Epicycle

Financial cosmology The JC’s guide to theoretical physics in the markets.™ →Go uptown An ad hoc hypothesis yesterday. Index: Click ᐅ to expand: Cosmology Lexophysics Tell me more Sign up for our newsletter — or just get in touch: for ½ a weekly 🍺 you get to consult JC. Ask about it here.

In Ptolemaic and other geocentric astronomies, epicycles were necessary features of orbital trajectories. They were needed to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets and the presupposition that they were all orbiting the earth, to explain the fact that they weren’t going round in circles like you would expect, but in weird, eccentric wobbly orbits.

In a nutshell the theory imagined epicycles to be little mini orbits around the large orbits each body was taking around the earth, and when that didn‘t quite fit either, even smaller mini-orbits around the mini orbits, around the main orbit. very twisty and turny, but still calculable.

Of course it later became apparent that the planets weren’t orbiting the Earth at all, but were prescribing simple, lazy ellipses around the sun.

Why mention this on a wiki largely devoted to complaining about modern legal practice in financial services? Because of its metaphorical power, of course. The existence of epicycles was classic “ad hoc hypothesis” — a desperate attempt to shore up a research programme that was otherwise in crisis, because no-one wants to give up a cosmological theory that has worked perfectly well for twelve centuries.