Oh no not another free will thread.

[Edwardo Piet]

They don't know why or how it happens.  The random aspect is a mystery. 

Yes, the seemingly random aspect is a mystery.

But when I say that I think that the only things that can actually be known absolutely is by logic... I'm including mathematics.

The reason why 2+2=4 is because any other result is mathematically impossible. In the same way that the reason why all bachelors are unmarried is because anything else is logically impossible. Math is logic with numbers and logic is math with words. Basically. It's all the same sort of proccess.

So much a mystery, that the prevailing theories are 1) It's truly random.  2) That new instances of reality are created for each event, so both result 1 and result 2 happen.

Sure, it all seems truly random but this is still the experience of reality we're talking about, rather than objective reality. In absolutely objective reality outside of our experience there may be causes for all these seemingly random events but we'll never be able to know absolutely objective reality outside of our experience.