Does Dark Matter Exist?

Merging Galaxy Cluster Abell 520. Photo credit: NASA.
Merging Galaxy Cluster Abell 520. Photo credit: NASA.

Dark matter is one of the big questions of cosmology. While it is believed to be partly responsible for the formation of galaxies and was suggested to make up more than 84% of the matter in the universe, modern observations infer that dark matter exists but has not yet been directly discovered. This is a big question, indeed, and also a problem. As recently mentioned in an article for Discover, “No one has ever detected a single dark matter particle, and no one can say for certain what it would consist of.” The article then goes on to explore an alternative, radical possibility: that dark matter simply is not there.

This option is being tested by Stacy McGaugh, an astronomer at Case Western Research University in Cleveland, whose work is supported by a grant from the John Templeton Foundation. He has doubted the orthodoxy for over two decades after losing faith in the dark matter hypothesis, and now poses the conundrum in a different way: instead of assuming that the universe is pervaded by some unknown form of invisible mass, what if the law of gravity needs to be modified?

An idea called Modified Newtonian Dynamics, or MOND, tweaks the laws of gravity proposed by Isaac Newton. MOND advocates suggest that galaxy dynamics and other puzzling aspects of the universe may be explained if gravity plays by different rules than commonly thought—and without involving dark matter. McGaugh’s project seeks to illuminate the dark matter problem through the study of tidal dwarf galaxies, which are small galaxies born in the chaos of galaxy interactions. These galaxies may provide an innovative laboratory in which to compare dark matter explanations alongside MOND.

It requires dedication to challenge the status quo, especially when it rests on the work of towering figures such as Newton. While McGaugh admits that his research has exposed him to criticism, he says that “science is not a consensus endeavor” and accepts that MOND faces many challenges as a theory. Yet, MOND has not been disproved, and McGaugh is sure it warrants further investigation. “The formula has predictive power,” he says, “so it’s got to be telling us something.”