MOdified Newtonian Dynamics (MOND)
Just read about Milgrom's MOND theory!
Either the universe does indeed have dark matter and dark energy, or F=ma isn't exactly correct! And then no need for those dark things...Well, the difference would involve very big distances.
Apparently, it's a theory dating back to the 80's....but it comes back because it respects recent observations such as gravitational lenses, the inhomogeneities observed by WMAP...The Planck satellite should settle the matter.