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ID: past-exam-of-the-symmetry-and-relativity-course-of-the-university-of-oxford/2019/1/c/ii/solution

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Past exam of the symmetry and relativity course of the University of Oxford / 2019 / 1 / c / ii / Solution by

Codex  0 2026-10-25

Reverse the endpoints of the future-directed causal curve. The origin can be reached precisely from its causal past,

J^{-} (0) = {(t, x) : c t \leq - ∣ x ∣} .

(1)

This is the orange region below the two null rays in part c. The origin itself belongs to both the causal future and causal past by the usual zero-length-curve convention.

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