speed of light

noun phrase

: a fundamental physical constant that is the speed at which electromagnetic radiation propagates in a vacuum and that has a value fixed by international convention of 299,792,458 meters per second

—symbol c

Example Sentences

Recent Examples on the Web

In less than a second, the entire star turns itself inside out, sending out a shockwave of its own material, racing away at nearly the speed of light. —Popular Mechanics, 18 Apr. 2023

Directed energy weapons—like high-energy #lasers—could be used to disrupt or destroy targets at the speed of light. —Alain Sherter, CBS News, 17 Apr. 2023

Material accumulates around black holes, is heated to billions of degrees and reaches nearly the speed of light. —Ashley Strickland, CNN, 14 Apr. 2023

So in fact, correlations caused by quantum entanglement cannot be used to send signals faster than the speed of light. —Juan Maldacena, Scientific American, 1 Nov. 2016

And for internet speeds faster than the speed of light (OK, perhaps not that fast), the AT&T Fiber/DirecTV Stream bundle is the ideal choice. —Stefanie Waldek, EW.com, 10 Apr. 2023

In a world where biology moves at the speed of light, those risks can get out of hand. —Michael Specter, STAT, 6 Apr. 2023

No – the distance is rate (speed of light) times time (a year). —Danya Gainor, CNN, 31 Mar. 2023

The baby black hole would produce jets of highly energetic particles moving near the speed of light, powerful enough to pierce through the remains of the progenitor star, emitting X-rays and gamma rays. —Jennifer Ouellette, Ars Technica, 30 Mar. 2023

See More

Word History

First Known Use

1823, in the meaning defined above

Kids Definition

speed of light

: a fundamental physical constant that is the speed at which electromagnetic radiation travels in a vacuum and that has a value of 299,792,458 meters per second