Why are computers not sentient yet?
Computers have not been around for very long (although perhaps longer than one might think). They are now, however, ubiquitous and clearly here to stay. It has something to do with their universality, which is also why these things are getting more and more powerful at every instant. Given how powerful they already are, in a sense it's flattering that no machine -that we know of- has yet reached consciousness. But how long will this last? How will we know when a machine really becomes conscious? What does this word even mean? How will this new consciousness arise? And what will happen next?
The usual answers to these five questions are, in order:
1. not long;
2. with a Turing test or a variant of it;
3. we don't know but we don't need to know for the Turing test;
4. we have no idea;
5. something big, hopefully nothing bad.
On the last two questions however, screenwriters are actually not short of ideas.