Phantom singularities and their quantum fate: general relativity and
  beyond
  Cosmological observations allow the possibility that dark energy is caused by
phantom fields. These fields typically lead to the occurrence of singularities
in the late Universe. We review here the status of phantom singularities and
their possible avoidance in a quantum theory of gravity. We first introduce
phantom energy and discuss its behavior in cosmology. We then list the various
types of singularities that can occur from its presence. We also discuss the
possibility that phantom behavior is mimicked by an alternative theory of
gravity. We finally address the quantum cosmology of these models and discuss
in which sense the phantom singularities can be avoided.
