The fastest speed that two objects can travel is known as the speed of light. This number has been a universal measurement for centuries, and scientists have gotten increasingly accurate estimates. In fact, in 1941, the scientific community adopted a standard value for the speed of light: 299,774 kilometers per second. However, despite the constant value, the speed is still not fully understood.
The speed of light
Throughout the early modern period, scientists didn’t know whether light travelled at a fast, finite rate or whether it simply travelled at the same pace as time. The Greek philosopher Empedocles, for example, proposed that light must travel at a constant speed. Aristotle countered his view by pointing out that light must be instantaneous. Likewise, Anicius Boethius was accused of sorcery, attempting to measure the speed of light.
Physicists began making increasingly more accurate measurements of the speed of light in the seventeenth and eighteenth century. British physicist James Bradley, for instance, measured the apparent position of stars, a common technique for determining light speed. His calculation was accurate to within 1% of the real value.
Reach the Earth
Another early method of calculating the speed of light was carried out by Danish astronomer Ole Roemer. He studied the moon Io of Jupiter and made predictions about the eclipse period. When he compared his calculations with observations, he discovered that the moon appeared to lag behind Jupiter. Using inaccurate calculations for the distance between Earth and Jupiter, he predicted that light would take a longer time to reach the Earth.
Other scientists, including French optical physicist Leon Foucault, made similar experiments. Their measurements suggested that the intensity of light decreased by a factor of four after a given amount of time had passed. They also determined that the speed of light was slightly lower than its accepted value today.
Amount of time
The next step was taken by French physicist Armand Fizeau, who independently tested his theory. He set up a device that used a toothed wheel to steer a beam of light through a gap. As the light traveled through the gap, it was caught by a ray of light in a neighboring gap. These measurements led Fizeau to calculate the amount of time that it took for the light to travel through the gap. Eventually, he determined that the speed of light was 299,774 kilometers per second.
The speed of light
Another scientist who was trying to calculate the speed of light was American physicist Albert A. Michelson. After experimenting with his methods, he found that the speed of light was actually slightly lower than his estimate. Although Michelson died before completing his experiments, his work helped lead to more accurate estimates of the speed of light.
In the twentieth century, radio technology provided new methods for measuring the speed of light. Radio waves travel at a consistent rate, and this allows scientists to measure the speed of light. By using this technology, the scientific community compiled a standard value for the speed of light, which was 299,774 kilometers per second.