The microwave waveguide hypothesis proposes that ball lightning could be sustained by microwave radiation channeled through atmospheric waveguides — natural ducts formed by layers of air at different temperatures and humidity levels. During thunderstorms, intense electromagnetic radiation generated by lightning discharges could become trapped in these atmospheric ducts, focusing microwave energy into a confined region that ionizes the air and creates a visible, glowing sphere. The theory, developed by several independent researchers, offers an elegant explanation for ball lightning's ability to travel along specific paths (following the waveguide) and its tendency to enter buildings through windows and doors (where the waveguide intersects with structures). It also explains why ball lightning often appears to move horizontally rather than rising or falling under gravity.
Critics note that the theory requires very specific atmospheric conditions that may be difficult to achieve in practice, and that the energy levels involved would likely cause significant heating of nearby objects — which is not always observed in ball lightning encounters.