speed of light in vacuum
Also known as lightspeed, Planck speed, light speed, speed of electromagnetic waves in vacuum, vacuum speed of light, speed of light in a vacuum, velocity of light, luminal speed
speed of electromagnetic waves in vacuum
AI overview
The speed of light in a vacuum is how fast electromagnetic waves travel through empty space, which is approximately 186,000 miles per second (or about 300,000 kilometers per second). This speed is important because it's a fundamental constant of nature that serves as a cosmic speed limit—nothing can travel faster than light, and it plays a crucial role in physics, astronomy, and our understanding of how the universe works.
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Wikidata facts
Show 5 more facts
- Commons category
- Speed of light
- numeric value
- 220000
- conversion to standard unit
- 670616629.384
- conversion to SI unit
- 299792458.0147178
- unit symbol
- c
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Article
The speed of light in vacuum, often called simply the speed of light and commonly denoted c, is a universal physical constant exactly equal to 299792458 m⋅s. It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1⁄299792458 second. The value 299,792,458 metres per second is approximately 1 billion kilometres per hour; 700 million miles per hour. For other approximations of c valid for various units and size scales see the infobox.
All forms of electromagnetic radiation, including visible light, travel in vacuum at the speed c as do massless particles and field perturbations, such as gravitational waves. The speed of light is the same for all observers, no matter their relative velocity. As a result, massless particles and waves travel at c in a vacuum regardless of the motion of the source or the inertial reference frame of the observer. The speed of light is the upper limit for the speed at which information, matter, or energy can travel through space. Particles with nonzero rest mass can be accelerated to approach c but can never reach it, regardless of the frame of reference in which their speed is measured.