  We discuss a possible scenario to induce a bubble universe using buildable
bubbles. First, we observe that if there is no violation of the null energy
condition, all bubbles are buildable and do not have inflation if their initial
conditions are assigned along the in-going null surface in an almost flat
background. However, if the null energy condition is sufficiently violated,
then the generation of a bubble universe is possible. Second, the author will
observe that a sufficient violation of the null energy condition may be
possible using a buildable bubble due to the Hawking radiation of a de Sitter
space. Note that buildable bubbles seem surely to be allowed in quantum
gravity. Therefore, if this scenario is correct, the generation of a bubble
universe and the violation of unitarity should be allowed in quantum gravity.
