Consider the lattice Z2 that gives you a square grid and each edge is open w probability is p
Let θ(p) is the probability that the connected component that contains the origin is infinite.
Intuitively this should be an increasing function.
pc:=inf{p>0∣θp>0}=21
Idea is that we uniformaly assign a value to each edge, and close edge if value is more that p. Coupling argument.
Extension to Zd, all corresponding pc(d) are strictly
theta grows lineary from pc and drops exponentially as it goes below it. so there is some notion of a sharp phase transition for a lattice of a finite size.
What if origin is not any special vertex, then what is the probability of there existing an infinite cluster in the lattice.