DeepMind ships MuJoCo 4.0 with speculative contacts to fix collision tunneling
lukas_m_ziegler · x · 2026-11-09
Google DeepMind released MuJoCo 4.0, the first major version of the world's most widely used robotics physics engine since 2023.
The headline fix targets a subtle but fundamental flaw: collision detection only checks positions at discrete timesteps, so thin or fast objects can move farther than their own thickness in one step and tunnel straight through others. Traditional fixes — smaller timesteps or inflated margins — trade away speed or accuracy.
The new speculative contacts approach sweeps each fast-moving geom forward through the step to find when it would hit something, then hands the solver an ordinary contact constraint that stops motion at the surface — no sub-stepping required.
Other updates include deformables solved implicitly together with rigid bodies, joints and tendons, keeping cables, cloth and shells stable.
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