All of Brian Holtz's Comments + Replies

Indeed! And what about the 7th phase shift? I must be missing something here. We're pointing to just two particular transitions in all of human history. I fear we're calling them "phase shifts" to convince ourselves that there is a simple underlying phenomenon which has law-ordained "phases". How can we assume that there will be a coherent series of N>2 such "phase shifts"? How can we assume that they will follow some simple mathematical function with just a handful of parameters? 

I guess this makes me even more of a singularity skeptic than Hanson... (read more)

1Ege Erdil1y
In general you can't assume anything like this, but you also can't assume that the present growth rate will continue forever (or anything else, really) for similar reasons. The point is that to make forecasts about future economic transitions you need some kind of model, and the model in this post is meant to provide the outside view on how often such transitions have occured. The less controversial version of this, namely people fitting a production function such as f(K,L)=AKαL1−α to the GDP of different countries with L,K,A denoting labor stock, capital stock and total factor productivity respectively, and then assuming some law of motion like Δlog(At+1)=(μ−σ2/2)+σεt is the basis of a whole lot of macroeconomic modeling . For example, the entirety of the real business cycle school probably falls into this category. In my view this is much less plausible and in fact this model is immediately refuted by the data since μ has changed so much over the span of thousands of years. If you don't like this real business cycle inspired model, what do you use instead to make forecasts? Clearly one kind of model you should keep in mind is the phase transition model, and it achieves a much better fit with data at the expense of only two or three parameters over the real business cycle model. I'm not saying you should treat the model's forecasts as gospel (and I don't, my forecasts are not identical to what the model outputs) but it's definitely valuable to see what this type of model has to say. The same goes for Roodman's stochastic hyperbolic growth model. Kurzweil's marshaled trends in individual technologies are highly unreliable because they don't tell us anything about economic transformation directly, and the supposed connections of his measures to such a transformation are quite tenuous. In my view Hanson's paper has a poor methodology and model specification (something I hope to remedy at some point in the future) but his general approach is much more justified beca