  It has been argued that a particular type of quantum-vacuum variable $q$ can
provide a solution to the main cosmological constant problem and possibly also
give a cold-dark-matter component. We now show that the same $q$-field may
suggest a new interpretation of the big bang, namely as a quantum phase
transition between topologically inequivalent vacua. These two vacua are
characterized by the equilibrium values $q=\pm \, q_{0}$ and there is a
kink-type solution $q(t)$ interpolating between $q=- q_{0}$ for $t\to -\infty$
and $q= +q_{0}$ for $t\to \infty$, with conformal symmetry for $q=0$ at $t=0$.
