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

Solar flares are made up of electromagnetic radiation that travel from the Sun at the speed of light and can reach Earth in about eight minutes.

From BBC

Their picture shows the galaxy NGC 5128 and its relativistic jet - beams of radiation and particles travelling close to the speed of light.

From BBC

The signal crossed the solar system at the speed of light, covering a distance of about 158 million miles in just 14 minutes.

From Los Angeles Times

A particle that has no mass usually moves at the speed of light.

From Science Daily

It holds that in the first sliver of time after the universe’s birth, the fabric of space-time accelerated outward to speeds far faster than the speed of light.

From New York Times