Graviton Dispersion and the Compton-Wavelength Bound from GW150914

If the graviton has a rest mass, gravitational waves disperse: their lower frequencies travel slower, and a chirping binary signal would arrive smeared relative to the massless waveform. GW150914 swept from about 35 to 150 Hz over a path of about 410 Mpc, and its waveform matched the massless prediction closely. A simplified coherence version of the test, allowing a tenth of a second of differential arrival across the band, bounds the graviton mass at 3.24e-22 eV per c-squared, corresponding to a Compton wavelength above 3.83e+12 km; the collaboration's full phase-based analysis reached about 1.2 x 10^-22 eV per c-squared, stronger because it uses the waveform's phase evolution rather than a single coherence time. The framework examined here treats gravitational waves as massless disturbances of the geometry travelling at c; the observation is consistent with that statement. Computed from published data; not a new measurement.