  Scalar field theory with an asymmetric potential is studied at zero
temperature and high-temperature for phi^4 theory with both phi and phi^3
symmetry breaking. The equations of motion are solved numerically to obtain
O(4) symmetric and O(3) cylindrical symmetric bounce solutions. These solutions
control the rates for tunneling from the false vacuum to the true vacuum by
bubble formation. The range of validity of the thin-wall approximation (TWA) is
investigated. An analytical solution for the bounce is presented, which
reproduces the action in the thin-wall as well as the thick-wall limits.
