Simulating Gravity in C++

The brief

I wanted to understand what physics engines actually do under the hood, starting with the simplest honest version: Newtonian gravity, no shortcuts, no engine. Every force computed pairwise, every frame.

The build

• Newtonian n-body core — pairwise F = G·m₁m₂/r² across all bodies, O(n²) and unapologetic about it at this scale
• Velocity Verlet integration — chosen over naive Euler after watching orbits visibly decay; Verlet conserves energy well enough that stable two- and three-body configurations survive indefinitely
• OpenGL + GLFW rendering — immediate-mode trails showing each body's orbit history, fixed 60 FPS timestep decoupled from render
• Tunable scenarios — figure-eight three-body choreography, binary star + planet, and a randomized N-body cloud

What I learned

Integration choice is the simulation. The same forces with Euler vs. Verlet produce visibly different universes within seconds. Also: C++ ownership of GPU resources is its own curriculum — RAII wrappers around GL buffers saved me from leak-hunting.