This is an explanatory proposal, not an established fact.
The proposition
Some transition between a lifeless planet and a widely detectable civilization could be very difficult. The argument does not establish which transition, or whether it lies in our past or future.
Supporting argument
The tension between many potential opportunities and limited observable evidence motivates examining bottlenecks.
Counterarguments
Civilizations might be hard to detect, short-lived, non-expanding or outside the searches performed. A lack of detections alone cannot select one explanation.
Origin
Robin Hanson’s 1998 working paper develops the argument linked here.
How could it be tested?
Compare models with observations of life, planetary environments and the reach of actual civilization searches.
Known limitations
The difficult transition is not identified. Conclusions depend on selection effects and assumptions about expansion and detectability.
Sources
The Great Filter — Are We Almost Past It?
Robin Hanson
A theoretical argument about selection effects and difficult transitions; not evidence of a specific cosmic barrier.
Record history
- Version 1 · Oct 2, 2026 — Initial source-led edition