What would happen if all digital data was lost?

The immediate losses are obvious and recoverable in principle: communications, media, software. The unrecoverable losses are the records that constitute rather than describe things. A bank balance is not a report of money sitting somewhere, it is the money; a land registry entry is what property ownership consists of in most jurisdictions; a medical record is the only account of what was done to a patient and why. Losing those does not damage a system, it dissolves the underlying claims, and the paper backups that would once have reconstituted them have largely been retired. Scientific and engineering knowledge is comparatively safe because it is published redundantly across many institutions and still exists on paper in libraries. The reason this is extrapolated rather than speculative is that the mechanics are well understood from smaller cases — organisations that lose their records without backups generally do not recover, and the pattern scales.

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 GPS stopped working? Timing, not navigation, is the real dependency — mobile networks, power grids and financial systems all use GPS clocks.
• 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.