space.com: Distinguished University Professor Glenn Starkman, vice-chair of the Department of Physics, explained what we know—and don’t know—about dark matter, including the two most prevalent explanations for it: that there is “more stuff [matter] that we don’t see with our telescopes,” or that “Newton’s laws and even [gravity] are wrong on the scale of galaxies and everything bigger.” Starkman explained the latter idea is usually called modified gravity or Modified Newtonian Dynamics.

As seen in The Daily
and Space.com – What is dark matter?