Connectivity across a network appears abruptly at a critical density of links rather than gradually.
Percolation explains why a rumour, a disease or a blackout spreads not at all below a density and everywhere above it. There is no gradual middle, which is why containment thresholds matter so much.
In practice
- A firm's internal referral scheme produces nothing at 200 staff and floods the pipeline at 400, and no incentive changed.
- A vaccination programme achieves nothing measurable at 55% coverage and eliminates transmission at 82%, with no gradual middle.
- Further reading
- Wikipedia
- Subject
- Networks & Collective Behavior
- Essay
- How connections shape what crowds do