Theories of Everything with Curt Jaimungal Time Travel in Physics: “We Still Don't Know”
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Mar 16, 2026 J.B. Manchak, a UC Irvine philosopher of physics known for rigorous theorems about general relativity and time travel, explores why even complete local data can leave the universe globally unknowable. He discusses closed timelike curves, Cauchy surfaces and determinism, Malament–Hogarth spacetimes and computability, Heraclitus space-times, and connections between cosmic underdetermination and ideas about the self.
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GR Is Many Competing Model Collections
- General relativity (GR) is a family of models, not a single theory, so claims like "GR is deterministic" depend on which subclass of models you choose.
- J.B. Manchak explains that removing "pathological" models is often metaphysical, so determinism can be obtained only by quietly shrinking the allowed model space.
Time Travel In GR Is Causal Looping Not Hollywood Rewriting
- GR permits closed timelike curves (time travel) in some exact solutions, but these don't allow Hollywood-style past-changing paradoxes.
- Time travel in GR appears as worldlines that loop in the causal structure; whether they're physical remains unsettled.
Cauchy Surfaces Link Initial Data To Determinism
- A Cauchy surface is a spacelike slice that every causal curve meets, and a spacetime with one is globally hyperbolic, enabling unique evolution from initial data.
- If extensions exist that ruin global hyperbolicity, a Cauchy horizon appears and determinism (unique evolution) can fail.