One of my favorite Dilbert cartoons features a lizardlike creature that’s billed as a “random number generator,” but that only ever seems to spit out the number nine. Dilbert asks his guide, “Are you sure that’s random?” The guide replies, “That’s the problem with randomness. You can never be sure.”

It’s funny (at least to me), but is it true? Can you ever be reasonably sure that something is random, in the same sense you can be reasonably sure something is not random (for example, because it consists of endless nines)? Even if a sequence looked random, how could you ever rule out the possibility that it had a hidden deterministic pattern? And what exactly do we mean by “random,” anyway?
http://www.americanscientist.org/iss...int/issue.aspx