Oh no not another free will thread.

[henryp]

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

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.

Regarding 2, not quite (if we're talking about the Many Worlds Interpretation, that is). It's not like new instances are being created for each event, more like there are preexisting worlds for each instance of the "collective event". The branches aren't being formed as we speak, they exist already and instances of us are following these various branches along the way based on some predetermined pattern.

So, what's the smallest possible unit of time?