Speed of light

speed of light

The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299792458 metres per second (approximately 3.00×10⁸ m/s, approximately 186,282 mi/s); it is exact because the length of the metre is defined from this constant and the international standard for time.^[2] According tospecial relativity, c is the maximum speed at which all matter and hence information in the universe can travel. It is the speed at which all massless particles and changes of the associated fields (including light, a type of electromagnetic radiation, and gravitational waves) travel in vacuum. Such particles and waves travel at c regardless of the motion of the source or the inertial reference frame of the observer. In the theory of relativity, c interrelates space and time, and also appears in the famous equation of mass–energy equivalence E = mc².^[3]

^{what is E=mc2}

^{This formula states that the equivalent energy (E) can be calculated as the mass (m) multiplied by the speed of light (c = about 3×108m/s) squared. (Similarly, anything having energy exhibits a corresponding mass m given by its energy E divided by the speed of light squared c².) Because the speed of light is a very large number in everyday units, the formula implies that even an everyday object at rest with a modest amount of mass has a very large amount of energy intrinsically. Chemical, nuclear, and other energy transformationsmay cause a system to lose some of its energy content (and thus some corresponding mass), releasing it as light (radiant) orthermal energy for example.}