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Eta C
2003-Apr-15, 04:16 PM
I wasn't sure whether to put this here or in against the mainstream. The deciding factor was that the article was published in Physical Review Letters, probably one of the most respected journals in the community.

http://www.aip.org/enews/physnews/2003/split/631-2.html

The usual problem with using black holes as wormholes is that the tidal forces they generate on any extended object would rip it apart before it could go anywhere. The article discusses possible situations where a black hole could have a composite structure where some parts of it have lower tidal forces that could be withstood. It ends up, however, concluding that there are other, not yet understood factors (such as a working quantum theory of gravity) that may still make wormhole travel impossilbe even if these composite black holes exist.

(edit for spelling)

Argos
2003-Apr-15, 06:25 PM
It think you wouldn´t need effects of quantum nature to disturb the “weak” regions of such a BH. It seems to me that “compact” sources of radiation, like the interstellar gas and dust, not to mention denser objects, fall continuously into a black hole, generating powerful bursts of energy, overwhelming the mild blow of the cosmic background radiation. So, stable weak regions would hardly form. However, this model could work in less dense regions of the universe, or in inactive BH´s, the ones which exhausted the matter in the neighborhood, being subjected only to the CBR.

Another apparent problem is that, in the moment a spaceship – a “compact” extended object – falls in the BH it must disturb the weak region, causing it to destabilize, closing the inter-universal doorway. Also, it looks like once you enter the event horizon, the weak region must be reached and crossed before the tidal effects become unsustainable for the ship, what can occur very quickly.

But I suspect that even the weak regions would still be too strong for an ordinary object to withstand.

Argos
2003-Apr-16, 03:24 PM
I would like to see the smart ones having a word on this thread. It seems very interesting to me.

Eta C
2003-Apr-16, 04:24 PM
I haven't had a chance to look at the paper yet. Unfortunately, I can't post a link to the journal itself, PRL requires a subscription. I'll take a read and get back to it.

Eta C
2003-Apr-16, 07:01 PM
OK, here's a summary of the article (PhysRevLett vol 90 num 12 Page 121101-1) .

There is more than one type of black hole. The classic, Schwarzschild version has a singularity that induces infitite tidal forces that would force any object passing the event horizon to crush down to a volume of 0. Clearly bad news for travel. Other black holes, however, have what the author describes as a null singularity. Inside such a black hole is a "Cauchy horizon" that encompasses the normal singularity. Between the CH and the singularity is a region where the tidal forces, while great, are bounded. To quote the paper "The occurrence of the null singularity inside realistic black holes ...leaves open the possibility that extended objects could traverse the CH only mildly affected, and reemerge in another universe (or a distant portion of our universe), in practice uning the black hole as a portal for hyperspace travel."

The existance of such a black hole, however, depends on the flow of material into the hole. If the flow rate is too great, the normal singularity would fill the entire event horizon and block it off. What the paper proves is that such a threshold exists. That is, there is a flow rate under which a CH would exist. However what the paper does not do is calculate what that rate is. It is model dependant and would vary from hole to hole. The authors point out that all black holes are bathed in the cosmic background radiation, and it may well be that even that low level is enough to exceed the threshold.

In short, there are conditions under which a black hole may be used as a wormhole without destroying the material passing through, but it's not certain these conditions exist in the universe.

(I may be close to setting a record for a one sided thread here. sorry). :oops:

Argos
2003-Apr-16, 10:02 PM
(I may be close to setting a record for a one sided thread here.

Don´t worry. It happens all the time with me.:)