> I think strong AI isn't that far away

But we don't even have intelligent humans yet!

But seriously, I am not sure it can be said to be near or far. Think of it analogously to physical capability. Have we developed 'strong' Artificial Physical Ability? Do we define and measure our physical machines in comparison to human physical abilities? Was the aim of inventing machines just to make artificial humans? No, we develop every kind of physical machine, and in fact we really aim to make all the kinds of things that are not like what humans do.

So why shouldn't informational machines be the same? Is what humans do with information the only thing possible to do, and the only thing we might want to do? No. We won't be making AI to be like humans much, but for a great range of other, non-human-like, applications. Using human intelligence as a single simple measure just will not work or mean anything much.

We think of 'strong AI' as being an ultimate image of the future, but really it diverts us from imagining the much greater range of possibilities the future really holds.

I think his proposition is roughly, that a singular technology grows on an S-curve, but as each one technology slows another picks up the baton and runs with it, and the totality (sum of S-curves) has historically looked exponential, and promises to continue.

Ahh, now that is an interesting angle, but that would suggest that the rate of introduction of new technologies is linear and that every new technology must have a period of exponential growth initially.

(Or I suppose... That the rate of introduction of technologies with initially exponential growth rates is linear. You could ignore those without exponential growth rate provide that a constant number did.)

I think basically at any one time there are a lot of competing new-born technologies, and it's only in retrospect that we can see which of them will go exponential through a feedback cycle of improvement and growing adoption.

It's not so much that technology always goes exponential. It's that in retrospect, we notice the ones that did.

I don't think he predicts exponential growth will continue indefinitely. Where did you get that from?

This line: "Kurzweil calls it the law of accelerating returns: technological progress happens exponentially, not linearly."

He doesn't bracket his law with exponentially to a 'certain point' or 'is currently happening'. He claims it is a law that all technological progress currently happens and will always happen exponentially.

Perhaps I am misreading him, but I interpret predictions as claims that exponential growth will always continue.

Anyway. That aside, You can't use an exponential curve to make predictions about the future if you accept that the curve will end at some point. If you accept the curve will change and you can't know the point of change then you can't use it to make a prediction.