How Far is Video Generation from World Model: A Physical Law Perspective
Authors: name: Bingyi Kang, name: Yang Yue, name: Rui Lu, name: Zhijie Lin, name: Yang Zhao, name: Kaixin Wang, name: Gao Huang, name: Jiashi Feng

OpenAI's Sora highlights the potential of video generation for developing
world models that adhere to fundamental physical laws. However, the ability of
video generation models to discover such laws purely from visual data without
human priors can be questioned. A world model learning the true law should give
predictions robust to nuances and correctly extrapolate on unseen scenarios. In
this work, we evaluate across three key scenarios: in-distribution,
out-of-distribution, and combinatorial generalization. We developed a 2D
simulation testbed for object movement and collisions to generate videos
deterministically governed by one or more classical mechanics laws. This
provides an unlimited supply of data for large-scale experimentation and
enables quantitative evaluation of whether the generated videos adhere to
physical laws. We trained diffusion-based video generation models to predict
object movements based on initial frames. Our scaling experiments show perfect
generalization within the distribution, measurable scaling behavior for
combinatorial generalization, but failure in out-of-distribution scenarios.
Further experiments reveal two key insights about the generalization mechanisms
of these models: (1) the models fail to abstract general physical rules and
instead exhibit "case-based" generalization behavior, i.e., mimicking the
closest training example; (2) when generalizing to new cases, models are
observed to prioritize different factors when referencing training data: color
> size > velocity > shape. Our study suggests that scaling alone is
insufficient for video generation models to uncover fundamental physical laws,
despite its role in Sora's broader success. See our project page at
https://phyworld.github.io