What makes a world model? A four-part test that foundation models, digital twins fail
marinkazitnik · x · 2026-09-18
Marinka Zitnik proposes one test for world models: does the model represent a system state, accept a specified action, predict the resulting state, and continue simulating from that prediction? By this standard, foundation models can serve as encoders but aren't world models; digital twins mirroring only current state don't qualify either. Virtual cells, embryos, and patients remain aspirational, each exposing a gap: virtual cells often fail to beat linear baselines in poorly covered contexts; embryo atlases observe different cells per stage with few interventions; xHealth records span years but treatments are selected, not randomized.
Related event: Harvard Team Publishes Biomedical World Models Framework in Cell(8 posts)→
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