By Tompson Hsu On June 30th, 1905, Albert Einstein published the article "On the Electrodynamics of Moving Bodies." The article was the first to detail his vision of special relativity, which said that the laws of physics are the same for all non-accelerating observers (i.e., the person looking) and that the speed of light in a vacuum, or lack of air, is independent of how the observers are moving. Yet Einstein could not have developed his theory without the breakthroughs that came before his time—while Einstein was indeed a genius, special relativity simply could not have been theorized before his time. There was simply no good experimental foundation up until James Clark Maxwell completed his theory of electromagnetism in 1873. To trace the developments further back to their origin would be to include Sir Isaac Newton’s Principia in 1687, where classic Newtonian mechanics were first introduced. (Newtonian mechanics imply the universality and absoluteness of time, which played a key role in the development of special relativity. These mechanics mean that, no matter where you are in the world, time will always progress the same. This turns out to be false for some special cases, hence the “special” in “special relativity”.) Other notable discoveries include the 1887 Michelson-Morley experiment, the Lorentz transformations, written by Woldemar Voigt in the same year. Let’s go into more detail. The principle of relativity says that uniform motion cannot be detected. Post-Copernican thought accepted that the Earth was not motionless, and, in fact, spun, but the question remained as to why we couldn’t feel it. Newton’s idea satisfied this with the observation that acceleration and force were tied together, which helped develop a “theory of relativity” in which one’s own motion was undetectable. However, in making these observations, Newton had assumed that light was a group of rapidly-moving particles that obeyed the principle of relativity(instead of a wave, as seen in Thomas Young’s famous two-slit experiment where two light sources created interference patterns, or ripples). After light was found to be in a wave, most scientists of this time began searching for something called the luminiferous ether (also known as just the aether). The thought process went like this: if sound waves are carried by air, and tidal waves by water, surely there had to be something which carried waves of light? The existence of ether became widely accepted; however, there was one small problem--no experiments managed to prove the existence of ether. Augustin-Jean Fresnel, a French physicist, came up with an idea for “Ether drag”, which was a hypothesis stating that ether was dragged by lenses and other optically dense objects, so that the refractive index (the amount that light slows when entering optically dense stuff) was tuned to cancel out first order effects of ether currents. According to Fresnel, this was why past experiments failed, yet after a second order of (unsuccessful) experiments, the 19th century attempts to detect ether currents culminated only in astounding failure Maxwell’s 1873 theories of electromagnetism showed us that a “light wave” was an electromagnetic wave, which applied ether to the transmission of these waves, too. A problem then arose—if Maxwell’s electrodynamic theories were based on the existence of ether, why did no experimentation ever show it? H.A. Lorentz redefined ether as being fixed and immobile, creating the 20th century Maxwell-Lorentz theory, which posited that ether existed but would never be measurable. It was in this scenario that Einstein showed his genius and saw past this unsatisfying resolution; whereas most scientists accepted the idea of the flawed experiment and the correct theory, he instead found the correct experiment and the flawed theory. Einstein’s theory of special relativity removed the ether and the idea of a medium for light in its entirety, assuming instead that the laws of physics and the speed of light worked the same regardless of how the observer was moving. To summarize, the environment that bred Einstein’s 1905 theory of special relativity came from Newton’s first proposal of particulate light, then Fresnel’s discovery of light as a wave, from which came the convoluted notion of the existence of an ether (a medium through which light supposedly travelled). Experiments to prove this ether’s existence failed, but the ideas for Fresnel drag and Maxwell’s electromagnetic theories further propped up ether and its existence, as well as Lorentz conclusion that ether was simply not observable. It was in this scenario where Einstein established one of the most important scientific discoveries by placing experimentation above the flawed theories preceding his. CITATIONSNorton, John D. “Origins of Special Relativity.” Origins of Special Relativity, www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/origins/index.html. “History of Special Relativity.” Nobelprize.org, www.nobelprize.org/educational/physics/relativity/history-1.html. SUGGESTED READINGS"Special Relativity":
http://www.einstein-online.info/elementary/specialRT/special_relativity.html Einstein for Beginners by J. Schwartz and M. McGuinness
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