Paper: Analogy is Just an Analogy

Gravity well animation (NASA)I do not object to this paper so much as to the reporting on it. The paper itself (Middleton, C., & Langston, M. “Circular orbits on a warped spandex fabric.”  arXiv:1312.3893) is a comparison of the “orbital” paths of a marble on a stretchable fabric surface compared to the paths of masses through space as described by general relativity, which it finds to be not mathematically comparable. The image of a weight deforming a fabric surface as an analogy for how masses create gravitational fields that affect the paths of moving masses through space is often used as a popular presentation of the ideas of relativity. What puzzles me is the idea that any physicist would be, in the words of the Physics arXiv Blog, “shocked” by the realization that the analogy of marbles rolling on fabric doesn’t work exactly like masses moving through relatavistic space. I suspect that most physicists have long realized that this image is just that: a roughly approximate image that is helpful to get the basic idea, but is by no means perfect.

Image: NASA

Comments are closed.