If I use a simple algorithm to generate all the numbers from 000,000,000 to 999,999,999, is there a rule for determining how many of these digit sequences are "random"? Slightly more complex algorithms generate the irrational numbers. Are these digit sequences random? For any finite length of the digit sequence of an irrational number, the next digit is determined, not random. It would appear that a true random number generator must be based on something that can be safely said to be not determined by any algorithm, such as a quantum level physical process. Does this take the notion of a "random variable" from mathematics to physics?