I agree with you that economics has nowhere near as much predictive power as physics (trained in physics, stuck in the financial-sector as a boring quant - I can testify to both). Nor it has infallible foundations (rational behaviour? game-theory based "utility" maximization? VNM utilities?)
I also agree with you that aggregate demand as a macroeconomic quantity is hard to measure as are many macroeconomic variables. But nowhere does Hayek disprove the existence of aggregate demand (whether business cycles are caused by monetary policy or fiscal policy or some other factor is debatable - their end effect is always on aggregate demand).
But statistical observations of the aggregate often lead to great discoveries and the foundation of a subject. Max Planck's enormous set of highly aggregate experimental data (without him knowing the mechanism by which light operates) led him to formulate the "quantum" hypothesis (ie light is quantized as photons) - which was the founding stone for quantum mechanics and all the great stuff that followed.
We have such numbers in engineering - the Reynold's number, the Nusselt number etc. We don't know how they arise from chaotic microscopic behaviour but we do know these quantities exist. They have a profound effect on the onset of turbulence in fluid flow, onset of convection in heat-transfer and a whole lot more. The effects themselves can be measured and be tallied with a "Reynold's number" of say 3000 (which is again based on conduit dimensions, pressure gradient, viscosity - all measurable quantities but we don't how they tie up together to give rise to turbulence). Never stopped us from making pumps and engines and life better for the world.
As an aside, Hayek's theory and the whole Austrian school of thought is the least empirical of all such branches. So you contradict yourself.
Even Milton Friedman declared himself "an enormous admirer of Hayek, but not for his economics. I think Prices and Production is a very flawed book. I think his [Pure Theory of Capital] is unreadable. On the other hand, The Road to Serfdom is one of the great books of our time." (copied verbatim from Wikipedia).
There is a difference between normative economics (which the political leaders and Paul Krugman propound - ie the "That's how it should be" class) and positive economics (which, as a subject, deals with discovering mechanisms of the economy and searching for empirically verifiable variables that can validate those mechanisms). I think you're confusing the two.
There is a difference between normative economics (which
the political leaders and Paul Krugman propound - ie the
"That's how it should be" class) and positive economics
Well, sure, but there can be no obligation to do that which cannot be done. Let's say you believe that the Federal Reserve's QE and money printing activities are like monkeying around with the number of shares in the cap table, that this nothing to do with the process of wealth creation, and that they downplay the effects of ruinous inflation on economies (viz. Weimar 1924, Argentina 2001). Then the positive and normative are tightly linked. You should not do X (normative) because X will lead to disaster (positive).
I also agree with you that aggregate demand as a macroeconomic quantity is hard to measure as are many macroeconomic variables. But nowhere does Hayek disprove the existence of aggregate demand (whether business cycles are caused by monetary policy or fiscal policy or some other factor is debatable - their end effect is always on aggregate demand).
But statistical observations of the aggregate often lead to great discoveries and the foundation of a subject. Max Planck's enormous set of highly aggregate experimental data (without him knowing the mechanism by which light operates) led him to formulate the "quantum" hypothesis (ie light is quantized as photons) - which was the founding stone for quantum mechanics and all the great stuff that followed.
We have such numbers in engineering - the Reynold's number, the Nusselt number etc. We don't know how they arise from chaotic microscopic behaviour but we do know these quantities exist. They have a profound effect on the onset of turbulence in fluid flow, onset of convection in heat-transfer and a whole lot more. The effects themselves can be measured and be tallied with a "Reynold's number" of say 3000 (which is again based on conduit dimensions, pressure gradient, viscosity - all measurable quantities but we don't how they tie up together to give rise to turbulence). Never stopped us from making pumps and engines and life better for the world.
As an aside, Hayek's theory and the whole Austrian school of thought is the least empirical of all such branches. So you contradict yourself.
Even Milton Friedman declared himself "an enormous admirer of Hayek, but not for his economics. I think Prices and Production is a very flawed book. I think his [Pure Theory of Capital] is unreadable. On the other hand, The Road to Serfdom is one of the great books of our time." (copied verbatim from Wikipedia).
There is a difference between normative economics (which the political leaders and Paul Krugman propound - ie the "That's how it should be" class) and positive economics (which, as a subject, deals with discovering mechanisms of the economy and searching for empirically verifiable variables that can validate those mechanisms). I think you're confusing the two.