A stochastic lattice model where infection spreads to neighbors at rate λ and heals spontaneously at rate 1. At the critical point λ_c ≈ 1.6488 the system exhibits directed percolation universality.
density: 0.000 | t = 0
The contact process on Z² belongs to the directed percolation universality class (Pomeau 1986; Janssen 1981). Below λ_c the active phase dies; above it a stationary infected density persists. Critical exponents: β ≈ 0.584, ν_⊥ ≈ 0.733, ν_∥ ≈ 1.295.