That black-hole space-time curvature thing

Sarah Marr (
Thu, 11 Sep 1997 16:35:09 +0100

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.

When space-time distorts why do the objects around feel the effects of that
distortion as forces acting on their undistorted state? An analogy: take a
latex sheet (I know you all have them at home, you can't fool me) and mark
it with a grid for reference purposes. Now, fasten the edges of the sheet
to a frame, place weight on it and watch it distort. Throw a coin on to
the sheet. You can still use the reference grid to identify the position of
the coin: it moves with the sheet, acting rather like a point. Now throw
another coin on. As the distortion of the sheet changes they will move
closer and further apart in your frame of reference, but in terms of the
grid on the sheet they will remain the same distance apart. And this is the
point. When space-time distorts, as I understand it, 'new' space-time is
not created, existing space-time merely stretches. But it stretches only in
the context of an external point of view. Anything within that space-time
would not see the stretching; a meter could become a kilometer from an
external perspective, but within that area of space-time the meter would
remain a meter. So where does the force in a black-hole come from. It's
perfectly understandable in terms of gravitational field theory, but I lose
it when space-time distortion is used to explain it. It seems to me that
space-time and the object are not separate, as the one distorts, so does
the other, each of its points remaining in the same relative position to
all its other points.

Or does space-time distortion cause the creation of 'new' space-time?

Confused of the UK.

B e a u t y i s o n l y s i n d e e p.