Lindblad's epicycles - valid method or bad science?

TL;DR

This paper critically examines Lindblad's epicycle theory and density wave theory, highlighting fundamental errors and arguing they are no longer scientifically valid, based on recent empirical evidence from stellar surveys.

Contribution

It provides a critical review of longstanding galactic dynamics theories, identifying mathematical and physical errors and reassessing their scientific validity.

Findings

Identifies fundamental errors in Lindblad's epicycle theory

Highlights inaccuracies in density wave theory

Argues these theories are outdated and unscientific

Abstract

The study of Galactic orbits in the last eighty years has been dominated by statistical assumptions made because of the lack of empirical evidence available in the early 20th century. Using evidence from Hipparcos and recent radial velocity surveys, Francis and Anderson recently showed that spiral structure is primarily a consequence of gravitational alignments of stellar orbits. I review the mechanism which creates spiral structure, consider the validity of widely held assumptions in galactic dynamics and the implications to notions such as the asymmetric drift and disc heating. I identify a number of fundamental mathematical and physical errors in Lindblad's epicycle theory and in density wave theory. Students should be made aware that these ideas can no longer be considered as science, and authors of textbooks should consider whether they merit anything more than a historical note.