The Stagnation Hypothesis

I was sceptical about the stagnation hypothesis when i first heard it, and have since warmed up to it. I really got into it looking at the last 200 or so yearsand contrasting those with the thousands of years before. Whether progress has slowed down in the past is actually even less important than whether or not it could be sped up in the future. And sort of what are the range of possible futures? How much might it slow down? How much Might It Slow Down? What control do we have over this? Those are the questions i'm concerned with.