So, you can't really say yet with assurance that there is no cause for it.
Can you ever really find out "with assurance" though? If something truly has no cause then you'll never find a cause, but always wonder if there is a cause.
Kinda sucks, eh?
So far no one has even come close.
Here is a very interesting interview between talk radio host "Infidel Guy" and the astrophysicist Dr. Michio Kaku. In it he talks about QM, M-theory/string theory and some other stuff. Really is fun to listen to.