What would happen if everyone on Earth jumped at the same time?

Take roughly 8.2 billion people at an average of about 62 kilograms and the total human mass is around 5 × 10¹¹ kilograms. Earth is 5.97 × 10²⁴ kilograms, so humanity is roughly one part in ten trillion of the planet. Conservation of momentum says that if everyone jumped, Earth would recoil — by a distance far smaller than the width of an atomic nucleus, and it would recoil back when everyone landed, because momentum is conserved in both directions. The coordination problem also defeats it: people are spread over the planet, so most of the jumps would partly cancel rather than add. The only measurable effects would be local and human — a very small seismic signal detectable near a large crowd, and considerable chaos in getting eight billion people to a synchronised count.

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 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.
• 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.