What would happen if everyone lived to 150?

Two very different futures hide behind the same number. If the extra decades are healthy and productive, the working life could lengthen, pension systems would rebalance, and accumulated expertise would compound in a way no society has experienced. If instead the extra decades are frail, the ratio of care demand to carers rises to a level no health system has ever attempted, and the cost of chronic disease management dominates every budget. Population growth would accelerate sharply under any scenario as deaths fell while births continued, compounding resource pressures. Slower generational turnover has less obvious effects on institutions: property, senior positions and political power would circulate far more slowly, and there is a long-standing argument in the history of science that fields advance partly as their leading figures retire. This is marked speculative because every important consequence depends on human institutional response rather than on biology.

How confident this is

This is speculation. The scenario is far enough outside anything observed that the answer depends heavily on which assumptions you start from — treat it as a thought experiment, not a prediction.

Society

• What would happen if everyone stopped having children? Schools would empty within a decade, the workforce would begin shrinking in about twenty years, and the last human would die in roughly a century.
• What would happen if everyone stopped eating meat? A large drop in agricultural emissions and land use, offset by disruption to a billion livelihoods and some regions with no alternative.
• What would happen if antibiotics stopped working? Routine surgery, chemotherapy and childbirth would all become far more dangerous — this is already happening slowly.
• What would happen if all jobs were automated? The production problem would be solved and the distribution problem would not — nobody has demonstrated the second half.
• What would happen if half the world's population disappeared? Not abundance — the collapse of specialised supply chains, because modern systems need specific people rather than a certain number of them.
• What would happen if the world's population doubled overnight? Food is the binding constraint — global production feeds around 8 billion, and doubling demand cannot be met from existing stocks.
• What would happen if everyone worked a four-day week? Trials generally show output holding steady with better wellbeing — but the results come from office work, not from hospitals or factories.
• What would happen if everyone drove an electric car? Urban air quality would improve immediately; the grid would need roughly a quarter more electricity, and mining demand would rise sharply.
• What would happen if everyone spoke the same language? Trade and science would get modestly easier, and roughly seven thousand languages worth of knowledge would be lost.
• What would happen if nobody paid taxes? Everything funded collectively stops — roads, courts, defence, schools, health systems and pensions — within weeks to months.
• What would happen if all borders opened? Economic models suggest a very large rise in global output, and nobody can model the political response, which is the part that would decide it.