Abstract:
For Newtonian dynamics to hold over galactic scales, large amounts of dark matter (DM)
are required which would dominate cosmic structures. Accounting for the strong obser-
vational evidence that the universe is accelerating requires the presence of an unknown
dark energy (DE) component constituting about 70% of the matter. Several ingenious
ongoing experiments to detect the DM particles have so far led to negative results.
Moreover, the comparable proportions of the DM and DE at the present epoch appear
unnatural and not predicted by any theory. For these reasons, alternative ideas like
MOND and modification of gravity or general relativity over cosmic scales hav e been
proposed. It is shown in this paper that these alternate ideas may not be easily distin-
guishable f rom the usual DM or DE hypotheses. Sp ecific examples are given to illustrate
this point that the modified theories are special cases of a generalized DM paradigm.
