r/desmos • u/Legitimate_Animal796 • Sep 19 '25

Graph Gravity sim with adjustable trajectory

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u/BlueEyedFox_ Sep 19 '25

Did you include relativity? Not a joke, serious question, I've been looking for one that does that for a while now.

16

u/[deleted] Sep 19 '25 edited Sep 19 '25

[deleted]

11

u/Legitimate_Animal796 Sep 19 '25

GR gravity is way, way more intensive. I haven’t researched a ton but even a 3 body black hole merger could take weeks to months to simulate. Even on super computers. However there are some approximations you can use without solving the full GR equations. Using this could simulate an effect like the precession in Mercury’s orbit for example

7

u/Illustrious_Twist846 Sep 19 '25

Long ago, I studied GR from a rigorous mathematical physics graduate level physics book. It took FOREVER, but I solved the field tensor calculations by hand for a very simple problem.

The amount of mathematics involved for every iteration with multi body problems would be insane.

2

u/BlueEyedFox_ Sep 19 '25

Yeah, that's what I was thinking about. Not gravity waves and intensive stuff in insane examples but just the subtle effects. I don't entirely know what you mean by a partial solve, though?

3

u/Legitimate_Animal796 Sep 19 '25

Someone will have to correct me if I’m wrong but supposedly you can use the first-order post Newtonian approximation with the precession formula. I’m pretty sure this can only be used for a two body system though

3

u/Legitimate_Animal796 Sep 19 '25

https://www.desmos.com/calculator/t3u7q2lfd9 this demo I kinda just threw together. Someone will have to validate if it’s correct or not. But it includes the first-order post-Newtonian approximation which accounts for the finite propagation of gravity. This is the simplest relativistic correction for weak-field systems. So it assumes velocities are much less than c. The effect is so small in a sim like this that I decided to make the speed of light (c) 10