The Number
My prompt:
I've been thinking about cataclysms.
Say humanity faces the prospect of a civilisation-ending disaster - a planet-killing asteroid hurtling towards Earth, for example - and say that disaster is x years away (from the present day). What, given our current technological and organisational capabilities, is the smallest value of x compatible with our survival?
The disaster will be a discrete event rendering Earth instantly and irreversibly uninhabitable. Survival will necessarily involve leaving the planet.
Criterion for survival: at least 100 million humans in the short-term and the subsequent persistence of human civilisation for at least a few centuries.
Given the uncertainty inherent in projections of technological progress, it may be useful to
1. Outline a number of different scenarios and
2. Assume that the prospect of annihilation focuses minds and leads to several Manhattan Project-like initiatives.
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Responses: GPT-5 Thinking, Gemini 2.5 Pro
