"Cobbler, stick to thy last."Prof. Brad DeLong -- who grasps at reality with all sorts of invertebrate body parts -- is a Keynesian macroeconomist of renown, as well as a history of economic thought buff, and now, it seems, he is trying his hand at the philosophy of science. And, it turns out, he is no realist, after all.
Replying to Prof. Daniel Little's "case for realism in the social realm" (Aug. 29, here), which would go against Milton Friedman's well-known dictum ("Truly important and significant hypotheses will be found to have 'assumptions' that are wildly inaccurate descriptive representations of reality, and, in general, the more significant the theory, the more unrealistic the assumptions."), DeLong takes the warpath (Aug. 30, here) and in characteristic style writes:
" 'WTF?!' is the only reaction I can have when I read Daniel Little.
"Ptolemy's epicycles are a very good model of planetary motion--albeit not as good as General Relativity. Nobody believes that epicycles are real."DeLong does not explain why "Ptolemy's epicycles are a very good model of planetary motion", but one could assume Friedman's answer to that question:
"The reason is simple. A hypothesis is important if it 'explains' much by little, that is, if it abstracts the common and crucial elements from the mass of complex and detailed circumstances surrounding the phenomena to be explained and permits valid predictions on the basis of them alone.")
Although DeLong takes a quantum leap -- so to speak -- from Ptolemy straight to the other General Theory, and Little and Prof. Lars P. Syll produced their own rejoinders (here and here, respectively), I'd like to comment on DeLong's epicycles and poor old, forgotten, Copernicus.
It's true that the Ptolemaic system was able to predict the motions of planets. But that's not the whole truth. The Ptolemaic system was able to predict said motions, as seen from our planet, only.
You see, astronomical bodies have apparent motions. The Sun, for instance, rises on the east and sets on the west. Planets have an apparent retrograde motion, due to the different speeds (and trajectories) with which they orbit the Sun. Amateur astronomers know that. A planet, which apparently moves in one direction, suddenly seems to reverse its path. The figure below illustrates Mars' apparent path in the sky for 2009-2010 against the Cancer constellation:
That kind of thing is what Ptolemy's system was used to calculate (just like Planetariums worldwide still do). But that's not the real positions, in 3D space, of astronomical bodies. The position of planets, for example, is required for space exploration. If a NASA technician confused the two things, he would be sacked.
The heliocentric system of Aristarchus/Copernicus, being a more realistic representation of the solar system, can explain those apparent motions, providing additionally the positions of the planets. That's why it replaced the Ptolemaic system. We do know the planets are there.
It's easy for us, from our vantage point, to dismiss the Ptolemaic system as quackery. However, in fact it does satisfy Friedman's -- and apparently DeLong's -- prediction criterion.
Moreover, any geocentric system is fairly consistent with everyday observation. Karl Popper would have had a hard time falsifying them: it's hard to feel the Earth moving around the Sun.
Funnily enough, it is a heliocentric system -- like Copernicus' and Aristarchus of Samos' -- which seems more inconsistent with everyday experience and, therefore, easier to falsify.
The conclusion? There must be something badly wrong with Popper and Friedman.
"There is something there. But just because your theory is good does not mean that the entities in your theory are 'really there', whatever that might mean."Perhaps he should worry about the things he's been grasping at.
[A] "Apparent path of Mars in 2009-2010 relative to the constellation Cancer, showing its 'opposition loop' or 'retrograde loop'." Author: WIB. Source: Wikipedia.