LeCun's world model pitch: predict representations, not pixels, and plan via MPC-style cost minimization

le_james94 · x · 2026-10-13

lejames94 recaps LeCun's ETH world-model lecture: predict the next state given an action, then plan by minimizing a cost — "very classical stuff in optimal control going back to the 1960s" (model predictive control). What's new: it predicts representations, not pixels.

His slide explains why: pixel-level prediction averages incompatible futures into a blur, while JEPA maps encode(x)+action to encode(y), letting the encoder drop whatever can't be predicted. The catch is collapse — an encoder outputting a constant makes prediction trivial — addressed with regularizers like SIReg. The planning loop: perceive, propose actions, predict, score (cost zero = done), optimize.

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