Fold a piece of paper 42 times and it would reach the Moon

Take an ordinary sheet of paper, about 0.1 millimeters thick. Fold it in half and it’s twice as thick. Fold again, four times as thick. Keep going, and after just 42 folds the stack would stretch from Earth all the way to the Moon.

It sounds absurd, and that is exactly the point. The trick is exponential growth. Each fold doesn’t add a fixed amount of thickness — it doubles what came before. After n folds, the height is 0.1 millimeters times 2 raised to the power n, and that little exponent does staggering work.

The early folds feel unremarkable. Seven folds gets you a wad about as thick as a notebook; ten folds, roughly the width of a hand. Our intuition, tuned to things that grow by adding, quietly assumes the next fold will add about as much as the last. It doesn’t — each fold contributes more than every previous fold combined. So the doublings compound on top of one another, and the numbers run away fast. By 20 folds the stack is over a million times thicker than the original sheet; by 30 folds, a billion times; by 40 folds, a trillion.

Run the arithmetic to 42 folds and the height passes 439,000 kilometers — comfortably beyond the roughly 384,000-kilometer distance to the Moon. (After 41 folds you’re already closer to the Moon than to the ground, and just nine more folds beyond 42 would carry you past the Sun.)

You can’t actually do it — real paper jams after about seven or eight folds. This is a thought experiment, a favorite in math classrooms precisely because the answer feels impossible right up until you check it. Doubling is quietly one of the most powerful forces in mathematics.