This appears to be an unpopular idea on hn, but: We are nowhere close to developing sentient machines. We have made no progress toward it, we're not getting closer. Statistical optimization and sentience are parallel lines. No matter how far you travel down one, you don't get any closer to the other.

If "evil killer robots" are created, it won't be because of advances in big data or deep learning or any other buzzword. It'll happen independently, potentially aided by current state of the art techniques but not because of them. It could happen at any time, some guy in his basement could be on the verge of a breakthrough as we speak. But google's ability to detect cat faces or Watson's winning on jeopardy are not signs of a coming apocalypse. It's highly unlikely that we can cluster or gradient descent our way to human level of intelligence, no matter how many cores or hidden layers are used.

This whole "famous people are worried about AI" thing is understandably media friendly, but it's a bit of a distraction. Fortunately the majority of active researchers aren't taking it seriously at all.