What would happen if nobody paid taxes?

Government spending in developed economies typically runs between a third and a half of national output, and nearly all of it is recurrent rather than capital: salaries, pensions, transfers and contracts that fall due monthly. Ending tax receipts does not gradually degrade services, it defaults on them, starting with whatever is paid soonest. Borrowing could bridge a very short gap, but sovereign debt is priced on the ability to tax, so the borrowing capacity would disappear at the same moment as the revenue. Courts and policing are the deepest layer, because contracts and property rights are enforced through them, and without enforcement most commercial activity contracts sharply — which is why states with weak tax capacity tend to have weak markets rather than free ones. The historical cases that approximate this, in states that lost the ability to collect revenue, do not resemble prosperity.

How confident this is

This is a reasoned extrapolation rather than an observation. The mechanism is understood, but the scale of the consequences depends on assumptions that could reasonably be argued differently.

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 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 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.