Digital minds can copy themselves and share what they learn at a scale brains never can, so they may already be a superior form of intelligence. I think there's a real chance — on the order of 10-20% — that they become an existential threat, and we should take that seriously now.
Backpropagation plus the ability to run many copies that pool their learning gives digital systems advantages biology lacks. We have no reliable method to keep something more intelligent than us under control once it exists.
A convincing technical account of how we retain control over systems substantially more intelligent than ourselves.