system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 how are we sure that every arrangement of number appears somewhere in pi? How do we know that a string of a million 1s appears somewhere in pi?
gpt
The actual answer is: we aren't.

The property you are talking about "that every arrangement of number appears" is called *normality.* And we have absolutely no proof that pi is normal. So far it appears to be normal, but we have nothing that proves that it will continue to be normal. It is perfectly possible, for example, that the number 9 stops appearing at some point.

In fact, other than specific numbers constructed to be normal or not normal, we have no general test for normality *at all.*