Anything that can be cut can also be sewn. It is mathematically possible to take two black hole geometries, and sew them together along their "tears". This gives rise to wormhole solutions to Einstein's equations, in which two otherwise separate "universes" are connected by a throat, or tunnel, as shown in the top figure above. Such wormholes could also connect different regions of the same universe, as in the bottom picture. In principle this would enable us to take shortcuts to distant parts of the Universe just like they do in Star Trek. The problem is that within Einstein's theory such wormholes are very unstable. The throats tend to collapse in a much shorter time than it would take to get through to the other side, so that traversing such wormholes is in practice impossible.
This then is how Einstein's gravity works. In the word's of John Wheeler: Matter tells space how to curve, and space tells matter how to move. So what is a black hole in this context? Clearly the more matter I put in the center of the sheet, the deeper the well that I create, and the harder it is for matter to "climb out" . According to Einstein's theory, if I pack enough matter into a small enough volume, the well will get so deep that the matter inside can never escape. A circle of no return forms. Any matter that passes the point of no return can no longer escape to the outside world. It necessarily keeps collapsing, moving towards the center. The well gets deeper and deeper until finally a hole is literally torn in the fabric of spacetime: the density of matter at the center becomes essentially inifinite, at least to the extent that Einstein's theory of gravity is still valid. Thus, what I mean by " a hole in the fabric of spacetime" is: a tiny region of space where the known laws of physics break down. A black hole is a region of space so tightly packed with matter, that nothing, not even light can escape. Hidden at its (crunchy?) center is a tear in the fabric of spacetime. Anything that falls into this region of space is irrevocably lost to the rest of the universe. No light can emerge or pass through this region, so it appears totally black. In some sense therefore, a black hole marks a boundary to spacetime: a horizon beyond which no one can see without travelling through it. This radius of no return is called the event horizon of the black hole.
Gina "Nanogirl" Miller
"The science of nanotechnology, solutions for the future."
>From: Anders Sandberg <firstname.lastname@example.org>
>"Gina Miller" <email@example.com> writes:
>> Anything placed inside of a worm hole, the excessive gravitational
>> pull of the black hole would rip apart long before it passed
>> either a wormhole or a white hole.
>Please don't mix up the holes, they are very different. A stable
>traversible wormhole is a possible solution of GR (assuming some
>matter fields) and would have a very different topology from black
>holes and white holes.
>> We can't even really discover
>> whether either phenomenon exists!
>Actually, black holes seem to have moved out from the "weird
>possibility" category among astrophysicist and into the "odd object"
>category. I get the impression that the confidence in the data
>supporting their existence is rather high these days.
>Wormholes are still in the theoretical physics toybox. The
>Censorship Theorem seems to limit them, unless we can find a way to
>mess up the null energy condition :-)
>Anders Sandberg Towards
>GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+
!y Gina "Nanogirl" Miller Nanotechnology Industries Web Page http://www.nanoindustries.com E-mail firstname.lastname@example.org Alternate E-mail email@example.com "The science of nanotechnology, solutions for the future." _______________________________________________________________ Get Free Email and Do More On The Web. Visit http://www.msn.com