Modified Newtonian Dynamics (MOND). It's been the dissenting voice in the modern Great Debate about dark matter.

On one side are the dark matter scientists who think there's a vast category of phenomenon out there FAR beyond our current science. That the universe is far larger and more complex than we currently know, and so we must dedicate ourselves to exploring the unexplored. The other side, the

On the other you have the MOND scientists, who hope they can prevent that horizon from flying away from them by tweaking the math on some physical laws. It basically adds a term to our old physics equations to explain why low acceleration systems experience significantly different forces than the high-acceleration systems with which we are more familiar -- though their explanations for WHY the math ought be tweaked I always found totally unsatisfactory -- to make the current, easy-to-grock laws fit the observations.

With the big problem being that it doesn't work. It explains some galactic motion, but not all. It sometimes fits wide binary star systems kind of OK, but more often doesn't. It completely fails to explain the lensing and motion of huge galactic clusters. At this point, MOND has basically been falsified. Repeatedly, predictions it made have failed.

Dark matter theories -- that is, the theories that say there are who new categories of stuff out there we don't understand at all -- still are the best explanation. That means we're closer to the starting line of understanding the cosmos instead of the finish line many wanted us to be nearing. But I think there's a razor in there somewhere, about trusting the scientist who understands the limits of our knowledge over the one who seems confident we nearly know everything.