The strength of the strong force
It reminds of the alternative to dark matter that is MOND, stating that the law of gravity behaves as 1/r at large distances (as opposed to 1/r2 at our scale) [0]. I personally like it because it seems less ad hoc than to posit the existence of invisible matter, and similar in my mind to the special relativity adjustment. (Do not take this endorsement too seriously, of course.)However: "The most serious problem facing Milgrom's law is that it cannot eliminate the need for dark matter in all astrophysical systems: galaxy clusters show a residual mass discrepancy even when analyzed using MOND. The fact that some form of unseen mass must exist in these systems detracts from the adequacy of MOND as a solution to the missing mass problem, although the amount of extra mass required is a fifth that of a Newtonian analysis, and there is no requirement that the missing mass be non-baryonic." [0][0] https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics