If you think it would take a long time for 85 billion people to post to this thread, consider the alternative! It will also take a long time for 85 billion people to not post to this thread!

It is said that the current world population of 6.5 billion represents one-fifth of the people who have been alive in the last five thousand years. That means that in five thousand years there have only been 32.5 billion people who have not posted to this thread. In order for 85 billion people to have not posted to this thread, we'll have to wait for another 52.5 billion people to have been born and lived their lives without having posted to this thread.

How long will that take? I dunno. It probably won't take another five thousand years, but it ain't gonna happen next week.