Gravitational-Wave Standard Siren Distances in a Bounced Cosmology: From GW170817 to Third-Generation Reach

Gravitational-wave standard sirens measure luminosity distance from the waveform alone, and their sensitivity to a bounced cosmology grows steeply with the redshift their detectors reach. The nearby event GW170817, at about 44 Mpc, has its distance interpretation shifted by -0.009 percent at epsilon = 0.10, far below its 15 percent distance uncertainty. At redshift 0.5, representative of second-generation bright sirens, the shift is -0.51 percent; at redshift 1.0, -1.01 percent; and at redshift 2.0, within third-generation reach, -1.72 percent. Since the expansion rate inferred from a siren at fixed redshift scales inversely with its distance, these are also the fractional biases an uncorrected standard-frame analysis would carry. A catalogue of sirens at redshift near one with percent distances would bound the bounce amplitude near epsilon = 0.100, making sirens, within a decade, competitive with the acoustic scale as frame witnesses while sharing none of its physics. This study is computed from stated assumptions, not measured.