Cosmic microwave background
Known in the field of extragalactic astronomy for his early work on Low Surface Brightness Galaxies and the elemental abundances in HII Regions, McGaugh has also contributed to the study of the kinematics of galaxies, being among the first to point out that low surface brightness galaxies are dark matter dominated and that they pose the cuspy halo problem. He also coined the expression "baryonic Tully–Fisher relation." He predicted the first to second peak amplitude ratio of the acoustic power spectrum of the Cosmic microwave background radiation. McGaugh found surprising support for the Modified Newtonian dynamics proposed by Mordehai Milgrom as an alternative to Dark matter in his work on Low Surface Brightness Galaxies. This has proven to be very controversial since it implies the non-existence of the non-baryonic dark matter that is central to physical cosmology.