  In quantum theory it is generally assumed that there exists a special state
called the vacuum state and that this state is a lower bound to the energy.
However it has recently been demonstrated that this is not necessarily the case
for some situations [5]. In order to clarify the situation we will consider a
"very simple" field theory in the Heisenberg picture consisting of a quanitized
fermion field with zero mass pariticles in 1-1D space-time interacting with a
classical electrical potential. It will be shown that for this example there is
no lower bound to the energy.
