speed of light

[speed uhv lahyt]

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.

Word History and Origins

Origin of speed of light¹

First recorded in 1820–25

Example Sentences

Cosmic rays -- high-energy particles moving close to the speed of light -- are known to arrive from within the Milky Way and from more distant regions of the universe.

Read more on Science Daily

"Our method performs the same kinds of operations that today's GPUs handle, like convolutions and attention layers, but does them all at the speed of light," says Dr. Zhang.

Read more on Science Daily

Solar flares are bursts of electromagnetic radiation that travel from the Sun at the speed of light, reaching Earth in just over eight minutes.

Read more on BBC

Yet the two black holes involved in GW231123 were spinning near the speed of light -- the fastest ever observed -- making such a scenario improbable.

Read more on Science Daily

Blazars are a type of active galaxy powered by supermassive black holes that shoot out powerful, narrow jets of particles and radiation at nearly the speed of light.

Read more on Science Daily