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# Brad DeLong's Grasping Reality 2019-11-02 23:36:16

Summary:
Doug Jones: Copernicus Versus the Scientific Method https://logarithmichistory.wordpress.com/2019/11/02/copernicus-versus-the-scientific-method-5/: 'Ptolemy needed to assume that the five planets (not counting the sun and moon) have both cycles (the big circles) and epicycles (the little circles).... Some of the cycles and epicycles vary independently, while others are exactly tied to the motions of the sun. For Mercury and Venus, the epicycles vary independently, taking different periods of time (88 days, 225 days) to complete a circuit. Their cycles, by contrast, take exactly one Earth year to complete a circuit. Furthermore, the deferent, the point at center of each epicycle, is always exactly in line with the sun. For Mars, Jupiter and Saturn on the other hand, it’s the other way

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Doug Jones: Copernicus Versus the Scientific Method https://logarithmichistory.wordpress.com/2019/11/02/copernicus-versus-the-scientific-method-5/: 'Ptolemy needed to assume that the five planets (not counting the sun and moon) have both cycles (the big circles) and epicycles (the little circles).... Some of the cycles and epicycles vary independently, while others are exactly tied to the motions of the sun. For Mercury and Venus, the epicycles vary independently, taking different periods of time (88 days, 225 days) to complete a circuit. Their cycles, by contrast, take exactly one Earth year to complete a circuit. Furthermore, the deferent, the point at center of each epicycle, is always exactly in line with the sun. For Mars, Jupiter and Saturn on the other hand, it’s the other way around. The cycles vary independently (1.88, 11.86, and 29.46 years to make a complete circuit). But the epicycles take exactly one Earth year... [and] the line from deferent to planet is exactly parallel to the line from Earth to Sun.... Copernicus’s model, by contrast, doesn’t just replace five circles (the cycles for Mercury and Venus, and the epicycles for Mars, Jupiter and Saturn) with one (for the Earth going around the Sun). It also automatically explains why the five superfluous cycles show an otherwise unexplained synchronic parallelism. People who read Copernicus 1543 book carefully (not many at first) could see he had a real explanation for something that’s just a mysterious coincidence in Ptolemy.... Solomonoff induction... can explain why Copernicanism is a better theory.... Bayes’ Rule.... And where do scientists get their prior probabilities?... Solomonoff... He argues that we can use the theory of algorithmic complexity, as developed by Kolmogorov.... If your theory were turned into a computer program, how long would the program be? The longer the program, the lower the prior probability, where probabilities fall off exponentially with length of program...

J. Bradford DeLong is Professor of Economics at the University of California at Berkeley and a research associate at the National Bureau of Economic Research. He was Deputy Assistant US Treasury Secretary during the Clinton Administration, where he was heavily involved in budget and trade negotiations. His role in designing the bailout of Mexico during the 1994 peso crisis placed him at the forefront of Latin America’s transformation into a region of open economies, and cemented his stature as a leading voice in economic-policy debates.