Contact Process: Directed Percolation Absorbing Transition

Spacetime diagram of infection spreading. Active ↔ absorbing phase transition at λ_c ≈ 3.298 (1D).

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Density ρ
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Phase
0
Timestep
Infection rate λ 3.30
Recovery rate μ 1.00
Initial density 0.50
Contact process: each active site infects neighbors at rate λ, recovers at rate μ. Critical point λ_c/μ ≈ 3.298 (1D DP universality). Below: absorbing state (extinction); above: active phase. Spacetime diagram grows downward — active (infected) sites in purple, extinct in dark. Critical exponents: β≈0.276, ν∥≈1.734, ν⊥≈1.097 (exact in d=1; not mean-field).