Anders Sandberg (
Sat, 21 Dec 1996 15:13:06 +0100 (MET)

On Fri, 20 Dec 1996, Michael Lorrey wrote:

> One should also be able to travel into the
> past with a simple black hole, according to the latest from Hawking.

How is that supposed to work?

> > > 2) The very rapid rotation would cause the cylinder to fly apart.
> Neutronium has such a high gravity gradient that it is self supporting,
> as evidenced by black holes that spin nearly at the speed of light.

Well, black holes doesn't consist of neutronium at all (the matter has
left the picture), rather a self-sustaining curvature of spacetime
(gravitonium?). Neutronium can't withstand too fast rotation since the
pressure drops low enough for it to turn into normal matter; it has an
excellent pressure strength, but no tensile strength. Black holes are
similarly limited, above a certain limit angular momentum and charge the
Kerr solution vanishes and we get something else (unfortunately you cannot
accelerate a black hole beyond this limit according to some theorem, see
_Gravity_ by Misner, Thorne, Wheeler).

Anders Sandberg Towards Ascension!
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y