What would happen if GPS stopped working?

Satellite navigation systems broadcast an extremely precise time signal, and that signal has quietly become the world's reference clock. Mobile networks use it to synchronise base stations, power grids use it to timestamp phasor measurements across long distances, financial exchanges use it to order transactions to regulatory requirements, and broadcasters use it to keep transmitters aligned. Losing it degrades all of those on different timescales, since most systems hold local oscillators that drift slowly — hours to days of holdover before errors accumulate. The navigation loss is the visible part and the more recoverable one: aviation and shipping retain inertial and radio navigation, and road transport falls back on maps. This is not purely hypothetical, since regional GPS jamming and spoofing are now routine in several parts of the world, and a 2016 ground software error that put a 13-microsecond offset into the constellation caused measurable disruption to telecoms.

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.

Everyday systems

• What would happen if everyone on Earth jumped at the same time? Essentially nothing. All of humanity together is about one ten-trillionth of Earth's mass.
• What would happen if the internet went down? Payments fail first, then logistics — most physical supply chains now depend on network connectivity rather than the other way round.
• What would happen if all the power went out worldwide? Water supply is the first life-critical failure — most tap water is pumped, and pumping stops when the grid does.
• How much space would it take for everyone on Earth to stand in one place? About 2,000 square kilometres — smaller than Luxembourg, and less than twice the area of Los Angeles.
• What would happen if money stopped existing? Trade would collapse to what barter can support, and something money-like would be reinvented within weeks.
• What would happen if all the satellites stopped working? Weather forecasting would lose most of its accuracy beyond a day or two, along with navigation, timing and most long-range communications.
• What would happen if all refrigeration stopped? Food waste would rise enormously and the vaccine cold chain would fail — refrigeration is a public health system, not a convenience.
• What would happen if the water supply stopped? Three days for drinking, but sanitation fails first — waterborne disease is what historically kills people in a water outage.
• What would happen if all digital data was lost? Ownership would be the deepest problem — land registries, bank balances and medical records exist almost entirely as data.