The Nature of Light - Research Paper in Physics

Measurements of the speed of light have been one of the most experimented topics since the time of Galileo. The methods and precision of measuring the speed have varied over time with the original scientists using raw methods that could not allow them to determine the exact speed of light. Most of these scientists believed that the speed of light was infinite, that it traveled instantly from point to point. Aristotle, one of the most influential philosophers and scientists in history, believed also believed that light travels at an infinite speed. However, with advancement in technology, the subsequent scientists developed a more advanced method of measuring the speed of light, resulting in the dismission of the notion that the speed of light is infinite. After a series of experiments by different scientists, the speed of light in a vacuum is currently commonly accepted to be 299,792.458 km/s. The paper discusses a series of experiments that were carried out by different scientists in an attempt to determine the exact speed of light.Galileo was the first scientist ever to be recorded in 1638 to have established the speed of light. He developed a straightforward method by using lamps together with his assistant. The two lamps were covered and uncovered at will. The two scientist would try to uncover the two lamps at an interval depending on when his assistant sees the light from his lantern with Galileo starting and his assistant uncovering his immediately he notices the light on the other lamp. He measured the distance between the two lamps and recorded the elapsed time.

Figure 1: Example of Galileo's Method. N.d. Graphic. N.p.

Using the two measurements, Galileo argued that he would measure the speed of light. However, the time difference was minimal, and at times he could barely record anything resulting in his conclusion that the speed of light is very rapid if it is not instantaneous (Caes, 2011). He did not have a proper time to determine the duration that the light took from one lamp to the other. However, he developed a rudimentary method of measuring the time that was not just inefficient but also useless bearing in mind that the speed of light is extremely high. He used a water clock to record time by measuring the amount of water that emptied from a container immediately after seeing the light from his assistant. Based on the instruments that he used in the experiment, he could not come up with the exact speed of light, but he assumed that the speed of light is ten times faster than the speed of sound. His discovery ignited other scientists to research the same topic, and this led to a series of findings.

Galileo's findings prompted much subsequent research that was carried by different scientists in an attempt to determine the speed of light. The results of the following experiments registered remarkable improvements as compared to the initial work by Galileo. Danish Ole Roemer was the first scientist to carry out further research on Galileo's work. In 1676 while working out at Paris Observatory, Roamer accidentally developed the idea of determining the speed of light while working on the orbit of lo, the innermost of the four big satellites that were discovered by Galileo in 1610. In trying to determine the orbital period of the satellite, he timed the eclipses of lo by Jupiter. Such an observation played an integral role in the subsequent studies in the seventeenth century. Initially, Galileo had presumed that the tables of the orbital motion of the satellite of the Jupiter would be used as a clock for reading the absolute time. However, it eventually turned out to be impractical, prompting Roemer to come up with unexpected practical eclipse data that played an integral role in determining the speed of light. In this experiment, Roamer measured the speed of light by timing eclipses of Jupiter's moon lo. The figure 1.00 below helps in understanding entirely how he experimented in an attempt to establish the speed of light.

Figure 2: Example of Roemers Method. N.d. Graphic. n.p. Web. http://www.daviddarling.info/encyclopedia/S/speedlight.htmlIn observing the shadows of the moons of Jupiter, Roamer discovered that lo made a complete orbit after 1.76 days. Despite consistency in the time the orbit took, sometimes in the year, the position of lo around Jupiter would be behind schedule. At times, lo would appear to be over speeding and slow down in its orbit. However, under close observation, Roamer discovered that lo was ahead of schedule when the Earth and Jupiter were close together, and lo would be behind the schedule when they were farther apart. According to his interpretation, light does not take time to travel between two points. When the Earth is closer to the Jupiter, light travels faster from Jupiter to Earth. Hence lo appears to be ahead of schedule. Conversely, when Earth and Jupiter are far apart, light takes more time to travel from Jupiter to Earth. Hence lo appears to be behind schedule. Using the knowledge of the diameter of the Earth's orbit and the measurements he obtained from the delay in time eclipses, Roamer was able to determine the speed of light as 200000 Km/sec. The value is not close to the universally accepted value, but it was a decent approximation for the time because it was on the right order of magnitude despite the fact that the actual distances between the planets were not known.

The findings of Roamer reinvigorated the interest of other scientists to determine the speed of light. James Bradley also attempted to establish the speed of light in 1728 by carrying out an experiment that would yield a more precise result as compared to the research findings of his predecessors. He used more advanced tools in determining the speed of light hence his research findings were more elaborate and accurate. His experiment was constituted mainly by the use of stellar aberration that was a representation of the ratio of the speed of Earth as it orbits the sun to the speed of light. Since he had the knowledge of the speed of Earth around the sun, and with the measurements of the angle of stellar aberration, he estimated the speed of light to be around 301,000 km/s.

Bradley Aberration of the straight line

Figure 3: Example of Bradley's Method. N.d. Graphic. n.p. Web.

<http://www.conspiracyoflight.com/Esclangon/Aberration_and_Esclangon.html>.

Fizeau was a French physicist who advanced the experiments that were done by the first scientists in an attempt to establish the speed of light. His test was composed of a source of light, a mirror, and a toothed wheel. To measure the speed of light, Fizeau shone a light between the teeth of a wheel that was rotating rapidly. He used a mirror that he placed five miles away to reflect back the beam through the same gap through the teeth of the wheel. The wheel contained over a hundred teeth, and it rotated a hundred times in a second. This made it easier to measure a fraction of a second. He varied the speed of the wheel to determine at what speed the wheel was spinning too fast for the light to pass through between the gap of the teeth, to the mirror and back through the same gap. He knew the distance between the mirror and the wheel, and by dividing the length by two, he could easily find the speed of light. Fizeau measured the speed of light to be 313,300 Km/s (Granser, 2004).

Figure 4: Example of Fizeau's Method. N.d. Graphic. n.p. Web. <http://spie.org/x32833.xml>.

Leon Foucault, another French physicist, repeated the experiment that Fizeau had done. The setup of his experiment was similar with that of Fizeau apart from the teethed wheel that was missing in the experiment. The procedure of his experiment was not complicated as he just shone a light on a rotating mirror which bounced back to the remote fixed mirror which bounced back the light back through an angle that was not exact with the initial angle by which it hit the mirror. He measured the angle and the distance between the two mirrors. Using the two measurements, he was able to establish the speed of light. Over the years, Leon advanced his experiment and eventually determined the speed of light as 299,796 Km/s in 1862 (Caes, 2011).

Figure 5: Example of Foucault's Method. N.d. Graphic. n.p. Web.<http://www.pas.rochester.edu/~pavone/particlewww/teachers/demonstrations/FoucaultDemonstration_files/image002.jpg>

In 1864, James Clerk Maxwell proposed his theory of electromagnetism that completely changed the way in which the speed of light could be measured. Mostly, his idea showed that light is, in fact, electromagnetic waves and only made up a small part of the electromagnetic spectrum. This opened up new ways to measure the speed of light in that scientists could now measure the speed of electromagnetic waves that werent necessarily light, to determine this speed. Also, in 1888, Heinrich Hertz created and measured electromagnetic waves in his laboratory and found that they traveled at the same speed as visible light which even suggested that they are the same.

Wilhelm Weber and Rudolf Kohlrausch also made a remarkable improvement in the precision of speed of light in 1857 by adopting the information that had been gathered by former scientists in their experiment. They used the new information on light and electromagnetism to determine the speed of light by measuring the magnetic permeability and electric permittivity of free space. The method was also adopted by Rosa and Dorsey in 1907 to determine the speed of light as 299,788 km/s which was the most accurate measurement by then (Granser, 2004). However, with advancements in technology and with more scientists developing an interest in determining the speed of light, more advanced and accurate methods were developed to assess light speed. K.D. Froome invented the machine in 1958 using a microwave interferometer and a Kerr cell shutter. Using the device, Froome measured the speed of light as 299.792.5 km/s. The development of lasers in the 1970s lead to high spectral stability and accurate cesium clocks which allowed for much more precise measurements. By 1970, the speed of light was known within an error of plus or minus 1 m/s, and in 1983, the meter was redefined internationally as the distance light travels in a vacuum in 1/299,792,458 of a second. This definition of the meter made the official speed of light in a space precisely 299,792.458 km/s 2 ("National Bureau of Standards," 1983).

Feynman also contributed to the research of nature of light. However, his contribution was based on duality particle-wave. He experimented in 1965 to determine whether light comes out in particles or waves. He developed a simple experiment in which he directed a specific material towards a wall with two small slits that can easily be opened and closed. The two slits block some elements while others pass quickly through them, depending on the slit that is opened. Particular patterns form on the backstop that indicates whether the material passing through the two slits are in particles or waveform.

References

Caes, C. (2011). The Scientist's Guide to Physics: Discovering the Speed of Light. Rosen Young Adult.

Daukantas, P. (2009). Ole Romer and the Speed of Light. Optics and Photonics News, 20(7), 42. doi:10.1364/opn.20.7.000042

Granser, H. (2004). AVO and the nature of light. The Leading Edge, 23(11), 1153-1154. doi:10.1190/1.1825936

National Bureau of Standards. (1983). doi:10.6028/nbs.sp.643