Pushed to their limit, these considerations lead to the
anthropic principle (see [5, 6, 7] and references therein):
there is a selection principle for our Universe to have a
much lower vacuum energy than expected on dimensional
grounds. Such a rationale is popular in the context
of theories with multiple universes or multiverses,
such as string theory (with the many string vacua) or
eternal inflation (with the many bubbles which are not