Facts and guesses
Apparently, according to Katie Melua,
"There are nine million bicycles in Beijing,
That's a fact, It's a thing we can't deny".
Not only that, but
"We are twelve billion light years from the edge,
That's a guess, No-one can ever say it's true"
I doubt anyone has ever counted all the bicycles in Beijing, but we can guess that there might be that many. According to the UN, Beijing has a population of approximately 13.82 million people, so nine million bicycles doesn't sound too crazy. You could argue that there is possibly more evidence to back up the second line than the first. Astronomers have measured the age of the Universe in several different ways and come up with similar answers (13.7 billion light years incidentally), but that doesn't make it a fact. It's not really a guess either, we have quite a bit of proof, but it is still a theory, that's the way science works. It's nice to see light years used as a measure of distance though!