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

Examples of speed of light in a Sentence

Recent Examples on the Web

At relativistic speeds — that is near the speed of light — time moves more slowly, which would mean the electron beam wouldn't have enough time to spread out, keeping the beam focused. —Victoria Corless, Space.com, 22 Jan. 2025

The ever-changing world of design can be as fickle as the wind, with trends coming and going often at the speed of light. —Roger Sands, Forbes, 21 Jan. 2025

This article was updated on Jan. 17, 2024 to reflect the amount of money Musk spent helping Trump win the 2024 election as $250 million and the correct speed of light. —Robert A. Kopack, The Conversation, 17 Jan. 2025

The beauty of the all-optical design is that the calculation speed is determined by the speed of light and the frequency of the optical pulses. —The Physics Arxiv Blog, Discover Magazine, 16 Jan. 2025

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