speed of light

American  

[speed uhv lahyt] / ˈspid əv ˈlaɪt /

noun

1. Physics, Optics. a fundamental universal constant, the speed at which light and all forms of electromagnetic radiation travel in a vacuum, standardized as 186,282.4 miles per second (299,792,458 meters per second).

   The speed of light, often represented by the letter c, figures prominently in modern physics, as in Einstein’s famous equation E = mc2, which expresses the relation between mass (m) and energy (E).

2. an extremely fast rate.

   They gobbled those appetizers up at the speed of light.

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Etymology

Origin of speed of light

First recorded in 1820–25

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Example Sentences

See Examples For:

speed of light

By colliding heavy ions at nearly the speed of light, researchers can briefly separate quarks and gluons and produce tiny amounts of the same kind of matter that existed during the universe's first microseconds.

From Science Daily ● Oct. 6, 2026

And while optical networks can carry data at – almost - the speed of light, installing and maintaining them will still proceed at human speed.

From BBC ● Sep. 22, 2026

That is 100,000 times faster than a commercial airplane, or more than eight percent of the speed of light, making it the fastest star ever detected in our galaxy.

From Barron's ● Aug. 20, 2026

When atomic nuclei crash into one another at nearly the speed of light, they briefly produce quark-gluon plasma, an extraordinarily hot state of matter in which quarks and gluons can move freely.

From Science Daily ● Aug. 3, 2026

Kept them moving at the speed of light, the speed of sound—faster than anybody had ever flown before.

From "We'll Fly Away" by Bryan Bliss

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