Method
How the numbers are computed
The equation is a way of talking about the tree, not a literal multiplication of independent numbers. The actual computation plays the tree out many thousands of times and counts how often each end state is reached.
How a run works
For each longevity scenario, the tree is played out many thousands of times. Nodes are visited in dependency order. A world event whose dependencies all came true comes true with its probability for that scenario, and otherwise stays false. Nodes already resolved in the real world are fixed at their outcome. Choice points are never sampled: each fork is set to the option John currently plans to take. A tier is reached when everything it requires came true, and the number reported for a tier is the fraction of play-throughs that reached it.
Every probability on a node is conditional: it is the chance the node resolves yes before the scenario's window closes, given that its dependencies resolve. That is the number a person can actually estimate ("if we have cheap launch, how likely is orbital manufacturing at scale by 2070?"), and it is what the dependency order makes honest.
The decision comparison repeats the run once per option at each choice point, with the other options forced off, and reports how far each option moves the headline number from the current plan. The difference between the runs is the value of the decision, and it is what makes the project a decision tool rather than a forecast only.
The full methodology document, including the calibration score (the standard measure of how well
probabilities match outcomes, computed on resolved leaves each year), is roadmap step 12 and is rendered
here at website step 23. Until then, the compute script itself is the reference:
scripts/compute.py.
The five longevity scenarios
The deadline is John's expected date of natural death, and it is not a constant, because longevity research moves it. So the whole tree is run once per scenario, and a node's probability may never fall as the window lengthens.
| Key | Scenario | Window closes |
|---|---|---|
baseline | Baseline, no extension beyond current trends | 2071 ± 8 (refined 2026-09-08) |
moderate | Moderate extension | 2080 |
strong | Strong extension | 2095 |
radical | Radical extension, a 150-year life | 2136 |
open | Escape velocity, window open | no deadline |
The Contact Clause, beside the equation
Underneath the whole project is a dream with no practical place in the product: communing with a vastly superior intelligence of a different perspective. Drake's equation was about contact with other minds; the Belt Equation is about becoming the kind of people who could be out there to make it. The Contact Clause reconnects them. It is a term C, published beside the equation and never multiplied into it, because nothing about the Belt depends on it. Each rung follows the same rule as every node: it is in only because it has a resolution criterion.