In the context of the Universe, the speed of light is c, or 299,792,458 metres per second. This speed is the universal physical constant. However, it is not the same for all objects in the Universe. In our daily lives, we are affected by the speed of light in different ways.
Albert Einstein
Albert Einstein’s theory of relativity is based on the assumption that the speed of light in a vacuum is absolutely constant. This principle is considered to be a basic physical law. However, Einstein postulated that, in order to maintain this constant speed, space and time must be warped.
Einstein considered the ether theory, but it proved to be a less than reliable way of predicting the real world. In particular, the idea of a hypothetical ether was troubling to him. He also felt bothered by the fact that Galilean relativity was being tossed aside in favor of this hypothetical ether. This led him to pose a new question: what happens to the light wave if it is traveling at the speed of light?
To answer this question, Einstein proposed a mathematical formula. According to this formula, the speed of light is the distance divided by the time. Using this equation, astronomers can determine the distance between Earth and other planets. This distance is measured in light years.
James Bradley
The astronomical measurements of James Bradley, who lived in the eighteenth century, proved to be crucial for the discovery of the Speed of Light. They provided the first experimental evidence of the earth’s motion around the sun, and contradicted the popular belief that the earth is stationary at the center of the universe. Bradley used a simple home telescope to make his observations. He was inspired by an idea that seemed to defy reason, and he continued to make observations until he had a firm grasp on the subject.
Bradley’s measurements were extremely accurate. He measured the angle of starlight and the speed of light, and derived an equation for the speed of light. The equation was proved to be accurate to one percent. The equation he used to calculate the velocity of light was based on the relative motion between the observer and the source.
Bradley’s findings were based on a new method that proved the speed of light to be nearly ten thousand times faster than that of Earth’s surface. In addition to his measurements, Bradley also discovered another method to measure the speed of light. The telescope axis was tilted by a small angle in the direction of Earth’s rotation. This angle, when multiplied by the speed of light, gave Bradley an accurate estimate of 301,000 miles per second.
James Romer
There is a significant amount of misunderstanding about the speed of light. Einstein himself claimed that the speed of light is not instantaneous, but is extraordinarily rapid. He came to this conclusion by using a water clock to measure the lag in light and concluded that light must travel faster than sound. However, the exact speed of light has never been known.
Although Romer never published a formal description of his method, it is clear that he did use the method in his work. Though he may have been opposed by Picard and Cassini, his Journal des Scavans article makes clear that he was using this method. In fact, the date of the journal article suggests that Romer had observed eclipses on the Galilean moons as early as 8 July 1676.
Romer then calculated how much extra time light took to travel from Jupiter to Earth in a particular orbit. His data came from thirty observations of eclipses on Io made between 1671 and 1673. He found that the extra time was eleven minutes. This figure is higher than the actual value of light, which is 299,792 km/s.
Albert Michelson
During his studies at the Naval Academy, Michelson showed great aptitude in optics and other sciences. He was soon made a physics instructor and made strides in measuring the speed of light. His experiments were much more precise than any previous measurement, and gained him much respect as a scientist. Michelson also spent two years in Europe, where he refined his methods and discovered a new technique for measuring the speed of light.
The first test was conducted on a mountain in California. At that time, the United States Geodetic Survey team was preparing a project to measure air speed. However, Michelson wasn’t satisfied with the results from the Mt. Wilson experiment, and he didn’t trust the USGS team. Therefore, he chose an experiment in Orange County. Michelson asked his friend James Irvine Jr. to drive him to a low, flat field.
During his final decade at Cal Tech, Michelson continued his work and worked to extend the round-trip distance of light by 22 miles. He then spun an 8-sided prism at over 30,000 rpm. This resulted in a measurement of 186,285 miles per second. In his final year of life, Michelson died at age 78 in Pasadena.
Albert Einstein’s headlight
Albert Einstein’s Special Theory of Relativity states that the speed of light does not change when the source of light changes. Thus, light that travels from a stationary source travels at 300,000 km/sec. This fact explains why Einstein said that a headlight will always travel at the same speed as the source of light.
Einstein’s thought experiment is one of the most famous contributions to the study of light. Einstein was fascinated by light as a teenager when he asked himself a simple question: “What would it be like to ride my bike on a beam of light?” His research led him to develop the special theory of relativity in 1905, which states that light always travels at the same speed.
Einstein realized that if light traveled at the speed of light, a spaceship would turn on its headlights before stopping at a stop. Because of this, the beam of light would reach its destination. Einstein also showed that the speed of light in space was the same for everyone, regardless of their position.
James Bradley’s estimate
In 1727, British astronomer James Bradley estimated the speed of light. He used stellar parallax to calculate this value. This measurement was very accurate, and Bradley was within 0.5% of the actual value. Bradley believed in the particle theory of light, which would eventually become widely accepted. However, it was not until the nineteenth century that the wave theory of light was widely accepted, and astronomers were able to use the same methods to determine the speed of light.
Bradley was rewarded for his observations by the Royal Society, which recommended him as the next astronomer royal. He was also awarded a PS250 annual stipend and a grant of PS1,000 to purchase instruments. He then married Susannah Peach, and they had one daughter.
Bradley’s estimate was accurate, as the actual speed of light is much higher than what humans can measure. His measurements, while accurate, are still 20 times higher than what Einstein and Foucault had predicted.
