The space between Earth's surface and the ionosphere forms a resonant cavity — a waveguide approximately 60 km tall that wraps around the entire planet. When lightning strikes (about 50 times per second globally), it excites electromagnetic standing waves in this cavity.
These standing waves resonate at specific frequencies. The fundamental mode is approximately 7.83 Hz, with harmonics at roughly 14.3, 20.8, 27.3, 33.8, 39, and 45 Hz.
The ionosphere acts as a gate between the electromagnetic chaos of space and the relatively calm electromagnetic environment at Earth's surface. Without this gate, the solar wind and cosmic radiation would make the surface uninhabitable.
The Schumann resonances are the ringing frequency of the gate itself. They're what you hear when you tap on the filter between space and ground.
The fundamental frequency of 7.83 Hz sits at the boundary between theta and alpha brainwave bands — the transition zone between drowsy meditation and alert awareness. Whether this is coincidence or consequence is an open question.
Schumann resonance amplitudes fluctuate with global lightning activity, solar wind conditions, and ionospheric disturbances. The frequencies themselves are remarkably stable, but their power varies. During geomagnetic storms, the gate shakes.