Electromagnetic field: Encyclopedia II - Electromagnetic field - The field as a stream of moving photons

Electromagnetic field - The field as a stream of moving photons

Alternative interpretation would be that the field is not actually a velocity field, but a flux density field of photonic fluid, which is constantly moving at the same speed: the speed of light, independent of the speed of the observer (the charged object). Photonic fluid never changes speed but can change net direction and the intensity of its net movement in that direction.

The velocity field interpretation is related to the hypothesis of a luminiferous aether through which electromagnetic waves would propagate. The proposition that the motion of the earth relative to the aether might be detectable (i.e. through an "aether wind") was disproven by the Michelson-Morley experiment, whereupon it was argued that the experiment had disproved the very existence of the aether. This opinion prevailed, but remains disputed by some who equate the classical concept of the aether with the modern notion of a quantum electrodynamic fluid. (The disputants argue that proving that the earth does not travel through an "aether wind" is no more nor less significant than proving that the earth does not travel through its own gravitational or magnetic fields.) The necessity of an aether was seen to have vanished when it was replaced by Einstein's theory of relativity.

According to special relativity, the Lorentz force equation reduces to the equation

The magnetic field becomes a relativistic by-product of the electric field, i.e. Lorentz transformations cause magnetic fields to be induced from electric fields, and vice versa. So the photonic fluid describes the electric field, and relativistic effects account for the derivative magnetic field. (This can be derived by applying a Lorentz transformation to a simplified version of Maxwell's equations, and it is mentioned by Einstein in his paper On The Electrodynamics Of Moving Bodies [1].)

The speed of light is invariant under a Lorentz transformation, but the velocity of light is changed. The component of the velocity of light parallel to the boost is left unchanged, but the transverse component is rotated: it is accelerated in a direction parallel to the boost. The addition of special relativity allows the combination of the electric and magnetic fields into a single tensor field. The tensor character of this combined electromagnetic field implies that the field is anisotropic with respect to the velocity of the charged particle on which it produces a force: the Lorentz force varies with the velocity of the charged particle.

Adapted from the Wikipedia article "The field as a stream of moving photons", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki