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The '''speed of light''' in a vacuum (postulated to be constant for all inertial observers by the [[Special Theory of Relativity]]) is exactly 299,792,458 meters per second (approximately 186,282.3 miles per second). As the speed of light is now used to define the [[SI]] meter, this is now the value ''by definition''.
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The '''speed of light''' in a vacuum (postulated to be constant for all inertial observers by the [[Special Theory of Relativity]]) is currently exactly 299,792,458 meters per second (approximately 186,282.3 miles per second), though likely was higher in the past. As the speed of light is now used to define the [[SI]] meter, this is now the value ''by definition''.
    
In physics, it is often represented in equations by the letter '''c,''' as in
 
In physics, it is often represented in equations by the letter '''c,''' as in

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