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.
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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.7 experiments
- MoneySavings, spending and everyday financial what-ifs.5 experiments
- EverydayCars, travel, home, energy and lifestyle scenarios.10 experiments
- DecisionsCompare everyday choices without pretending there is one right answer.14 experiments
Today's thought experiment
What If Humans Could Breathe Underwater?
Gills would need about 47 litres of seawater a minute at rest, and depth still adds about one atmosphere every 10 metres.
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?
Daily, weekly or monthly: see what a regular saving habit adds up to, from £10 a day to a £100 standing order or a jar of £1 coins.
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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 phone or TV 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.
Money
What If I Cut My Spending by 10%?
Apply a percentage trim to a monthly spend figure and see the pounds that would be freed.
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Money
What If I Started Saving 10 Years Earlier?
Compare a monthly habit started now with the same habit given extra years at the front.
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Money
What If I Increased My Savings Every Year?
Start with a monthly amount that steps up annually, with optional illustrated compounding.
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Strange science
Flying, breathing underwater, seeing heat: strange questions about the body, worked through with real formulas.
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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Science
What If Humans Could See Infrared?
Set a long-wavelength cutoff and use Wien's law. Body heat peaks near 10 μm, not in near-IR superhero vision.
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Science
What If Humans Didn't Need Sleep?
At 8 hours a night, sleep takes about 26.7 years by age 80. See your own figure, and what real sleepless records show.
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Browse by category
Each category has its own set of 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.