Periodic Spectral Modulations Arise from Non-random Spacing of Spectral Absorption Lines

In recent publications, Borra (2013); Borra & Trottier (2016); Borra (2017) claimed the discovery of ultra-short ($10^{-12}\,$s) optical pulses originating from stars and galaxies, asserted to be sent by extraterrestrial intelligence. I show that these signals are not astrophysical or instrumental in nature, but originate from the non-random spacings of spectral absorption lines. They can be shown to arise in their clearest form in synthetic solar spectra, as these do not suffer from noise.