Biology

The headline stands at 0.5% by 2071. If one of these settled tomorrow and nothing else changed, the whole tree is played out again and the headline lands where the figure says. This is the site saying in advance what a milestone is worth, before it happens: when one of them lands, the entry that records it quotes what was predicted here. These come from playing the tree out 20,000 times per scenario, which is a throw of the dice: anything smaller than about 0.10 points is inside the noise, so read the order rather than the last decimal.

• A crew off Earth lives for a year with most of its food produced on site and its water and air recycled +0.1 points if yes 0.5% today · 0.6% if it happened · 0.0% if it turned out no (−0.5 points)
• A staple crop is grown from seed to harvest off Earth +0.1 points if yes 0.5% today · 0.6% if it happened · 0.0% if it turned out no (−0.5 points)
• A crew lives for a month in a spinning spacecraft that produces artificial gravity +0.1 points if yes 0.5% today · 0.6% if it happened · 0.5% if it turned out no (too small to tell apart from chance)
• A major operation under anaesthesia is performed off Earth and the patient survives too small to tell apart from chance if yes 0.5% today · 0.5% if it happened · 0.0% if it turned out no (−0.5 points)
• People live for a year in a spinning habitat with Earth-normal gravity too small to tell apart from chance if yes 0.5% today · 0.5% if it happened · 0.4% if it turned out no (too small to tell apart from chance)
• A shielding system flown in space cuts the deep-space radiation dose to a crew by half too small to tell apart from chance if yes 0.5% today · 0.5% if it happened · 0.0% if it turned out no (−0.5 points)
• A person lives a full year in partial gravity and comes home without disqualifying harm too small to tell apart from chance if yes 0.5% today · 0.5% if it happened · 0.4% if it turned out no (−0.1 points)
• Humans can live off Earth long term, by partial gravity or by a spinning habitat too small to tell apart from chance if yes 0.5% today · 0.5% if it happened · 0.0% if it turned out no (−0.5 points)

3 other open steps under this factor are worth nothing to the headline, because the headline does not rest on them at any remove: A mammal is conceived, born, and weaned in partial gravity, A child is born off Earth and raised there through early childhood, A treatment is approved that makes people substantially more resistant to chronic space radiation. Most belong to the tiers above the one the headline asks about.

• Forty-one steps had their criteria tightened so that two readers would agree when each has happened, with no number moved for that alone 2026-09-20 The tree itself changed
• Nine steps were added to the tree, seven of them new requirements on the chain, which is most of why the headline fell in this run 2026-09-20 The tree itself changed
• A child born off Earth no longer needs the partial-gravity milestones if the child lives in an Earth-gravity habitat 2026-09-20 The tree itself changed
• A person living a year in partial gravity and coming home fit was raised: the bar is one person, at any gravity in the range, with repeated attempts 2026-09-20 Changed my mind
• A year in a spinning habitat at Earth gravity was raised: given the spin test and hundred-metre assembly, ten people for a year is a deployment, not a breakthrough 2026-09-20 Changed my mind
• A year off Earth on mostly home-grown food, water and air came down: shipping food is cheap and farming is a settlement-scale project 2026-09-20 Changed my mind

• A crew lives for a month in a spinning spacecraft that produces artificial gravity B-crewed-spin-gravity-demonstration
  70%baseline scenario, as of 2026-09-08
  By 2031 Not yet
• A mammal is conceived, born, and weaned in partial gravity B-mammal-born-and-weaned-in-partial-gravity
  80%baseline scenario, as of 2026-09-08
  By 2031 Not yet
• A staple crop is grown from seed to harvest off Earth B-staple-crop-grown-from-seed-to-harvest-off-earth
  75%baseline scenario, as of 2026-09-20
  By 2031 Not yet
• A crew off Earth lives for a year with most of its food produced on site and its water and air recycled B-closed-loop-life-support-year-off-earth
  35%baseline scenario, as of 2026-09-19
  Within 20 years Not yet needed for Settlement
• A major operation under anaesthesia is performed off Earth and the patient survives B-major-operation-under-anaesthesia-performed-off-earth
  45%baseline scenario, as of 2026-09-20
  Within 20 years Not yet needed for Settlement
• A person lives a full year in partial gravity and comes home without disqualifying harm B-human-year-in-partial-gravity-without-disqualifying-harm
  45%baseline scenario, as of 2026-09-19
  Within 20 years Not yet
• A shielding system flown in space cuts the deep-space radiation dose to a crew by half B-shielding-halves-deep-space-radiation-dose
  50%baseline scenario, as of 2026-09-08
  Within 20 years Not yet needed for Slow Expanse
• A child is born off Earth and raised there through early childhood B-human-child-born-off-earth
  15%baseline scenario, as of 2026-09-08
  Whole window Not yet needed for Full Expanse
• A treatment is approved that makes people substantially more resistant to chronic space radiation B-radiation-resistance-treatment-for-humans
  8%baseline scenario, as of 2026-09-08
  Whole window Not yet Long shot
• Humans can live off Earth long term, by partial gravity or by a spinning habitat B-long-term-off-earth-living-by-some-route
  100%baseline scenario, as of 2026-09-08
  Whole window Not yet needed for Settlement
• People live for a year in a spinning habitat with Earth-normal gravity B-earth-gravity-habitat-occupied-for-a-year
  35%baseline scenario, as of 2026-09-19
  Whole window Not yet