From the cosmic appearance rate of grabby civilisations to the statistical silence of our sky — five linked frameworks building a consistent picture of why we don't see anyone, and what that means for OC.
Hanson et al. (2021) divide civilisations into "grabby" (expanding at fraction s of c, permanently colonising volumes) and "quiet" (staying local). The model has three parameters: n (hard steps, ~6 from Earth history), s (expansion speed), and k (appearance rate). At the Hanson best-estimate parameters (n=6, s=0.5c), only ~0.1–1% of the observable universe is currently colonised by grabby aliens — consistent with the observed silence. The nearest grabby alien is expected to be ~1–10 Gly away, and their expanding front will reach us in ~1–10 Gyr. This sets the cosmic context: quiet civilisations like ours must exist in the unclaimed gaps.
→ Open Grabby Aliens (n=6, s=0.5c, Hanson estimate) → Open Grabby Aliens (optimistic: n=3, s=0.9c)The Drake Monte Carlo samples all seven Drake factors from probability distributions, running 10,000 simulations to produce a distribution of N (communicating civilisations in the Milky Way). The median N is highly sensitive to the final factor L (civilisation lifetime). At L ~ 10,000 years and optimistic biological factors, the median N ~ 20–100. At pessimistic L ~ 100 years, median N ~ 0.01. The Drake equation is consistent with rare or common civilisations — the uncertainty spans 6 orders of magnitude.
→ Open Drake Monte Carlo (default parameters)The Great Filter represents whatever evolutionary step(s) are astronomically rare, making visible spacefaring civilisations essentially non-existent. The question isn't whether a filter exists (we know one does — we don't see galactic colonisation) but whether it's behind us (making us a rare success) or ahead of us (threatening our future). The Great Filter tool implements Hanson's framework: combine the N estimate from Stage 2 with Hart's colonisation argument to derive the implied filter strength at each step from chemistry to civilisation.
→ Open Great Filter (default)Sandberg et al. proposed that advanced civilisations may "aestivate" — hibernate at low metabolic rates during the hot current epoch, waiting for a cooler, lower-entropy universe where computation is more efficient (the Landauer limit drops with temperature). The computational gain from waiting: L_final × (T_now/T_CMB_final) where T_CMB falls as the universe expands. At current temperatures, every joule buys ~3×10⁹ times fewer bit erasures than it will in 10 trillion years. This means an advanced civilisation that hibernates preserves resources for an astronomically larger payoff.
→ Open Aestivation CalculatorThe Passive SETI tool implements Civiletti's (2025) geometrical framework: if N civilisations each broadcast for duration δ, the probability that at least one signal cone intersects our location at this moment is P(≥1) = 1 − (1 − δ/T_universe)^N. Combining with the Drake N estimate from Stage 2 and the filter constraints from Stage 3: if N ~ 100 and δ ~ 10⁶ years, P ~ 0.7% at any given moment. We are likely missing most signals, not because they don't exist but because of the thin temporal window of overlap.
→ Open Passive SETI (Civiletti framework)