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How fast does electromagnetic radiation travel in a vacuum?
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Electromagnetic radiation, including light, travels in a vacuum at a constant speed defined as exactly 299,792,458 metres per second (approximately 186,282 miles per second).12
This value, denoted by the symbol c, is a fundamental constant of nature. It serves as the universal upper limit for the propagation speed of signals and the velocity of all material particles. In physics, this speed is determined by the permittivity and magnetic permeability of free space. The relationship is expressed through James Clerk Maxwell's electromagnetic wave theory, which unified the fields of electricity, magnetism, and optics by demonstrating that light is an electromagnetic disturbance.23