The universe remains a mysterious place, and one of the biggest mysteries confronting astronomers today is that "the amount of mass we can see through our telescopes is not enough to keep galaxies from spinning apart." Since the 1930's, this shortfall has been covered by dark matter, a hypothetical substance which has never actually been observed. On the Weizmann Wave, we can consider an alternative called MOND (Modified Newtonian Dynamics) which "posits that gravity works differently on the intergalactic scale." In fact, University of Maryland researcher Stacy McGaugh recently published a paper that says for low surface brightness galaxies, MOND works better than dark matter. But on Starts With a Bang!, Ethan Siegel says MOND was designed to work for rotating galaxies, and "the problem is it doesn't do anything else." To successfully model large-scale phenomena such as the cosmic microwave background radiation, there needs to be five times more mass in the universe than we can observe. But what or where it is, nobody knows.