光速
kōsoku[ko̞ːso̞kɯ̟]
The English phrase "speed of light" is translated into Japanese as 光速 (kōsoku).
In Japanese, the term is used to refer to the speed of electromagnetic radiation in a perfect vacuum.
Meaning: the speed of electromagnetic radiation in a perfect vacuum (noun)
What does it mean word for word?
The word 光速 is a compound of 光 meaning 'light' and 速 meaning 'speed'.
Which one should you use?
There are different ways to express this concept depending on the context. The technical and formal term is 光速. For a more descriptive and common way to say 'the speed of light' in everyday conversation, you can use 光の速さ. Additionally, the informal phrase 光のスピード uses an English loanword to express the same idea.
How do you pronounce it?
kōsoku
Did you know?
- In some Japanese sci-fi contexts, the concept of 'faster than light' is expressed as 超光速, where 超 means 'super' or 'transcend'.
- In Japanese, the word 光速 can be used metaphorically to describe a person's extremely fast reaction time or the speed at which a task is completed.
- In Japanese pop culture, particularly in anime and manga, the phrase 光速の拳 (a 'light-speed punch') is a common trope used to describe characters moving faster than the eye can see.
Examples in context
- 光速で進む宇宙船は、未来の技術を象徴しています。A spaceship traveling at the speed of light symbolizes future technology.
- 光の速さってほんとうにすごいんだよ。The speed of light is really amazing, you know.
- 光速は非常に速い。kousoku wa hijou ni hayai.The speed of light is extremely fast.
- 光速の計算は難しい。kousoku no keisan wa muzukashii.Calculating the speed of light is difficult.
- 宇宙では光速が限界だ。uchuu de wa kousoku ga genkai da.In the universe, the speed of light is the limit.
Example conversation
Two siblings are talking about a science fiction movie.
- 陽葵 Himariこの映画の宇宙船は光速で飛べるんだよ。kono eiga no uchūsen wa kōsoku de toberu n da yo.The spaceship in this movie can fly at the speed of light.
- 陽太 Yota本当にそんなことが可能なのかな？hontō ni sonna koto ga kanō na no kana?I wonder if that's actually possible.
- 陽葵 Himari科学的に考えると難しいと思うけどね。kagakuteki ni kangaeru to muzukashii to omou kedo ne.I think it's difficult if you think about it scientifically.
- 陽太 Yotaでも、想像するとワクワクするね。demo, sōzō suru to wakuwaku suru ne.But it's exciting to imagine.
Sources
- Wiktionary, “speed of light” translations and entries 光速, CC BY-SA 4.0, dump of 2026-09-26.
