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 Against a backdrop of an ultra-competitive music industry that changes at the speed of light, holding onto that belief without getting hurt can be incredibly difficult. Jenna Wang, Peoplemag, 9 Feb. 2024 These wrinkles, called gravitational waves, travel through the universe at the speed of light and carry information about the epic cosmic phenomena that created them, such as massive collisions between two black holes, two neutron stars or one of each. Christian Thorsberg, Smithsonian Magazine, 30 Jan. 2024 Contributor As technology evolved, some would proclaim at the speed of light, artificial intelligence (AI) has emerged as a driving force of innovation across various sectors. Nick Kasmik, USA TODAY, 27 Jan. 2024 Leftovers from the Big Bang, wimps are invisible and slow, compared with the speed of light, and can only be detected through their gravitational effect on other objects. Dennis Overbye, New York Times, 26 Jan. 2024 At this time, the cosmos was dominated by radiation — photons and other particles moving close to the speed of light. Steve Nadis, Quanta Magazine, 1 Feb. 2024 The greater a telescope's light-gathering capacity, the deeper its view across the universe—and deeper and deeper views across space and (because the speed of light is finite) time are what a search for the expansion rate of the universe requires. Richard Panek, Scientific American, 14 Nov. 2023 Later, measurements tended to underestimate the value, leading some physicists to suggest that the speed of light was changing. Luke Caldwell, Scientific American, 16 Jan. 2024 Traveling at the speed of light, the video signal took 101 seconds to reach Earth, sent at the system’s maximum bit rate of 267 megabits per second, NASA said. Stephen Clark, Ars Technica, 30 Dec. 2023

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'speed of light.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

First Known Use

1823, in the meaning defined above

Time Traveler
The first known use of speed of light was in 1823

Dictionary Entries Near speed of light

Cite this Entry

“Speed of light.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/speed%20of%20light. Accessed 19 Mar. 2024.

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

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