If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare

Authors: Robin Hanson, Daniel Martin, Calvin McCarter, and Jonathan Paulson

Background: The Drake equation has been used to estimate the density of hard-to-see “quiet” aliens. We instead estimate easy-to-see “loud” aliens. 

Objective: To estimate and find implications of a model of “grabby” civilizations (GC), who expand fast and long, and change their volumes’ appearances. To motivate this model by estimating human earliness. 

Methods: Using a model of star formation, habitability, and advanced life arrival via hard steps, we estimate that humans are very early, unless GCs set a deadline. We fit a three parameter model of GCs via: 1) arrival power of 3-9 from the number of hard steps in Earth history, 2) arrival constant from assuming inform distribution over the rank of today among GC origin dates, and 3) expansion speed > c/2 from our not seeing any GC volumes in our sky. We simulate this model to get distributions over outcomes, and how they vary with model parameters. 


  • 40-50% of universe volume filled by GCs on average at GC origin dates.
  • ~200Myr – 2Gyr till we meet GC, if we become GC
  • ~10^5- 3*10^7 galaxies in each GC controlled volume
  • If GCs arise from non-grabby civilizations (NGCs), a depressingly low transition chance (< ∼10^−4) seems required to expect even one other NGC ever active in our galaxy.

Conclusions: Existing data are sufficient to motivate and estimate a model of loud aliens, saying where they are and when we will see or meet them.