  Tunneling in quantum field theory is worth understanding properly, not least
because it controls the long term fate of our universe. There are however, a
number of features of tunneling rate calculations which lack a desirable
transparency, such as the necessity of analytic continuation, the
appropriateness of using an effective instead of classical potential, and the
sensitivity to short-distance physics. This paper attempts to review in
pedagogical detail the physical origin of tunneling and its connection to the
path integral. Both the traditional potential-deformation method and a recent
more direct propagator-based method are discussed. Some new insights from using
approximate semi-classical solutions are presented. In addition, we explore the
sensitivity of the lifetime of our universe to short distance physics, such as
quantum gravity, emphasizing a number of important subtleties.
