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1. Robert McNees (mcnees@mastodon.social)'s status on Tuesday, 14-Nov-2023 19:57:15 UTC Robert McNees

   Black holes!

   The plot below shows two observers in the Schwarzschild spacetime. One falls inward along a timelike radial geodesic (purple), another (green) remains at a fixed value of the radial coordinate r.

   The infalling observer emits radial signals (red) at equal proper time intervals. These signals move outward along null geodesics, and the stationary observer receives them with decreasing frequency.