Episode 65: Causality, Time and the Experiment Paradox with Michal Eckstein
Physics Frontiers
00:00
The Causal Cone in General Relativity Can Change Directions
In general relativity, the causal cone can actually change direction. It's always the same shape locally, but once you move around, it can twist. In some pathological situation, it can form a causal loop. Hocking theorem shows that this condition is equivalent to the existence of a global time in the universe and so a cosmic time if you wish.
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