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  2. Speed of light - Wikipedia

    en.wikipedia.org/wiki/Speed_of_Light

    v. t. e. The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour).

  3. One-way speed of light - Wikipedia

    en.wikipedia.org/wiki/One-way_speed_of_light

    So the average speed for the round trip remains the experimentally verifiable two-way speed, whereas the one-way speed of light is allowed to take the form in opposite directions: κ can have values between 0 and 1. In the extreme as κ approaches 1, light might propagate in one direction instantaneously, provided it takes the entire round-trip ...

  4. Michelson–Morley experiment - Wikipedia

    en.wikipedia.org/wiki/Michelson–Morley_experiment

    Michelson–Morley experiment. For interference experiments on matter, see Hughes–Drever experiment. The Michelson–Morley experiment was an attempt to measure the motion of the Earth relative to the luminiferous aether, [ A 1 ] a supposed medium permeating space that was thought to be the carrier of light waves.

  5. Electromagnetic wave equation - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_wave_equation

    is the speed of light (i.e. phase velocity) in a medium with permeability μ, and permittivity ε, and ∇ 2 is the Laplace operator. In a vacuum, v ph = c 0 = 299 792 458 m/s, a fundamental physical constant. [1] The electromagnetic wave equation derives from Maxwell's equations.

  6. Light - Wikipedia

    en.wikipedia.org/wiki/Light

    The speed of light in vacuum is defined to be exactly 299 792 458 m/s (approx. 186,282 miles per second). The fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light. All forms of electromagnetic radiation move at exactly this same speed in vacuum.

  7. Fizeau's measurement of the speed of light in air - Wikipedia

    en.wikipedia.org/wiki/Fizeau's_measurement_of_the...

    At 3 times the speed it was again eclipsed. [3] [4] Given the rotational speed of the wheel and the distance between the wheel and the mirror, Fizeau was able to calculate a value of 2 × 8633m × 720 × 25.2/s = 313,274,304 m/s for the speed of light. Fizeau's value for the speed of light was about 5% too high. [5] The correct value is ...

  8. Rømer's determination of the speed of light - Wikipedia

    en.wikipedia.org/wiki/Rømer's_determination_of...

    The engraving is probably posthumous. Rømer's determination of the speed of light was the demonstration in 1676 that light has an apprehensible, measurable speed and so does not travel instantaneously. The discovery is usually attributed to Danish astronomer Ole Rømer, [ note 1 ] who was working at the Royal Observatory in Paris at the time.

  9. Rapidity - Wikipedia

    en.wikipedia.org/wiki/Rapidity

    Rapidity is the value of artanh (v / c) for velocity v and speed of light c. In special relativity, the classical concept of velocity is converted to rapidity to accommodate the limit determined by the speed of light. Velocities must be combined by Einstein's velocity-addition formula. For low speeds, rapidity and velocity are almost exactly ...