  The quantum inequalities, and the closely related quantum interest
conjecture, impose restrictions on the distribution of the energy density
measured by any time-like observer, potentially preventing the existence of
exotic phenomena such as Alcubierre warp-drives or traversable wormholes. It
has already been proved that both assertions can be reduced to statements
concerning the existence or non-existence of bound states of a certain
1-dimensional quantum mechanical Hamiltonian. Using this approach, we will
informally review a simple variational proof of one version of the Quantum
Interest conjecture in (3+1)-dimensional Minkowski space.
