Alternatives to Dark Matter and Dark Energy

We review the underpinnings of the standard Newton-Einstein theory of gravity, and identifywhere it could possibly go wrong. In particular, we discuss the logical independence from eachother of the general covariance principle, the equivalence principle and the Einstein equations, anddiscuss how to constrain the matter energy-momentum tensor which serves as the source of gravity.We identify the a priori assumption of the validity of standard gravity on all distance scales as theroot cause of the dark matter and dark energy problems, and discuss how the freedom currentlypresent in gravitational theory can enable us to construct candidate alternatives to the standardtheory in which the dark matter and dark energy problems could then be resolved. We identifythree generic aspects of these alternate approaches: that it is a universal acceleration scale whichdetermines when a luminous Newtonian expectation is to fail to fit data, that there is a globalcosmological effect on local galactic motions which can replace galactic dark matter, and that tosolve the cosmological constant problem it is not necessary to quench the cosmological constantitself, but only the amount by which it gravitates.