Gravitational Waves Sourced by Magnetic Stress at a Bounce: A Peak in the Ground-Based Band at an Unreachable Amplitude

A magnetic field at a bounce is a source of gravitational waves, and the bounce fixes the source's characteristic frequency with unusual precision. The horizon frequency at the turnaround, redshifted by the expansion since, lands at 3.08e+01 hertz today, squarely in the band of ground-based interferometers. The amplitude is another matter. For the largest magnetic fraction compatible with microwave limits, about two millionths of the turnaround density, the present gravitational-wave fraction is 3.25e-18, nine orders of magnitude below current stochastic-background sensitivity. Reaching detectability would require a bounce magnetic fraction of 3.33e-02, which exceeds the microwave-compatible fraction by a factor 1.75e+04 in energy and would therefore demand a post-bounce decay channel that removes the field while leaving its gravitational waves. A detected stochastic background near thirty hertz with a horizon-shaped spectrum would thus be evidence not merely of a bounce magnetic field but of a bounce magnetic field that was destroyed; a null result, at any foreseeable sensitivity, says almost nothing. Both halves of that statement are computed here. The estimates are order-of-magnitude by stated design, not measurements.