Peter Krautzberger · on the web

kids, exponential growth and 42

Last week, I was lucky enough to attend the W3C workshop on ebooks in NYC. This allowed me to visit some old and very dear friends. In a conversation with one of their kids, I pulled out a classic that I like very much.

Today, I did some fact checking and -- lo and behold -- the answer was not 52 but 42! That is, of course, fantastic.

Anyway, the question I asked was: how thick is an piece of regular office paper if you fold it 52 42 times?

The answer is: it would reach all the way to the moon!

That usually surprises kids (and non-kids) and is a nice example for the surprises of exponential growth. In fact, it also surprises me and I'm always somewhat nervous when a kid takes me up on the offer of checking that the number is actually correct.

For this you first have to decide what paper you're looking at. A piece of A4 paper (I'm German after all) is on average 0.1 mm. That's actually hard to estimate but it's what I eventually found on the interwebs; if you have the time, I invite you to delve into the art of density and calipers.

When you fold it 42 times, it's as if you stacked test pieces of paper on top of each other. So the thickness is x 0.1mm, which is ~439,804 km (and a kilometer is 1,000,000 milimeter).

The moon is on average 384,400km from earth, and 405,410km at its farthest -- so we'll get there no matter what day. If, that is, we could fold a piece of paper 42 times.

For what it's worth, the world record for folding paper is 13 times -- achieved by high schoolers on MIT's campus in 2011.