"It's a fudge factor," says Nieto. "And there's a fudge factor in every galaxy." ...[Stacy] Milgrom, a 57-year-old physicist at the Weizmann Institute in Rehovot, Israel, argues that a fudge factor like dark matter isn't necessary if physicists make just one small tweak to Newton's laws of gravity... Milgrom proposed that Newton's laws might change at these paltry accelerations. Below a transition acceleration equal to one 10-billionth of a meter per second per second... the force of gravity might no longer be directly proportional to acceleration, as decreed by Newton. -- Tim Folger, "Nailing Down Gravity", pp 36-38
All I know is that gravity is my enemy these days.