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We have a metal rod travelling through vacuum space towards a cosmic Schwarzschild Black Hole.

The proportions of the black hole and the metal rod are such that the metal rod is twice the Schwarzschild radius in length.

We should call each end of the rod, Point A and Point B.

If the rod enters the black hole in such a way as to be on a straight trajectory (like a spear) towards the singularity, what effects if any would be caused by passing through the horizon.

To be more accurate, when Point A reaches the singularity, what effects do we see on Point B?

I am aware that no energy will travel ‘back in time’ along the rod, but I’m interested in how the curvature at the horizon will affect Point B

Will the rod be affected by anything other than Hawking Radiation?

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    $\begingroup$ As you observe the rod from outside, it approaches the zero length at the horizon and never crosses it. Even in the frame of the point B, the point A does not cross the horizon before the point B. Thus your question is based on a wrong premise, $\endgroup$
    – safesphere
    Commented Jan 4, 2021 at 15:31
  • $\begingroup$ @safesphere - how about if we attached a measuring device that took into account the inherent vibration from the rod’s composition - a device that we removed before Point B hit the Event Horizon - would we measure anything additional (apart from possible effects from Hawking Radiation)? $\endgroup$
    – Wookie
    Commented Jan 4, 2021 at 17:00
  • $\begingroup$ @safesphere - aha! So, Points A and B reach EH simultaneously. No further questions. $\endgroup$
    – Wookie
    Commented Jan 4, 2021 at 17:10

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Nothing special happens at the event horizon. The curvature of spacetime is not especially large there compared to other places.

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    $\begingroup$ When I compute the Kretschmann scalar $K$ (a measure of spacetime curvature) at the event horizon of a Schwarzschild black hole with the mass of the Sun, and compare it to $K$ at the surface of the Earth, I find that the former is $10^{31}$ larger than the latter. (!) Doesn't the surface of the Earth count as an "other place"? And isn't $10^{31}$ "especially large" rather than "not especially large"? $\endgroup$
    – G. Smith
    Commented Jan 4, 2021 at 1:26
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    $\begingroup$ @G.Smith : I suspect that "other places" was meant to be "other places nearby". $\endgroup$
    – WillO
    Commented Jan 4, 2021 at 2:16
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    $\begingroup$ The “nothing special” mantra refers to the frame of a falling observer. In this question, the OP observes the rod from outside and in his frame everything that happens to the rod at the horizon is very special. The rod shrinks in length to near zero, freezes in time, and disappears from existence while its entire energy converts to the gravitational energy of a black hole. The horizon is a very special region as far as the entire universe is concerned. $\endgroup$
    – safesphere
    Commented Jan 4, 2021 at 15:29
  • $\begingroup$ Nice - concise - thank you $\endgroup$
    – Wookie
    Commented Jan 5, 2021 at 22:03

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