Equation: phi_tt = laplacian(phi) - m^2 phi - lambda phi^3 (units c = hbar = 1, V = m^2 phi^2/2 + lambda phi^4/4). Dispersion of free waves: omega^2 = k^2 + m^2. Leapfrog integration, 96 x 96 lattice. A wave packet is a classical stand-in for a quantum of the field.