| The concept of the invisible ether or | | | | abstractions. However the most important of |
| 'aether' is an old concept dating to the time | | | | these was conducted by american scientists |
| of the ancient Greeks. They considered the | | | | Michelson and Morley. Their experiment |
| ether as that medium which permeated all of | | | | considered another alleged effect of a |
| the universe and even believed the ether to | | | | different aether theory which came to be |
| be another element. Along with Earth, Wind, | | | | known as the aether wind. Since the aether |
| Fire and Water Aristotle proposed that the | | | | permeated the entire universe, the earth |
| ether should be treated as the fifth element | | | | would move within the ether as it spun on its |
| or quintessence; this term which literally | | | | axis and moved within the solar system about |
| means 'fifth element' has even survived down | | | | the sun. This movement of the earth with |
| to the present day to explain an exotic form | | | | respect to the aether gave rise rise to the |
| of 'dark energy' which is crucial in some | | | | idea that it would be possible to detect an |
| cosmological models. These ideas spread | | | | 'ether wind' which would be sensed because of |
| throughout the world until the advent of a | | | | the aforementioned movement. Thus, their |
| new springtime in scientific thought. The | | | | experiment was essentially an attempt to |
| first person in the modern era to conceive of | | | | detect the so-called ether wind. This |
| the idea of an underlying ether to support | | | | mysterious zephyr would be nearly impossible |
| the movement of light waves was seventeenth | | | | to detect because the aether only |
| century dutch scientist Christiaan | | | | infinitesimally affected the surrounding |
| Huygens.Many others followed in expressing | | | | material world. Michelson first experimented |
| their opinions on the ether concept. Whilst | | | | in 1881 with a primitive version of his |
| Isaac Newton disagreed with Huygens wave | | | | interferometer; a mechanism designed to |
| theory he also wrote about the 'aethereal | | | | measure the wave like properties of light. |
| medium' although he expressed his | | | | He would follow this by combining forces with |
| consternation in not knowing what the aether | | | | Morley in the most famous 'null' experiment |
| was. Newton later renounced the ether theory | | | | of physics.In this investigation, Michelson |
| because in his mind the infinite stationary | | | | utilized an improved version of his |
| ether would interrupt the motions of the | | | | interferometer device. Michelson's apparatus |
| enormous masses (the stars and planets) as | | | | would help him win the Nobel prize for his |
| they moved in space. This rejection was | | | | optical precision instruments and the |
| reinforced by some other problematical wave | | | | investigations carried out with them. His |
| properties which were not explicable at the | | | | most important study being what became known |
| time; most notably, the production of a | | | | as the Michelson Morley experiment of 1887. |
| double image when light passes through | | | | Michelson and Morley used a beam splitter |
| certain translucent materials. This property | | | | made of a partially transparent mirror and |
| of matter known as 'birefringence' was an | | | | two other mirrors arranged horizontally and |
| important hurdle to be overcome for a proper | | | | vertically from a light source. When a beam |
| understanding of the wave nature of | | | | of light traveled from a source of coherent |
| light.Some time later (1720) whilst working | | | | light to the half-silvered mirror (the |
| on other astronomical issues related to light | | | | semitransparent mirror) it is transmitted to |
| and the cosmos, English scientist James | | | | either of the horizontal or vertical mirrors. |
| Bradley made observations in hopes of | | | | When the light returned to the eyepiece of |
| quantifying a parallax. This effect is an | | | | an observer the separately returning light |
| apparent motion of foreground objects in | | | | waves would combine destructively or |
| comparison to those in the background. | | | | constructively. This phenomenon is known as |
| Whilst he was unable to discern this parallax | | | | the interference effect for light. It was |
| effect he happened to reveal another effect | | | | hoped that a shifting of the interference |
| which is prevalent in cosmological | | | | fringes from that which was normally |
| observations; this other effect is known as | | | | predicted would be able to ascertain the |
| stellar aberration. Bradley was able to | | | | existence of the aether wind.To detect this |
| easily describe this aberration in terms of | | | | effect, the Michelson interferometer was |
| Newton's particle theory of light. However, | | | | prepared in such a manner as to minimize any |
| to do so in light of the wave or undulatory | | | | and all extraneous sources of experimental |
| theory was difficult at best since to do so | | | | error. It was located in a lower level of a |
| would have required a 'motionless' medium; | | | | stone edifice to eliminate heat and |
| the static nature of this ether concept was | | | | oscillatory effects which might comprise the |
| of course the property which had originally | | | | experimental results. Additionally, the |
| caused Newton's denial of the idea.But | | | | interferometer was mounted atop a marble slab |
| Newton's acolytes would find themselves in a | | | | that was floated in a basin of mercury. This |
| difficult position when it was shown that | | | | was so that the apparatus could be moved |
| birefringence could be explained through | | | | through a variety of positions with respect |
| another interpretation of the nature of | | | | to the invisible ether. But despite their |
| light. If light was treated as being in a | | | | many preparations the experiment did not |
| side to side action or 'transverse motion' | | | | yield the expected fringe patterns. Thus, |
| then birefringence could be attributed to a | | | | Michelson and Morley concluded that there was |
| light wave rather than the particle or | | | | no evidence for the existence of the ether. |
| corpuscular theory of Newton. This along | | | | Others would replicate the experiment in |
| with the detection of an interference effect | | | | different incarnations which modified the |
| for light by Thomas Young in 1801 renewed the | | | | premise of the experiment. Each and every |
| ascendancy of the wave theory of light. | | | | one returning a similar negative result. |
| These findings however carried with them all | | | | Modern theorists have taken these results and |
| of the preconceived notions prevalent in the | | | | those of many other experiments as being |
| scientific mind. Since it was assumed that | | | | indicative of the non-existence of the |
| waves like water and sound waves required a | | | | aether. However, even the negative result of |
| medium of propagation, it was similarly | | | | Michelson Morley has come in to question as |
| assumed that light still needed a medium or | | | | far back as 1933.In that year, Dayton Miller |
| ether for its waves to be transmitted across | | | | demonstrated the fact that even though the |
| the universe.However, further problems would | | | | duo's experiment had not specifically found |
| afflict the ether theory. Because of the | | | | the expected range of interference patterns, |
| unique properties of a transverse wave it | | | | they had found an interesting little noticed |
| became apparent that this hypothetical | | | | effect. Miller then went on to suggest that |
| explanation required the ether to be a solid. | | | | Michelson Morley had found an experimental |
| In response, Cauchy, Green and Stokes | | | | sine wave like set of data that correlated |
| contributed theoretical and mathematical | | | | well with the predicted pattern of data. He |
| observations to an 'entrainment' hypothesis | | | | also described how thermal and directional |
| which later came to be known as the 'ether | | | | assumptions inherent in the experimental |
| drag' concept. But nothing would give more | | | | arrangement may have impacted badly on the |
| impetus to these ideas than when James Clerk | | | | fringe interference data. Thus, the test may |
| Maxwell's equations (1870s) required the | | | | have been performed in an imperfectly |
| constancy of the speed of light (c). When | | | | conceived experimental setup and with a built |
| the implications of Maxwell's equations are | | | | in mathematical bias against the detection of |
| worked out by physicists, it was understood | | | | an appropriate outcome. Thus, in the future |
| that as a result of the need for a constant | | | | the aether theory in some form or another may |
| speed of light only one reference frame could | | | | still be sustainable as a foundational theory |
| meet this requirement under the teachings of | | | | of physics.Perhaps it is best to leave with |
| Galilean Newtonian relativity. Therefore, | | | | these ideas as expressed in 1920 by Einstein |
| scientists expected that there existed a | | | | who stated that he believed the ether theory |
| unique absolute reference frame which would | | | | to still be relevant to his ideas on space |
| comply with this need; as a result, the ether | | | | and time:"More careful reflection teaches us, |
| would again be stationary.As a consequence, | | | | however, that the special theory of |
| by the late nineteenth century the aether was | | | | relativity does not compel us to deny ether. |
| assumed to be an immovable rigid medium. | | | | We may assume the existence of an ether"he |
| However, earlier previous theories existed as | | | | continued:"Recapitulating, we may say that |
| to the nature of the aether. One of the most | | | | according to the general theory of relativity |
| famous of these is known as the 'aether drag' | | | | space is endowed with physical qualities; in |
| hypothesis. In this concept, the aether is a | | | | this sense, therefore, there exists an |
| special environment within which light moves. | | | | ether"and finally:"According to the general |
| Also, this aether would be connected to all | | | | theory of relativity space without ether is |
| material objects and would move along with | | | | unthinkable; for in such space there not only |
| them. Measuring the speed of light in such a | | | | would be no propagation of light, but also no |
| system would render a constant velocity for | | | | possibility of existence for standards of |
| light no matter where one tested for light's | | | | space and time (measuring-rods and clocks), |
| speed. This 'aether drag' idea originated in | | | | nor therefore any space-time intervals in the |
| the aftermath of Francois Arago's experiment | | | | physical sense. But this ether may not be |
| which appeared to show the constancy of the | | | | thought of as endowed with the quality |
| speed of light. Arago believed that | | | | characteristic of ponderable media, as |
| refractive indexes would change when measured | | | | consisting of parts which may be tracked |
| at different times of the day or year as a | | | | through time. The idea of motion may not be |
| result of stellar and earthly motion. In | | | | applied to it."Michael Strauss is an engineer |
| spite of his efforts, he did not notice any | | | | and author of Requiem for Relativity the |
| change in the refractive indexes so | | | | Collapse of Special Relativity, a serious |
| measured.Many other experiments would follow; | | | | critique on the fallacies of Special |
| these were performed in order to find | | | | Relativity. |
| evidence of the aether in its many different | | | | |