Two fields
taking turns
A changing electric field makes a magnetic one, and a changing magnetic field makes an electric one. Neither can stop without the other, so the pair travels — at a speed the two constants of free space fix between them.
lawE and B are perpendicular to each other and to the direction of travel, in phase, with c = 1/√(ε₀μ₀).
tryOrbit until you are looking straight down the axis of travel.
noticeFrom that angle the wave collapses to a cross: the two fields peak together, never one after the other.
in lifeRadio, wifi, microwaves and visible light are all this picture, differing only in wavelength.
found byMaxwell predicted it in 1865 from his equations; Hertz generated and detected it in 1887.