  Scalar quintessence seems epicyclic because one can choose the potential to
reproduce any cosmology (I review the construction) and because the properties
of this scalar seem to raise more questions than they answer. This is why there
has been so much recent interest in modified gravity. I review the powerful
theorem of Ostrogradski which demonstrates that the only potentially stable,
local modification of general relativity is to make the Lagrangian an arbitrary
function of the Ricci scalar. Such a theory can certainly reproduce the current
phase of cosmic acceleration without Dark Energy. However, this explanation
again seems epicyclic in that one can construct a function of the Ricci scalar
to support any cosmology (I give the technique). Models of this form are also
liable to problems in the way they couple to matter, both in terms of matter's
impact upon them and in terms of the long range gravitational force they
predict. Because of these problems my own preference for avoiding Dark Energy
is to bypass Ostrogradski's theorem by considering the fully nonlocal effective
action built up by quantum gravitational processes during the epoch of
primordial inflation.
