WorldFeatured
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 would happen if…?
Change the question. See what happens.
Explore strange scientific scenarios, test everyday choices and discover surprising things about your own life.
Explore IfSketch
Half the shelves are strange. Half are useful. Neither is a quiz.
- WorldEarth, space and large-scale hypotheticals.10 experiments
- SciencePhysics, biology and scientific thought experiments.10 experiments
- Your LifeTime, habits, routines and personalised life calculations.10 experiments
- MoneySavings, spending and everyday financial what-ifs.10 experiments
- EverydayCars, travel, home, energy and lifestyle scenarios.10 experiments
- Weird & WonderfulStrange, surprising and highly shareable questions.5 experiments
- DecisionsCompare everyday choices without pretending there is one right answer.17 experiments
Today's thought experiment
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.
Change the variablesChosen from the library by calendar day — not a popularity contest. Tomorrow it will be a different question.
Featured experiments
Six editor's picks — one from each corner of the library.
WorldInteresting
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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Your LifeFeatured
How Much of Your Life Have You Spent Sleeping?
Turn a typical night into years, days and a share of the life you have already lived.
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MoneyFeatured
What If I Saved £10 Every Day?
A rounder daily habit, stretched over more years, with a gentle illustrated rate you can turn off.
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EverydayFeatured
What if I walked instead of drove?
Compare walking a repeated local journey with driving it, using your distance, weekly rhythm and a simplified cost per kilometre.
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ScienceEditor's pick
What If Gravity Stopped?
Weight vanishes; velocity does not. Earth goes straight, air expands, people float. A thought experiment with a timer.
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Your life, in hours
Sleep, work, commuting, screens. The arithmetic is personal because the inputs are yours.
Your Life
How Much of Your Life Have You Spent Working?
Estimate hours, days and years in paid work from your age, start age, weekly hours and holidays.
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Your Life
How Much Time Have You Spent Commuting?
Add up years of two-way journeys from minutes, days per week and holiday weeks.
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Your Life
How Much Time Have You Spent on Your Phone?
Convert daily screen minutes into hours, days and years from the age you started.
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The world, slightly broken
Stop the spin. Lose the Moon. Double gravity. Simplified physics with the assumptions left on.
World
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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World
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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World
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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Money as a habit
Educational estimates. Contributions and illustrated growth are kept apart on purpose.
MoneyTry this
What If I Saved £5 Every Day?
Turn a small daily amount into a running total over the years, with optional illustrated interest.
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Money
What If I Saved £100 Every Month?
A standing-order-shaped habit: monthly amount, years, and an optional illustrated rate.
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Money
What If I Stopped Buying Takeaways?
Price a takeaway habit over the years. About spending, not about diet.
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Weird & wonderful
The questions people actually share. The models stay honest.
Weirdalso in World
What If Everyone Disappeared?
A scientific succession timeline: power, water, plants, buildings. Pick a year and see a sober sketch of that moment.
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Weirdalso in Science
What If Humans Could Fly?
A hover-power estimate from weight and wingspan. Muscle-powered human flight is borderline; history agrees, barely.
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Weirdalso in Science
What If Humans Could Breathe Underwater?
Depth still costs about one atmosphere every ten metres. Gills and oxygenated liquids are different thought experiments.
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Pick a rabbit hole
Each door is a real category with its own experiments.
What IfSketch is
An independent interactive website for curious questions. You change a variable. A transparent model updates. You leave knowing what the number actually means — and where it stops being physics and starts being a sketch.