Wormholes

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Anthony Smales - 30 Mar 2005 16:00 GMT

I read recently that if you go into the throat of the gravity well of a
black hole, you might (if you survived), be ejected into another universe
via the anti-gravity white hole.

I'm not at all sure about this - we must remember that the gravity well
'throat' operates all around a black hole - so if you get dragged in and
spat out of the other side, you appear round the back of the black hole -
i.e. on the opposite side of it to where you began - but you are still in
the same connected region of spacetime.

The only way I could see a gateway to another universe or 'wormhole'
appearing would be if 2 universes collided and tore a hole in spacetime,
then the surfaces join together and form the wormhole - and this really is a
connection between one universe and another.

So maybe there could be 2 types of black hole? The black hole caused by a
collapsing star would not create a wormhole and the black hole caused by a
collision of universes is essentially a wormhole. (?)

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Anthony Smales - 30 Mar 2005 16:17 GMT

So I mean maybe there are 2 types of black hole - one that contains a
singularity but no wormhole and its gravity operates in every bi-directional
vector), and one that is a wormhole but does not contain a singularity
(although the gravity well is just as intense, but only operates in one
bi-directional vector).

--

>I read recently that if you go into the throat of the gravity well of a
>black hole, you might (if you survived), be ejected into another universe
[quoted text clipped - 14 lines]
> collapsing star would not create a wormhole and the black hole caused by a
> collision of universes is essentially a wormhole. (?)

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Ben Rudiak-Gould - 30 Mar 2005 17:48 GMT

> I read recently that if you go into the throat of the gravity well of a
> black hole, you might (if you survived), be ejected into another universe
> via the anti-gravity white hole.

This needs lots of qualification. In certain models of a black hole, it's
theoretically possible to avoid the singularity and escape, via a white
hole, into another flat (gravity-free) region of spacetime. In one model
(the Kerr solution) the singularity is shaped like a ring instead of a
point, and if you fly through the ring you end up in an anti-spacetime where
gravity is repulsive. This is *not* the same as a white hole. A white hole
is the time-reversal of a black hole, and has the same attractive field as a
black hole.

> I'm not at all sure about this - we must remember that the gravity well
> 'throat' operates all around a black hole - so if you get dragged in and
> spat out of the other side, you appear round the back of the black hole -
> i.e. on the opposite side of it to where you began - but you are still in
> the same connected region of spacetime.

Spacetime is really really warped in the vicinity of a black hole. Your
intuition about "the other side" doesn't apply here. Not even close.

> The only way I could see a gateway to another universe or 'wormhole'
> appearing would be if 2 universes collided and tore a hole in spacetime,
> then the surfaces join together and form the wormhole - and this really is a
> connection between one universe and another.

Curved space doesn't mean curved into some higher dimension. Universes
can't/won't collide in the way you envision. (The idea of "branes" is quite
different, and in any case it's highly speculative.) Spacetime isn't a
fabric, decades of popular science writing notwithstanding.

The reason people talk about "another universe" is the same reason they talk
about the universe being larger than the part that we can see -- if you
extrapolate in a natural way from what you can see, that's what you end up
predicting. In the case of black holes, the way this is done mathematically
is called "analytic continuation". No one is sure what physical significance
should be attached to the space on the other side of the wormhole that shows
up when you do this. I suspect that nine out of ten physicists would say
that it's a meaningless mathematical artifact.

-- Ben

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Natural Science Forum / Physics / Relativity / March 2005

Wormholes