Talk:Worldgate
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DD: While I see no problem, in principle, with your enshrining Hawking's Chronology Protection Conjecture (CPC) as 'canonical YW science' (though it is far from being the rigorous consequence of Einstein's equations combined with various reasonable physical assumptions that the Penrose-Hawking singularity theorems and the no-hair theorem are—for one thing, the CPC would have to be a consequence of a theory of quantum gravity, and such a theory is still an elusive prospect), I am concerned that it doesn't do what you appear to want it to: The CPC states, generally, that there is no way to make a time machine, even using exotic matter, but says nothing specifically about whether you can create wormholes, with or without exotic matter, just as long as you don't turn them into time machines. (For instance, even if you overcame the challenges of creating a wormhole1, the CPC would have some other effect—most likely due to quantum gravity—prevent you from turning the wormhole into a time machine.)2 What you are looking for appears to be something like Friedman, Schleich and Witt's Topological Censorship Theorem3, which is a rigorous theorem in classical general relativity, one of whose consequences is that traversable wormholes have to be held open by some sort of exotic matter. Alternatively, you could have been thinking of Hawking's Chronology Protection Theorem4, which, while another rigorous theorem in classical general relativity, does not appear to be as well known as any of the previous results, perhaps due to the fact that its statement about time machines' necessity for exotic matter is considerably weakened by having quite a bit of 'wiggle room' in its many hypotheses.
In addition, a recent result of Visser, Kar and Dadhich (reported here) shows that one only needs an arbitrarily small amount of exotic matter to hold open certain types of traversable wormholes, so you might want to rethink having a threshold amount of exotic matter. Also, if I may be so bold as to enquire, why does an increasing population density lead to the accumulation of exotic matter? (In addition, I have to wonder why you're being so relativistically fastidious here, considering that you've allowed wizardry to break far more fundamental laws of physics blatantly in canon—e.g., the slightly faster than lightspeed particles from Nita's linac in WAW5—particularly as faster than lightspeed travel implies time travel!6)
1 The conjecture would be entirely happy if you couldn't, though it has bigger fish to fry, as there are ways of creating a time machine that don't use wormholes.
2 Kip Thorne's excellent popularization, Black Holes and Time Warps: Einstein's Outrageous Legacy covers much of this (from his own first-hand perspective!) in its final chapter.
3 N.B.: This is a link to (an updated version of) the original paper—I can't find any sort of popular report on this result online. (Perhaps there's something in a magazine or one of the more recent of the many popular books on general relativity—Thorne's book is slightly too early.)
4 This is also a link to the original article, though only its abstract will be available unless you are somewhere (e.g., a library) that has a PROLA subscription. (I can't remember whether the theorem is covered in Thorne.)
5 While the particles could just have been accelerated to slightly faster than the speed of light in some surrounding medium (e.g., air) and still remained below the famous 'universal speed limit' of ~3 × 108 m/s (c, the speed of light in vacuum), as is the case in the Čerenkov effect, such a situation would not need the given proviso that it could only be done using wizardry.
6 I, of course, mean time travel in the strong sense here—i.e., travel backwards in time in some frame of reference—as the statement is pretty meaningless otherwise. —Nathan 23:34, 9 Jul 2006 (EDT)
[edit] Grammar
Fourth paragraph, first sentence.
Single or multiple, such gates seem to have a natural affinity for places where other nodes or nexi of mass transport can be found, and as a result wizards have either anchored locally occurring worldgates in in such places, or encouraged them to migrate into them.
Please fix. --Emiwai 13:01, 24 May 2007 (EDT)
