"regarding the compatibility of free will and determinism, some compatibilists have argued that the human soul is very much separate from the outside world"
this is speculative obviously, but he argue that the soul is entangled with the microtubs in our brain or something..
https://en.wikipedia.org/wiki/Stuart_Hameroff
I think it's an idea associated with singularity. That a specific cause exists. Events become as a chain link, one following the other, influenced only by it's immediate past.
Finding a specific cause works for material observations. With abstract thought the topic turns to discussions of Origins. It's a philosophical question. Science has nothing to say except to make the measurements.