in the geocentric models of the solar system (universe?), planets were said to move in circular paths. it was observed that the planets did not appear to move in this way, as during certain periods they enter “retrograde” motion, appearing to move backwards for a while, then return to moving forwards. in order to explain this deviation from the explanation, the epicycle was added. the epicycle, as you might predict from the name, is a cycle on top of another cycle. in this case, a circle that the planet moves around, which itself moves around the sun.
we understand that this view of the solar system was incorrect. the retrograde phenomenon is now explained by elliptical orbits, and has been validated by centuries of increasingly accurate predictions and observations.
this brings us to the more generalized pattern language meaning of epicycle that I’d like to introduce. the source of this pattern is a rich seam of newly useful words, the structure of scientific revolutions by thomas khun. khun’s use of the term “epicycle” refers to extensions of an existing scientific paradigm in the face of observations that the theory doesn’t explain. these extensions are marked by the diminished beauty when compared to the original theory. here I’m using “beauty” and “simplicity” interchangeably. khun suggests that the appearance of epicycles is a sign that a new paradigm is needed, and may arrive. the new paradigm can succeed to the degree that it escapes the framing of the old theory and finds a new, simpler way to explain the new observations. the next paradigm for the original epicycles was the kepler’s elliptical orbits.