interferometer. Because I lack the equipment to measure the interference pattern precisely, I will instead measure the displacement of one of the mirrors needed to make the interference pattern appear again at different times. For this we have to setup a relative 0 to measure the values from. Originally carry out the experiment at exactly (1200 hours), place the variable mirror at 1m from the slide-show. Then using the precision displacer move the mirror until an interference pattern appears. Record the distance from the slide-show to the variable mirror this length will be the starting length for all experiments (T). PROCEDURE After calibration: I. Place the variable meter at Tm from the slide-show; II. Record the local time and date; III. Use the convex lens to determine if an interference pattern is visible; IV. If not, move the micrometer from the precision displacer clockwise; V. Keep looking through the convex lens until an inference pattern appears. When the pattern is visible record the distance from the slide-show to the variable mirror, and the time. SAFETY The lasers used in this recreation have a very low power therefore the risk of a laser induced eye injury is relatively low. However, the use of eye protection is still required, in the form of light polarized goggles. Results and Conclusion

Returning to the original question of this dissertation, no the luminiferous aether theories were not capable of explaining all of the light phenomena by themselves. However, all proposed hypothesis gave a reasonable mechanical model, thus a set of formulas to predict the evolution of a system, for certain phenomenon and conditions. Theoretically these theories were sufficiently good enough to be used as tools in mathematical calculations. However, experimentally they could not be explained by nature. Answering the question: "Why were the luminiferous aether theories, of the nineteenth century, unsuccessful at explaining the behaviour of light?", after this research I would answer: "The luminiferous aether theories of the nineteenth century were capable, as a whole, to explain all-natural light phenomenon, however all proposed theories failed to describe what was mechanically happening.". Later during the 20th century used Lorentz aether theory to base his theory of Special Relativity. In this theory Einstein states a physical model that did not require an aether and was capable of explaining all light phenomena. Since then the aether theory has been left as an incomplete failed theory, however equations and systems based on the aether are still used now a days by physicists due to their accuracy.

My personal opinion is that the aether theory will return to modern physics. The gap between Relativity and requires an intermediate theory to create a complete physical model and I believe the aether theory could act as an intermediate plenum/medium for both quantum and relativistic phenomena to occur. Recently the mathematician Stephen Wolfram release what he called "A fundamental theory of physics" which explained the universe and its interactions as nodes in a constantly evolving hyper-graph. This theory resembles and is based on older corpuscular aether theories. Bibliography

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3. www.dictionary.com . 2020. Diffraction | Definition of Diffraction at Dictionary.com. [ONLINE] Available at: https://www.dictionary.com/browse/diffraction. [Accessed 10 June 2020].

4. R. S., Shankland., 1964. Michelson-Morley Experiment. American Journal of Physics, doi: https://doi.org/10.1119/1.1970063, Volume 32, Issue 1, pp. 107-114.

5. N. Correa, P. and N. Correa, A., 2000. CONSEQUENCES OF THE NULL RESULTS OF THE MICHELSON-MORLEY EXPERIMENT: THE DEMISE OF THE STATIONARY AETHER, THE RISE OF SPECIAL RELATIVITY, AND THE HEURISTIC CONCEPT OF THE PHOTON. 1st ed. Canada: Akronos Publishing.

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10. Kenneth D. Oglesby Kenneth D. Oglesby, (2018), main-qimg- fe00b0d090464bed589cd2eb40e9715d [ONLINE]. Available at: https://s1.qwant.com/thumbr/0x380/8/5/e50b584fb095b2f7bbcc0f765cc22568700092f27362 7933727fea1aefbc06/main-qimg-fe00b0d090464bed589cd2eb40e9715d.jpg?u=https%3A %2F%2Fqph.fs.quoracdn.net%2Fmain-qimg- fe00b0d090464bed589cd2eb40e9715d&q=0&b=1&p=0&a=1 [Accessed 11 June 2020].