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What happens to a planet if you change one of the things we take for granted? These experiments look at Earth, the Moon and the Sun with simplified physics you can actually turn. They are thought experiments with numbers attached — useful for building intuition, not for predicting a real catastrophe.
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- What If Earth Stopped Spinning? Stop the spin over a time you choose and see the winds and the new length of a day.
- What If the Moon Disappeared? Tonight's tides and darker skies, kept apart from the slow, long-term question of Earth's tilt.
- What If the Sun Disappeared? Sunlight is 8 minutes 19 seconds old, so you'd have a short wait before the dark.
- What If Everyone Jumped? Why billions of people jumping at once barely nudges the planet.
- What If Earth's Gravity Doubled? Twice the gravity, and what it does to your weight and how high you can jump.
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What If Earth Stopped Spinning?
Remove Earth's spin over a time you choose and see the leftover eastward speed, the winds, and the new length of a day.
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10 interactive experiments.
What If Earth Stopped Spinning?
Remove Earth's spin over a time you choose and see the leftover eastward speed, the winds, and the new length of a day.
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What If the Moon Disappeared?
Take the Moon away and separate tonight's tides and darker skies from the slow, million-year question of Earth's tilt.
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What If the Sun Disappeared?
Light and gravity from the Sun are 8 minutes 19 seconds old. After that, Earth goes straight and the dark is not instant ice.
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What If Earth's Gravity Doubled?
Scale surface gravity and compare weight and jump height. Same takeoff energy, higher g, lower flight.
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What If Earth Had Two Moons?
Add a second moon with a mass ratio and a distance in lunar units. Tidal forces add in a simplified way — not a three-body simulation.
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What If Everyone Jumped?
Eight billion people take the same standing jump. Earth's recoil is real — and so small the planet does not notice, especially once everyone lands.
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What If Earth's Atmosphere Disappeared?
Dial remaining pressure from today's sea-level air toward vacuum. Sound, sky, boiling water and radiation change on different clocks.
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What If Earth Rotated Twice as Fast?
Spin Earth faster and watch the day shrink, equatorial speed rise, and a small centrifugal lightening at your latitude.
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What If Everyone Disappeared?
A scientific succession timeline: power, water, plants, buildings. Pick a year and see what that moment would look like.
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What If Earth Was Twice as Large?
Enlarge Earth's radius two ways: keep density (g rises with R) or keep mass (g falls as 1/R²). The assumption is the whole experiment.
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How the world experiments work
Each page changes one thing about the Earth, Moon or Sun, then follows a simplified physical model to see what changes. You can turn the main input and watch the results move. The maths is shown, so you can see why a stopped Earth means huge winds or why everyone jumping does next to nothing.
Which one to try first
If you're picking one, try the Earth stopping spinning: it's the most dramatic and the easiest to picture. The Moon and Sun disappearing are good next steps, as they show how much we lean on both without noticing. For something lighter, everyone jumping at once is a nice lesson in just how big the planet is.
Big what-ifs, simple models
Here's the catch: real planets are complicated, and these models keep things simple so you can follow them. They're for building intuition, not predicting a real catastrophe. Sources and assumptions are listed on every page if you'd like to dig deeper.