  The averaged null energy conditions (ANEC) states that, along a complete null
curve, the negative energy fluctuations of a quantum field must be balanced by
positive energy fluctuations. We use the AdS/CFT correspondence to prove the
ANEC for a class of strongly coupled conformal field theories in flat
spacetime. A violation of the ANEC in the field theory would lead to acausal
propagation of signals in the bulk.
