This document contains comments about the article Geodesics in general relativity in Wikipedia
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In the last paragraph I explain my own opinion.

### Introduction

The article starts with the following sentence.
Importantly, the world line of a particle free from all external, non-gravitational forces is a particular type of geodesic.
That is one of the most simple examples?
In general relativity, gravity can be regarded as not a force but a consequence of a curved spacetime geometry where the source of curvature is the stress–energy tensor (representing matter, for instance).
My understanding is that matter can be described by a stress-energy tensor which physical means that the path of an object follows a geodesic in spacetime.
Thus, for example, the path of a planet orbiting a star is the projection of a geodesic of the curved four-dimensional (4-D) spacetime geometry around the star onto three-dimensional (3-D) space.
My understanding is that I would change space into: space and time.

### 1. Mathematical expression

The quantity on the left-hand-side of this equation is the acceleration of a particle, so this equation is analogous to Newton's laws of motion, which likewise provide formulae for the acceleration of a particle.
My understanding is that a particle can also be a planet or a star considered as a point mass.

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Created: 2 March 2019

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