The symbol 'c' for the speed of light likely comes from the Latin word "celeritas," meaning swiftness or speed. While sometimes attributed to Einstein, he used 'V' in his early work. 'c' became the standard symbol later, possibly arising from the study of electromagnetic waves where 'c' represented a constant in Maxwell's equations. Its precise origin remains somewhat uncertain, but the connection to "celeritas" and the established use of 'c' for wave propagation constants are the most probable explanations.
The 2004 post by John Baez, titled "Why is c the symbol for the speed of light?", delves into the historical etymology of using c to represent this fundamental physical constant. The most straightforward explanation, while not definitively proven, is that c stands for "constant" or "celeritas," the Latin word for "swiftness" or "speed."
Baez elucidates that the use of c became firmly established in the late 19th century, primarily through the influence of James Clerk Maxwell's work on electromagnetism. Maxwell himself utilized various notations, including V, representing velocity, for the speed of electromagnetic waves. However, he also sometimes employed the symbol c, possibly deriving from Weber and Kohlrausch's earlier work where they denoted the ratio of electrostatic to electromagnetic units of charge with c. This ratio, as later confirmed, was numerically equal to the speed of light.
The post carefully dissects the historical progression, pointing out that Einstein initially used V in his 1905 papers on special relativity, later switching to c, likely due to the growing convention within the physics community. Furthermore, the connection to "constant" might have resonated with Einstein's emphasis on the constancy of the speed of light as a fundamental postulate of his theory.
The post also explores alternative theories, acknowledging the possibility that c might have arisen from other related terms. While "celeritas" is a plausible candidate, the direct link lacks definitive historical evidence. The text carefully avoids presenting this as a conclusive explanation but rather a compelling possibility given the context.
In summary, while the exact origin of using c for the speed of light remains somewhat shrouded in historical ambiguity, the prevailing theory connects it to the word "constant" and potentially to "celeritas." Maxwell's influence, coupled with the widespread adoption cemented by Einstein's work, solidified the use of c as the universally recognized symbol for this fundamental constant in physics. While alternative explanations exist, the connection to "constant" and the established usage within the emerging field of electromagnetism and relativity provide the most compelling narrative for understanding why c became the standard representation of the speed of light.
Summary of Comments ( 79 )
https://news.ycombinator.com/item?id=43472663
The Hacker News comments discuss the origin of "c" for the speed of light, with most agreeing it likely comes from "constant" or the Latin "celeritas" (swiftness). Some debate whether Maxwell originally used "V" or another symbol, and whether "c" became standard before Einstein. A compelling comment highlights the difference between defining c as the speed of light versus recognizing it as a fundamental constant relating space and time, with implications beyond just light. Another interesting point raised is that "c" represents the speed of causality, the fastest rate at which information can propagate, regardless of the medium. There's also brief discussion of the historical context of measuring the speed of light and the development of electromagnetic theory.
The Hacker News post linked discusses the origin of "c" representing the speed of light. Several commenters offer insights and perspectives on the topic, generating a robust discussion.
One of the most compelling threads involves the debate about whether "c" originates from "constant" or "celeritas" (Latin for swiftness). Multiple users weigh in, citing historical texts and scientific literature. Some argue that "constant" is a backronym, meaning the association was made after "c" was already in use. Others contend that "constant" was indeed the original intention, representing the constant speed of light, a fundamental concept in physics. The discussion delves into the nuances of historical scientific notation, with users dissecting the evolution of the symbol's meaning over time.
Another interesting point raised is Maxwell's use of "V" for the speed of light in his original equations. This observation leads to speculation about the transition from "V" to "c," with some commenters suggesting that Einstein's later work solidified the use of "c."
Several users also discuss the broader context of symbols used in physics, highlighting the somewhat arbitrary nature of such designations. They point out how different symbols gain acceptance through convention and widespread usage. This discussion touches on the evolution of scientific language and the role of historical context in shaping our understanding of fundamental concepts.
Finally, some comments provide further resources, including links to relevant articles and books, allowing readers to delve deeper into the history of the speed of light and its symbolic representation. Overall, the comments section offers a fascinating exploration of the question, showcasing the collective knowledge and curiosity of the Hacker News community.