Phrase

1. A rhetorical question asked to show that the person asking it neither knows the answer nor knows who might.

   It could be one or the other, or both. Who knows?

   Do you think I'll get married before I turn 30? - Who knows, you might never marry.

2. A rhetorical question asked to express the idea that anything is possible or that anything could happen.

   Who knows? Maybe someday he'll finish writing his book and make lots of money selling it.

   Since she hasn't studied at all I don't think she'll pass the test, but who knows? She might pull a Homer and actually pass; I doubt it though.