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I have heard the claim over and over that you won't feel anything when crossing the event horizon as the curvature is not very large. But the fundamental fact remains that information cannot pass through the event horizon so you cannot feel your feet when they have passed it.

Is there a way to cross the even horizon at reasonable speed in radial direction (below say 0.01*c )? So what would it really be like?

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    $\begingroup$ If you could include a reference to the recent "firewall" paper, it would make the question more topical. $\endgroup$
    – Ron Maimon
    Commented Sep 23, 2012 at 20:45
  • $\begingroup$ Related: physics.stackexchange.com/q/32693/2451 $\endgroup$
    – Qmechanic ♦
    Commented Sep 23, 2012 at 20:52
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    $\begingroup$ According to classical general relativity, one doesn't even notice when he crosses the event horizon: the space around it is mildly curved and indistinguishable from a patch of nearly-flat Minkowski space. There were very recent speculations that there is a firewall on the horizon of an old black hole, after all, due to some quantum-information issues black holes have to satisfy, see physics.stackexchange.com/questions/38005/… for the controversy. $\endgroup$
    – Luboš Motl
    Commented Sep 24, 2012 at 5:58

2 Answers 2

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You always cross the event horizon at the speed of light. There is no way to cross it at a lower speed.

But ...

Your frame is locally just Minkowski space, and nerve impulses from your feet reach your brain just as they always have done. Other observers might argue that it's actually your brain moving towards the nerve impulses faster than light rather than the nerve impulses managing to move outwards, but this is an interpretation based on the co-ordinate system they are using. In your co-ordinate system you will notice nothing unusual.

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  • $\begingroup$ Doesn't falling at the escape velocity require freefalling the whole way from infinite distance? If so, wouldn't rocket thrusters pointed toward the event horizon for even a moment be enough to keep you from reaching the speed of light when you reach the event horizon? $\endgroup$
    – Gumby The Green
    Commented Apr 3, 2022 at 8:54
  • $\begingroup$ No, if you're free falling than you hit the horizon at $c$ (relative to a shell observer) regardless of where you start from. This seems odd, but relative to a shell observer the acceleration at the horizon goes to infinity so it can always accelerate you to $c$ even if you start from rest a gnat's whisker from the horizon. But as discussed in the other question the meaning of the speed is ambiguous. $\endgroup$
    – John Rennie
    Commented Apr 3, 2022 at 8:57
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It depends on the size of the black hole. With small ones (a few solar masses) the tidal forces are strong enough to "spaghettify" your body as you approach the event horizon.

With supermassive (a million solar masses) black holes the gravity gradient is very small and the tidal forces are so low that you won't feel anything until well after you have crossed the horizon. According to this site, the tidal force on your body at the horizon is $10^6$g for a 30 solar mass hole, but only 1g for a 30,000 solar mass hole.

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