General Relativity and Cosmology: Unsolved Questions and Future
  Directions
  For the last 100 years, General Relativity (GR) has taken over the
gravitational theory mantle held by Newtonian Gravity for the previous 200
years. This article reviews the status of GR in terms of its self-consistency,
completeness, and the evidence provided by observations, which have allowed GR
to remain the champion of gravitational theories against several other classes
of competing theories. We pay particular attention to the role of GR and
gravity in cosmology, one of the areas in which one gravity dominates and new
phenomena and effects challenge the orthodoxy. We also review other areas where
there are likely conflicts pointing to the need to replace or revise GR to
represent correctly observations and consistent theoretical framework.
Observations have long been key both to the theoretical liveliness and
viability of GR. We conclude with a discussion of the likely developments over
the next 100 years.
