The whole computing power doubling every 18 months theory has been mostly accurate, but what's really terrifying is the exponential growth. If processing power continues to grow at the rate it's currently growing, we could soon be in possession of computers more powerful than the human brain. AIIIIEEEE...
This interesting little video gives a visual demonstration of this, comparing the volume of Lake Michigan to the number of calculations per second our brain can handle. The lake slowly filling represents how quickly computational power is catching up to brain power. What's interesting is just how rapid the tail end of progress is, mostly because of exponential growth.
Folks, Skynet will become self aware. There's nothing we can do about this. We can only pray to our primitive gods for mercy.