The tree · Contact Clause · World event · Root: on the scale of the whole window
An intelligence not descended from us is detected
A signal or structure that only technology could have made (a technosignature), evidence of life more complex than microbes on another world (a biosignature), or an artefact. Low probability, fully resolvable. The instruments that would find it, a radio array on the far side of the Moon and a telescope at the Sun's gravitational focus, are the kind of large off-Earth projects the rest of the tree makes possible.
What counts as it having happened
A detection of a signal or structure that only technology could have made, of evidence of life more complex than microbes beyond Earth, or of an artefact of non-human origin is confirmed by at least two independent teams and accepted as such in the peer-reviewed record.
Settled by: The peer-reviewed record, two independent confirmations
Probability, by longevity scenario
| baseline2071 ± 8 | moderate2080 | strong2095 | radical2136 | openno deadline |
|---|---|---|---|---|
| 5% | 7% | 10% | 18% | 30% |
Each number is the chance this resolves yes before that scenario's window closes, given that everything it depends on resolves first. Estimated 2026-09-19.
Why these numbers: Sixty years of nothing; the planned instruments widen the search by orders of magnitude but cannot make anything be there.
How it could happen, and where physics would have to give way
Long shots belong in the tree by the first founding rule; the second says they must be written plausibly all the way to the edge of the impossible, with the mechanism named and the breaking point stated plainly.
The mechanism: Instruments improve in steps that are already planned: a far-side lunar radio array shielded from Earth's noise, a telescope placed where the Sun's gravity focuses light from other stars, and spectrographs that read the air of nearby planets. Each step widens what could be seen. If anything is there within reach, one of these finds it; the remaining step is the confirmation by a second team.
The breaking point: Detection needs something to exist within reach and to be visible with the instruments we can build. Sixty years of listening have found nothing, and every model of how common such signals should be rests on guesses. The node cannot be made likelier by engineering alone.
Think this node is wrong, missing a dependency, or estimated badly?
Open an issue about it, or read
how critique gets folded into the tree.
The record itself is data/C-contact.toml in the public repository.