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    Robert McNees (mcnees@mastodon.social)'s status on Tuesday, 25-Jun-2024 23:49:22 JSTRobert McNeesRobert McNees
    in reply to

    In general relativity, the causal structure of spacetime traps things behind a horizon. No rocket can overcome that.

    Think of general relativity as laying out rules for how things are allowed to move. The rules in a black hole spacetime simply don’t allow trajectories that pass behind the horizon of a black hole and then make it back outside. Once something crosses over, the only allowed motions take it further in.

    I recently posted an illustrated thread about this!
    https://mastodon.social/@mcnees/111410664694892538

    In conversationabout a year ago from mastodon.socialpermalink

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      Robert McNees (@mcnees@mastodon.social)
      from Robert McNees
      Attached: 1 image 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.
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