What would happen if half the world's population disappeared?

The intuition that halving the population halves demand and leaves everything twice as plentiful assumes the economy is a warehouse rather than a network. Modern production depends on specialisation: a single missing category of expertise — control system engineers, anaesthetists, refinery operators — stops an entire chain regardless of how much surplus exists elsewhere. Randomly removing half of everyone would leave many critical roles unstaffed simultaneously and many machines without anyone who knows how to run them. Historically the closest analogue is the Black Death, which killed perhaps a third to a half of Europe's population over a few years and did raise real wages for survivors substantially — but that was an agrarian economy with shallow specialisation, and the lesson does not transfer cleanly. The financial system would face a second, separate problem, since debts, pensions and asset prices are all claims on future production by a population that no longer exists.

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 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 lived to 150? It depends entirely on whether those are healthy years — extended lifespan without extended healthspan makes almost everything worse.
• 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.