Think of a random number between one and ten. Most likely, you chose seven—so exactly how random was your choice? Turns out that generating a truly random number is more difficult than you might think—but this video should help you get to grips with the problem.

Truth is, finding a process that spits out purely random digits isn't so easy. But it's just about possible with a bit of mathematics and the help of, uh, a small lump of radiative material. [YouTube]