possibility that pointed out by Coleman and E.Weinberg is, even at the classical level one tunes the mass of the scalar field to be zero, quantum correction is able to modify the effective potential, turning the point that enjoys the whole symmetry of the theory from a local minimum to a maximum, and generate new minima (vacuum) at configurations with less symmetry. Therefore spontaneous symmetry breaking can have a pure quantum origin. Another important point about the mechanism is, the potential remains flat with the quantum correction, if we introduce an appropriate counter-term to cancel the mass renormalization, with the minimum/maximum transition induced by a Log-like term. Therefore it gives a natural arena for the idea of slow-roll inflation introduced by Linde, Albrecht and Steinhardt, which is still playing the dominant role among the theories of early universe. Dimensional transmutation In the original paper of Coleman-Weinberg, as well as in the thesis of Erick Weinberg, Coleman and Weinberg discussed the renormalization of the couplings in various theories, and introduced the concept of "dimensional transmutation"---the running of coupling constants renders some coupling determined by an arbitrary energy scale, therefore although classically one starts from a theory in which there are several arbitrary dimensionless constants, one ends up with a theory with an arbitrary dimensionful parameter. The graceful exit problem of old inflation In a paper with Alan Guth, Erick Weinberg discussed the possibility of ending the inflation with thermalization of vacuum bubbles. The original proposal of inflation is, the exponentially growing phase ends via the nucleation of Coleman-de Luccia bubbles with a low vacuum energy, these bubbles collide and thermalize, leaving a homogeneous universe with high temperature. However, as the exponential growth of the near-de Sitter universe dilutes the bubbles nucleated, it is not obvious that the bubbles will really coalesse, in fact Guth and Weinberg proved the following statements: "If the nucleation rate is sufficiently slow compared to the expansion rate, then the probability of any certain point in the universe to lie within an infinite volume bubble cluster will vanish, in another word, bubbles don't percolate the whole universe if the nucleation rate is small" "In any pre-chosen coordinate system, any typical bubble will dominate its own cluster. In other words, for any bubble, the probability for the cluster it belongs to extend beyond this bubble by a large coordinate distance is suppressed when the nucleation rate is small"