Speed of light Earth increases becomes greater than the speed of light. In classical physics, light is described as a type of electromagnetic wave. The classical behaviour of the electromagnetic field is described by Maxwell's equations, which predict that the speed "c" with which electromagnetic waves (such as light) propagate through the vacuum is related to the distributed capacitance and inductance of the vacuum, otherwise respectively known as the electric constant "ε" and the magnetic constant "μ", by the equation In modern quantum physics, the electromagnetic field is described by the theory of quantum electrodynamics (QED). In this theory, light is described by
Speed of light precise measurements, in 1975 the speed of light was known to be with a measurement uncertainty of 4 parts per billion. In 1983, the metre was redefined in the International System of Units (SI) as the distance travelled by light in vacuum in 1/ of a second. The speed of light in vacuum is usually denoted by a lowercase , for "constant" or the Latin (meaning "swiftness, celerity"). In 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch had used for a different constant later shown to equal times the speed of light in vacuum. Historically, the symbol "V" was used as