The 2D surfaces that generate Newtonian and general relativistic orbits with small eccentricities

TL;DR

This paper introduces cylindrically symmetric 2D surfaces that approximate Newtonian and relativistic orbits with small eccentricities, providing visual and experimental tools to compare gravitational theories.

Contribution

It presents a novel 2D construct that closely approximates small-eccentricity orbits in Newtonian and relativistic gravitation, enhancing conceptual understanding.

Findings

Surfaces cannot exactly reproduce arbitrary orbits but approximate small-eccentricity orbits well.

The surfaces illustrate differences between Newtonian and relativistic orbital precession.

Potential for educational use with 3D printing to explore gravitational predictions.

Abstract

Embedding diagrams prove to be quite useful when learning general relativity as they offer a way of visualizing spacetime curvature through warped two dimensional (2D) surfaces. In this manuscript we present a different 2D construct that also serves as a useful conceptual tool for gaining insight into gravitation, in particular, orbital dynamics - namely the cylindrically symmetric surfaces that generate Newtonian and general relativistic orbits with small eccentricities. Although we first show that no such surface exists that can exactly reproduce the arbitrary bound orbits of Newtonian gravitation or of general relativity (or, more generally, of any spherically symmetric potential), surfaces do exist that closely approximate the resulting orbital motion for small eccentricities; exactly the regime that describes the motion of the solar system planets. These surfaces help to illustrate the similarities, as well as the differences, between the two theories of gravitation (i.e. stationary elliptical orbits in Newtonian gravitation and precessing elliptical-like orbits in general relativity) and offer, in this age of 3D printing, an opportunity for students and instructors to experimentally explore the predictions made by each.