Historically, scientists had difficulty accurately measuring the value of the speed of light (c) due to various technical and conceptual challenges. The reason they didn't use the straightforward definition "the distance traveled by light in one second" as the definition of the speed of light lies in the difficulty of measuring distances and time intervals with sufficient precision.
Here are some key reasons why measuring the speed of light was challenging:
Limited experimental tools: In the early days of scientific inquiry, scientists lacked the advanced instrumentation we have today. They had to rely on basic tools and techniques to measure distances and time intervals, which introduced uncertainties in their measurements.
Finite speed of light: The finite speed of light itself posed a challenge. When conducting experiments, scientists had to account for the time taken by light to travel from the source to the detector. This led to systematic errors and inaccuracies in their measurements.
High speed of light: While the speed of light is finite, it is incredibly fast. Traditional methods for measuring speeds were not sensitive enough to accurately determine the value of c.
Conceptual issues: Before the development of the theory of electromagnetism, the nature of light and its propagation were not fully understood. Early ideas about the "ether," a hypothetical medium through which light was believed to propagate, added complexity to the experiments.
Despite these challenges, attempts to measure the speed of light began in the 17th century. One of the first successful measurements was made by Ole Rømer in 1676, who used observations of Jupiter's moons to estimate the speed of light. However, his method still suffered from limitations.
It wasn't until the 19th century that more accurate measurements were achieved. Techniques like Fizeau's experiment (1849) and Michelson's interferometer (1879) significantly improved the precision of measurements, but it was still challenging to obtain highly accurate values for c.
Eventually, the value of the speed of light was established through a combination of different experimental approaches, theoretical developments in electromagnetism (Maxwell's equations), and an understanding of the fundamental properties of free space (permeability and permittivity). The modern value of the speed of light, approximately 299,792,458 meters per second, is now a well-established constant and forms the basis for the definition of the meter in the International System of Units (SI).