Mundo puts a simulator inside the world model for inspectable physics

The Mundo world-model project on Hugging Face separates an explicit scene representation, a physics simulator and a video renderer. A MuJoCo demo shows free fall cannot reveal an object's mass, while a sideways force can, suggesting state should be checked before rendering.

• Mundo keeps a 3D proxy, a physics scene program, a simulator and a video renderer separate
• In free fall mass cancels out and cannot be inferred from the trajectory
• A sideways force F gives displacement x = F·t²/(2·mass), revealing mass
• MuJoCo 3.17.0 demo: 1 kg and 10 kg under 1 N move 0.08 m and 0.008 m