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  "body": "\n## Summary\n\nA Lorentzian manifold is a [[pseudo-Riemannian manifold|GH6CXWFNDJ]] whose metric has exactly one negative direction at each point.\nIt is the mathematical model of spacetime in general relativity.\nIts tangent vectors split into timelike, null and spacelike vectors, which gives each tangent space a light cone.\n\n## Explanations\n\n### L1 human\n\nIn a Lorentzian manifold one direction plays the role of time and the others play the role of space.\nThe metric measures time with the opposite sign from space.\nAt each point the vectors of squared length zero form a double cone, the light cone, along which light travels.\nMinkowski space $\\R^4$ with metric $-dt^2 + dx^2 + dy^2 + dz^2$ is the flat example.\nThe vector $(1, 0, 0, 0)$ has squared length $-1$ and points in a time direction, while $(1, 1, 0, 0)$ lies on the light cone.\n",
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