# Re: That black-hole space-time curvature thing

Eliezer S. Yudkowsky (sentience@pobox.com)
Thu, 11 Sep 1997 12:41:06 -0500

Sarah Marr wrote:
>
> Ok, so what I've never quite understood is this: why does the extreme
> curvature of space-time at the event horizon of a small black whole tear
> the intrepid astronaut to bits? More importantly, here's why I don't
> understand it.

My previous post can be summarized as follows:

Everything moves in straight lines unless a force acts on it. Since gravity
is the curvature of space, not a force, objects in free fall move in straight
spacetime lines. A tossed ball moves in a straight line; the Earth moves in a
straight line around the sun.

Suppose you fall into a black hole. Since the curvature near a black hole is
very different from one point to another, different parts of your body have
different ideas of what constitutes a "straight line". Your tensile strength
isn't enough to hold them together, so your body parts all go their separate
ways. Not necessarily in different spatial directions, but certainly at
different velocities - since "velocity" means "direction in spacetime".
(Curvature controls change in direction, and thus acceleration.)

```--
sentience@pobox.com      Eliezer S. Yudkowsky
http://tezcat.com/~eliezer/singularity.html
http://tezcat.com/~eliezer/algernon.html
Disclaimer:  Unless otherwise specified, I'm not telling you
everything I think I know.
```