Evidence for Dark Matter
- Known Unknowns
“As we know, There are known knowns.
There are things we know we know.
We also know There are known unknowns.
- That is to say We know there are some things
We do not know.
- But there are also unknown unknowns,
The ones we don't know We don't know."
• -- Donald Rumsfeld, Secretary of Defense,
February 12, 2002, Department of Defense news briefing